Biochem Exam 2 Questions
Km is _______ the Vmax.
-1/2
Enzyme is ___________ by first phase of the reaction.
-altered
Acid acts as _________________ while oxygen acts as a ___________________.
-an electrophile -a nucleophile
Enzymes with the cofactor removed are known as
-apoenzymes
In Chymotrypsin, histidine 57 acts as a ___________________.
-base catalyst
The rate or velocity of a reaction is the change of a ___________________________ of reactant or product ___________________________
-concentration -per unit of time
Irreversible inhibition is a _________________ reaction.
-covalent
Amino acids help ______________ to occur and are ______________________
-enzymatic reaction -critical for the intermediate steps
Noncompetitive Inhibitor changes the.....
-enzyme conformation
The specificity of an enzyme results from the ______________________.
-exact three-dimensional shape and structure of the active site
Aspartate binds with __________ coming off of Histidine.
-hydrogen
What is the km?
-it is a measure of the affinity of an enzyme for its substrate.
The number of substrate molecules converted to product per unit of time is ______________.
-kcat
Which enzyme category includes redox reactions (transfer of electrons)?
-oxidoreductases *ex. alcohol dehydrogenase
What is an enzyme that breaks down peptide bonds through hydrolysis?
-protease
Several factors contribute to enzyme catalysis. The most important are:
-proximity and strain effects where the substrate must come in close proximity of the active site. -Electrostatic Effects where charge distribution in the largely anhydrous active site may help position the substrate.
Inhibitors ____________ enzyme activity.
-reduce
Which enzyme inhibition can be counteracted by increasing substrate levels or removing the inhibitor?
-reversible inhibition
Chymotrypsin is a ______________ of 27,000 D
-serine protease
In any reaction, only molecules that reach the ___________________ can convert into product molecules.
-transition state
Most reactions involve _____________ substrates in ___________ classes.
-two or more -two
After Histidine returns to its normal state and the peptide bond is cleaved, ____________ enters the active site.
-water
TRUE statements about enzymes (part 1)
1) Enzymes make reactions 10^3 to 10^20 times faster. 2) Enzymes lower the amount of energy needed for a reaction. 3)Enzymes speed up the attainment of a reaction equilibrium. 4) Enzymes are USUALLY proteins
TRUE statements about enzymes (part 2)
1)The word enzyme is from a Greek word meaning "in yeast." 2)The first enzyme was crystallized in 1926. 3) Enzymes can couple two different reactions.
michaelis-menten equation
1. assumes the formation of an *enzyme-substrate complex: ES* 2. assumes that the *ES is in rapid equilibrium with free enzyme E + S* 3. assumes that the breakdown of ES (k2) to form product, P, is slower than: a) formation of ES (k1) b) breakdown of ES to re-form E and S (k-1)
competitive inhibition, y int. =
1/vmax
Pepsin becomes activated at a pH of
2
Chymotrypsin becomes activated at a pH of
8
Find Kcat for a reaction in which Vmax is 4 *10^-4 mol*min-1 and the reaction mixture contains one microgram of enzyme (The molecular weight of the enzyme is 200,000 D)
8 * 10^7 min-1
45) Lipid-anchored membrane proteins that link to an isoprenoid chain via the sulfur atom of cysteine are called ________ proteins. A) prenylated B) sulfide-linked C) cysteine-anchored D) prostaglandins
: A Page Ref: Section 9-10
20) Which type of sphingolipid can also be classified as a phospholipid? A) Sphingomyelins. B) Cerebrosides. C) Gangliosides. D) Neurosides.
: A Page Ref: Section 9-5
33) Which would you expect for the fatty acyl chains of the membrane phospholipids of bacteria grown at low temperature? A) Proportion of unsaturated fatty acyl groups increases. B) Proportion of unsaturated fatty acyl groups decreases. C) No change in the proportion of saturated versus unsaturated acyl groups. D) More cholesterol is produced and is inserted between the fatty acyl chains of the membrane.
: A Page Ref: Section 9-9
Alcohol dehydrogenase without NAD+ is called a _______: A) Apoenzyme B) Holoenzyme C) Substrate D) Cofactor E) Coenzyme
A
G proteins: A) consist of three subunits, Gα, Gβ, and Gγ. D) A and B B) hydrolyze GTP to GMP + Pi + Pi. E) A and C C) completely span the cell membrane.
A
Define the terms "cofactor" and "coenzyme."
A cofactor is any chemical component required for enzyme activity; it includes both organic molecules, called "coenzymes," and inorganic ions.
first order reactions
A → P is a first-order reaction, with units of s-1 v = k[A]^1 = k[A] is the rate law
From the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of μM/s and substrate concentration of the x-axis in units of μM, what is the Vmax? A) 0.24 μM/s B) 18 μM C) 0.2 μM D) 0.24 μM E) 0.12 μM/s
A) 0.24 μM/s
Section 5-9 68) Phosphorylation that changes an enzyme's activity is an example of ________. A) covalent modification B) allosteric regulation C) sequential modification D) site-directed mutagenesis
: A covalent modification
27) Eicosanoids participate in a variety of physiological responses and are derived from A) waxes. B) arachidonic acid. C) cholesterol. D) isoprene.
: B Page Ref: Section 9-7
Section 5-7 52) An enzyme is irreversibly inhibited by diisopropylfluorophosphate (DFP). What does this show? A) The enzyme has been denatured by DFP. B) Serine is likely an important residue in the active site. C) DFP is an allosteric modulator of the enzyme. D) DFP is an analog of the enzyme's substrate.
: B serine is an important residue in the active site
A ligand that binds to a receptor to elicit a biological effect is known as a(n) A) antagonist B) agonist C) protagonist D) inverse agonist
B
A pore that simultaneously transports two different molecules in the same direction is called a(n) A) promiscuous pore D) node of Ranviera B) symporter E) equilibrium transporter C) antiporter
B
What amino acid performs the nucleophilic attack during the chymotrypsin mechanism? A) Ser B) His C) Lys D) Cys E) Thr
A) Ser
Which of the conditions below represents a steady state? A) d[S]/dt = 0 B) d[ES]/dt = 0 C) d[P]/dt = 0 D) d[S]/dt = d[P]/dt
B
Would you expect that CTP would be an allosteric inhibitor or activator of ATCase? A) activator B) inhibitor C) no effect
B
: Section 6-4 35) Acid-base catalysis is estimated to accelerate a typical enzymatic reaction by what factor? A) 1 to 2 fold increase. B) 10 to 100 fold increase. C) 106 fold increase. D) 1023 fold increase.
B 10 to 100 fold
17) Examine the cyclic D-monosaccharide shown below. The ring structure is the ________ and the linear form of this monosaccharide must be a(n) ________. A) α anomer; ketose B) β anomer; ketose C) α anomer; aldose D) β anomer; aldose
B Page Ref: Section 8-2
21) Who received a Nobel Prize in 1937 for his work on the structures of carbohydrates and the synthesis of Vitamin C? A) Linus Pauling. B) Walter Haworth. C) Max Perutz. D) Emil Fisher.
B Page Ref: Section 8-2
35) You have two bottles, each of which contains a white, crystalline substance. Your lab director tells you that one contains lactose and the other sucrose. Your job is to determine which bottle contains which sugar. Which procedure would you use? A) Test both for solubility in water. Sucrose is very soluble; lactose is only minimally soluble. B) Test for the ability to reduce Ag+. Only lactose will react. C) Dissolve each in water and record the pH. Lactose is far more acidic than sucrose. D) React each with bromine (Br2) water. Only sucrose will react.
B Page Ref: Section 8-5
49) Cellulose is not highly branched because it A) does not have a polysaccharide backbone. B) does not have α(1→6) linkages. C) does not have β(1→4) linkages. D) is insoluble in water.
B Page Ref: Section 8-6
52) Termites and cows have bacteria in their digestive tracts that can obtain glucose from plant cellulose because they have enzymes that can attack A) α-D-glucoside. B) β-D-glucoside. C) cellulose branch points. D) hydrogen bonds in cellulose fibrils.
B Page Ref: Section 8-6
Which is not true about β-sheets? A) The side-chains of all amino acids point to the same side of the sheet. B) The polypeptide chains in the sheet are nearly fully extended. C) The range of allowed phi and psi angles is broader than for those in the α-helix. D) In antiparallel sheets the hydrogen bonds between adjacent strands are nearly perpendicular to the backbones of the strands.
A) The side-chains of all amino acids point to the same side of the sheet.
Which protein in the blood is responsible for converting fibrinogen to fibrin? A) thrombin B) factor X C) factor VII D) factor VIIa E) prothrombin
A) Thrombin
A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic site is termed a(n):
A)allosteric inhibitor.
which factor contributes to primary structure?
AA sequence
What is the most effective way to increase the rate of a biochemical reaction?
Add a catalyst
A typical β barrel transmembrane protein contains ____ β strands. A) 1-7 D) Any of the above B) 8-22 E) None of the above C) 23-36
B
The most efficient enzymes have kcat/KM values that approach A) k2 B) k1 C) k-1 D) k-1 + k2 E) 1012 M•s-1
B
: Section 6-7 58) Glycoside hydrolases such as bacterial cellulase have been shown to differ in mechanisms from that of lysozyme. They A) are alkaline catalysts. B) form a boat form of the sugar. C) form a covalent sugar-enzyme intermediate. D) do not distort the substrate. E) have no active site side chain interactions.
C form a covalent sugar-enzyme intermediate
: Section 6-3 31) Superoxide dismutase enzyme catalysis is faster than the rate of diffusion because it A) is an acid-base catalyst. B) is a two-step reaction. C) has an electric field around the active site. D) occurs in very high quantities in cells.
C has an electric field around the active site
Blood coagulation involves:
B) zymogen activation. and C) serine proteases.
A good transition-state analog:
B)binds to the enzyme more tightly than the substrate
Which will be different for a catalyzed reaction versus an uncatalyzed reaction? Select one: A. Ground state energy. B. Activation energy. C. Free energy change. D. All of the above.
B. Activation energy.
The following questions (29 and 30) refer to the overall transformation shown in the following reaction: 28. Which of the following is (are) true? A) The [ES] will remain constant if k2>k1 and k−1< k2. B) The reaction is zero order with respect to [S] if [S]>>[E] C) It describes a double displacement reaction D) All of the above are true. E) None of the above is true.
B) The reaction is zero order with respect to [S] if [S]>>[E]
Which of the following amino acids is capable of acting as a general acid or general base at physiological pH? A. glycine B. histidine C. tyrosine D. tryptophan E. proline
B. histidine
Which of the following is correct in regards to the diagram above? A) X=A, Y=B, Z=P B) X=B, Y=A, Z=Q C) X=E, Y=A, Z=E D) X=E, Y=B, Z=Q E) X=E, Y=B, Z=P
B) X=B, Y=A, Z=Q
The principle forces holding subunits of an oligomeric protein to each other are ________. A) peptide bonds B) hydrophobic interactions C) covalent bonds D) disulfide bonds
B) hydrophobic interactions
A reaction is carried out in the presence and absence of an inhibitor, and initial velocities are plotted as a function of substrate concentration in the graph below. What type of inhibitor is this? A) competitive inhibitor D) uncompetitive inhibitor B) noncompetitive inhibitor E) irreversible inhibitor C) mixed inhibitor
C
ABC transporters are examples of A) passive diffusion D) secondary active transport B) facilitated transport E) tertiary active transport C) primary active transport
C
Glycosphingolipids with complex carbohydrate head groups that often serve as cellular receptors are A) cerebrosides D) eicosanoids B) steroids E) sphingomyelin C) gangliosides
C
In the Lineweaver-Burk double reciprocal plot the slope is equal to _____. A) 1/[S] B) 1/V C) Km/Vmax D) 1/Vmax E) -1/Km
C
The initial velocity (v0) of an enzyme-catalyzed reaction A) decreases as the substrate concentration increases B) is lowest when the enzyme is saturated with substrate C) is dependent upon the substrate concentration D) is independent of the pH of the solution E) all of the above
C
Which of the following is (are) not found as covalently attached anchors in lipid-linked proteins: A) isoprenoid groups D) glycosylphosphatidyl inositol groups B) fatty acids E) all of the above C) cholesterol and other sterols
C
What is the slope of the line for the Lineweaver--Burk Plot?
- km/Vmax
Based on the figure in the questions above, which of the following expressions would correctly define Km
B = Km
The mechanism of action of lysozyme includes
(All of the above) - Distortion of the substrate - Acid catalysis - Proximity effects - Formation of a half-chair sugar form
Chitin is
(All of the above) - Found in insect and crustacean shells - Found in fungi cell walls - Composed of N- acetlyglucosamine subunits - Composed of linear fibrils like cellulose
Michaelis-Menten Kinetics
*Equations* Km Vmax kcat kcat/Km
The breakdown of dopamine is catalyzed by the enzyme monoamine oxidase (MAO). What is the final concentration of product if the starting dopamine concentration is 0.050 M and the reaction runs for 5 seconds. (Assume the rate constant for the reaction is 0.249 s−1.) A) 0.050 M B) 0.014 M C) 0.018 M D) 1.2 M E) 0.025 M
B) 0.014 M
Find the initial velocity for an enzymatic reaction when Vmax = 6.5 × 10-5 mol•sec-1, [S] = 3.0 × 10-3 M, KM = 4.5 × 10-3 M and the enzyme concentration at time zero is 1.5 × 10-2 μM. A) 3.9 × 10-5 mol•sec-1 B) 2.6 × 10-5 mol•sec-1 C) 1.4 × 10-2 mol•sec-1 D) 8.7 × 10-3 mol•sec-1 E) Not enough information is given to make this calculation
B) 2.6 × 10-5 mol•sec-1
KM A) is the concentration of substrate where the enzyme achieves ½ Vmax. B) is equal to Ks. C) measures the stability of the product D) is high if the enzyme has high affinity for the substrate. E) All of the above are correct.
A) is the concentration of substrate where the enzyme achieves ½ Vmax.
Water soluble hormones: (hydrophilic)
AA and peptides bind receptor @ cell surface which triggers 2nd messengers inside cell.
The final product of oxidative phosphorylation in aerobic respiration is
ATP
Which mode(s) of catalysis is/are classified as chemical effects?
Acid-base catalysis and Covalent catalysis
What is the velocity of a first-order reaction at 37oC when the reactant concentration is 6 × 10-2 M and the rate constant is 8 × 103 sec-1? A) 1.33 × 105 M-1•sec-1 B) 1.33 × 105 M•sec C) 7.5 × 10-2 M•sec D) 4.8 × 102 M•sec-1) Not enough data are given to make this calculation
D) 4.8 × 102 M•sec-1
Which atom is the reactive center on biotin?
Arrow 1 (NH on left)
What are the three main amino acids found in the catalytic triad of chymotrypsin?
Asp, His, Ser
Aspartate and lysine are in the active site of an enzyme. They are both known to participate directly in catalysis, the pKa's of the residues are found to be 3.2 and 9.6. The optimum pH for the enzyme is 6.4. Which forms of these 2 residues will predominate when the enzyme is most active?
Aspartate is deprotonated; Lysine is protonated
An enzyme has two inhibitors with KI values of 2 x 10-3 M and 2 x 10-6 M. The inhibitor that binds more tightly has KI =______. A) 2 x 10-3 M B) 2 x 10-6 M
B
If the concentration of the inhibitor (dodecyl gallate) in this study is 0.031 mM, what is the value of KI? A) 0.0095 mM B) 0.017 mM C) 0.061 mM D) 0.053 mM
B
In competitive inhibition, increasing the concentration of substrate: A) Decreases the overall rate of the reaction B) Increases the overall rate of the reaction C) Is without effect D) The observed effect depends on the inhibitor E) Competitive inhibitors do not affect the rate of the reaction
B
The transformation of a monosaccharide into its ______ occurs easily and does not require the assistance of a catalyst. A) epimer D) diastereomer B) anomer E) none of the above C) sugar alcohol
B
What is the initial velocity of a reaction when Vmax = 3.6 x 10-3 mol/s, KM = 4.5 mM, and [S] = 1.5 mM? A) 8.7 μmol/s D) 30 μmol/s B) 0.9 mmol/s E) Not enough information to calculate C) 14 mmol/s
B
Which of the following is a secondary messenger? A) Cortisol B) cAMP C) Insulin D) G protein E) Epinephrine
B
39) A reducing sugar is one that A) contains a b(1→1) link. B) has a hemiacetal group. C) can reduce Cu2+ but not Ag+. D) makes you lose weight.
B Page Ref: Section 8-5
: Section 6-2 14) On the energy diagram below, which point represents an intermediate? A) Point 1 B) Point 2 C) Point 3 D) Point 4
B point 2
If the Asp in the chymotrypsin active site was mutated to another amino acid, which of the following would be considered an invisible mutation in that it is least likely to impact the function of the enzyme? A) Asp --> Asn B) Asp --> Glu C) Asp --> His D) Asp --> Ser E) Asp --> Lys
B) Asp --> Glu
The Michaelis constant is defined as _____. A) KM = k2 / k1 B) KM = (k2 + k-1) / k1 C) KM = (k2 - k-1) / k1 D) KM = (k2 + k1) / k-1 E) KM = (k2 - k1) / k-1
B) KM = (k2 + k-1) / k1
How many intermediates are indicated by the energy diagram below? Select one: A. One B. Two C. Three D. Four
B. Two (graph with three transition states and two intermediates)
The E + S --> E + P reaction is
Bimolecular
28) The abbreviation for glucose is ________. A) Glu B) Gcs C) Glc D) Gluc
C Page Ref: Section 8-4
What three amino acids are found in the catalytic triad of chymotrypsin? A) Glu, His, Thr B) Ser, Arg, Cys C) Asp, His, Ser D) Cys, Lys, Glu E) Asn, His, Thr
C) Asp, His, Ser
An enzyme that catalyzes conversions of L-sugars to D-sugars is called a(n) ________. Select one: A. synthase B. synthetase C. isomerase D. lyase E. hydrolase
C. isomerase
The fully oxidized form of carbon produced by our bodies is_______.
Carbon dioxide
The mediation of _________ is required for the transport of fatty acids through the inner mitochondrial membrane and into the mitochondrial matrix.
Carnitine
Transanimation requires which enzyme?
Coenzyme pyridoxal-5-P (Vitamin B6)
Opposing processes occur in different compartments of the cell:
Compartmentation
In ______, the inhibitor binds to a site involved in both substrate binding & catalysis
Competitive Inhibition
A type of inhibitor that binds at the enzyme active site and can be negated by high concentrations of the substrate.
Competitive inhibitor
The idea that binding of one molecule of oxygen to hemoglobin enhances further binding of oxygen to hemoglobin is called ___________.
Cooperativity
Compounds that function as 'mixed inhibitors' A) interfere with substrate binding to the enzyme B) bind to the enzyme reversibly C) can bind to the enzyme/substrate complex D) all of the above E) none of the above
D
A Lineweaver-Burk plot is also referred to as I. a sigmoidal plot. II. a linear plot. III. a Michaelis-Menten plot. IV. a double reciprocal plot. A) II B) II, III C) IV D) II, IV E) III, IV
D) II, IV
When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state? A) dipole-dipole interaction B) electrostatic interaction C) hydrogen bond D) low-barrier hydrogen bond E) covalent bond
D) Low-barrier hydrogen bond
The movement of ________ is key to understanding chemical and enzymatic reactions. Select one: A. electrophiles B. nucleophiles C. neutrons D. electrons
D. electrons
All are true for catalysts EXCEPT: a. They work by lowering the energy of activation. b. The average energy of the reaction is unchanged. c. They combine transiently with the reactants promoting a reactive transition state condition. d. They are regenerated after each reaction cycle. e. All are true.
E
Cellulose is A) sometimes called starch B) a linear polymer of glucose with α(1→4) linkages C) a linear copolymer of glucose and galactose D) a branched polymer of glucose E) a linear polymer of glucose with β(1→4) linkages
E
Which of the following is a feature of protease inhibitor specific for trypsin? A) contains a positive charge to mimic the charge of the substrate B) ability to interact with the Ser of the catalytic triad C) inability to form the tetrahedral intermediate D) high affinity for the enzyme active site E) all of the above
E) All of the above
Which of the following statements regarding allosteric enzymes is true? A) they are always oligomeric B) they are generally found at regulatory sites in metabolic pathways C) they are subject to regulation by both positive and negative effectors D) a plot of velocity versus [substrate] often yields a sigmoidal curve E) all of the above
E) All of the above
Catalysts are effective because they: A. decrease the rate of the reverse reaction B. stabilize the transition state C. decrease the activation energy of a reaction D. increase the energy released during a reaction E. B and C
E. B and C
A noncompetitive inhibitor forms an __________________________ complex.
EI + S----> EIS
In complex I of the ETC, the major sources of NADH include electrons coming from:
Fatty acid oxidation & the citric acid cycle
Both glycogenesis and glycogenolysis are controlled primarily by the interplay between the two hormones, insulin and _________.
Glucagon
When [S] = KM, ν0 = (_____)× (Vmax). A) [S] B) 0.75 C) 0.5 D) KM E) kcat
C) 0.5
If a Lineweaver-Burk plot gave a line with an equation of y = 0.25 x + 0.34, what are the values of KM and Vmax if the substrate concentration is in mM and the velocity in mM/s? A) 0.085 mM and 0.34 mM/s B) 2.9 mM and 0.023 mM/s C) 0.74 mM and 2.9 mM/s D) 0.37 mM and 1.4 mM/s E) 1.35 mM and .034 mM/s
C) 0.74 mM and 2.9 mM/s
The enzyme complexes I & IV which comprise the electron transport chain are found in what part of the mitochondria?
Inner Mitochondrial membrane
Different enzymes that catalyze the same reaction, although may be found in different tissues, are known as
Isozymes
The redox cofactor ubiquinone is necessary for converting energy from electron transport to the form of chemical bond energy in ATP. In which organelle would you expect to find most ubiquinone?
Mitochondria
In the Lineweaver-Burk plot of an enzyme reaction, the Km is given by the _____.
Negative reciprocal of the x-intercept
Epimers:
OH change at stereogenic center.
OTL:
Open Tight Loose
The conjugate base for HPO4^2- is...
PO4^3-
A pathway for glucose oxidation that produces reducing power for biosynthetic processes and five carbon sugars for nucleotide synthesis, but NO ATP.
PPP
Overall simple reaction of stoichiometry involves A------>P. P is equal to?
Products
This diagram refers to a (an)
Random bisubstrate reaction
Overall simple reaction of stoichiometry involves A---->P. A is equal to?
Reactants
How is the half-reaction Cu2+ + 2e-→ Cu classified?
Reduction reaction
Level of protein structure for :Hydrogen bonds between carbonyl and AA groups.
Secondary
What is the kcat for a reaction in which Vmax is 0.4 mmoles/min and the reaction mixture contains 5 10-6 micromoles of enzyme? A) 2 x 10-14 min-1 B) 2 x 10-11 min-1 C) 8 x 107 min-1 D) 4 x 108 min-1 E) 8 x 109 min-1
C) 8 x 107 min-1
If a Lineweaver-Burk plot gave a line with an equation of y = 0.490 x + 0.059, what is the velocity at a substrate concentration of 5 mM? The original units for substrate were in mM and velocity in mM/s. A) 0.288 mM/s B) 0.399 mM/s C) 2.51 mM/s D) 6.37 mM/s E) the velocity cannot be determined from this data
D) 6.37 mM/s
Chymotrypsin has a large specificity pocket to bind the aromatic amino acids while elastase has a very small specificity pocket meant to bind Ala or Gly. Which of the following amino acid substitutions changes the specificity pocket of chymotrypsin to that of elastase? A) Trp --> Ser B) Leu --> Ala C) Gly --> Val D) Lys --> Asp E) Val --> Asn
C) Gly --> Val
The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of ___________.
Specificity
Water insoluble hormones: (hydrophobic)
Steroids bind receptor inside cell, affect gene expression
Km is
The [S] that half-saturates the enzyme
If A --> B is a zero-order reaction, the rate is dependent on
The rate constant (Km)
Why does pH affect the activity of an enzyme?
The state of ionization of several amino acid side chains is affected by pH, and the activity of many enzymes requires that certain of the amino acid residue side chains be in a specific ionization state.
What is another name for vitamin B1?
Thiamine
The reactive center of coenzyme A is
Thiol group
uncompetitive inhibition-y intercept = alpha '/?
Vmax
In michaelis-menton kinetics the region of hyperbolic plot at which the reaction attains Vmax and there is no increase in initial velocity when substrate concentration is increased, this is considered to be ______________ with respect to the substrate.
Zeroeth order.
The rate of the reaction 2AB is dependent on ______.
[A]^2
large
___ Km means lots of dissociation (weak binding), e.g. 10^-2 M
lineweaver burk
a ___-___ plot can be used to present kinetic data and to calculate values for Km and Vmax useful for analysis of *inhibitors*
ping-pong reaction
a group-transfer reaction in which one or more products are released before all substrates have bound to the enzyme
most covalent catalysis is carried out by enzymes using a a. ping-pong kinetic mechanism b. sequential bisubstrate kinetic mechanism c. random bisubstrate kinetic mechanism d. simple unimolecular kinetic mechanism e. none of the above
a. ping-pong kinetic mechanism
Metabolism:
balancing act maintained by chemical signals such as hormones and neurotransmitters
2AB reaction is ______.
bimolecular
Chymotrypsin catalyzes the hydrolysis of a peptide bond and is therefore categorized as a _____. A) oxidoreductase B) transferase C) hydrolase D) lyase E) ligase
C) Hydrolase
Parallel lines on a Lineweaver-Burk plot indicate I. an increase in KM. II. decrease in KM. III. decrease in Vmax. IV. uncompetitive inhibition. A) I, IV B) II, III, IV C) I or II, III D) I or III, II E) I, III, IV
C) I or II, III
How does a catalyst increase the rate of a reaction? A) it makes the reaction more exergonic B) it increases the temperature of the reaction C) it allows reacting molecules to more easily form the transition state D) it causes a localized increase in the concentration of reactants E) none of the above
C) It allows reacting molecules to more easily form the transition state
A lead compound would be most promising if it had: A) KI = 4.7 × 105 M. B) KI = 1.5 × 108 M. C) KI = 1.5 × 10-8 M. D) KI = 4.7 × 10-5 M. E) KM = 4.7 × 105 M.
C) KI = 1.5 × 10-8 M
Which of the following is NOT required for the decarboxylation of pyruvate to form acetyl-CoA? a. NAD+ b. Lipoic acid c. ATP d. CoA e. FAD
c. ATP
In the enzyme catalyzed decarboxylation of acetoacetate, a Schiff base is formed between the ketone of acetoacetate and a _____ residue in the active site of the enzyme. A) Arg B) Asn C) Lys D) Glu E) Ser
C) Lys
The free energy of activation, ΔG‡, is defined as:
c. The energy required to raise the average energy of one mole of reactant to the transition state energy.
Citrate is transported out of the mitochondria into the cytosol for use in the biosynthesis of: a. glucose b. cholesterol c. fatty acids d. amino acids e. insulin
c. fatty acids
D-glucose and D-galactose are epimers. What does this statement mean? a. they are mirror images b. one is a six and the other is a five-membered cyclic form c. they differ only in the configuration about one carbon atom d. the proteins tend to be water soluble e. None of the above
c. they differ only in the config. about one C atom
In a bisubstrate reaction, reactant A binds and is then converted to product C. Next, reactant B binds and is then converted to product D. An experiment showed that B cannot bind without C being released first. What mechanism is indicated by this data? A) ordered mechanism B) random mechanism C) ping pong mechanism D) cooperative mechanism E) none of the above
C) Ping pong mechanism
How is trypsinogen converted to trypsin?
C) Proteolysis of trypsinogen forms trypsin.
Michaelis-Menten: another name for the intermediate, ES, = the ES _________
complex
The 3 most common homopolysaccharides found in nature are cellulose, starch, and ____________.
glycogen
michaelis-menten equation
is the fundamental equation of enzyme kinetics
In the ATP synthase enzyme the tight configuration:
is when phosphorylation occurs.
double-displacement (ping-pong) bisubstrate
mechanisms are characterized by parallel lines
When a reaction is at zero order, the rate is....
not affected by adding more substrate
Since pH (hydrogen ion concentration) affects enzyme function, there is an.....
optimum pH
remove phosphates from an enzyme, protein
phosphatases
What is the formation of the reaction?
the rate of the formation of enzyme-substrate complex (k1)
Invariant AA in a protein are presumed..
to be essential to the structure and function of the protein.
second order, molecularity=
two
sequential (single-displacement) reaction
two classes: random ordered
Inhibition type, acts to reduce the amount of ES that produces product
uncompetitive inhibition
Which of the following is the most effective way to increase the rate of a biochemical reaction? A) increase the temperature B) increase the concentrations of the reactants C) increase or decrease the pH D) add a catalyst E) none of the above
D) Add a catalyst
Loops and turns in proteins are A) regions that let a polypeptide chain fold back on itself. B) stretches of non-repeating three dimensional structures in proteins. C) regions causing direction change in the polypeptide backbone. D) All of the above.
D) All of the above
Protein kinases are involved in A) the digestion of drugs to potentially toxic byproducts. B) the degradation of enzymes to the component amino acids. C) the phosphorylation of a wide variety of proteins. D) the metabolism of drugs to water soluble, excretable compounds. E) all of the above
C) the phosphorylation of a wide variety of proteins.
A transition-state analog:
C)resembles the transition-state structure of the normal enzyme-substrate complex
For enzymes in which the slowest (rate-limiting) step is the reaction: ES--k2-->P, Km becomes equivalent to:
C)the dissociation constant, Kd, for the ES complex.
Penicillin and related drugs inhibit the enzyme [blank]; this enzyme is produced by
C)transpeptidase; bacteria
Allosteric enzymes:
C)usually have more than one polypeptide chain.
Zymogens are inactive enzyme precursors which are made active by Select one: A. a change in folding only. B. methylation of particular residues. C. selective proteolysis. D. a change in pH.
C. selective proteolysis.
Biotin-
CO2 groups
N-acetylglutamate activates...
Carbamoyl phosphate synthetase
Unlike coenzymes that are prosthetic groups, ____ are altered in the course of an enzyme reaction and dissociate from the active site.
Cosubstrates
The activation of the enzyme glycogen phosphorylase by phosphorylation is an example of which type of enzymatic regulation?
Covalent modification
Why will the km be low if the k1 (formation) is high?
-at this point there is a higher affinity for the substrate which causes enzyme complex formation
How can a biochemist provide a straight line to measure the enzyme-substrate complex reaction rate?
-by taking the reciprocal of the Michaelis--Menten equation which obtains a more accurate determination of the values.
In order for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity, A) [S] would need to be 2KM B) not enough information is given to make this calculation C) [S] would need to be 50% greater than KM D) [S] would need to be 3KM E) [S] would need to be 3/4KM
D
The major site of alcohol detoxification is A) Intestine B) Kidney C) Pancreas D) Liver E) Stomach
D
14) Which is a product of the intramolecular cyclization of D-tagatose to form a furanose? A) I B) II C) III D) IV
D Page Ref: Section 8-2
20) In solution α-D-glucopyranose and β-D-glucopyranose ________. A) rapidly polymerize to form a heteropolymer B) can never exist together C) form a racemic mixture D) form an equilibrium mixture
D Page Ref: Section 8-2
Changes in ionizable groups could....
-change structure of the enzyme
25) Ribitol is a A) sugar phosphate. B) deoxy sugar. C) amino sugar. D) sugar alcohol.
D Page Ref: Section 8-4
Which enzyme category often causes an isomer (same number and types of atoms but different structure) to change from one isomer to another?
-isomerases *ex. alanine racemase
In first order linear reactions, slope= what?
-k
Most enzymes are _________________ than their substrate.
-much larger
Electrons flow from a ___________________________.
-nucleophile to an electrophile
What are electron-rich atoms?
-nucleophiles
Histidine makes a ______________ attack on hydroxyl of Serine which is an ____________ because it as a partial positive charge on the hydrogen.
-nucleophilic -electrophile
Mechanisms ______________________ enzymes are known in significant detail.
-of only a few
Enzymes catalyze reactions using one or more of the following mechanisms (3):
-orienting substrates (most common) -inducing strain in substrates -adding charges to substrates
The specificity of an enzyme for a particular substrate depends on a ____________________.
-precise interlock known as the "lock and key" model
Enzyme inhibition can be _______________ or ______________.
-reversible -irreversible
The active site of most enzymes is only a __________________ of the whole protein.
-small region
57) The main reasons that glycoproteins are so diverse when compared to other proteoglycans are A) they may contain different sugars in different combinations and chain lengths. B) β or α-glycosidic linkages may join various carbon atoms in the sugars. C) they are found in both bacterial, plant and animal cells. D) A and B. E) All of the above.
D Page Ref: Section 8-7
59) The major proteoglycan in cartilage is ________. A) hyaluronic acid B) cellobiose C) link protein D) aggrecan
D Page Ref: Section 8-7
What applies to transition states?
1)Chemical bonds are in the process of being formed and broken. 2) Have lifetimes on the order of 10-14 to 10-13 seconds. 3) Differ in energy from the ground state by the activation energy.
: Section 6-3 27) What shape would a graph of reaction velocity versus pH have for an enzyme that uses both a proton donor and a proton acceptor during catalysis (both acid and base catalysis)? A) Sigmoidal. B) Hyperbolic. C) Exponential. D) Bell-shaped. E) Linear.
D bell shaped
: Section 6-6 51) The role of serine at the active site of serine proteases is to act as a(n) ________ catalyst, while the histidine residue serves as a(n) ________ catalyst. A) strong; weak B) weak; strong C) acid-base; covalent D) covalent; acid-base E) anionic; ionic
D covalent; acid base
For the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of uM/s and substrate concentration of the x-axis in units of uM, what is the Km
18 uM
Below is the structure of cyclic D-monosaccharide. Which is the anomeric carbon atom?
2
An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the Km for that substrate. After 9 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 mol. If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 mol) of product to be formed? A) 1.5 min B) 13.5 min C) 27 min D) 3 min E) 6 min
27 min
n=number of half lives, if half life is 3 days, then over fifteen days, n=?
5
Classes of enzymes
6 classes: oxidoreductases transferases hydrolases lyases isomerases ligases
29) Mitochondria differ from other cellular structures such as lysozomes or nuclei by having ________. A) a double membrane B) lipid-anchored membrane proteins C) a high level of cholesterol in the membrane D) allowing the free passage of free fatty acids across the membrane
: A Page Ref: Section 9-8
Section 5-7 47) Which equilibrium below applies to noncompetitive inhibition? A) I B) II C) III D) IV
: B II
22) A deficiency in the synthesis of sphingomyelins or cerebrosides will most likely result in the improper formation of A) cell surfaces. B) cell to cell communication. C) nerve cells. D) blood groups. E) All of the above.
: C Page Ref: Section 9-5
Section 5-3 25) The time that is required for an enzyme to convert one substrate molecule into one product molecule is A) Km. B) kcat. C) 1/Km. D) 1/kcat.
: D 1/kcat
46) Which statement is false about lipid-anchored membrane proteins? A) They are found on either leaflet of the plasma membrane. B) Like integral membrane proteins, they are permanently associated with the membrane. C) The covalent link to the membrane can involve the phosphate group of the lipid anchor. D) The protein portion that can be removed by treatment with phospholipase most resembles an integral membrane protein.
: D Page Ref: Section 9-10
Section 5-9 69) Examples of multienzyme complexes include A) fatty acid synthase. B) tryptophan synthase. C) isomerase. D) A and B. E) All of the above.
: D fatty acid synthase AND tryptophan synthase
17) Ethanolamine, serine and choline can be cleaved from glycerophospholipids by treatment with A) phospholipase A1. B) phospholipase A2. C) phospholipase B. D) phospholipase C. E) phospholipase D.
: E Page Ref: Section 9-4
Insulin _____ glycogen synthesis and _____ nutrient mobilization. A) activates; inhibits D) inhibits; activates B) activates; activates E) activates; has no effect on C) inhibits; inhibits
A
Tertiary structure of proteins describe A) polypeptide folding. B) bringing amino acids far apart in primary structure close together. C) stabilizing protein structure by non-covalent interaction. D) disulfide bridges. E) All of the above.
A) All of the above
Based on the figure below, which of the following expressions would be correct
D = 1/Vmax
The most common enzyme inhibitors are competitive inhibitors: T/F
True
True or false, all first ordered reactions are similar with slope -k when linear, etc. regardless of whether they are pertaining to radioactive materials or enzymatic, etc.
True
True or false, substances with higher binding efficiencies need less of the substance to impact the enzyme
True
What is the activated form of the monomer required to produce glycogen?
UDP-glucose
If the substrate concentration [S] equals the KM, then v0 equals 1/2 ______
VMax
THF-
Various Carbon groups
competitive inhibition, slope=alpha KM/
Vmax
turnover number (Kcat)
___ ___ is the number of substrate molecules converted to product per enzyme molecule per unit of time (sec^-1), when E is saturated with substrate *if the M-M model fits, then: k2 = Kcat = Vmax/Et*
Vmax
___ is a constant is the theoretical maximal rate of the reaction (but it is never achieved in reality) is asymptotically approached as substrate is increased
One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions ofzinc deficiency, when the enzyme may lack zinc, it would be referred to as the: A) apoenzyme. B) coenzyme. C) holoenzyme. D) prosthetic group. E) substrate.
a
steady-state assumption
a condition for the application of the michaelis -menten model to an enzymatic reaction, in which the concentration of the ES complex remains unchanged over the course of the reaction
The proximity effect of speeding an enzyme-catalyzed reaction is explained by ________.
a large loss of entropy when reactive groups are brought close to each other
In the reaction below, Y- is ________. Y- + CH2X → CH2Y + X-
a nucleophile
ATP synthesis and mitochondrial electron transport are coupled by..
a proton gradient
single-displacement reaction
a reaction in which a group is transferred from one molecule to another in a concerted fashion (with no intermediates)
ordered
a sequential reaction with a compulsory order of substrate addition to the enzyme
random
a sequential reaction without a compulsory order of substrate addition to the enzyme
The substrate specificity of serine proteases is primarily due to
a specificity pocket in the protein.
Lineweaver-Burk double reciprocal plots and types of inhibitors
a) Competitive b) Pure non-competitive c) Mixed non-competitive d) Uncompetitive
Bisubstrate reactions
a) Sequential (single-displacement): random or ordered b) Ping-pong (double-displacement)
Which one of the following statements is true of enzyme catalysts?
D) They lower the activation energy for the conversion of substrate to product.
The molecule chymotrypsinogen is known as a(n) _____. A) apoenzyme B) holoenzyme C) protease inhibitor D) zymogen E) none of the above
D) Zymogen
Which of the following must be true for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity? A) [S] must be ¾KM B) [S] must be 1.5KM C) [S] must be 2KM D) [S] must be 3KM E) [S] must be 4KM
D) [S] must be 3KM
A compound that distorts the active site, rendering the enzyme catalytically inactive is called A) a uncompetitive inhibitor B) an allosteric effector C) an inactivator D) a competitive inhibitor E) none of the above
D) a competitive inhibitor
KM is A) a measure of the catalytic efficiency of the enzyme. B) equal to half of Vmax C) the rate constant for the reaction ES → E + P. D) the [S] that half-saturates the enzyme. E) a ratio of substrate concentration relative to catalytic power.
D) the [S] that half-saturates the enzyme.
The role of the metal ion (Mg2+) in catalysis by enolase is to:
D)facilitate general base catalysis.
Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as: E+S<--k1--k-1-->ES--k2--> E+P, Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression:
D)k-1 [ES] + k2 [ES].
In addition to serine and aspartate which of the following amino acids is a member of the catalytic triad? A. threonine B. tyrosine C. glutamine D. histidine E. glycine
D. histidine
The non-enzymatic hydrolysis of sucrose into glucose and fructose is an example of a pseudo first-order reaction because Select one: A. no enzymes are involved. B. water has no role in the reaction. C. water is present at concentrations proportional to the sucrose. D. water is of such high concentration as to be considered constant.
D. water is of such high concentration as to be considered constant.
Multiple polypeptides are linked by what type of bond?
DISULFIDE
A compound that reduces the concentration of enzyme available for substrate binding is called: A) a transition-state analog B) a non-competitive inhibitor C) an allosteric effector D) an enzyme inactivator E) a competitive inhibitor
E
All are characteristics of ribozymes EXCEPT: a. They emerge from the reaction unchanged. b. They are substrate specific. c. They enhance the reaction rate. d. They are RNA molecules. e. All are true.
E
All are characteristics of the enzyme hexokinase EXCEPT: a. It is not highly specific and will catalyze phosphorylation of a number of hexoses at the six position. b. Hexoses bind the active site and induce a solvent inaccessible fit to the hexose. c. Glycerol may fit into the active site, but it does not bind to induce a conformational change necessary for catalysis. d. When a hexose binds the active site, the active site is modified to promote changes in the substrate to a transitional-state intermediate. e. All are true.
E
Enzyme activity in cells is controlled by processes including: A) temporary covalent modifications. B) modulation of expression levels. C) feedback inhibition. D) binding to allosteric effectors. E) all of the above.
E
Enzyme control is accomplished in which of the following ways? A) Genetic control B) Covalent modification C) Allosteric regulation D) Compartmentation E) All of the above are correct
E
In the Lineweaver-Burk double reciprocal plot the horizontal intercept is equal to _________. A) 1/[S] B) 1/V C) Km/Vmax D) 1/Vmax E) -1/Km
E
Ion channels can open in response to which of the following A) Changes in membrane potential D) A and C B) Changes in pH E) All of the above C) Binding of a specific ligand
E
Membrane fluidity is influenced by A) van der Waals contacts D) cholesterol concentration within the membrane B) acyl chain length E) all of the above C) degree of acyl chain saturation
E
Which of the following can be a hormone? A) amino acid derivatives D) eicosanoids B) steroids E) all of the above C) polypeptides
E
Which of the following is not an important metal in biological systems? A) Na+ B) K+ C) Mg++ D) Cu++ E) Ba++
E
If an enzyme-catalyzed reaction with a KM of 3.5 mM has a velocity of 5 mM/min at a substrate concentration of 0.5 mM, what is the Vmax? A) 0.625 mM/min B) 15 mM/min C) 17.5 mM/min D) 35 mM/min E) 40 mM/min
E) 40 mM/min
Which of the following is true regarding heparin? A) it is an allosteric activator of antithrombin B) it is a sulfated polysaccharide C) it simultaneously binds to antithrombin and the target of antithrombin D) it is used clinically as an anticoagulant E) all of the above
E) All of the above
What amino acid residue present in the specificity pocket allows trypsin to bind to peptides containing Arg or Lys? A) Ser B) His C) Lys D) Val E) Asp
E) Asp
An inhibitor that binds to the active site only in the absence of the substrate and in a reversible fashion is a(n) _____. A) allosteric inhibitor B) suicide substrate C) mixed inhibitor D) noncompetitive inhibitor E) competitive inhibitor
E) Competitive inhibitor
Compounds that function as "mixed inhibitors" I. interfere with substrate binding to the enzyme. II. bind to the enzyme reversibly. III. can bind to the enzyme/substrate complex. A) I B) II C) III D) II, III E) I, II, III
E) I, II, III
Which of the following amino acids can participate in covalent catalysis? A. tryptophan B. tyrosine C. serine D. histidine E. both C and D are correct
E. both C and D are correct
Which of the following is not present in the active site of alcohol dehydrogenase? A. Zn++ B. histidine C. cysteine D. NAD+ E. proline
E. proline
When oxygen is bound to the heme group of myoglobin, it is coordinated between ____________ and ___________.
E7 His; Fe2+ of heme
In uncompetitive inhibition, the inhibitor binds only to the ______.
ES complex
Triglyceride (TAG) function?
Energy storage
Isoprene function?
Essential oils of plants
Which step in an enzyme-catalyzed reaction was assumed.. to be negligible by Michaelis and Menton?
Formation of ES from E + P.
An enzyme is generated by a transcriptional activator:
Genetic control
What heteropolysaccharide family is described as a chain of repeating disaccharide units?
Glucosaminoglycans
Which AA does not exhibit chirality?
Glycine
Which represents a hydride ion?
H-
Osmosis occurs in order to relieve concentration gradients across membrane. is cells are placed in HYPOtonic solution they will swell and burst as water rushes in to relieve the gradient. this process is known as ..
Hemolysis
An enzyme family called the _________ catalyze the phosphorylation of hexoses in the body.
Hexokinases
What amino acid would most likely be found in the active site of an enzyme that uses acid-base catalysis?
His
The property of water that is most responsible for its unique thermal properties and utility as a biological solvent is:
Hydrogen Bonding
Which is a product of the intramolecular cyclization of D-tagatose to from a furanose?
IV
The term synthetase is included in which class of enzymes a. Ligases b. hydrolases c. transferases d. lyases e. isomerases
Ligases
The R-groups of which AA could participate in the formation of salt bridge electrostatic interaction?
Lysine & Glutamate
Fatty acid synthesis begins with the carboxylation of acetyl CoA to form ____________.
Malonyl-CoA
Ubiquitin proteasomal system (UPS)
Marks proteins for degradation
Steroid function?
Membrane fluidity
Which type of atom is involved in the reactive center of lipoamide?
Sulfur
An example of an antioxidant enzyme made in our bodies is:
Superoxide dismutase
Transitions states bind to their enzymes more tightly than their substrates do
T
Vitamin deficiency diseases are a result of the lack of formation of certain coenzymes.
T
Intermediates are more stable and have longer lifetimes than transition states
TRUE
Nucleophiles are often anions or have unshared e-s: T or F
TRUE
What level of protein structure involves hydrophobic interaction, electrostatic interactions, hydrogen bonds and covalent bonds between the side chains of AA that are far apart in the AA sequence?
Tertiary structure
rectangular hyperbolic
The Michaelis-Menten equation describes a "___ ___" dependence of v on [S]
For an endothermic reaction the be spontaneous, what must occur?
The entropy must increase substantially
An enzyme used in both glycolysis and gluconeogenesis is: a. 3-phosphoglycerate kinase b. glucose 6-phosphatase c. hexokinase d. PFK-1 e pyruvate kinase
a. 3-phosphoglycerate kinase
In the glutamate:aspartate aminotransferase catalyzed reaction mechanism, glutamate would react with ____________ to form α-ketoglutarate.
a. E-pyridoxal phosphate complex
In uncompetitive inhibition:
a. I combines only with ES.
Which statement is correct about the Michaelis-Menten constant, Km, for the kinetic mechanism below? k1 k2 E + S ↔ ES → E + P k-1
a. It is numerically equal to the substrate concentration required to achieve one half the maximum velocity.
In the reaction mechanism below, _________ are competitive for binding to free enzyme E.
a. P and A
Exergonic reactions (negative delta G) proceed only after the addition of a small amount of energy called the _______________________.
activation energy (Ea)
Post prandial-
after a meal
Enzyme activity may be controlled by ________ effectors
allosteric
Reversible, non covalent regulation that requires effector molecules:
allosteric regulation
One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the: A) apoenzyme. B) coenzyme. C) holoenzyme. D) prosthetic group. E) substrate.
apoenzyme.
which of the following statements regarding enzymes and transition states is true a. stabilization of the transition state must be less than stabilization of ES for catalysis to occur b. binding of substrate to an enzyme often causes strain, thus promoting transition state formation c. the transition state conformation of an enzyme catalyzed reaction is identical to the conformation seen in the uncatalyzed transition state d. formation of the transition state always assures that the reaction will proceed to product e. none of the above are true
b. (binding of substrate to an enzyme often causes strain, thus promoting transition state formation)
in the chymotrypsin reaction mechanism there is a low barrier hydrogen bond (LBHB) formed between a. Asp 102 and Ser 195 b. Asp 102 and His 57 c. His 57 and Ser 195 d. Ser 195 and carbonyl oxygen in peptide bond e. none of the above
b. asp 102 and his 57
Malonate inhibition of succinate dehydrogenase is an example of:
b. competitive inhibition.
When blood glucose is abnormally low the pancrease releases: a. insulin b. glucagon c. epinephrine d. trypsin e. glucose
b. glucagon
The catalytically active complex of an apoenzyme and its prosthetic group is referred to a(n) _______________.
b. holoenzyme
Drugs called statins lower cholesterol levels because they: a. bind bile salts b. inhibit HMG-CoA reductase c. bind serum cholesterol d. degrade HMG-CoA reductase
b. inhibit HMG-CoA reductase
The proteins of electron transport/oxidative phosphorylation are located within the: a. outer mitochondrial membrane b. inner mitochondrial membrane c. cytosol d. endoplasmic reticulum
b. inner mitochondrial membrane
Which amino acid is least likely to participate in the acid-base catalysis? a. aspartate b. leucine c. lysine d. histidine
b. leucine: nonpolar
The International Units of an enzyme are based on the:
b. micromoles of product formed per minute.
AA catabolism-
begins with deanimation.
We study kinetics to discover ___________ affinities
binding
Liklihood and/or strength of something binding can be described by
binding affinity
Living cells use ______________________ to increase rates of chemical reactions.
biological catalysts
kinetics
branch of science concerned with the *rates of reactions*
For an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. Which of the following would be closest to the value of Vmax? [S] (mM) Vo(mM/min) 1.0 2.0 4.0 2.8
c. 3.19 mM/min
In the enzyme catalyzed reaction sequence below, can the E-PO4- intermediate be predicted and why?
c. No, the reaction is random single-displacement.
How do catalysts work to accelerate a chemical reaction?
c. They lower the energy of activation.
The active site of a certain enzyme contains a serine residue. When the enzyme is incubated for a short time with its substrate, a form of the enzyme in which the active site serine is acetylated can be isolated and purified. In the native protein the serine is never found to be acetylated. This information supports: a. intermediate stabilization effects b. a polar gorup catalytic mechanism c. a covalent catalysis mode d. the acid-base catalysis mode
c. a covalent catalysis mode
Which of the following statements describes integral membrane proteins? a. they do not completely span the lipid bilayer b. they are easily removed by changes in pH or high salt c. amino acids that contact the membrane are hydrophobic d. the proteins tend to be water soluble e. None of the above
c. amino acids that contact the membrane are hydrophobic
A good transition state analog a. is too unstable to isolate b. binds covalently to the enzyme c. binds to the enzyme more tightly than the substrate d. binds very weakly to the enzyme
c. binds to the enzyme more tightly than the substrate
Mitochondria: a. carry out glycolysis b. make lipoprotein c. carry out citric acid cycle d. synthesize sterols e. hydroxylate drugs
c. carry out citric acid cycle (not glycolysis, which occurs in cytosol)
Which of the following monsaccharides is not an aldose? a. ribose b. glucose c. fructose d. galactose
c. fructose
Enzymes work by:
c. lowering the activation energy of the reaction
Epinephrine triggers an increased glycogen breakdown in muscle by causing a. activation of hexokinase b. activation of PFK c. conversion of glycogen phosphorylase b to glycogen phosphorylase a d. the Pasteur effect
c. pg 376
Penicillin is an example of a mechanism-based enzyme inactivator and is a(n):
c. suicide substrate.
Which of these statements about facilitated diffusion across a membrane is true? a. It can increase the size of a transmembrane concentration gradient of the diffusing solute b. its rate is limited by the solubility of the transported solute in the nonpolar interior of the lipid bilayer c. A specific membrane protein promotes the movement of the solute through the membrane d. it is responsible for the transport of gases such as O2, N2, and Ch3 across biological membranes
c. uses specific membrane pros
In transforming the Michaelis-Menten equation into a straight line equation, y = mx + b, the Lineweaver-Burk double reciprocal plot, which of the following is NOT a true representation?
c. x-intercept is 1/Km
Which as a higher affinity for the substrate: carbonic anhydrase (km of 0.026 M) or catalase (km of 1.1 M)?
carbonic anhydrase (km of 0.026 M) because it has a lower km
Which enzyme below is fastest?
catalase, k cat= 10^7
What is the catalytic mechanism where two substrates are along a single binding surface? -ex. NMP kinases bringing two nucleotides together
catalysis by approximation
A ___________________ is any substance that speeds up a chemical reaction without itself being used up.
catalyst
We study kinetics to discover Max. ____________ rates
catalytic
The most efficient enzymes have values near the diffusion controlled upper limit, known as __________ __________
catalytic perfection
definitions
catalytic power, specificity, cofactors (metal ions, coenzymes)
Histidine functions at a pH of _______ and its pka is ________.
-8 -6
What is the triad of amino acids in the active site of serine proteases?
-Aspartate 102 -Histidine 57 -Serine 195
Which has a higher turnover rate which means measure of rate substrate is being converted into product: carbonic anhydrase 4*10^5 s-1 kcat or catalase (4*10^7 s-1 kcat)?
-Catalase because it has a higher turnover rate or kcat
______________ bind reversibly to the enzyme at the active site, thus competing with substrate binding.
-Competitive inhibition
Which reaction occurs when first product is released before second substrate binds?
-Double--Displacement Reaction
Which order is rate= k[A]1?
-First order
Which order is unimolecular meaning no collisions are required?
-First order
_______________ is a key amino acid in many enzymes because....
-Histidine -its side chain has a pka of 6.0 which is right at physiological pH. This causes it to act as an acid or base (protonating and deprotonating substrates)
What are the steps for the mechanism of chymotrypsin catalysis?
-Histidine 57 removes hydrogen from Serine 195 hydroxyl and becomes a electrophile -Serine 195's nucleophilic oxygen attacks carbonyl C of substrate -Histidine 57 donates hydrogen (becoming nucleophilic) to nitrogen of sissile peptide bond, which causes the tetrahedral intermediate to decompose -The portion (the C-terminal end) of the original substrate with the new amino terminus diffuses away -Water donates hydrogen to Histidine 57 (becomes an electrophile again) -Resulting hydroxide attacks carbonyl of remaining substrate -Histidine 57 donates hydrogen (becomes nucleophile) to Serine 195's oxygen, which leads to the collapse of the second tetrahedral intermediate -The portion (N-terminal end) of the original substrate with new carboxylate terminus diffuses away.
_____________________________ instituted a naming convention for enzymes based upon the type of chemical reaction catalyzed.
-International Union of Biochemistry (IUB)
Which enzyme inhibition occurs when the inhibitor permanently impairs the enzyme?
-Irreversible inhibition (poisons or toxins)
What is the straight-line graph for the enzyme-substrate complex reaction rate?
-Lineweaver--Burk Plot
What relates the concept of enzyme substrate complexes?
-Michaelis--Menten Kinetics -E+S--k1-->ES--k2--> E+P <--k-1--
_______________ can bind reversibly to the enzyme-substate (ES) complex at a site other than the active site. This is known as the allosteric site.
-Noncompetitive inhibitor
What are the 6 major Enzyme categories?
-Oxidoreductases -Transferases -Hydrolases -Lyases -Isomerases -Ligases
Which order is bimolecular and does require collisions?
-Second order
Which order is rate= k[A]1[B]1?
-Second order
Which reaction CANNOT precede until all substrates are bound to the enzyme active site?
-Sequential Reaction (ordered and random)
___________________ are a type of inhibition that involves binding only after substrate is bound.
-Uncompetitive
What is the Michaelis--Menten equation?
-V= Vmax*[S]/[S] + km
__________ is the maximum velocity a reaction can attain.
-Vmax
What type of curve is the Michaelis--Menten graph?
-a hyperbolic curve which eventually plateaus off because enzymes are running out.
Base acts as ____________ while water acts as _____________.
-a nucleophile -an electrophile
The _______________ of enzymes are lined with amino acids that create a ____________________________.
-active sites -microenvironment conducive to catalysis
Serine proteases hydrolyze peptide bonds _____________ to aromatic acids.
-adjacent
________________ catalyzes the reversible oxidation of aldehydes or ketones.
-alcohol dehydrogenase
Uncompetitive inhibitors bind at the __________________.
-allosteric site
In living systems, inhibitors ______________ because they regulate metabolic pathways.
-are important
Histidine is actually _______________, and it has a lone pair on the other nitrogen atom which makes it a _____________.
-aromatic -nucleophile (electron rich)
coenzymes..
-assist in catalysis -are chemically altered in the reaction -transiently bind to the enzyme. They are NOT part of the AA sequence of the enzyme.
Since Histidine becomes positive when the hydrogen from Serine binds to its nitrogen, it is now acting as a _________________.
-base because it is accepting the hydrogen
Living systems _____________________ temperature without _______________________.
-cannot increase -the risk of damaging structures, so they use catalysts
Residues can be _________________ or ____________________
-catalytic -noncatalytic
Scientists use x-ray crystallography, chemical inactivation, and modeling to understand ____________________ of organisms.
-catalytic mechanisms
Change in environmental factor could....
-change the enzyme structure and therefore function
Uncompetitive inhibition km and Vmax are ____________ although ratio is _______________.
-changed -the same
In competitive inhibition, km__________ but vmax __________.
-changes (becomes greater) -stays the same
NAD+ is a very common ________________.
-coenzyme
In reversible oxidation of alcohols to aldehydes or ketones, zinc acts as a _________________.
-cofactor
Some enzymes require certain nonprotein components to function known as....
-cofactors (minerals) -coenzymes (vitamins)
What are the three types of reversible inhibition?
-competitive -noncompetitive -uncompetitive
In Chymotrypsin, serine 195 acts as a __________________.
-covalent catalysis
The probable mechanism of chymotrypsin involves a two step reaction known as.....
-covalent catalysis
What is the formation of an unstable covalent bond with a nucleophilic group and an electrophilic group on the enzyme?
-covalent catalysis
Enzymes are proteins that become ___________________ at high temperatures.
-denatured
Normally, aspartic acid needs to be _______________ to function.
-deprotonated (aspartate)
Order is useful in....
-describing reactions; it is typically determined experimentally.
The ______________ of a reaction can be predicted if ____________ is known, but ______ the ________________ of the reaction.
-direction -delta G (free energy) -not -rate
Biochemists _______ like hyperbolic graphs.
-do not because it is harder to measure. It provides an equation (y=mx+b).
____________________ plots may be used to distinguish competitive, noncompetitive, and uncompetitive inhibition.
-double-reciprocal
What are electron-deficient atoms?
-electrophiles
Kinetics also measures the.....
-enzyme affinity for the substrates and inhibitors.
The higher the temperature, the _______________ the reaction rate due to.....
-faster -increased number of collisions
The ________________________ is the amount of energy to convert 1 mol of substrate (reactant) from the ground state to the ____________________.
-free energy of activation (delta G++) -transition state
Examples of reactive intermediates include.....
-free radicals, carbocations, and carbanions
Side chains of amino acids (e.g. histidine, lysine, and aspartate) can be used as _______________________.
-general acids or bases
What is the time for one-half of the reactant to be consumed?
-half-life
Name a feature of transition metals that make them efficient cofactors?
-have high concentration of positive charge -can act as lewis acid -can exist as a variety of valence states -are efficient electrophiles
Intact functional enzymes with cofactors are ________________________.
-holoenzymes
In reversible oxidation of alcohols to aldehydes or ketones, NAD+ is used as a _____________.
-hydride (H-) (ion acceptor)
After Histidine makes a nucleophilic attack on the hydroxyl of serine, the.....
-hydrogen comes off and becomes part of Histidine which then makes Histidine positive.
Which enzyme category hydrolyzes a molecule by adding water to break a bond?
-hydrolases *ex. pepsin and chymotrypsin
The change in enzyme shape caused by substate binding is called ___________________.
-induced fit
Enzymes have both the ________________ and _______________ model.
-induced fit -lock and key
Uncompetitive inhibitors are ________________ at low substrate concentrations.
-ineffective
The velocity at the beginning of a reaction when the concentration of substrate greatly ______________ enzyme concentration.
-initial velocity (v--subzero) -exceeds
One or more ________________ may form during the course of a reaction.
-intermediates
Catalytic activity is related to ________________ of the active site.
-ionic state
What is the kcat formula?
-kcat is the Vmax over the total enzyme concentration. -kcat= Vmax/[Et]
In terms of the "lock and key" model, the substrate is the ___________.
-key
If k-1 + k2 (depletion) are high, the km will be....
-large
Which enzyme category forms bonds?
-ligases *ex. pyruvate carboxylase
In terms of the "lock and key" model, the enzyme is the _____________.
-lock
Stabilizing the transition state, _______________ the free energy of activation (Ea) and _______________ reaction rate.
-lowers -increases
Which enzyme category often has to do with double bonds?
-lyases *ex. pyruvate decarboxylase
What are noncatalytic residues?
-other side chains that are important in the positioning of the substrate as well as making the environment for the active site conductive for the substrate to bind
Increasing substrate concentration _______________ competitive inhibition.
-overcomes
Increased substrate concentration ________________ reverses noncompetitive inhibition
-partially -this is only for pure noncompetitive inhibition
Eventually as time continues, the line on the graph __________________.
-plateaus
Acid-Base catalysis involves _____________ which is an important factor in chemical reactions.
-proton transfer
Information about reaction rates is the ___________________ study of enzyme catalysis, or enzyme kinetics.
-quantitative
Hydrolysis for an ester takes place if the pH is ______________.
-raised -this is known as hydroxide ion catalysis
A ___________________ is a step-by-step description of a reaction.
-reaction mechanism
What are catalytic residues?
-side chains that are protonated (electrophile) or deprotonated (nucleophile) that are critical in the step-by-step process known as "catalytic mechanism"
Induced fit at least partly explains why enzymes are ________________.
-so large
What reflects the relationship between the catalytic rate and substrate binding affinity?
-specificity constant (kcat/km)
Thermodynamics can predict whether a reaction is ___________________ but can not predict _______________
-spontaneous -rate
In Chymotrypsin, aspartate 102 is known for _________________ histidine.
-stabilizing
In noncompetitive inhibition, km _____________ but Vmax _____________.
-stays the same -changes (will be lower with noncompetitive inhibitor)
In catalytic mechanisms, there is often a ___________________.
-tetrahedral intermediate
Will rate be low or high if the km is low?
-the rate will be high if the km value is low because enzyme substrate (ES) complex is forming quickly
Will the rate be low or high if the km is high?
-the rate will be low because the enzyme-substrate complex is not forming quickly due to a lower affinity for the substrate
Why will the km be large if the depletion (k-1 + k2) is high?
-there is not a high affinity for the substrate which causes enzyme-substrate complex formation
Two other functions of enzymes are.....
-to provide a framework so that the amino acids of the active site are properly positioned -to participate in the small changes in protein shape that allow induced fit
Which enzyme category transfers functional groups such as a methyl or phosphate group?
-transferases *ex. hexokinase
Serine proteases have a _______________ of amino acids in their active site.
-triad
kcat is also known as the __________________.
-turnover number
effects of temperature on enzyme activity
1) enzyme rate typically doubles in rate for every 10º C, as long as the enzyme is stable and active 2) at higher temperatures, the protein becomes unstable and denaturation occurs (loss of structure and function)
The assumptions made in calculating the Michaelis-Menten Equation include
1) that the formation and decomposition of ES is the same for a period of time.B) that 2)that the concentration of the substrate is much greater than the concentration of 3) that the value of k-2 can be ignored.
FALSE statements about enzymes
1)Enzymes are chemically unchanged during the actual catalytic process. 2) Enzymes are always made of protein.
SOD (superoxide dismutase) is an enzyme that reacts faster than the rate of diffusion of the substrate to the active site due to
1)its negative charge. 2) electrostatic effects. 3) the deep channel in the enzyme protein. 4) the copper atom at the active site.
Unlike typical catalyzed reactions in organic chemistry enzyme reactions are...
1)usually stereospecific. 2) reaction specific. 3) essentially 100% efficient. 4) modulated to change activity levels.
25) The time that is required for an enzyme to convert one substrate molecule into one product molecule is a
1/kat
Acid-base catalysis is estimated to accelerate a typical enzymatic reaction by what factor?
10 to 100 fold increase
If the rate constant for the enzyme catalyzed reaction is 2 X 10^5/sec and the rate constant for the uncatalyzed reaction is 2 X 10^-6/sec, the catalytic power of the enzyme is:
10^11
In the B-oxidation of fatty acids the sequence of events is:
1: oxidation (FAD) 2: hydration 3: oxidation (NAD) 4: thiolysis
In the glycolytic pathway (oxidation of glucose to pyruvate) ____________ moles of ATP are invested per mole of glucose entering the pathway.
2
How many molecules of ATP are generated when two molecules of acetyl coA are converted to four molecules of CO2 via the citric acid cycle? Explain.
20 isocitrate dehydrogenase: 2.5 Alpha ketoglutarate dehydrogenase: 2.5 succinyl-coA synthase: 1.0 succinate dehydrogenase complex: 1.5 malate dehydrogenase: 2.5 10 * 2 = 20
On the energy diagram below, which point represents a transition state?
3 (second peak)
Calculate the pH of a mixture of 0.30M acetic Acid and 0.10 M sodium acetate . The Ka of acetic acid is 1.73 x10^-5.
4.28
Section 5-4 31) The enymatic rate constant (kcat/Km) of orotidine 5'-phosphate decarboxylase is 6 × 107 M-1s-1 and the nonenzymatic rate constant (kn) is 3 × 10-16 s-1. What is the value of the enzyme's catalytic proficiency? A) 2 × 1023 M-1 B) 5 × 10-24 M C) 12 × 10-9 M-1s-2 D) 8.3 × 107 Ms2 E) Cannot calculate the proficiency without knowing the value of Vmax.
: A 2 x 10^23
49) Why should it not be surprising that for many cells water requires a protein for its transport across a membrane? A) Water is very polar which inhibits its free diffusion across the membrane. B) All molecules require transport proteins to cross a membrane. C) The transport protein is needed to prevent the hydrolysis of the phospholipid chains as water crosses the membrane. D) There is never a concentration gradient for water across the membrane to drive its transport.
: A Page Ref: Section 9-11
50) In the mitochondria phosphate ion (PO43-) and H+ are transported together from the intermembrane space into the matrix. Which statement applies? A) The transport protein is a symport. B) The transport protein must have a relatively large central channel to accommodate both ions. C) The interior of the transport protein must be uncharged. D) All of the above.
: A Page Ref: Section 9-11
55) Valinomycin is an antibiotic that kills bacteria by surrounding K+ ions and shuttling them down their concentration gradient and across membranes. Which might be a cause of cell death? A) Disruption of secondary transport processes that depend on the K+ concentration gradient. B) Change in the pH of the bacterial cytosol. C) Blocking of bacterial pores with K+ ions. D) Massive denaturation of bacterial proteins upon change of the K+ concentration.
: A Page Ref: Section 9-11
60) Which statement is not true about G proteins? A) They are integral membrane proteins. B) They are multisubunit proteins consisting of α, β and γ subunits. C) They are slowly inactivated by their own GTPase activity. D) They act as transducers for hormones.
: A Page Ref: Section 9-12
62) The toxins from cholera and whooping cough both interfere with the proper functioning of ________. A) G proteins B) DNA polymerase C) ATP synthesis D) protein kinase A
: A Page Ref: Section 9-12
63) Which is not involved in signal transduction? A) Glycolytic pathway. B) Receptor tyrosine kinases. C) Adenylyl cyclase pathway. D) Inositol-phospholipid pathway.
: A Page Ref: Section 9-12
5) Which statement is true about the usual concentration of free fatty acids in cells? A) The concentration is low because it could disrupt cell membranes. B) The concentration is low because fatty acids are synthesized in the extracellular fluid. C) The concentration is high because of the demand for fatty acids in cell membranes. D) The concentration is high because the mitochondria are continuously synthesizing them.
: A Page Ref: Section 9-2
Section 5-4 29) The ratio of kcat/Km for each of two different substrates present in equal concentrations in an enzyme reaction will measure enzyme affinity because A) the rates of P formation are given by the values found for each substrate. B) the rates of P formation are the same for each substrate. C) it is an indication of the formation of ES for each substrate. D) All of the above.
: A The rates of P formation are given by the values found for each substrate
Section 5-9 58) Two curves showing the rate versus substrate concentration are shown below for an enzyme-catalyzed reaction. One curve is for the reaction in the presence of substance X. The other curve is for data in the absence of substance X. Examine the curves and tell which statement below is true. A) X is an activator of the enzyme. B) The catalysis shows Michaelis-Menten kinetics. with or without X. C) X increases the activation energy for the catalytic reaction. D) X could be a competitive inhibitor.
: A X is an activator of the enzyme
Section 5-9 67) Interconvertible enzymes ________. A) are those controlled by covalent modification B) follow a concerted mechanism to go back and forth between the T and R states C) catalyze reactions to covalently modify another enzyme D) are allosteric modulators
: A are those controlled by COVALENT modification
Section 5-7 51) The following data were obtained in the presence and absence of inhibitor. What type of inhibition is shown? Substrate concentration (millimolar) Rate without inhibitor (mmol/min) Rate with inhibitor (mmol/min) 0.100 2.5 1.6 0.200 4.2 2.9 0.500 6.6 5.1 0.750 7.4 6.2 1.000 9.9 9.8 2.000 10.0 10.1 A) Competitive. B) Uncompetitive. C) Noncompetitive. D) Irreversible. E) Cannot tell inhibition type from the information given.
: A competitive
Section 5-9 62) The ________ theory explains cooperative binding by suggesting all subunits of a given protein have the same conformation, either all R or all T. A) concerted B) entropy-driven C) sequential D) simultaneous
: A concerted
Section 5-7 48) Ethanol (CH3CH2OH) is an alcohol found in beverages. It is oxidized in the body to acetaldehyde by the enzyme alcohol dehydrogenase. Methanol (CH3OH), also known as wood alcohol, is converted to formaldehyde by the same enzyme. Acetaldehyde is toxic, but formaldehyde is far more toxic to humans, which is why the ingestion of relatively small amounts of methanol can cause blindness or death. One treatment for mild methanol poisoning is the administration of ethanol. Why might a doctor choose this treatment? A) Ethanol acts as a competitive inhibitor with respect to methanol as a substrate for the alcohol dehydrogenase and therefore slows the formation of formaldehyde. B) Ethanol likely irreversibly binds to alcohol dehydrogenase which prevents the formation of formaldehyde. C) The ethanol is likely an uncompetitive inhibitor and binds to a site other than the active site of the enzyme. D) The doctor has given up on the patient and administers ethanol for sedation.
: A ethanol acts as a competitive inhibitor with respect to methanol as a substrate for the alcohol dehydrogenase and therefore slows the formation of formaldehyde
Section 5-9 61) The "T" state refers to the ________. A) inactive conformation of the enzyme B) transition state of the product C) form of the enzyme without the modulator bound at the regulatory site D) denatured form of the enzyme
: A inactive conformation of the enzyme
Section 5-9 55) Which statement is false about allosteric regulation? A) It is usually the mode of regulation for the last step in reaction pathways since this step produces the final product. B) Cellular response is faster with allosteric control than by controlling enzyme concentration in the cell. C) The regulation usually is important to the conservation of energy and materials in cells. D) Allosteric modulators bind non-covalently at sites other than the active site and induce conformational changes in the enzyme.
: A it is usually the mode of regulation for the last step in reaction pathways since the step produces the final product
Section 5-9 60) Allosteric modulators seldom resemble the substrate or product of the enzyme. What does this observation show? A) Modulators likely bind at a site other than the active site. B) Modulators always act as activators. C) Modulators bind non-covalently to the enzyme. D) The enzyme catalyzes more than one reaction.
: A modulator likely bond at a site other than the active site
Section 5-2 12) When there are two substrates in a reaction, the reaction is said to be second order if ________. A) the reaction is first order with respect to each substrate concentration B) the maximum rate is independent of either substrate's concentration C) the substrate concentrations are equal D) it proceeds at twice the rate upon double the concentrations of both substrates
: A the reaction is first order with respect to each substrate concentration
Section 5-9 56) Which statement is false about regulatory enzymes that are controlled allosterically? A) They are always less active when a modulator is bound to them. B) They are often larger than other enzymes. C) They have more than one binding site. D) They often catalyze the first step in a reaction pathway.
: A they are always less active when a modulator is bound to them
Section 5-2 11) When two different substrates react to form two different products, the rate constants for each separate substrate can be determined by A) varying one substrate at a time, keeping the other in excess. B) varying both substrates and measuring the appearance of the two products. C) limiting one substrate and varying the other. D) keeping both substrate concentrations high and detecting one product at a time.
: A varying one subtance at a time, keeping the other in excess
Section 5-3 24) The expression: Vmax = k2[E]total applies to A) zero order kinetics of an enzyme-catalyzed reaction. B) first order kinetics of an enzyme-catalyzed reaction. C) second order kinetics of an enzyme-catalyzed reaction. D) only the initial part (near time = zero) of an enzyme-catalyzed reaction.
: A zero order kinetics of an enzyme catalyzed reaction
Section 5-3 23) Calculate the value of the maximum velocity for an enzyme-catalyzed reaction that follows Michaelis-Menton kinetics if the initial velocity is 6 mM/s at a substrate concentration of 6 mM. The KM for the enzyme system is 2 mM. A) 4.5 mM B) 8 mM C) 8.75 mM D) 12 mM E) 66 mM
: B 8 mM
40) Determination of the tertiary structure of a membrane protein finds that the outer surface is composed primarily of hydrophobic residues. Which conclusion is most likely from this observation? A) It is a lipid-anchored membrane protein. B) It is an integral protein. C) The protein must be involved in passive transport. D) The protein can undergo transverse diffusion.
: B Page Ref: Section 9-10
41) Membrane passive transport and transport by channels and pores requires ________. A) energy input B) a protein carrier C) hexanoic acid D) ion gradients
: B Page Ref: Section 9-10
43) Which type of membrane protein might be dissociated from the membrane by changing the pH or the ionic strength? A) Integral membrane protein. B) Peripheral membrane protein. C) Lipid-anchored membrane protein. D) All of the above.
: B Page Ref: Section 9-10 / 44) You have purified a cell membrane and wish to isolate a transport protein from it. Which treatment might you select? A) Add a detergent. B) Change the ionic strength. C) React with a protease. D) Add phenylisothiocyanate (PITC). Answer: A Page Ref: Section 9-10
52) If the concentration of a solute is the same both inside and outside the cell, what might you expect with regard to its transport by a membrane protein? A) Since there is no concentration gradient, no transport either in or out of the cell is possible. B) Movement of the solute across the membrane could occur and cause accumulation on one side of the membrane by an active transport protein. C) The transport protein has been saturated. D) The solute must be phosphorylated with a phosphate group from ATP before further transport can occur.
: B Page Ref: Section 9-11
54) Which can serve as an energy source for secondary active transport? A) Light. B) Ion concentration gradient. C) Electron transport. D) ATP → ADP.
: B Page Ref: Section 9-11
56) The membrane transport protein Na+-K+ ATPase carries both Na+ and K+ ions across the plasma membrane. Typically the concentration of K+ inside cells is about 30 times higher inside the cell than outside. The concentration of Na+ is about 20 times less inside the cell than outside. Based on this information, which statement below is false? A) The proper functioning of Na+-K+ ATPase could serve as an energy source for secondary active transport proteins. B) It is a symport. C) Transport of Na+ and K+ must be coupled to an exergonic reaction. D) Na+-K+ ATPase likely undergoes conformational changes during transport.
: B Page Ref: Section 9-11
15) Triacylglycerols are not found in cell membranes because they are A) amphipathic. B) not amphipathic. C) not abundant in cells. D) charged at biological pH.
: B Page Ref: Section 9-3
18) Glycerophospholipids have ________ heads and long ________ fatty acid tails. A) polar; polar B) polar; hydrophobic C) hydrophobic; polar D) hydrophobic; hydrophobic
: B Page Ref: Section 9-4
24) Sterols are steroids which have A) a hydroxyl group at position C-17. B) a hydroxyl group at position C-3. C) the ability to accumulate as plaques in blood vessels. D) 5 fused rings instead of 4 fused rings. E) hydroxyl groups at both position C-3 and C-17.
: B Page Ref: Section 9-6
26) Which is not a function of cholesterol in mammals? A) Precursor of bile salts. B) Transport of Ca2+ across membranes. C) Modulate the fluidity of membranes. D) Precursor of steroid hormones.
: B Page Ref: Section 9-6
28) Triacylglycerols cannot form lipid bilayers because they A) have hydrophobic tails. B) do not have polar heads. C) cannot associate with cholesterol. D) have polar heads. E) cannot engage in hydrophobic interactions.
: B Page Ref: Section 9-8
32) A sea creature richer in ________ can more likely live or migrate to an area of low temperature. A) arachidonic acid B) unsaturated fatty acids C) saturated fatty acids D) eicosanoids E) All of the above
: B Page Ref: Section 9-9
38) Regions on cell membranes called lipid rafts form because A) membrane proteins form them. B) cholesterol preferentially associates with sphingolipids. C) certain membrane protein patches aggregate. D) cholesterol and proteins bind to form them.
: B Page Ref: Section 9-9
Section 5-7 46) Nonclassical competitive inhibition involves ________. A) binding of the substrate at both the active site and at the inhibitor site B) binding of either the substrate to the active site or the inhibitor to its own binding site thus preventing the other from binding C) binding of the inhibitor to the substrate followed by binding of this complex to the active site D) chemical removal of the substrate from the active site by reaction with the inhibitor
: B binding of either the substrate to the active site or the inhibitor to its own binding site thus preventing the other from binding
Section 5-5 36) The Km values for enzyme reactions such as A + B → C + D A) cannot be determined using the Lineweaver-Burk plot analysis. B) can be determined by holding one (A or B) at high concentration, while varying the concentration of the other substrate. C) can be determined for one substrate and not the other. D) do not indicate the efficiency of the enzyme.
: B can be determined by holding one at high concentration, while varying the other substrate
Section 5-1 9) In a first order enzyme-catalyzed reaction, the velocity of the reaction is proportional to the ________, while in a zero order enzyme-catalyzed reaction, the velocity of the reaction is proportional to the ________. A) amount of enzyme; concentration of substrate B) concentration of substrate; amount of enzyme C) concentration of substrate; speed of the reaction D) speed of the reaction; concentration of substrate
: B concentration of the substrate; amount of enzyme
Section 5-6 42) Which statement is true about the removal of reversible inhibitors from enzyme solutions? A) PAGE is the primary technique used for this purpose. B) Dialysis and gel filtration are often used. C) These inhibitors cannot be separated from the enzyme without treatment with diisopropylfluorophosphate. D) Removal of reversible inhibitors is extremely difficult and can be achieved only after many purification steps.
: B dialysis and gel filtration are often used
2) Which of the following statements is FALSE? A) The word enzyme is from a Greek word meaning "in yeast." B) Enzymes are always made of protein. C) The first enzyme was crystallized in 1926. D) Enzymes can couple two different reactions.
: B enzymes are always made of protein
Section 5-5 37) Which might be a method used for distinguishing among several mechanistic possibilities in a multi-substrate reaction? A) Measure Km in the presence of one substrate at a time. B) Measure the rate with respect to one substrate while varying the concentration of another substrate. C) Measure the rate while adding inactivators for all but one substrate. D) Any of the above.
: B measure the rate with respect to one substrate while varying the concentration of another substrate
Section 5-10 70) In a multienzyme complex the process of directly transferring a product of one reaction to the next active site without allowing it to enter the bulk solvent is termed ________. A) a ping-pong reaction B) metabolite channeling C) the activity pathway D) the sequential mode
: B metabolite channeling
Section 5-7 50) In ________ inhibition the inhibitor binds at a site other than the active site, but alters the active site to prevent binding of the normal substrate. A) classical competitive B) non-classical competitive C) noncompetitive D) uncompetitive E) irreversible
: B non classical competitive
Section 5-6 39) Two substances are used to produce a certain biological product in an enzyme-catalyzed reaction. It is found that both substrates must bind to the enzyme, first one, then the other before the product is produced. This is an example of a(n) ________. A) linear reaction B) ordered sequential reaction C) random sequential reaction D) ping-pong reaction
: B ordered sequential reaction
Section 5-9 59) In E. coli ________ is an activator and ________ is a negative allosteric modulator of the enzyme phosphofructokinase-1. A) DFP; phosphoenolpyruvate B) phosphoenolpyruvate; ATP C) ADP; phosphoenolpyruvate D) fructose-6-phosphate; ADP
: C ADP; Phosphoenolpyruvate
1) Which of the following statements is FALSE? A) Enzymes make reactions 103 to 1020 times faster. B) Enzymes lower the amount of energy needed for a reaction. C) Enzymes are chemically unchanged during the actual catalytic process. D) Enzymes speed up the attainment of a reaction equilibrium. E) Enzymes are usually proteins.
: C Enzymes are chemically unchanged during the actual catalytic process
47) Facilitated diffusion (passive transport) through a biological membrane is A) generally irreversible. B) driven by the ATP to ADP conversion. C) driven by a concentration gradient. D) endergonic.
: C Page Ref: Section 9-11
48) Which does not apply to the diffusion of O2, CO2 and small hydrophobic molecules across a membrane? A) Diffusion is driven by the concentration gradient across the membrane. B) The diffusion is spontaneous and there is a decrease in free energy as diffusion occurs. C) The transport is saturable. D) Membrane proteins are not needed for the diffusion process.
: C Page Ref: Section 9-11
53) Which is not a similarity between active transport proteins and enzymes? A) Both undergo conformational changes upon binding a substrate. B) Both are susceptible to inhibition. C) Both cause chemical modification to the substrate. D) Both can reach a saturation limit.
: C Page Ref: Section 9-11
58) In signal transduction what is an effector enzyme? A) An integral membrane protein that changes conformation upon binding of a ligand to a cell surface receptor. B) A small molecule that diffuses within a cell and carries a signal to its ultimate destination. C) A protein bound on the interior of a cell membrane that generates a second messenger. D) Protein bound on the exterior surface of a cell and is the receptor site for a ligand.
: C Page Ref: Section 9-12
61) In the adenyl cyclase signaling pathway the second messenger(s) is(are) ________. A) ATP and GTP B) protein kinase A C) cyclic AMP or cyclic GMP D) AMP
: C Page Ref: Section 9-12
4) A fatty acid designated as 20:0 is ________, while one that is designated 20:3 D5,8,11 is ________. A) simple; complex B) complex; simple C) saturated; unsaturated D) unsaturated; saturated E) monounsaturated; polyunsaturated
: C Page Ref: Section 9-2
6) Which statement is true about the most common naturally occurring fatty acids? A) They have 50-100 carbon atoms and an even number of carbon atoms. B) They have 50-100 carbon atoms and an odd number of carbon atoms. C) They have 12-20 carbon atoms and an even number of carbon atoms. D) They have 12-20 carbon atoms and an odd number of carbon atoms.
: C Page Ref: Section 9-2
7) A fatty acid designated w-3 A) has three double bonds. B) is saturated. C) has a double bond three carbons from the end of the chain. D) has a double bond three carbons from the a-carbon.
: C Page Ref: Section 9-2
9) Plasma levels of cholesterol and triglycerides are elevated by A) sphingolipids B) cis-fatty acids. C) trans-fatty acids. D) plant oils.
: C Page Ref: Section 9-2
14) Triglycerols containing only saturated long chain fatty acids tend to remain ________ at room temperature. A) unsaturated B) liquid C) solid D) oils
: C Page Ref: Section 9-3
19) Like plasmologens, sphingolipids are found in relative abundance in A) bacteria. B) plant cells. C) nerve cells. D) intestinal cells. E) All of the above.
: C Page Ref: Section 9-5
25) Cholesterol is converted to cholesteryl esters for ________ in cells and are ________ (more, less) hydrophobic than glycerophospholipids. A) transport; more B) transport; less C) storage; more D) storage; less E) synthesis; more
: C Page Ref: Section 9-6
34) Liposomes consist of ________ bilayers that enclose an aqueous compartment where drugs can be contained for delivery to specific tissues if target proteins are present. A) cholesterol B) membrane protein C) phospholipids D) detergents
: C Page Ref: Section 9-9
36) Diffusion of membrane proteins was demonstrated by fusing human cells and mouse cells that had membrane proteins labeled with ________ of different colors. A) radioactivity B) fluorescent dyes C) fluorescent antibodies D) fluorescent lipids
: C Page Ref: Section 9-9
37) Phospholipids can move from one layer to the other in a cell membrane bilayer by A) lateral diffusion. B) biosynthesis. C) flippases and floppases. D) increased diffusion.
: C Page Ref: Section 9-9
39) Which statement is false about lipid rafts? A) Membrane proteins help maintain the integrity of membrane rafts. B) They are distributed non-uniformly on the mammal cell surfaces. C) They occur mostly on the outer mitochondrial membrane. D) They are patches of cholesterol associated with sphingolipids.
: C Page Ref: Section 9-9
Section 5-4 32) It is difficult to determine either Km or Vmax from a graph of velocity vs. substrate concentration because A) too much substrate is required to determine them. B) the graph is sigmoidal. C) an asymptotic value must be determined from the graph. D) the points on the graph are often not spread out on the hyperbola.
: C an asymptomatic value must be determined from the graph
Section 5-2 10) The main difference between chemical and enzyme kinetics is that A) enzyme reactions are altered by pH. B) enzyme reactions depend on the concentration of the substrate. C) enzyme reactions depend on the concentration of the enzyme and its recycling. D) the rate constant for the formation of products is k2.
: C enzyme reactions depend on the concentration of the enzyme and it's recycling
5) Most of the known enzymes are ________. A) oxidoreductases B) transferases C) hydrolases D) lyases E) isomerases
: C hydrolases
Section 5-9 64) Which statement is false about the sequential theory? A) It treats the concerted theory as a limiting simple case. B) It allows for a distribution of high and low affinity subunits in the same protein. C) It assumes more than one conformation of a particular subunit can have high affinity for the ligand. D) It is also called the ligand-induced theory and is more general than the concerted theory.
: C it assumes more than one conformation of a particular subunit can have high affinity for the ligand
Section 5-7 44) An inhibitor binds to a site other than the active site of the enzyme. Which statement below correlates with this observation? A) It must be a competitive inhibitor. B) The inhibition must be irreversible. C) It could be noncompetitive or uncompetitive inhibition. D) It could be irreversible, competitive, noncompetitive or uncompetitive. The data do not relate to the type of inhibition.
: C it could be noncompetitive or uncompetitive
Section 5-9 66) Which statement is false about covalent modification? A) It is reversible. B) It is slightly slower than allosteric regulation. C) It usually uses the same enzyme for activation and inactivation. D) All of the above.
: C it usually uses the same enzyme for activation and inactivation
Section 5-4 28) How is the catalytic proficiency defined? A) It is the reciprocal of the turnover number. B) It is the logarithm of the Michaelis-Menton constant. C) It is equal to the rate constants for a reaction in the presence of the enzyme divided by the rate constant for the same reaction in the absence of the enzyme. D) It is the rate of the enzyme-catalyzed reaction in the presences of a standard concentration of enzyme.
: C it's equal to the rate constants for the reaction in the presence of the enzyme divided by the rate constant for the same reaction in the absence of the enzyme
Section 5-7 49) What type of inhibition is indicated by the data graphed below? A) Competitive. B) Uncompetitive. C) Noncompetitive. D) Irreversible.
: C noncompetitive
Section 5-3 27) The catalytic proficiency of an enzyme is the ________. A) turnover number B) Km/[E] C) rate constant with the enzyme divided by the rate constant without the enzyme D) rate constant with the enzyme times the rate constant without the enzyme
: C rate constant with the enzyme divided by rate constant without the enzyme
Section 5-6 41) In a ping-pong reaction which does not occur? A) One product is released before a second substrate is bound. B) The enzyme covalently binds a portion of the first substrate. C) The enzyme is permanently converted to an altered form by the first substrate. D) A group is transferred from one substrate to another.
: C the enzyme is permanently converted to an altered form by the first substrate
Section 5-3 21) The assumptions made in calculating the Michaelis-Menten Equation include A) that the formation and decomposition of ES is the same for a period of time. B) that the concentration of the substrate is much greater than the concentration of E. C) that the value of k-2 can be ignored. D) A, B and C. E) A and B only.
: D A B C
Section 5-7 43) What distinguishes reversible inhibitors from irreversible inhibitors? A) Reversible inhibitors are not covalently bound to enzymes but irreversible inhibitors are. B) There is an equilibrium between bound and unbound reversible inhibitor. There usually is little back reaction for the binding of an irreversible inhibitor. C) Reversible inhibitors can often be retrieved (purified) from solutions of enzymes, but irreversible inhibitors will react with enzyme and no longer be retrievable in their original form. D) All of the above. E) A and B only.
: D ALL OF THE ABOVE
Section 5-9 57) Which are correlated with allosteric enzymes that do not follow typical Michaelis-Menten kinetics? A) Cooperative binding of the substrate. B) Sigmoidal curves of velocity when S is varied. C) Changes in conformation of the enzyme when S binds. D) All of the above.
: D ALL OF THE ABOVE
1) Lipids may be either hydrophobic or ________. A) hydrophilic B) amphoteric C) inorganic D) amphipathic
: D Page Ref: 9-Introduction
2) ________ are the simplest lipids but they may be a part of or a source of many complex lipids. A) Triglycerols B) Carbohydrates C) Terpenes D) Fatty acids E) Waxes
: D Page Ref: Section 9-1
3) Isoprenoids are lipids which neither contain nor are derived from fatty acids and include A) steroids. B) waxes. C) terpenes. D) A and C only. E) A, B, and C.
: D Page Ref: Section 9-1
42) When red-blood cells are treated extensively with protease most membrane proteins are broken down into small peptides. However, some proteins are very resistant to this treatment. If cleavage by protease is the only type of reaction that occurs in this treatment, how is this explained? A) They are lipid-anchored membrane proteins. B) They are peripheral proteins. C) They contain at least 2 disulfide bonds. D) They are integral (intrinsic) membrane proteins.
: D Page Ref: Section 9-10
51) Another name for facilitated diffusion is ________. A) active transport B) transverse diffusion C) lateral diffusion D) passive transport
: D Page Ref: Section 9-11
57) Very large molecules (macromolecules) can be transported across membranes by ________. A) pores or channels with very large openings through the center B) active transport proteins C) diffusion down a concentration gradient D) endocytosis or exocytosis
: D Page Ref: Section 9-11
59) Which does not generally use a signal transduction mechanism? A) Hydrophilic hormones. B) Neurotransmitters. C) Growth factors. D) Steroids.
: D Page Ref: Section 9-12
10) Fatty acids required in the diet of mammals are called A) important. B) dietary. C) saturated. D) essential. E) esters.
: D Page Ref: Section 9-2
8) Trans fatty acids have physical properties like those of A) w-3 fatty acids. B) cis-fatty acids. C) unsaturated fatty acids. D) saturated fatty acids.
: D Page Ref: Section 9-2
11) Most lipids in the average human diet are A) unsaturated fatty acids. B) saturated fatty acids. C) glycerophospholipids. D) triacylglycerols.
: D Page Ref: Section 9-3
21) An unknown lipid is treated with a mixture of phospholipases A1, A2, C and D. Since no glycerol is formed after this treatment, the lipid is most likely A) phosphatidylethanolamine. B) phosphatidylcholine. C) plasmologen. D) ceramide. E) a mixture of A and B.
: D Page Ref: Section 9-5
23) Tay-Sachs disease results from A) a deficiency of GM2. B) defective lysosomes. C) malfunction of cerebroside metabolism. D) the accumulation of GM2.
: D Page Ref: Section 9-5
35) What is the role of cholesterol in animal cell membranes? A) Blocks the association of the fatty acyl chains of phospholipids at high temperature. B) Aids in the transport of small hydrophobic molecules across the membrane. C) Is a receptor site for hormones on the surface of membranes. D) Broadens the temperature range of optimum membrane fluidity.
: D Page Ref: Section 9-9
Section 5-4 30) Which statement is true about catalytic proficiencies? A) They are very useful for determining second-order rate constants. B) From them you can calculate the amount of enzyme needed to achieve a specific rate of reaction. C) They can easily be determined from the Lineweaver-Burk plot. D) They are difficult to determine because the reactions without the enzyme are extremely slow.
: D They are difficult to determine because reactions without the enzymes are extremely slow
Section 5-5 33) The reason to rewrite the Michaelis-Menten equation (such as the Lineweaver-Burk plot) is to A) visualize reactions better. B) form enzyme kinetic data as a hyperbolic curve. C) calculate catalytic proficiency. D) calculate Vmax and Km.
: D calculate Vmax and Km
Section 5-2 19) Which enzyme below is fastest? A) Kinase, kcat = 103. B) Papain, kcat = 10. C) Carboxypeptidase, kcat = 102. D) Catalase, kcat = 107.
: D catalase, kcat = 107
Section 5-10 71) Which is not a reason for metabolite channeling? A) Protection of intermediates from degradation. B) Increasing the overall rate of a reaction. C) Producing locally high concentrations of intermediates. D) Ensuring the enzyme is properly regulated.
: D ensuring the enzyme is properly regulated
Section 5-8 54) Which is not an explanation of why site-directed mutagenesis is a more powerful tool than many other techniques for determining important residues in an enzyme? A) It is a more specific technique than irreversible inhibition experiments. B) It can be used on enzymes for which no specific irreversible inhibitor is known. C) It allows for testing of the specific function of amino acid side chains in an enzyme. D) It is especially useful for enzymes whose sequence is not known.
: D it is especially useful for the enzymes whose sequence is not known
Section 5-6 38) In a certain enzyme-catalyzed reaction the following steps occur: 1. A phosphate group on substrate A is transferred to a side chain of an active site residue of the enzyme. 2. The dephosphorylated form of substrate A dissociates from the enzyme. 3. Substrate B enters the active site and is phosphorylated with simultaneous regeneration of the enzyme in its original form. What kind of kinetic mechanism is described? A) Random. B) Sequential. C) Ordered. D) Ping-pong.
: D ping pong
Section 5-9 63) Protein A has four identical subunits, each of which binds one molecule of ligand Y. The binding of one molecule of Y to one of the subunits induces a conformational change in neighboring subunits that enhances the binding of additional units of Y. This is an example of ________. A) negative cooperativity B) competitive activation C) symmetry-driven binding D) the sequential theory
: D the sequential theory
Section 5-9 65) The quaternary structure of hemoglobin changes from the T state to the R state ________. A) only after four molecules of O2 are bound B) after the binding of one molecule of O2 causes a change in the primary structure C) when hemoglobin is completely deoxygenated D) when at least one subunit on each dimeric unit (αβ dimer) is oxygenated
: D when at least one subunit of each dimeric unit is oxygenated
Section 5-5 35) The Lineweaver-Burk plot and other linear transformation of the Michaelis-Menten curve of kinetics are valuable for A) determination of Km. B) determination of Vmax. C) determination of kcat. D) determination of types of enzyme inhibition. E) All of the above.
: E ALL OF THE ABOVE
12) Dietary triacylglycerols are digested as a result of A) lipase action. B) bile salts. C) micelle formation. D) diffusion and absorption by intestinal cells. E) All of the above.
: E Page Ref: Section 9-3
13) Adipocytes contain fat droplets which serve to provide an animal with A) increased cell volume. B) insulation. C) chemical energy. D) A and B above. E) B and C above.
: E Page Ref: Section 9-3
16) Polar heads of glycerophospholipids may be A) + charged. B) - charged. C) neutral, but polar. D) a mixture of + and - charges. E) All of the above.
: E Page Ref: Section 9-4
30) In a typical eukaryotic plasma membrane, A) oligosaccharides face outward, not toward the cytosol. B) proteins can move within the bilayer. C) lipids can move and diffuse through the bilayer. D) some lipids can rotate within the bilayer. E) All of the above.
: E Page Ref: Section 9-8
31) The arrangement of lipid bilayers and other components is the basis for the currently widely accepted description which is called the A) fluid model. B) lipid bilayer model. C) mosaic model. D) diffusion model. E) fluid mosaic model.
: E Page Ref: Section 9-8
3) Unlike typical catalyzed reactions in organic chemistry enzyme reactions are A) usually stereospecific. B) reaction specific. C) essentially 100% efficient. D) modulated to change activity levels. E) All of the above.
: E all of the above
8) Enzymes that join two substrates and require energy of a nucleoside triphosphate (such as ATP) to do so are called A) isomerases. B) lyases. C) ligases. D) synthetases. E) Both c and d.
: E ligases AND synthetases
With respect to oxygen saturation, hemoglobin is ___________ saturated at the pO2 of the lungs and ___________ saturated at the pO2 of the tissue.
>90%; between 30 and 70%
3) When a substrate and enzyme interact, the first chemical species formed is _____. A) enzyme-substrate complex B) enzyme-transition state complex C) enzyme-product complex D) enzyme plus product E) none of the above
A
Activity of the Ras protein is analogous to the _____ in terms of its ability to bind GTP. A) G protein α subunit D) calmodulin B) G protein β subunit E) all of the above C) G protein γ subunit
A
Alcohol dehydrogenase is an example of which of the following classes of enzymes? A) Oxidoreductases B) Transferase C) Hydrolase D) Lyase E) Isomerase
A
All are true for inhibitor I if it is a competitive inhibitor EXCEPT: a. It binds a site other than the active site. b. It is structurally similar to the substrate. c. EI does not give rise to E + P. d. For a given [I], v decreases. e. At some point, S can displace all of I on E.
A
Any sugar that has a free aldehyde group is called a(n) _____. A) reducing sugar D) aldohexose B) non-reducing sugar E) alditol C) ketose
A
Calculate the true Vmax (OD/min) and the true KM (mM) for the enzyme. A) Vmax = 0.66 OD/min; KM = 1.0 mM C) Vmax = 1.51 OD/min; KM = 1.0 mM B) Vmax = 0.23 OD/min; KM = 0.37 mM D) Vmax = 4.27 OD/min; KM = 2.75 mM
A
Competitive inhibition is revealed by______ on a Lineweaver-Burk plot. A) nonparallel lines that intersect on the y-axis B) parallel lines C) nonparallel lines that do not intersect on the y-axis
A
Consider the following diagram. What constitutes the activation energy for the forward reaction? A) C-A B) C-E C) E-A D) C-B E) E-D
A
How does cAMP influence glycogen breakdown? A) cAMP activates protein kinase A, which phosphorylates the enzyme phosphorylase kinase, which then activates glycogen phosphorylase to break down glycogen. B) cAMP activates protein kinase C, which phosphorylates the enzyme phosphorylase kinase, which then activates glycogen phosphorylase to break down glycogen. C) G protein produces cAMP, activating protein kinase A, which phosphorylates the enzyme phosphorylase kinase, which then activates glycogen phosphorylase to break down glycogen. D) cAMP activates adenylate cyclase which activates protein kinase A, which phosphorylates the enzyme phosphorylase kinase, which then activates glycogen phosphorylase to break down glycogen.
A
NADPH and NADH are coenzymes found in which class of enzymes? A) Dehydrogenases B) Ligases C) Hydrolases D) Transferases E) Both C and D are correct
A
Peanut oil contains a high percentage of monounsaturated triacylglycerols whereas vegetable oil contains a higher percentage of polyunsaturated triacylglycerols. A bottle of peanut oil and a bottle of vegetable oil are stored in a pantry with an outside wall. During a cold spell, which oil will freeze? A) peanut oil B) vegetable oil
A
Second-order reactions: A) occur when two reactants collide. B) are quite rare. C) have smaller rate constants than first-order reactions. D) are termolecular. E) are always faster than first-order reactions.
A
The catalytic constant, or kcat, is also known as the _____. A) turnover number D) diffusion number B) saturation number E) Menten number C) catalytic efficiency number
A
The catalytic triad common to many serine proteases involves shuttling of protons between (sequence in the catalytic triad): A. ser-his-asp B. his-ser-asp C. ser-his-his D. ser-asp-his E. cys-his-ser
A
The expression of the Michaelis constant is equal to: A) (K2 + K3)/K1 B) (K2 + K1)/K3 C) (K1 + K2)/K3 D) (K3 + K1) + K3 E) (K2/K1) + K3 Where K1 = the rate constant for ES formation K2 = the rate constant for ES dissociation K3 = the rate constant for product formation
A
The main enzyme used to detoxify alcohol in humans is A) ADH1 B) ADH2 C) ADH3 D) ADH4 E) All of the above
A
The most notable difference between _____ and other lipids is the presence of four fused rings. A) cholesterol D) plasmologens B) arachidonic acid E) triacylglycerols C) gangliosides
A
What limits the signaling activity of a G protein once it has been stimulated by an epinephrine binding receptor? A) GTPase activity of the alpha subunit C) Dephosphorylation of the trimeric complex B) Phosphorylation of the trimeric complex D) none of the above
A
What type of transport does not require the assistance of a membrane protein? A) simple diffusion D) active transport B) facilitated diffusion E) none of the above C) passive transport
A
Which amino acid in the aquaporin channel hydrogen bonds with water to prevent the movement of protons? A) Asn B) Leu C) Phe D) Val E) Ile
A
Which of the following does NOT occur when neurons are stimulated? A) Local depolarization results from the opening of Na+ channels allowing Na+ to leave the cell. B) Neighboring Na+ channels open in response to the change in membrane potential, resulting in a wave of depolarization. C) Depolarization stimulates the opening of voltage-gated K+ channels, resulting in repolarization. D) Recovery involves the movement of Na+ out of the cell and K+ into the cell. E) All of the above occur.
A
Which of the following is a coenzyme? A) NADP+ B) Zn++ C) Cu++ D) Insulin E) Oxytocin
A
Which of the following statements about the Na+/K+ transporter is (are) TRUE? A) Phosphate hydrolysis of the transporter releases K+ ions to the cytosol and results in a return to the original (resting) state of the transporter. B) Three K+ ions bind to the cytosolic face of the transporter. C) A phosphoryl group is transferred from GTP to a Glu residue on the transporter. D) Bound Na+ ions are released from the phosphorylated transporter to the extracellular medium and K+ ions bind to the dephosphorylated form. E) All are true
A
Which of the following would be the first to occur following opening of Ca2+ channels during acetylcholine-mediated neurotransmission to a muscle cell? A) binding of SNARE complex to synaptic vesicles and pre-synaptic membrane B) binding of acetylcholine to muscle cell receptors C) reuptake of acetylcholine by the nerve cell D) hydrolysis of acetylcholine by acetylcholinesterase E) release of acetylcholine by the nerve cell
A
Which of these characteristics is not found in naturally occurring fatty acids in mammals? A) they are found free and unassociated with other molecules B) they are amphipathic C) if unsaturated, they occur in the cis configuration D) most, but not all fatty acids contain an even number of carbon atoms
A
Which is a general term indicating a carbohydrate polymer? A) Glycan. B) Polycarb. C) Multimer. D) Oligosaccharide.
A Page Ref: 8-Introduction
10) The structures of D-ribose and D-arabinose are shown below. These two molecules are ________. A) epimers B) enantiomers C) tautomers D) anomers
A Page Ref: Section 8-1
9) The Fischer projections of linear D-glucose and D-galactose are shown below. These two molecules are ________. A) epimers B) enantiomers C) anomers D) structural (constitutional) isomers
A Page Ref: Section 8-1
15) Below is the Fischer projection of D-galactose. Which is the proper Haworth projection of β-D-galactopyranose? A) I B) II C) III D) IV
A Page Ref: Section 8-2
22) Pyranose rings are usually most stable when the ring adopts a ________ conformation with the bulkiest ring substituents in ________ positions. A) chair; equatorial B) chair; axial C) boat; equatorial D) boat; axial
A Page Ref: Section 8-3
23) Which are possible conformations of a furanose molecule? A) Envelope and twist. B) Chair and boat. C) Cis and trans. D) A and B.
A Page Ref: Section 8-3
29) What distinguishes an aldonic acid from an alduronic acid? A) The oxidation of the aldehyde group in an aldonic acid and the oxidation of the highest numbered carbon in the alduronic acid. B) Aldonic acids are derivatives of aldoses, alduronic acids are derivatives of ketoses. C) Aldonic acids are oxidized forms of linear monosaccharides; alduronic acids are oxidized forms of cyclic monosaccharides. D) The two terms are synonyms and are used interchangeably.
A Page Ref: Section 8-4
37) A monosaccharide whose anomeric carbon atom has a glycosidic bond to an alcohol, amine or thiol is a ________. A) glycoside B) glycoprotein C) heteroglycan D) glucoconjugate
A Page Ref: Section 8-5
38) What is the name of the disaccharide shown below that is formed by joining two monomers of D-glucose? A) β-D-glucopyranosyl-(1→4)-β-D-glucopyranose. B) α-D-glucopyranosyl-(1→4)-α-D-glucopyranose. C) β-D-glucofuranosyl-(1→4)-β-D-glucofuranose. D) α-D-glucopyranosyl-(1→3)-β-D-glucopyranose.
A Page Ref: Section 8-5
: Section 6-7 61) Which statement describes the mechanism of lysozyme's catalyzed reaction? A) It includes substrate distortion and stabilization of an unstable oxocarbocation intermediate. B) It requires lysozyme to be phosphorylated before catalysis can occur. C) The catalyzed reaction produces three important isolatable intermediates by converting the reaction into a four-step mechanism. D) All of the above.
A it includes a substrate distortion and stabilization of an unstable oxocarbocation intermediate
: Section 6-5 43) The proximity effect of speeding an enzyme-catalyzed reaction is explained by ________. A) a large loss of entropy when reactive groups are brought close to each other B) a large gain in entropy due to binding of the substrate C) a conversion of a reaction from endergonic to exergonic D) increasing the flexibility of the substrate by increasing its degrees of freedom of rotation
A large loss of entropy when reactive groups are brought close together
: Section 6-1 11) Which statement does not apply to transition states? A) Many have been detected experimentally. B) Chemical bonds are in the process of being formed and broken. C) Have lifetimes on the order of 10-14 to 10-13 seconds. D) Differ in energy from the ground state by the activation energy.
A many have been detected experimentally
1) A detailed description of a chemical reaction in terms of the molecular, atomic or subatomic events is called the reaction ________. A) mechanism B) pathway C) primary sequence D) motif
A mechanism
: Section 6-4 33) The graphs below all represent the same chemical reaction, but each employing a different catalyst. Which enzyme uses the most efficient mechanism of catalysis? A) See Graph I. B) See Graph II. C) See Graph III. D) See Graph IV.
A see graph I
: Section 6-6 50) The substrate specificity of serine proteases is primarily due to A) a specificity pocket in the protein. B) the positions of specific side chains of serine, histidine, and aspartate. C) distinct backbone conformations of the individual proteins. D) A and B. E) A, B and C.
A specificity pocket in the protein
: Section 6-3 22) The following pH dependence was found for the activity of a certain enzyme-catalyzed reaction. If it is known that the only two ionizable residues in the active site are both glutamates, which conclusion can be drawn? A) The glutamates have different microenvironments which cause their pKa's to differ. B) One of the glutamates must be amidated. C) Both glutamates have a pKa equal to 5.0. D) Both glutamates are deprotonated during the reaction.
A the glutamates have different micro environments which cause their pKa's to differ
Define the term "suicide inhibitor."
A suicide inhibitor is a molecule that is unreactive until it binds to the active site of an enzyme. In the active site, it undergoes the first chemical steps of the normal enzymatic reaction and is converted into a highly reactive species that combines irreversibly with the enzyme's active site, rendering the enzyme inactive towards substrate.
What is a zymogen (proenzyme)? Explain briefly with an example.
A zymogen is an inactive form of an enzyme that is activated by one or more proteolytic cleavages in its sequence. Chymotrypsinogen, trypsinogen, and proelastase are all zymogens, becoming chymotrypsin, trypsin, and elastase, respectively, after proper cleavage.
An uncatalyzed reaction has a rate of 4.2 x 10-7 sec-1. When an enzyme is added the rate is 3.2 x 104 sec-1. Calculate the rate enhancement caused by the enzyme. A) 7.6 x 1010 B) 3.2 x 104 C) 1.3 x 10-2 D) 7.4 x 10-3 E) cannot be determined
A) 7.6 x 1010
I propose to design a new drug which will act as an inhibitor for an enzyme. If I have used all current information about the mechanism of this enzyme to design this inhibitor and I carefully engineer it with similar chemical properties of the transition state, what type of inhibitor am I attempting to engineer and how will I know if I have succeeded? A) A competitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in Vmax. B) A competitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in KM. C) A uncompetitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in KM. D) A uncompetitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in Vmax. E) None of the above.
A) A competitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in Vmax.
During the formation of microfilaments, which of the following occurs? A) ATP hydrolysis is catalyzed by f-actin. B) F-actin polymerizes, becoming g-actin. C) None of these choices. D)ATP binds to f-actin. E) Polymerization proceeds quickly at first, then slows after about ten actin monomers have polymerized.
A) ATP hydrolysis is catalyzed by f-actin
The enzyme hexokinase catalyzes a reaction where its substrates are completely sequestered from the aqueous environment allowing for interactions to occur between enzyme and substrates that would not normally occur in an aqueous environment. What term describes this type of catalysis? A) electrostatic catalysis B) desolvation catalysis C) non-aqueous catalysis D) hydrogen-bonded catalysis E) closed-system catalysis
A) Electrostatic catalysis
The Michaelis constant KM is defined as I. (k-1 + k2)/k1 II. ½ Vmax III. [S] = [ES] IV. [ES]/2 A) I B) I, II C) II D) I, IV E) II, IV
A) I
How does a catalyst affect the overall G of an endergonic reaction? A) it has no effect B) the reaction becomes more endergonic C) the reaction has a G of zero D) the reaction becomes exergonic E) none of the above
A) It has no effect
A reversible inhibitor that binds to a site other than the active site regardless of whether or not the substrate is bound is a _____. A) noncompetitive inhibitor B) competitive inhibitor C) uncompetitive inhibitor D) allosteric inhibitor E) suicide substrate
A) Noncompetitive inhibitor
In a bisubstrate reaction, reactant A binds, followed by reactant B which then get converted to products C and D. An experiment showed that B cannot bind without A having bound first. What mechanism is indicated by this data? A) ordered mechanism B) random mechanism C) ping pong mechanism D) cooperative mechanism E) none of the above
A) Ordered mechanism
The following data were collected under conditions indicated in the graph below during the time period of 0-5 seconds. Upon plotting the Lineweaver-Burk plot, the information given in the table below was determined. Based on this available information which of the following is FALSE? x-intercept - 0.002 (Units on the x-axis are 1/M) y-intercept 0.005 (Units on the y-axis are 1/s) slope 2.50 A) The Vmax equals 200 M/s B) The Ks equals 500 M C) The kapp equals 200 per second D) The data was collected prior to reaching steady state. E) The kcat cannot be determined for this information.
A) The Vmax equals 200 M/s
In an enzyme mechanism that generates a negative charge in the transition state, which of the following would be most effective to have in the active site of the enzyme? A) transition metal cation B) Asp residue C) Gln residue D) transition metal anion E) none of the above
A) Transitional metal cation
How are the kinetics of an enzyme-catalyzed reaction affected by a mixed inhibitor? A) Vmax decreased, KM increased or decreased B) Vmax decreased, KM decreased C) Vmax decreased, KM increased D) Vmax unchanged, KM increased E) Vmax unchanged, KM increased or decreased
A) Vmax decreased, KM increased or decreased
In the plot below, can the KM be determined? If so, what is its value? A) Yes, it is 30 mM. B) Yes, it is 30 mM/sec. C) Yes, it is 60 mM/sec D) Yes, it is 60 mM E) No this data does not follow Michaelis-Menten kinetics
A) Yes, it is 30 mM.
A lab recently developed a new drug which is hypothesized to inhibit the enzyme cyclooxygenase-2 (COX-2) and reduce inflammation. In their first test they monitored the reaction of substrate as it is converted to product in the presence of the new drug (data shown below). If the hypothesis is correct the observed initial rate will be at least 2 times slower than the normal reaction without the drug. If the normal initial rate is 30 mM/s, does the data below indicate that the team has designed a successful inhibitor? A) Yes. B) No. C) This cannot be determined with the information given. D) The data is dependent on the maximal velocity. E) The answer is dependent on the substrate concentration.
A) Yes.
A new drug has been discovered which inhibits the reaction catalyzed by enzyme A. Based on the information shown below, what is this drug? A) competitive inhibitor B) uncompetitive inhibitor C) mixed inhibitor D) allosteric activator E) More information is required to answer the question.
A) competitive inhibitor
A Lineweaver-Burk plot is a _____. A) double reciprocal plot B) Michaelis-Menten plot C) sigmoidal plot D) hyperbolic plot E) logarithmic plot
A) double reciprocal plot
In the chymotrypsin mechanism, what is used to stabilize the negative charge on the carbonyl oxygen of the transition state? A) hydrogen bonding between the enzyme and the anion from the carbonyl oxygen B) electrostatic interaction of the positively charged His and carbonyl oxygen C) electrostatic interaction of the negatively charged Asp and carbonyl oxygen D) electrostatic interaction of the active site Zn2+ and carbonyl oxygen E) all of the above
A) hydrogen bonding between the enzyme and the anion from the carbonyl oxygen
Irreversible enzyme inhibitors A) inactivate the enzyme B) inhibit competitively C) maximize product by minimizing ESE+S D) behave allosterically E) function via Ping Pong mechanism
A) inactivate the enzyme
Reaction that is first order with respect to A and B A) is dependent on the concentration of A and B. B) is dependent on the concentration of A. C) has smaller rate constants than first-order reactions regardless of reactant concentration. D) is independent of reactant concentration. E) is always faster than first-order reactions due to loss of concentration dependence.
A) is dependent on the concentration of A and B.
A β-sandwich forms when A) two hydrophobic sides of β-sheets interact. B) two hydrophilic sides of β-sheets interact. C) an α-helix separates two β-sheets. D) two amphipathic α-helices interact.
A) two hydrophobic sides of β-sheets interact.
Which of the following properly expresses the Michaelis-Menten equation? A) vo = Vmax [S] / (KM + [S]) B) vo = Vmax KM / (KM + [S]) C) kcat = Vmax / [E]T D) Vmax = vo [S] / (KM + [S]) E) Vmax = vo KM / (KM + [S])
A) vo = Vmax [S] / (KM + [S])
Which of the following has not been shown to play a role in determining the specificity of protein kinases? A)Disulfide bonds near the phosphorylation site. B)Primary sequence at phosphorylation site C)Protein quaternary structure D)Protein tertiary structure E)Residues near the phosphorylation site
A)Disulfide bonds near the phosphorylation site
The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by: 1/V0 = Km /(Vmax[S]) + 1/Vmax, To determine Km from a double-reciprocal plot, you would:
A)multiply the reciprocal of the x-axis intercept by -1.
Which is appropriate for initial rate method experiments to analyze an enzyme-catalyzed reaction? Select one: A. Enzyme concentration is constant and the rate is measured at different substrate concentrations. B. The substrate and enzyme concentrations are varied inversely with respect to one another and the rate is measured. C. Both enzyme and substrate concentrations are constant. The temperature is varied and the rate is measured. D. Substrate concentration is constant and the rate is measured at different concentrations of enzyme.
A. Enzyme concentration is constant and the rate is measured at different substrate concentrations.
What is the minimum amount of energy required to bring about a chemical reaction? A. activation energy B. enthalpy of reaction C. free energy D. standard free energy E. transition state
A. activation energy
The hydrophobic cleft in globular proteins which bind substrate molecules is called the ________. Select one: A. active site B. modulator site C. activity site D. oligomeric site E. substrate pocket
A. active site
A chemical group that has a negative charge or an unshared electron pair may act as a(n) Select one: A. nucleophile. B. electrophile. C. neutrophile. D. transition state.
A. nucleophile.
Transanimation:
AA's synthesized from metabolic intermediates.
The activity of ATCase is increased by ____ and decreased by ____, which alter the conformation of the catalytic sites by stabilizing the R and the T states of the enzyme, respectively.
ATP, CTP
Michaelis-Menten kinetics is sometimes referred to as "saturation" kinetics. Why?
According to the Michaelis-Menten model of enzyme-substrate interaction, when [S] becomes very high, an enzyme molecule's active site will become occupied with a new substrate molecule as soon as it releases a product. Therefore, at very high [S], V0 does not increase with additional substrate, and the enzyme is said to be "saturated" with substrate.
Consider the energetics of a reaction pathway, the energy required to overcome the unstable intermediate is referred to as _________________, this is covered in the pathway of an enzyme catalyzed reaction.
Activation Energy
In contrast to inorganic catalysts, enzymes have an intricately shaped surface called: a. Substrate b. cofactor c. active site d. apoenzyme e. holoenzyme
Active Site
Vmax assumes that max velocity occurs when _____ the enzyme is fully occupied by substrate multipled by the rate constant
All
In a procedure for testing blood glucose, a drop of blood is placed on a paper strip impregnated with the enzyme glucose oxidase and the reagents necessary for the reaction B-D-Glucose + O2 --> D-Gluconolactone + H2O2 The peroxide produced causes a color change on the paper, which indicates how much glucose is present. Since glucose oxidase is specific for the B anomer of glucose, why can the total blood glucose be measured?
Alpha and beta anomers are in equilibrium and glucose oxidase displaces that equilibrium. Eventually glucose oxidase converts all glucose to D-gluconolactone
What amino acid residue present in the specificity pocket allows trypsin to bind peptides containing the basic residues, Arg or Lys?
Asp
An AAA has a allow acidic pI value. What AA is it likely to be?
Aspartic Acid
Which of the following statements about a plot of V0 vs. [S] for an enzyme that follows Michaelis-Menten kinetics is false? A) As [S] increases, the initial velocity of reaction V0 also increases. B) At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km. C) Km is the [S] at which V0 = 1/2 Vmax. D) The shape of the curve is a hyperbola. E) The y-axis is a rate term with units of m/min.
At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.
.An enzyme is considered to have evolved to its most efficient form if A) kcat is a large number B) kcat/KM is near the diffusion-controlled limit C) KM is a large number D) kcat/KM is a very small number E) KM is a small number
B
34) Metabolons are defined as: A) Multifunction enzymes B) Complexes that channel product molecules from one active site to another C) Metabolic intermediates D) Effector molecules E) Rate of flow of metabolites from one point to another
B
A toxin secreted by the bacterium Vibrio cholerae catalyzes the covalent attachment of an ADP-ribose group to the α subunit of the G protein. This results in the inhibition of the intrinsic GTPase activity of the G protein. How does this affect the activity of adenylate cyclase? How are intracellular levels of cAMP affected? A) Lasting activation of adenylate cyclase leads to low [cAMP] B) Lasting activation of adenylate cyclase leads to high [cAMP] C) Inactivation of adenylate cyclase leads to low [cAMP] D) Inactivation of adenylate cyclase leads to high [cAMP]
B
All are characteristics of ordered single-displacement reactions EXCEPT: a. Lineweaver-Burk plots with lines that intersect to the left of the 1/v axis. b. a chemically modified enzyme-intermediate. c. the lack of any exchange reaction activity. d. the lack of competitive substrate effects. e. single substrate initial binding activity.
B
All of the following statements about noncompetitive inhibition are true EXCEPT: a. They interact with the enzyme as well as the enzyme-substrate complex. b. Increasing the concentration of [S] can overcome the inhibition. c. The Vmax value does not remain the same as for a reaction that is not inhibited. d. The inhibitor can cause a conformational change in the enzyme. e. The inhibitor binds to a different site than does the substrate.
B
All of the following statements are true about the relationships between [S], Km and Vmax EXCEPT: a. As the [S] is increased, v approaches the limiting value, Vmax. b. Km = Vmax/2. c. The rate of the reaction, v, follows a first order rate equation v = K'[A] and K' = Vmax/Km. d. The rate of product formed, v, is at Vmax when [S] >> Km. e. Km and Vmax assist in finding the rate of the enzyme catalyzed reaction only if the reaction is irreversible.
B
Amylopectin contains primarily _____ glycosidic bonds with _____ glycosidic bonds as branch points. A) α(1→4); α(1→2) D) β(1→4); α(1→4) B) α(1→4); α(1→6) E) β(1→4); α(1→6) C) α(1→4); β(1→6)
B
An enzyme without it cofactor is called ________ A) Coenzyme B) Apoenzyme C) Holoenzyme D) Noncatalytic E) Isoenzyme
B
For a reaction A + B C, if the concentration of B is much larger than [A] so that [B] remains constant during the reaction while [A] is varied, the kinetics will be: A) sigmoidal B) pseudo-first-order C) unimolecular D) zero-order E) enzymatic
B
For the reaction, the steady state assumption assumes that A) [S] = [P] B) [ES] is constant C) [P]>>[E] D) [P] is constant E) k-1>>k2
B
Glucose is added to cells and the rate of glucose transport is plotted against glucose concentration. In the presence of the galactose derivative 6-O-benzyl-D-galactose, the curve is shifted to the right (with no other change). What kind of agent is 6-O-benzyl-D-galactose? A) activator D) inactivator B) competitive inhibitor E) none of the above C) noncompetitive inhibitor
B
If the half-life of a given reaction is constant (not dependant upon the initial conditions), the reaction must be: A) zeroth order B) first order C) second order D) diffusion controlled E) enzyme catalyzed
B
In an α-helical protein that spans a cell membrane, _____ would likely be in the center of the membrane while _____ would likely be associated with the polar head groups and _____ would likely be associated with the aqueous environment A) Trp; Asn; Ala D) Ile; Arg; Gln B) Leu; Gln; Asp E) Val; Ser; Thr C) Tyr; Glu; Gly
B
In pure noncompetitive inhibition, how does inhibitor binding affect KM and Vmax? A) KM is increased but Vmax is not changed. C) KM is increased but Vmax is decreased. B) KM is not changed but Vmax is decreased. D) Both KM and Vmax are decreased.
B
Metabolic flux is best defined as a: A) Lubrication enzyme that promotes the flow of reactants B) Rate of flow of metabolites from one point to another in a pathway C) Rate of a reaction D) Promoter molecule E) Both A and D are correct
B
PEP regulation of phosphofructokinase activity is a type of: A) suicide substrate inhibition D) none of the above B) allosteric regulation E) all of the above C) transition state inhibition
B
Parallel lines on a Lineweaver-Burk plot are diagnostic of: A) competitive inhibition. B) non-competitive inhibition. C) allosteric activation. D) allosteric inhibition. E) none of the above.
B
Phospholipase C cleaves PIP2, generating A) cAMP and PPi B) IP3 and DAG (inositol-1,4,5-trisphosphate and 1,2-diacylglycerol) C) IP3 and PPi D) cAMP and DAG E) IP3 and Pi
B
Plants can synthesize trienoic acids (fatty acids with 3 double bonds) by introducing another double bond into a dienoic acid. Would you expect plants growing at higher temperatures to convert more or less of their dienoic acids into trienoic acids? A) They would convert more. C) There would be no difference. B) They would convert less.
B
Rank the melting points of the following fatty acids: (1) cis-oleate (18:1) (2) trans-oleate (18:1) (3) linoleate (18:2) A) 1 > 2 > 3 D) 3 > 1 > 2 B) 2 > 1 > 3 E) none of the above C) 2 > 3 > 1
B
The affinity of enzyme binding to its substrate is approximated by the ________ value. A) Vmax D) vo B) KM E) none of the above C) [S]
B
The concentration of cytosolic Ca2+ is _____ the extracellular concentration. A) dependent on D) greater than B) less than E) linearly related to C) the same as
B
The ligand adenosine is added to heart cells in culture. The number of receptors bound to ligand is measured and that data plotted, as illustrated below. How would the curve change in the presence of caffeine? A) The maximum value for the fraction of ligand bound would decrease. B) The curve would shift right, but the maximum value of fraction bound would stay the same. C) The curve would shift right and the maximum value of fraction bound would decrease. D) The curve would shift left and the maximum value of fraction bound would decrease. E) No way to tell
B
The steady state assumption states that if: k1 = the rate constant for ES formation k2 = the rate constant for ES dissociation k3 = the rate constant for product formation A) k2 is highly negligible compared with k3 B) The rate of formation of ES is equal to the rate of its degradation over the course of the reaction C) The rate of formation of ES exceeds the rate of degradation over the course of the reaction D) k3 is negligible when compared to k2 E) Product concentration at the beginning of the reaction is low
B
Unlike proteins and oligonucleotides, polysaccharides A) are readily metabolized in the absence of specialized enzymes. B) often have branched structures. C) are achiral. D) are always very water soluble. E) are components of every known living organism.
B
What factor(s) are important in the high selectivity of the K+ channel? A) The pore is lined with negatively-charged carboxyl groups to coordinate the positive ion. B) A network of Tyr residues ensures that smaller ions like Na+ will be excluded. C) A loop connecting two of the helices constricts the pore to make it specific for K+. D) Coordinated H2O molecules restrict the size of the cation that can be transported. E) A and B are factors.
B
What is the ratio [Na+]in/[Na+]out created by depolarization in a nerve cell if the final potential is +50 mV at 37 °C? A) 6.4 × 106 B) 6.5 C) 1.5 D) 0.15 E) 1.6 × 10-7
B
What is the role of ATP in the allosteric regulation of ATCase? A) The KM increases in the presence of ATP and decreases affinity of the substrate B) The KM decreases in the presence of ATP and increases the affinity of the substrate C) ATP has no effect on the reaction
B
What reaction would NOT proceed via bimolecular elementary steps? a. C + D → T + U b. A reaction with a rate constant in the units of s-1. c. 2A → D + E d. A reaction with a molecularity of 2.
B
Which of the following open in response to an extracellular stimulus such as a neurotransmitter? A) mechanosensitive channels D) voltage-gated channels B) ligand-gated channels E) none of the above C) signal-gated channels
B
Which of the following residues would you expect in the membrane spanning portion of an integral membrane protein? A) Lys and Val B) Leu and Ile C) Glu and Asp D) A and B E) B and C
B
Which of the following types of inhibition can be reversed by addition of more substrate? A) noncompetitive inhibition D) irreversible inhibition B) competitive inhibition E) none of the above C) uncompetitive inhibition
B
Which of the following would be likely to form a bilayer in a solution containing only the lipid indicated? A) fatty acids D) cholesterol B) glycerophospholipids E) B and C C) triacylglycerols
B
Zymogens are a feature of what type of enzymatic control? A) Genetic control B) Covalent modification C) Allosteric regulation D) Compartmentation E) Both B and C are correct
B
: Section 6-3 29) An enzyme's active site contains an arginine residue and a glutamate residue with pKa's of 2.9 and 9.1, respectively. Both residues are actively involved in the catalytic mechanism and they are the only two ionizable residues in the active site. What would you expect for the optimum pH of the enzyme? A) 4.0 B) 6.0 C) 8.0 D) No pH can be determined since the information is irrelevant to the optimum pH.
B 6.0
: Section 6-5 39) When the concentration of a substrate inside a cell falls below the substrate concentration at half maximal velocity, ________. A) ES is formed more easily B) ES dissociates to E + S C) ES is closer to the ground state than to the transition state D) E + S is in equilibrium with ES E) the reaction will not proceed
B ES dissociates to E + S
: Section 6-1 5) Which represents a hydride ion? A) H2- B) H- C) H+ D) H3O+
B H-
: Section 6-3 28) Which graph might you expect for the pH profile of an enzyme's activity if the only ionizable residue in the active site is aspartate? A) I B) II C) III D) IV
B II
A saccharide is a ________. A) lipid B) carbohydrate C) nucleic acid D) protein
B Page Ref: 8-Introduction
8) Examine the Fischer projection below. How is this carbohydrate classified? A) L enantiomer; aldopentose. B) L enantiomer; ketopentose. C) D enantiomer; aldohexose. D) D enantiomer; ketopentose.
B Page Ref: Section 8-1
Which is true about naturally occurring monosaccharides? A) The L-isomers predominate. B) The D-isomers predominate. C) The L and D-isomers occur in equal ratios. D) The ratio of L and D-isomers varies widely depending on the source.
B Page Ref: Section 8-1
13) The functional group shown is a(n) ________. A) hemiacetal B) hemiketal C) acetal D) ketal
B Page Ref: Section 8-2
16) Below is the structure for a cyclic D-monosaccharide. Which is the anomeric carbon atom? A) 1 B) 2 C) 3 D) 4 E) 5
B Page Ref: Section 8-2
19) Anomers can be interconverted ________. A) by rotation about carbon-carbon bonds B) via a linear intermediate C) by an isotopic exchange reaction D) None of the above. Anomers cannot be interconverted.
B Page Ref: Section 8-2
42) When a sugar polymer is analyzed and found to have equal portions of reducing and non-reducing ends, it is likely that A) it shows directionality. B) it is linear. C) it is branched. D) it is branched, but not very highly. E) some of the internal glycosidic bonds are in equilibrium with open chain forms.
B Page Ref: Section 8-6
55) Nodulation factors are ________. A) polysaccharides that help maintain the integrity of tree bark B) lipo-oligosaccharides that stimulate the growth of nitrogen-fixing structures in plants C) polysaccharides used to store energy in the roots of plants D) lipo-saccharides that are often found in tumors
B Page Ref: Section 8-7
: Section 6-2 19) Site directed mutagenesis is used to study enzymes by A) changing the location of the active site. B) producing enzymes with different amino acid residues. C) producing enzymes with modified R groups. D) changing the pH of the environment.
B producing enzymes with amino acid residues
: Section 6-1 10) In this reaction, the carbon is ________. A) oxidized B) reduced C) neutralized D) hydrolyzed
B reduced
From the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of μM/s and substrate concentration of the x-axis in units of μM, what is the KM? A) 0.24 μM/s B) 18 μM C) 0.2 μM D) 0.24 μM E) 0.12 μM/s
B) 18 μM
What percentage of Vmax is obtained when the substrate is present at ¼ of the KM? ` A) 5% B) 20% C) 25% D) 80% E) 100%
B) 20%
Find kcat for a reaction in which Vmax is 4 × 10-4 mol•min-1 and the reaction mixture contains one microgram of enzyme (the molecular weight of the enzyme is 200,000 D). A) 2 × 10-11 min-1 B) 8 × 107 min-1 C) 8 × 109 min-1 D) 2 × 10-14 min-1 E) 4 × 108 min-1
B) 8 × 107 min-1
An enzyme that forms a covalent bond with its substrate during the course of a reaction is considered to undergo _____. A) acid-base catalysis B) covalent catalysis C) electrophilic catalysis D) metal ion catalysis E) none of the above
B) Covalent catalysis
What would you expect about the formation of an α-helix for a segment of a protein chain that contains lysine approximately every fourth residue with all other residues being mostly hydrophobic? A) Helix formation would be favored at low pH. B) Helix formation would be favored at high pH. C) Helix formation would be favored at neutral pH. D) Helix formation would never occur regardless of pH.
B) Helix formation would be favored at high pH.
A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _____. This indicates that at some point, the enzyme is _____. A) straight line; inhibited by product B) hyperbolic curve; saturated with substrate C) sigmoidal curve; inhibited by substrate D) hyperbolic curve; activated by substrate E) sigmoidal curve; saturated with substrate
B) Hyperbolic curve; saturated with substrate
The ability for an enzyme to change its shape upon substrate binding represents the concept of _____. A) lock and key B) induced fit C) proximity and orientation effects D) covalent catalysis E) none of the above
B) Induced fit
Conversion of factor X to factor Xa represents a(n) _____ form of activation; binding of antithrombin to thrombin represents a(n) _____ form of inhibition. A) reversible; reversible B) irreversible; reversible C) reversible; irreversible D) irreversible; irreversible E) none of the above since antithrombin is not an inhibitor of thrombin
B) Irreversible; reversible
Chymotrypsin catalyzes the hydrolysis of peptide bonds adjacent to _____ residues in a peptide. A) neutral polar B) nonpolar C) negatively charged D) positively charged E) all of the above since chymotrypsin has little substrate specificity
B) Nonpolar
What type of inhibition explains why even at very high substrate concentrations, enzyme activity will decrease as time increases? A) allosteric inhibition B) product inhibition C) transition state analogs D) irreversible inhibition E) uncompetitive inhibition
B) Product inhibition
Some irreversible inhibitors are called _____ because they bind to the active site of the enzyme and begin the catalytic process, just like a normal substrate. A) irreversible substrates B) suicide substrates C) noncompetitive substrates D) ping pong substrates E) allosteric substrates
B) Suicide substrates
What is true about the rotation about bonds in a protein backbone? A) The rotation is free about all bonds in the backbone, except for the bond between the nitrogen and the alpha carbon in proline residues. B) The bond between the carbonyl carbon and nitrogen is restricted. Other bonds are free to rotate depending only on steric hindrance or the presence of proline residues. C) All bonds in the backbone have restricted rotation and partial double-bond character. D) The rotation is free only about the peptide bond. The other bonds are restricted by steric hindrance and the presence of proline residues.
B) The bond between the carbonyl carbon and nitrogen is restricted. Other bonds are free to rotate depending only on steric hindrance or the presence of proline residues
Following several experiments, the data presented on the graph below was obtained. What can you determine from this graph? A) This data may have been collected both in the absence (solid line) and presence (dashed line) of a competitive inhibitor. B) This data may have been collected both in the absence (solid line) and presence (dashed line) of a mixed (noncompetitive) inhibitor. C) This data may have been collected both in the absence (solid line) and presence (dashed line) of mechanism based inhibitor. D) This data may have been collected both in the absence (solid line) and presence (dashed line) of an inhibitor which binds the active site. E) More than one of the above are correct.
B) This data may have been collected both in the absence (solid line) and presence (dashed line) of a mixed (noncompetitive) inhibitor.
A reversible inhibitor that only affects multisubstrate enzymes and binds to the enzyme only after one substrate has bound is a _____. A) noncompetitive inhibitor B) uncompetitive inhibitor C) competitive inhibitor D) allosteric inhibitor E) suicide substrate
B) Uncompetitive inhibitor
Of the following ions, which would be most likely to participate in metal ion catalysis? A) Na+ B) Zn2+ C) Ag+ D) K+ E) Ba2+
B) Zn2+
The catalytic efficiency of an enzyme can never exceed A) k2. B) k1. C) k-1. D) k-1 + k2. E) (k-1 + k2)/k1.
B) k1.
An enzyme is near maximum efficiency when A) its turnover number is near Vmax. B) kcat/KM is near 108 M-1s-1. C) k1 << k-1. D) kcat/KM is equal to kcat. E) KM is large when k2 exceeds k1.
B) kcat/KM is near 108 M-1s-1. `
For a reaction A + B → C, if the concentration of B is much larger than A so that [B] remains constant during the reaction while [A] is varied, the kinetics will be A) sigmoidal. B) pseudo-first-order. C) unimolecular. D) zero-order. E) hyperbolic.
B) pseudo-first-order.
Enzyme E is responsible for conversion of substrate X to product U. As a result of this conversion electrons are transported to a coenzyme (FAD) within Enzyme E. In order for the reaction to be completed, a second substrate NAD+ must also bind Enzyme E and collect stored electrons (which converts it to product, NADH). The graph below shows the data while varying X, with fixed concentrations of NAD+. What type of multi-substrate mechanism does enzyme E utilize? Substrates: X NAD+ ↓ ↓ Products: U NADH A) sequential - Ordered B) sequential - Random C) simultaneous addition D) Ping Pong E) Sequential but the data cannot differentiate between ordered and random.
B) sequential - Random
An extremely efficient enzyme has a _____ KM and a _____ kcat. A) small; small B) small; large C) large; large D) large; small E) kcat and KM do nothing to predict the efficiency of an enzyme
B) small; large
At substrate concentrations much lower than the enzyme concentration, A) the rate of reaction is expected to be inversely proportional to substrate concentration. B) the rate of reaction is expected to be directly proportional to substrate concentration. C) first order enzyme kinetics are not observed. D) the KM is lower. E) the rate of reaction is independent of substrate concentration.
B) the rate of reaction is expected to be directly proportional to substrate concentration.
Both water and glucose share an —OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase. Glucose, however, is about a million times more reactive as a substrate than water. The best explanation is that:
B)the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis.
On the energy diagram below, which arrow(s) represent the activation energy for the forward and reverse reactions? Select one: A. Arrow 1 is the activation energy for the forward reaction and arrow 3 is the activation energy for the reverse reaction. B. Arrow 1 is the activation energy for the forward reaction and arrow 2 is the activation energy for the reverse reaction. C. Arrow 3 is the activation energy for the forward reaction and arrow 2 is the activation energy for the reverse reaction. D. Arrow 1 is the activation energy for both the forward and reverse reactions.
B. Arrow 1 is the activation energy for the forward reaction and arrow 2 is the activation energy for the reverse reaction.
Which amino acid is least likely to participate in acid-base catalysis? Select one: A. Lysine. B. Valine. C. Aspartate. D. Histidine.
B. Valine.
An enzyme without a cofactor is called _________________ A. coenzyme B. apoenzyme C. holoenzyme D. noncatalytic E. isoenzyme
B. apoenzyme
The (lower, higher) the value of Km, the (less, more) tightly the enzyme is bound to the substrate. Select one or more: A. higher, more B. higher, less C. lower, less D. lower, more
B. higher, less D. lower, more
Which of the following classes of enzymes catalyze reactions involving the cleavage of bonds by the addition of water? A. transferase B. hydrolase C. lyase D. ligase E. isomerase
B. hydrolase
Oxidases, peroxidases, oxygenases or reductases are all Select one: A. lyases. B. oxidoreductases. C. hydrolases. D. synthetases. E. synthases.
B. oxidoreductases.
The Michaelis constant, Km, is equal to the ________. Select one: A. maximum velocity divided by two B. substrate concentration when the rate is equal to half its maximal value C. maximum velocity that any given enzyme reaction can achieve D. substrate concentration which gives the best enzyme assay for an enzyme reaction
B. substrate concentration when the rate is equal to half its maximal value
The initial velocity of an enzyme reaction (v0) describes Select one: A. the concentration of both at the start of the reaction. B. the rate of the reaction when the substrate and enzyme are first mixed. C. the concentration of the enzyme at maximal velocity. D. the concentration of substrate at maximal velocity.
B. the rate of the reaction when the substrate and enzyme are first mixed.
Nitrogen fixation is a process occurring in microorganism that are symbiotic with plant roots, in which N2 is reduced to NH3. why does this occur in our bodies?
Because don't have the enzymes needed to do that.
What shape would a graph of reaction velocity versus pH have for an enzyme that uses both a proton donor and a proton acceptor during catalysis (both acid and base catalysis)?
Bell-shaped
A membrane consisting only of phospholipids undergoes a sharp transition from the crystalline form to the fluid form as it is heated. What would be the effect on this transition in a membrane containing 80% phospholipid and 20% cholesterol? A) The same sharp transition would be observed, but the melting temperature would be lower. B) The same sharp transition would be observed, but the melting temperature would be higher. C) The shift from the crystalline to the fluid form would be more gradual. D) It would depend on the type of phosphilipid present.
C
A molecule moves across a membrane from a lower to a higher concentration with the aid of a membrane protein. This process is known as: A) chemiosmotic coupling C) active transport B) diffusion D) facilitated transport
C
All are distinctive features of enzymes EXCEPT: a. regulation. b. catalytic activity. c. ability to change ΔG. d. specificity. e. none is true.
C
All of the following are true statements about the transition state of a reaction EXCEPT: a. The transition state is not an appropriate indication of the rate of a reaction. b. The transition state is located at the height of a free energy diagram. c. The energy required to raise the average energy of one mole of reactant to the transition state is the free energy of activation. d. Reaching the transition state indicates that there is a high probability that the reaction will occur. e. The transition state energy level is the sum of the energy levels of the reactants and products.
C
Allosteric activators bind to enzymes A) in a way to inhibit substrate binding. B) and stabilize the 'T-state', which has a low substrate affinity. C) and stabilize the 'R-state', which has an enhanced substrate affinity. D) covalently. E) none of the above.
C
An enzyme is considered to have evolved to its most efficient form if A) kcat is a large number D) KM is a large number B) KM is a small number E) kcat/KM is a very small number C) kcat/KM is near the diffusion-controlled limit
C
Calculate the intracellular concentration of Na+ when the extracellular concentration is 120 mM and the membrane potential is -50 mV at 20°C. A) 16.5 M B) 0 C) 16.5 mM D) 1.14 mM E) 114 mM
C
Clusters of lipids and proteins in membranes are called ______. A) lipoproteins C) lipid rafts B) proteolipids D) integral lipid proteins
C
Consider the following reaction diagram. Which letter indicates the transition state? A) A; B) B; C) C; D) D; E) E
C
Feedback inhibition is a feature of what type of enzymatic control? A) Genetic control D) Compartmentalization B) Covalent modification E) Both B and C are correct. C) Allosteric regulation
C
How is an enzyme-catalyzed reaction affected by the addition of more enzyme? A) velocity is not effected B) velocity will increase only if more substrate is also added C) velocity will increase D) velocity will decrease E) none of the above
C
If the rate constant for the reaction: A + B → C is 0.25 mM-1•s-1 when [A] = [B], what is the substrate concentration under these conditions when v0 = 16 mM/s? A) 64 mM B) 2 mM C) 8 mM D) 4 mM E) 5 mM
C
Positive cooperativity is a feature of what type of enzymatic control? A) Genetic control B) Covalent modification C) Allosteric regulation D) Compartmentation E) Both B and C are correct
C
Regulatory enzymes are a feature of what type of enzymatic control? A) Genetic control B) Covalent modification C) Allosteric regulation D) Compartmentation E) Both B and C are correct
C
Specific activity is defined as A) Enzyme concentration that converts 1 mole of substrate to product per minute. B) Enzyme concentration that converts 1 mole of substrate to product per minute C) The number of I.U. per mg of protein D) The number of I. U. per gram of protein E) Enzyme concentration that converts 1 mm of substrate to product per minute.
C
The action of phospholipase C results in the formation of 2 second messengers. Which of these is soluble in the cytoplasm? A) diacylglycerol C) inositol trisphosphate B) phosphatidylinositol bisphosphate D) cAMP
C
The bonding of alcohols to the anomeric center of a carbohydrate results in the formation of a(n) __________ bond. A) anomeric B) amide C) glycosidic D) ester E) hydrogen
C
The production of cAMP by adenylate cyclase leads to the activation of protein kinase A, which _____________. A) Activates glycogen synthase D) Inhibits glycogen phosphorylase B) Inhibits hormone sensitive lipase E) C & D C) Activates phosphorylase kinase
C
What is the effect of cholesterol in a membrane? A) Increases membrane fluidity by preventing acyl chain packing. B) Reduces membrane fluidity by limiting acyl chain movement. C) Both of the above D) Neither of the above
C
What type of isomers are α-D-glucose and β-D-glucose? A) enantiomers B) epimers C) anomers D) diastereomers
C
Which is not a lipid-soluble vitamin?
C
Which of the following is a ligand of the β2-adrenergic receptor? A) tyrosine D) caffeine B) serotonin E) adenosine C) norepinephrine
C
Which of the following is glucose-6-phosphate? A) A D) D B) B E) none of the above C) C
C
Which of the following molecules stimulate the activation of lipases in muscle cells? A) insulin D) erythropoietin B) glucagon E) None of the options is true. C) epinephrine
C
Which of the following statements is NOT characteristic of kcat/Km? a. It corresponds to a second-order rate constant. b. It provides an excellent parameter for comparison of the catalytic efficiency of enzymes. c. It reflects the property of the enzyme when substrate concentration is at saturation. d. The upper limit for the kcat/Km value is fixed by the diffusion-controlled limit for reactions, which is 109 M-1 s-1. e. It is also referred to as the turnover number.
C
: Section 6-1 8) Cleavage of a C-C bond produces a carbanion that ________ both electrons and a carbocation that ________ both electrons. A) loses; loses B) loses; keeps C) keeps; loses D) keeps; keeps
C keeps; loses
: Section 6-5 38) Most Km values of enzymes for their substrates are on the order of ________ M. A) 10-2 B) 10-3 C) 10-4 D) 10-5 E) 10-6
C 10^-4
: Section 6-6 53) The catalytic triad of chymotrypsin and other serine proteases consists of A) three subunits of the enzyme. B) three amino acid residues adjacent in the primary structure which act to make serine a strong nucleophile. C) three amino acid residues close enough in space to make serine a strong nucleophile. D) three enzymes with very similar structural features. E) None of the above.
C 3 amino acid residues close enough in space to make serine a strong nucleophile
: Section 6-7 60) Which bond in the polysaccharide shown is cleaved by lysozyme? A) A B) B C) C D) D
C C
: Section 6-5 37) A thermodynamic pit occurs when A) ES is not very stable. B) ES forms faster than it dissociates. C) ES is highly stable. D) S is not bound tightly to an enzyme. E) S is positioned incorrectly to the enzyme.
C ES is highly stable
Which does not apply to dihydroxyacetone? A) Ketose. B) Triose. C) Chiral. D) Water-soluble.
C Page Ref: Section 8-1
Which structure is NOT a carbohydrate? A) B) C) D)
C Page Ref: Section 8-1
18) The compounds α-D-fructofuranose and β-D-fructofuranose are ________. A) enantiomers B) mutamers C) anomers D) conformational isomers
C Page Ref: Section 8-2
26) Ribitol is a sugar alcohol that is a component of A) vitamin C. B) RNA. C) FMN and FAD. D) NAD and NADH. E) sialic acid.
C Page Ref: Section 8-4
27) Which statement is false about the sugar units in DNA? A) They are cyclic in DNA. B) It is a deoxy form of ribose. C) It is an epimer of glucose. D) It has a D-configuration.
C Page Ref: Section 8-4
32) If glucose supplies the anomeric carbon atom in a glycosidic link, the resulting compound is classified as a ________. A) glycoside B) glycan C) glucoside D) glucosamine
C Page Ref: Section 8-5
36) The structure of a disaccharide is shown below. Which statement applies? A) Both rings A and B are in equilibrium with an open chain form. B) Only ring A is in equilibrium with an open chain form. C) Only ring B is in equilibrium with an open chain form. D) Neither ring is in equilibrium with an open chain form.
C Page Ref: Section 8-5
41) Which is a difference between maltose and cellobiose? A) One is in cellulose and the other in starch. B) One is linear and the other is branched. C) The glycosidic bond is different. D) The subunit sugars are not glucose for both. E) All of the above.
C Page Ref: Section 8-5
45) Both amylose and amylopectin molecules isolated from plant cells can contain as many as ________ glucose residues. A) 25 B) 500 C) 1000 D) 2000 E) 6000
C Page Ref: Section 8-6
50) Humans can digest limit dextrin that is formed from dietary plant starch using A) α-amylase. B) β-amylase. C) debranching enzyme. D) A and B. E) A, B, and C.
C Page Ref: Section 8-6
54) The elasticity and resistance to compression of connective tissue is due to A) the branching of the glycosaminoglycans there. B) the glycosidic linkage to the serine of proteins in the glycosaminoglycans. C) the carboxyl and sulfated groups in the glycosaminoglycans. D) the rigid structure of the glycosaminoglycans. E) All of the above.
C Page Ref: Section 8-6
56) The bacterial cell wall is sensitive to penicillin because it A) blocks the linkage of the MurNAc and GlcNAc subunits. B) blocks the pentaglycine bridge cross linkage. C) binds to an enzyme which recognizes D-alanine-D-alanine dipeptide. D) is not attacked by enzymes in animal cells. E) All of the above.
C Page Ref: Section 8-7
58) ________ contain NeuNAc residues and sulfated sugars, and their negative charges contribute to the viscosity of mucins. A) Proteoglycans B) N-linked polysaccharides C) O-linked polysaccharides D) Hyaluronic acid E) All of the above
C Page Ref: Section 8-7
: Section 6-2 17) An enzyme stabilizes the transition state that is bound in the active site. What effect will this have on the energy diagram below? The diagram shown below is for the uncatalyzed reaction. A) Energy of point 1 is raised. B) Energy of point 2 is raised. C) Energy of point 2 is lowered. D) Energy of point 3 is lowered. E) Energy of point 4 is raised.
C energy of point 3 is lowered
: Section 6-5 40) An update of Fischer's lock-and-key theory of enzyme specificity views the ________ as the lock and ________ as the key. A) enzyme; substrate B) substrate; enzyme C) enzyme; transition state D) transition state; enzyme E) substrate; transition state
C enzyme; transition state
: Section 6-6 55) The role of ser-195 in chymotrypsin cleavage of a peptide bond is that of a(n) A) acid catalyst. B) proximity effector. C) strong nucleophile. D) weak nucleophile.
C strong nucleophile
: Section 6-5 36) In the nonpolar environment of most enzyme active sites, which statement applies to charge-charge interactions between the enzyme and the substrate? A) They are rare due to the non-polar environment. B) They are frequent, but not very strong in the nonpolar environment. C) They are stronger in the nonpolar environment. D) The polarity of the active site has no effect on the strength of the charge-charge interactions.
C stronger in non-polar environments
: Section 6-6 56) Experiments on the bacterial serine protease subtilisin show that even when all three residues of the catalytic triad are mutated, the catalytic rate of the enzyme is still 3000 times the uncatalyzed reaction rate. Which mode of catalysis is likely responsible for this remaining catalytic activity? A) Acid-base catalysis. B) Covalent catalysis. C) Transition-state stabilization. D) Hydrophobic effects.
C transition state stabilization
: Section 6-6 49) Active trypsin formation by the action of enteropeptidase can be viewed as the master activation step because A) enteropeptidase can activate its own zymogen. B) it is allosterically controlled. C) trypsin activates other pancreatic zymogens. D) All of the above.
C trypsin activates other pancreatic zymogens
[S] = KM for a simple enzymatic reaction. When [S] is doubled the initial velocity is A) 2 Vmax B) equal to Vmax C) (1/3) Vmax D) 0.5 Vmax E) 2 KM/[S]
C) (1/3) Vmax
Based on the figure in the question above (question 54), which of the following expressions would correctly define KM? A) A= KM B) KM = A/2 C) B = KM D) C = - KM E) D= 1/ KM
C) B = KM
Which of the following explains how cell division is blocked by drugs that prevent proper microtubule function? A) The condensation of chromatin requires a microtubule skeleton. B) Production of new membranes for organelles and nucleus requires microtubules. C) Chromosomes separate along a microtubule spindle. D) Division of organelles between daughter cells requires organelle movement along microtubules.
C) Chromosomes separate along a microtubule spindle.
Which of the following is true about enzymes? A) enzymes show very little specificity for their substrates B) enzymes catalyze reactions in only one direction C) enzyme activities can often be regulated D) enzymes reaction rates are generally slower than other chemical catalysts E) enzymes operate under a wide range of temperatures and pH
C) Enzyme activities can often be regulated
________ clinical trials are focused on evaluating the efficacy of new drug candidates, and usually use _____ test. A) Phase 1; single blind B) Phase 1; double blind C) Phase 2; single blind D) Phase 2; double blind E) Phase 3; double blind
C) Phase 2; single blind
Which of the following occurs in hemoglobin upon oxygen binding? A) Hemoglobin changes from the R state to the T state. B) The heme Fe2+ is pulled out of the plane of the heme group. C) The central cavity between the four subunits is decreased in size. D) The His coordinated to the heme Fe2+ is pushed away from the heme group.
C) The central cavity will decrease in size
Zymogens are not enzymatically active because _____. A) they do not contain the cofactors required for catalysis B) they are the product of mutated genes C) their active sites are distorted and incapable of enzymatic activity D) the pH of their environment is not optimal for activity E) none of the above
C) Their active sites are distorted and incapable of enzymatic activity
Of all the species that enzymes bind, they are thought to bind most tightly to _____.Of all the species that enzymes bind, they are thought to bind most tightly to _____. A) substrates B) products C) transition states D) intermediates E) all are bound very tightly
C) Transition states
How are the kinetics of an enzyme-catalyzed reaction affected by a purely noncompetitive inhibitor? A) Vmax decreased, KM increased B) Vmax decreased, KM decreased C) Vmax decreased, KM unchanged D) Vmax unchanged, KM increased E) Vmax unchanged, KM decreased
C) Vmax decreased, KM unchanged
Which of the following represents a rapid and reversible mechanism to alter the activity of an enzyme? A) synthesis of more enzyme to increase activity B) degradation of enzyme to decrease activity C) covalent attachment of a phosphate group to increase or decrease activity D) movement of an enzyme from one cellular compartment to another E) none of the above
C) covalent attachment of a phosphate group to increase or decrease activity
The KM can be considered to be the same as the dissociation constant KS for E + S binding if A) the concentration of [ES] is unchanged. B) ES → E + P is fast compared to ES → E + S. C) k1 >> k2 D) k2 << k-1. E) this statement cannot be completed because KM can never approximate KS.
C) k1 >> k2
Proline is not often found in α-helices of proteins because it A) has a small, uncharged side chain. B) has a very bulky side chain. C) lacks a hydrogen atom on its amide nitrogen. D) interacts with adjacent amino acids.
C) lacks a hydrogen atom on its amide nitrogen.
The following questions (33 and 34) refer to the diagram (with boxes where it has been left incomplete): 32. This diagram refers to a (an) A) Ping Pong reaction. B) ordered bisubstrate reaction. C) random bisubstrate reaction. D) double order ping pong reaction E) X, Y, and Z must be provided in order to answer correctly
C) random bisubstrate reaction.
Allosteric activators A) bind via covalent attachment. B) stabilize conformations with higher Ks. C) stabilize conformations with higher substrate affinity. D) all of the above E) none of the above.
C) stabilize conformations with higher substrate affinity.
A histidine was determined to be the critical residue involved in an enzyme-catalyzed reaction. If the pKa of the histidine is known to be 6.5 in the active site and the pH of maximum catalytic activity is 7.2, what is likely the primary role of histidine in the catalytic reaction? Select one: A. Forms a covalent bond with the substrate. B. Stabilizes a charged intermediate. C. Acts as a proton donor or acceptor. D. Reduces the entropy of the substrate.
C. Acts as a proton donor or acceptor.
In the following chemical reaction which species is the reducing agent? CH4 + 2 O2 → CO2 + 2 H2O Select one: A. CO2 B. H2O C. CH4 D. O2
C. CH4
SAM-
Methyl groups
ES complex for Michaelis-Menten equation also known as the ____________ complex
Michaelis
After examining enzyme rate data, a model of enzyme behavior was developed and it is known as the ___________ - ____________ equation
Michaelis-Menten equation
Fundamental equation of enzyme kinetics
Michaelis-Menten equation
What fiber is paired with this protein that forms it: Actin?
Microfilaments: actin
What fiber is paired with this protein that forms it: Tubulin
Microtubules: tubulin
In contrast to inorganic catalysts, enzymes have an intricately shaped pocket where the substrate binds called the __________________. A. substrate B. cofacter C. active site D. apoenzyme E. holoenzyme
C. active site
In an enzyme reaction involving one enzyme and one substrate, the rate of the reaction depends on Select one: A. the enzyme concentration at first and the substrate concentration later on. B. enzyme concentration. C. both substrate and enzyme concentrations. D. substrate concentration.
C. both substrate and enzyme concentrations.
Which of the following statements is not true of enzymes? A. increase the reaction rate B. obey the laws of thermodynamics C. catalyses the forward reaction only D. does not affect the position of equilibrium E. not consumed by the reaction
C. catalyses the forward reaction only
Histidine is an ideal amino acid at neutral pH values at the active site of many enzymes because Select one: A. it is hydrophobic. B. it is not ionizable. C. its R group has a pKa of about 6 to 7 in most proteins. D. it engages in electron transfer.
C. its R group has a pKa of about 6 to 7 in most proteins.
Metabolic pathways that involve the degradation of large molecules to smaller ones are classified as ________.
Catabolic
Which sugar contains a Beta-1,4 linkage?
Cellulose
High levels of which molecule indicates high cell energy status?
Citrate & ATP
The ETC component that contains cyt a and catalyzes a 4e- reduction of O2 to form H2O is:
Complex IV
The reaction catalyzed by a certain phosphatase enzyme is found to follow ping-pong kinetics and involves the transfer of a phosphate group from substrate A to substrate B. Which mode of catalysis is likely for this reaction?
Covalent catalysis
Excretion of nitrogen in mammals-
Coverts Nitrogen to urea (ureotelic)
6) Which of the following expresses the velocity for an enzyme-catalyzed reaction that obeys Michaelis-Menten kinetics? A) v = k₁[E][S] B) v = k₁[E][S] - k⁻₁[ES] C) v = k₁[E][S] + k₂[ES] D) v = k₂[ES] E) v = k₂[ES] - k-₁[ES]
D
A pore that simultaneously transports two different molecules in different directions is called: A) a promiscuous pore D) an antiporter B) a symporter E) a gap junction C) an equilibrium machine
D
All known porins are _____ proteins composed of _____. A) monomeric; seven transmembrane α-helices D) trimeric; β-barrels B) dimeric; β-barrels E) trimeric; four transmembrane α-helices C) dimeric; three transmembrane α-helices
D
All of the following are properties of a coenzyme EXCEPT: a. They are usually actively involved in the catalytic reaction of the enzyme. b. They tend to be stable to heat. c. They can serve as intermediate carriers of functional groups. d. They are protein components. e. They may contain vitamins as part of their structure.
D
All of the following statements about competitive inhibition are correct EXCEPT: a. Competitive inhibitors are often chemical analogs of the substrate. b. For a group-specific enzyme, one substrate would be a competitive inhibitor of reactions of the other possible substrate. c. Sometimes a product of an enzyme-catalyzed reaction is a competitive inhibitor of its own production. d. In the presence of a competitive inhibitor, the apparent Km would be altered and Vmax would be decreased. e. Competitive inhibitors usually interact with the enzyme at the binding site for a substrate.
D
Enzyme studies are best carried out: A) In dilute aqueous solution B) In highly concentrated solutions of the enzyme C) In highly concentrated solutions of the substrate D) In the presence of an inert crowding agent E) In the presence of a membrane
D
How many stereoisomers are possible for a ketohexose? A) 2 B) 4 C) 6 D) 8 E) 12
D
In the Lineweaver-Burk double reciprocal plot the vertical intercept is equal to ____. A) 1/[S] B) 1/V C) Km/Vmax D) 1/Vmax E) -1/Km
D
O-linked oligosaccharides are commonly attached to the oxygen of _____. A) ribose B) tyrosine C) lysine D) threonine E) galactose
D
Pyruvate carboxylase is an example of which class of enzymes? A) Oxidoreductase B) Transferase C) Hydrolase D) Ligase E) Lyase
D
Segregation of biochemical pathways into different organelles in an example of which type of enzymatic regulation? A) Genetic control B) Covalent modification C) Allosteric regulation D) Compartmentation E) Both B and C are correct
D
Signal transduction can be mediated by two different types of receptors that use different pathways of activation. What do they share in common? A) They are both transmembrane proteins. B) The process begins with a conformational change induced by ligand binding. C) They all interact with G proteins. D) A and B are both true. E) All of the above are true.
D
The catalytic mechanism below is an example of: A. covalent nucleophilic catalysis. B. covalent electrophilic catalysis. C. specific base catalysis. D. general base catalysis. E. low barrier hydrogen bond catalysis.
D
The following questions refer to the overall transformation: E + S .<.....>k1/k2---> ES ......> k2...> P + E 29. The overall transformation A) is composed of two elementary reactions. B) can be zeroth order in [S] if [S]>>[E] C) may be described by the Michaelis-Menten equation if certain assumptions are made D) all of the above E) none of the above
D
What aspect of aquaporins is responsible for ensuring that protons are not transported with H2O? A) Asn residues disrupt the H-bonded water network. B) Hydrophobic residues line the pore and prevent passage of charged molecules. C) Basic residues line the pore and repel the positive charge. D) Both A and B E) All are true
D
What is the primary storage form of fatty acids? A) glycerophospholipids C) sphingolipids B) cholesterol D) triglycerides
D
What is the velocity of a first-order reaction when the reactant concentration is 6 x 10-2 M and the rate constant is 8 x 103 sec-1? A) 1.33 x 105 M-1•sec-1 B) 1.33 x 105 M•sec C) 7.5 x 10-2 M•sec D) 4.8 x 102 M•sec-1 E) not enough data are given to make this calculation
D
Which of the following amino acids cannot actively participate in a catalytic site? A) Serine B) Threonine C) Tyrosine D) Glycine E) Glutamine
D
Which of the following is not an example of a passive-mediated transporter? A) aquaporin D) Na+/K+ transporter B) ion channels E) none of the above C) glucose transporter, GLUT1
D
Which of the following would be positively charged at physiological pH? A) glucuronic acid D) glucosamine B) fructose-6-phosphate E) all of the above C) xylitol
D
: Section 6-1 4) In the reaction below, Y- is ________. Y- + CH2X → CH2Y + X- A) the leaving group B) the attacking electrophile C) the reaction intermediate D) a nucleophile
D a nucleophile
Which is not a glycoconjugate? A) Proteoglycan. B) Glycolipid. C) Glycoprotein. D) Homoglycan.
D Page Ref: 8-Introduction
7) The structure of D-arabinose is shown below. How many stereoisomers are possible for this molecule (including the one shown)? A) One B) Four C) Six D) Eight
D Page Ref: Section 8-1
11) The intramolecular cyclization reaction of glucose in solution ________. A) generates a chiral center B) yields a hemiacetal C) usually forms a pyranose D) All of the above
D Page Ref: Section 8-2
12) A ribopyranose contains ________ carbon atoms while a ribofuranose has ________ carbon atoms. A) 6, 5 B) 6, 6 C) 5, 6 D) 5, 5
D Page Ref: Section 8-2
24) Monosaccharide derivatives in which an amino group replaces one of the hydroxyl groups may have important roles in A) DNA structure. B) intermediary metabolisms. C) vitamin C. D) sialic acids. E) All of the above.
D Page Ref: Section 8-4
31) The chemical name for table sugar is ________ and it is a ________. A) lactose; monosaccharide B) lactose; disaccharide C) sucrose; monosaccharide D) sucrose; disaccharide
D Page Ref: Section 8-5
34) Hydrolysis of maltose will yield ________. A) glucose and galactose B) fructose and glucose C) glucose and mannose D) glucose only
D Page Ref: Section 8-5
43) Polysaccharide structure can be varied by differences in A) chain length (number of sugars in each polysaccharide). B) the kind(s) of sugars in each polysaccharides. C) the presence of branching. D) All of the above.
D Page Ref: Section 8-6
44) Amylose differs from amylopectin in that amylose A) has different monomers than amylopectin. B) has more glucose residues than amylopectin. C) is highly branched and amylopectin is not. D) forms a helix and no branch points.
D Page Ref: Section 8-6
46) Enzymes in the human intestine which are needed to degrade plant starch into limit dextrin are A) α-Amylase. B) β-Amylase. C) debranching enzymes. D) A and B. E) A, B, and C.
D Page Ref: Section 8-6
47) Amylase is a hydrolase that is an ________. A) endonuclease B) endoglycosidase C) exonuclease D) exoglycosidase that removes maltose E) exoglycosidase that removes glucose monomers
D Page Ref: Section 8-6
48) Which is not a similarity between glycogen and amylopectin? A) They each contain about 6000 glucose residues. B) Each has one reducing end and many nonreducing ends. C) Each is highly branched. D) Each has branches of similar chain length.
D Page Ref: Section 8-6
51) Highly branched cores of amlyopectin that are resistant to hydrolysis are called ________. A) core saccharides B) non-reducing saccharides C) dextran D) limit dextrins
D Page Ref: Section 8-6
: Section 6-3 30) The graph shows the rate of catalysis versus pH for an enzyme-catalyzed reaction. What conclusion can be made from the graph? A) The enzyme is completely denatured by pHs greater than 8 or less than 5. B) The substrate has four ionizable groups. C) At pH 6.2 all ionizable groups in the active site are protonated. D) The enzyme has an acidic and a basic amino acid in the active site. E) The enzyme has only one protonatable residue in the active site.
D The enzyme has an acidic and a basic amino acid in the active site
: Section 6-5 45) A key role of the hydroxyl group at position 6 in the purine ring in the formation of a transition state by the enzyme adenosine deaminase is obtained by comparing a ________ and a ________. A) competitive inhibitor; noncompetitive inhibitor B) transition state analog; normal substrate C) noncompetitive inhibitor; transition state analog D) competitive inhibitor; transition state analog E) All of the above.
D all of the above
: Section 6-3 24) The reaction catalyzed by a certain phosphatase enzyme is found to follow ping-pong kinetics and involves the transfer of a phosphate group from substrate A to substrate B. Which mode of catalysis is likely for this reaction? A) Sequential catalysis. B) Acid-base catalysis. C) Transfer catalysis. D) Covalent catalysis.
D covalent catalysis
: Section 6-6 57) What is the biological function of lysozyme? A) Converts trypsinogen to trypsin. B) Is a ligase that accelerates the polymerization of glycogen. C) It regulates vascular constriction in chickens. D) Hydrolyzes polysaccharides of bacterial cell walls.
D hydrolyze polysaccharides of bacterial cell walls
: Section 6-1 3) How is the half-reaction Cu2+ + 2e- → Cu classified? A) Free radical reaction. B) Electrophilic substitution reaction. C) Oxidation reaction. D) Reduction reaction. E) None of the above.
D reduction reaction
: Section 6-6 54) The roles of amino acid residues at the active site of enzymes can be determined by removing certain residues using the technique of A) specific hydrolysis. B) covalent binding. C) acylation of specific residues. D) site-directed mutagenesis. E) All of the above.
D site directed mutagenesis
: Section 6-6 52) Pepsin and trypsin are produced in the pancreas as zymogens. What might result if these two enzymes were not produced in the pancreas as zymogens, but as active pepsin and trypsin? A) They would not be transported to the intestine because of their native charge. B) They would not be folded properly by their chaperone molecules. C) They would associate into inactive oligomeric forms. D) They would begin to degrade and damage pancreatic proteins.
D they would begin to degrade and damage pancreatic proteins
: Section 6-5 47) Induced fit studies by Koshland using the enzyme hexokinase showed that there are enzyme forms A) which react with the hydroxyl group of water. B) which react only with ATP and glucose present together. C) which are hydrophobic, excluding the competing hydroxyl group from water. D) with and without glucose bound to each. E) that hydrolyze ATP.
D with and without glucose bound to each
If an enzyme-catalyzed reaction has a velocity of 2 mM/min and a Vmax of 10 mM/min when the substrate concentration is 0.5 mM, what is the KM? A) 0.2 mM B) 0.5 mM C) 1 mM D) 2 mM E) 5 mM
D) 2mM
During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play? A) general acid only B) general base only C) general acid then general base D) general base then general acid E) nucleophile
D) General base then general acid
Which of the following amino acids would be most likely found in the active site of an enzyme that uses acid-base catalysis? A) Asn B) Ser C) Met D) His E) Trp
D) His
Determine the KM and Vmax from the following graph. (Note: On the x-axis the minor tick mark spacing is 0.005; on the y-axis the minor tick mark spacing is 0.002) A) KM = [0.006]; Vmax = 0.0075/s B) KM = [0.196]; Vmax = 0.0075/s C) KM = [165]; Vmax = 33/s D) KM = [33]; Vmax = 167/s E) KM = [270]; Vmax x = 68/s
D) KM = [33]; Vmax = 167/s
If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a competitive inhibitor present, what difference would be seen? A) the y-intercept would be lower for the inhibited reaction B) the y-intercept would be higher for the inhibited reaction C) the slope would be less for the inhibited reaction D) the slope would be greater for the inhibited reaction E) none of the above
D) The close would be greater for the inhibited reaction
The highest point in a reaction coordinate diagram represents _____. A) an intermediate of the reaction pathway B) the reactants in an exergonic reaction C) the products in an endergonic reaction D) the transition state E) the overall G for the reaction
D) The transition state
How are the kinetics of an enzyme-catalyzed reaction affected by a competitive inhibitor? A) Vmax decreased, KM increased B) Vmax decreased, KM decreased C) Vmax decreased, KM unchanged D) Vmax unchanged, KM increased E) Vmax unchanged, KM decreased
D) Vmax unchanged, KM increased
Proteins with alpha helix regions called leucine zippers are A) often found in DNA binding proteins. B) amphipathic helices. C) part of pairs of helices that are wrapped around each other. D) All of the above.
D) all of the above
When is KM considered to be the same as the dissociation constant for the ES complex i.e., KM [E] [S] / [ES]. A) ES → E + P is fast compared to ES → E + S B) the turnover number is very large C) kcat/KM is near the diffusion-controlled limit D) k2 << k-1 E) KM can never be the same as the dissociation constant
D) k2 << k-1
What does the KI for a competitive inhibitor mean? A) higher KI values mean tighter binding to ES complex B) lower KI values mean tighter binding to ES complex C) higher KI values mean tighter binding to the enzyme D) lower KI values mean tighter binding to the enzyme E) KI values tell nothing about inhibitor binding
D) lower KI values mean tighter binding to the enzyme
Supersecondary structures that contain recognizable combinations of α-helices, β-strands and loops (e.g. the Greek Key) are called ________. A) domains B) folds C) homologous regions D) motifs
D) motifs
If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a noncompetitive inhibitor present, what difference would be seen? A) the y-intercept would be higher with slope unchanged for the inhibited reaction B) the y-intercept would be lower with larger slope for the inhibited reaction C) the y-intercept would be lower with smaller slope for the inhibited reaction D) the y-intercept would be higher with larger slope for the inhibited reaction E) the y-intercept would be higher with smaller slope for the inhibited reaction
D) the y-intercept would be higher with larger slope for the inhibited reaction
Which step in an enzyme-catalyzed reaction was assumed to be negligible by Michaelis and Menton? Select one: A. Conversion of ES to E + S. B. Formation of ES from E + S. C. Formation of E + P from ES. D. Formation of ES from E + P.
D. Formation of ES from E + P.
What is the shape of a typical plot of initial rate vs. substrate concentration for an enzyme catalyzed reaction that follows Michaelis-Menton kinetics? Select one: A. Sigmoidal. B. Parabolic. C. Sinusoidal. D. Hyperbolic. E. Bell curve
D. Hyperbolic.
The lock and key model of enzyme activity proposes that each A. enzyme can react with only a single substrate B. enzyme has a cofactor that promotes the catalytic activity C. substrate has a specific cofactor that binds it to the enzyme D. enzyme binds a specific substrate because the active site and substrate have complimentary structures E. Both A and B are correct
D. enzyme binds a specific substrate because the active site and substrate have complimentary structures
Replacement of the amino acid ________ at or near an active site of an enzyme is more likely to change enzyme activity than the replacement of ________ at or near the active site. Select one: A. histidine; aspartate B. leucine; isoleucine C. leucine; histidine D. histidine; leucine
D. histidine; leucine
Hexokinase is an example of which class of enzymes A. hydrolase B. lyase C. isomerase D. transferase E. ligase
D. transferase
All are true for kcat EXCEPT : a. referred to as the molecular activity of the enzyme. b. called the turnover number of the enzyme. c. measures the maximal catalytic activity or kinetic efficiency of an enzyme. d. defines the number of substrate molecules converted into product/enzyme molecule/unit of time when the enzyme is saturated with substrate. e. all are true
E
Desensitization of a G protein-coupled receptor is caused by phosphorylation of the receptor by a specific kinase. What protein recognizes the phosphorylated receptor? A) phospholipase C D) adenosine receptor B) the G protein γ subunit E) arrestin C) cAMP phosphodiesterase
E
In typical marine organisms, the intracellular concentrations of Na+ and Ca2+ are 10 mM and 0.1 μM, respectively. Extracellular concentrations of Na+ and Ca2+ are 450 mM and 4 mM, respectively. Calculate the free energy changes at 20°C for the transmembrane movement of these ions. In which direction do the ions move? Assume the membrane potential is -70 mV. A) Na+ moves in because ΔG = +16.0 kJ/mol; Ca2+ moves out because ΔG = -39.3 kJ/mol B) Na+ moves out because ΔG = -16.0 kJ/mol; Ca2+ moves in because ΔG = -32.6 kJ/mol C) Na+ moves out because ΔG = +2.5 kJ/mol;Ca2+ moves out because ΔG = +39.3 kJ/mol D) Na+ moves in because ΔG = -10.8 kJ/mol;Ca2+ moves in because ΔG = -22.5 kJ/mol E) Na+ moves in because ΔG = -16.0 kJ/mol;Ca2+ moves in because ΔG = -39.3 kJ/mol
E
The movement of glucose into a cell when blood sugar is high is accomplished by _____. The movement of K+ against its concentration gradient is accomplished by _____. A) simple diffusion; active transport D) simple diffusion; passive transport B) passive transport; passive transport E) passive transport; active transport C) active transport; membrane potential
E
What is (are) the advantages of protein phosphorylation as a signaling event? A) Phosphorylation is rapid and specific. B) Phosphorylation is enzymatically reversible. C) Phosphorylation can be amplified by cascade systems. D) A and B E) A, B, and C
E
Which of the following are characteristic of cellulose? A) highly extended fibers B) β(1→4) glycosidic bonds C) extensive hydrogen bonding between individual molecules D) unbranched polymer E) all of the above
E
Which of the following is a feature of transition metals that makes them efficient cofactors? A) Have a high concentration of positive charge B) Can act as a Lewis acid C) Have directed valences D) Can exist as a variety of valence states E) All of the above are correct.
E
Which of the following is not an assumption of the law of mass action? A) Forward reaction is linear B) Reverse reaction is linear C) System is homogenous D) Interacting molecules move randomly and independently of each other E) All are assumptions of the law of mass action
E
: Section 6-5 46) The induced fit model of enzyme activation includes A) contact (binding) of substrate. B) constant small and rapid motions of protein atoms. C) conversion of the enzyme to an active form. D) A and B. E) A, B, and C.
E A B C
33) Which classification(s) is(are) applicable to maltose? A) Nonreducing sugar. B) Reducing sugar. C) Peptidoglycan. D) Glucoside. E) Both B and D.
E Page Ref: Section 8-5
40) Naturally occurring glycosides have roles in cells which include A) building blocks of DNA. B) chemical signals to plants. C) food flavoring. D) units in cell membrane structure. E) All of the above.
E Page Ref: Section 8-5
: Section 6-4 34) SOD (superoxide dismutase) is an enzyme that reacts faster than the rate of diffusion of the substrate to the active site due to A) its negative charge. B) electrostatic effects. C) the deep channel in the enzyme protein. D) the copper atom at the active site. E) All of the above.
E all of the above
: Section 6-5 42) The enzyme has an active site which A) fits the substrate exactly. B) fits the transition state. C) may contain hydrogen bonds which are covalent-like. D) A and C. E) B and C.
E fits the transition state AND may contain H bonds which are covalent like
: Section 6-5 44) Transition state analogs should A) stabilize transition states. B) have a dissociation constant of 10-13 M or less. C) bind very tightly to the enzyme. D) A and C. E) B and C.
E have dissociation constant of 10^-13 M or less AND bin tightly to the enzyme
If an enzyme rate increases 10-fold for every 5.7 kJ/mol decrease in the energy of activation, what rate increase would be observed if three H-bonds were stabilizing the transition state with each H-bond having a strength of 21 kJ/mol? A) 11-fold increase B) 37-fold increase C) 60-fold increase D) 100-fold increase E) 1011-fold increase
E) 1011-fold increase
Which of the following is seen in a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis? A) an intermediate B) two distinct transition states C) reactants that are lower in energy than an intermediate D) products that are lower in energy than an intermediate E) all of the above
E) All of the above
Which of the following is true regarding transition state analogs? A) they are competitive inhibitors B) they bind to an active site with much higher affinity than most inhibitors C) they are much more stable than the transition state D) their affinity for an enzyme is often much greater that the substrate E) all of the above
E) All of the above
Which of the following types of enzyme-catalyzed reactions follows non-Michaelis-Menten kinetics? A) bisubstrate reactions with a random mechanism B) bisubstrate reactions with a ping pong mechanism C) bisubstrate reactions with an ordered mechanism D) allosteric enzyme reactions E) all of the above
E) All of the above
For the reaction, the steady state assumption A) implies that k1=k−1 B) implies that k−1 and k2 are such that the [ES] = k1[ES] C) [P]>>[E] D) [S] = [P] E) ES breakdown occurs at the same rate as ES formation
E) ES breakdown occurs at the same rate as ES formation
Enzyme activity in cells is controlled by which of the following? I. covalent modifications II. modulation of expression levels III. feedback inhibition IV. allosteric effectors A) I B) II C) III D) III, IV E) I, II, III, IV
E) I, II, III, IV
An organic molecule that is tightly bound to an enzyme and participates in an enzyme catalyzed reaction is specifically referred to as a _____. A) cofactor B) metal ion C) coenzyme D) cosubstrate E) prosthetic group
E) Prosthetic group
For a reaction A + B → C, if [B] is much larger than [A] so that [B] essentially remains constant over the course of the reaction, the kinetics will be _____. A) zero-order B) hyperbolic C) first-order D) sigmoidal E) pseudo first-order
E) Pseudo first-order
An extremely efficient enzyme called "efficase" catalyzes the conversion of "A" to "B." A researcher decides to mutate the enzyme in order to try to improve its performance. Following active site mutations, a significant reduction in the value of KM and Vmax was observed. Which of the following may have occurred? A) The affinity of the enzyme for the substrate was increased to a point which did not favor propagation (continuation) of the reaction. B) The decrease in Vmax was not related to the decrease in KM. C) If the reaction was first-order, the change in KM cannot have affected Vmax. D) The stability of E+S (E+A as written above) was increased, thereby increasing the KM. E) The reverse reaction (breakdown of EA to E+A) was favored, slowing the Vmax.
E) The reverse reaction (breakdown of EA to E+A) was favored, slowing the Vmax.
Which of the following must be true if the steady state assumption is to be used? A) [E]T = [ES] B) (k2 - k-1) / k1 = 1 C) k1[E][S] = k2[ES] D) k1[E][S] = k2[ES] - k-1[ES] E) d[ES] / dt = 0
E) d[ES] / dt = 0
Which of the following indicates that an enzyme has evolved to its most efficient form? A) kcat is a large number B) KM is a small number C) KM is a large number D) kcat/KM is a small number E) kcat/KM is near the diffusion-controlled limit
E) kcat/KM is near the diffusion-controlled limit
Pseudo-first-order reaction kinetics would be observed for the reaction A + B C A) if [A] or [B] > [C]. B) if [C]>[A] and [C]>[B]. C) if [A] or [B] = 0. D) if [C] = 0. E) none of the above
E) none of the above
Fourth-order reactions. A) have three or more sequential rate determining steps. B) require a 'Ping Pong' mechanism. C) are best analyzed using Lineweaver-Burk plots. D) exist only when enzymatically catalyzed. E) none of the above.
E) none of the above.
Which of the following statements about allosteric control of enzymatic activity is false? A)Allosteric effectors give rise to sigmoidal V0 vs. [S] kinetic plots. B)Allosteric proteins are generally composed of several subunits. C)An effector may either inhibit or activate an enzyme. D)Binding of the effector changes the conformation of the enzyme molecule. E)Heterotropic allosteric effectors compete with substrate for binding sites.
E)Heterotropic allosteric effectors compete with substrate for binding sites.
Enzymes act by A. decreasing the energy of activation of a reaction B. increasing the energy of activation of a reaction C. raising the temperature of a reaction D. providing a surface to favorably orient the reactants E. Both A and D are correct
E. Both A and D are correct
Which of the following is NOT a property of enzymes? A. capable of being regulated B. reaction rates high in comparison to uncatalyzed reaction C. highly specific D. lower the activation energy of a reaction E. all of the above are true
E. all of the above are true
The synthesis of enzymes in response to changing metabolic needs is referred to as: a. enzyme induction b. allosteric regulation c. negative feedback d. zymogen activation
Enzyme induction
Methanol (wood alcohol) is highly toxic because it is converted to formaldehyde in a reaction catalyzed by the enzyme alcohol dehydrogenase: NAD+ + methanol--> NADH + H+ + formaldehyde. Part of the medical treatment for methanol poisoning is to administer ethanol (ethyl alcohol) in amounts large enough to cause intoxication under normal circumstances. Explain this in terms of what you know about examples of enzymatic reactions.
Ethanol is a structural analog of methanol, and competes with methanol for the binding site of alcohol dehydrogenase, slowing the conversion of methanol to formaldehyde, and allowing its clearance by the kidneys. The effect of ethanol is that of a competitive inhibitor.
the oxidation of glucose molecules to form CO2 and H2O is a __________ process.
Exergonic
What fiber is paired with this protein that forms it: Collagen?
Extracellular support fibers: collagen
Disulfide bond formation between two cysteine residues appropriately located in a polypeptide chain drives protein folding into the proper configuration
F --> hydrophobic interactions; disulfide bonds only form after everything is already folded into domains
Ascorbic acid is necessary for the formation of hydroxyproline and hydroxylysine before they are incorporated into collagen protein molecules
FALSE -- after
(T/F) Homoglycans are used for storage, while heteroglycans are used for cell structure
False
(T/F) In bi-substrate reactions the substrate always bind to the enzyme in a specific order
False
Chemical modes of catalysis are more important than binding modes of catalysis in accounting for the accelerated rates of enzymatic reactions t or f
False
The subunits of a multisubunit protein are always identical
False
Water can easily penetrate and even pass thru the interior of a folded protein
False -- can't pass thru hydrophobic interior
Which of the following statements is false? A) A reaction may not occur at a detectable rate even though it has a favorable equilibrium. B) After a reaction, the enzyme involved becomes available to catalyze the reaction again. C) For S P, a catalyst shifts the reaction equilibrium to the right. D) Lowering the temperature of a reaction will lower the reaction rate. E) Substrate binds to an enzyme's active site.
For S P, a catalyst shifts the reaction equilibrium to the right.
Which energy consuming pathway occurring primarily in the liver, creates glucose from a variety of 3 carbon sources, including pyruvate, AA's and fats.
GlucoNEOgenesis
What type of bond links the monomers of a polysaccharide?
Glycosidic bond
Fatty acid degradation stimulates the citric acid cycle through the activation of pyruvate carboxylase by acetyl-CoA. Why would the activation of pyruvate carboxylase increase energy generation from fatty acids?
High levels of acetyl-CoA will stimulate pyruvate carboxylase to make OAA. This is often associated with the regulated step of 'neo', but here there is no mention of low blood sugar, just large amounts of FA breakdown. Therefore, pyruvate carboxylase would convert any pyruvate available to OAA to condense with the large amounts of acetyl-CoA coming in from -oxidation and this would stimulate the TCA cycle due to higher levels of citrate, which would lead to more production of ATP energy.
A person had recently eaten a high carb/low fat lunch and his cells have high concentrations of ATP, NADH and glucose-6-P, and now are actively synthesizing FA's for energy storage. What would be the fate of the glucose-6-P in his cells under these conditions.
His cells are in a high energy state, therefore G-6-P is not needed for ATP production and will inhibit hexokinase and therefore glycolysis. The most likely case is that G-6-P will be drawn out into the Pentose Phosphate pathway (regulated by G-6-P dh), to produce lots of NADPH needed for fatty acid synthesis.
Ascorbic acid is required for the production of __________ in collagen.
Hydroxyproline
Enzymes with a kcat / Km ratio of about 108 M-1s-1 are considered to show optimal catalytic efficiency. Fumarase, which catalyzes the reversible-dehydration reaction: fumarate + H2O<-->malate, has a ratio of turnover number to the Michaelis-Menten constant, (kcat / Km) of 1.6*10^8 for the substrate fumarate and 3.6 107 for the substrate malate. Because the turnover number for both substrates is nearly identical, what factors might be involved that explain the different ratio for the two substrates?
If the turnover number is nearly identical for both substrates, then the Km for malate must be much larger than for fumarate. Similar turnover numbers suggest no significant differences in rate of conversion of substrate to product, but the different Km values could possibly be explained by a stronger binding affinity of the enzyme for fumarate than for malate or some other aspect of the reaction mechanism that affects Km.
Chymotrypsin belongs to a group of proteolytic enzymes called the "serine proteases," many of which have an Asp, His, and Ser residue that are crucial to the catalytic mechanism. The serine hydroxyl functions as a nucleophile. What do the other two amino acids do to support this nucleophilic reaction?
In chymotrypsin, histidine functions as a general base, accepting a proton from the serine hydroxyl, thereby increasing serine's reactivity as a nucleophile. The negatively charged Asp stabilizes the positive charge that develops on the His
What fiber is paired with this protein that forms it: Keratin
Intermediate filaments: keratin
Which of the following is true of the binding energy derived from enzyme-substrate interactions? A) It cannot provide enough energy to explain the large rate accelerations brought about by enzymes. B) It is sometimes used to hold two substrates in the optimal orientation for reaction. C) It is the result of covalent bonds formed between enzyme and substrate. D) Most of it is derived from covalent bonds between enzyme and substrate. E) Most of it is used up simply binding the substrate to the enzyme.
It is sometimes used to hold two substrates in the optimal orientation for reaction.
in Eukaryotic cells what organelle possesses a double membrane system?
Mitochondria & Nucleus
binding constant of the inhibitor known as
KI
Write an equilibrium expression for the reaction S-->P and briefly explain the relationship between the value of the equilibrium constant and free energy.
Keq' = [P]/[S]. The value of Keq' reflects the difference between the free energy content of S and P. Free energy and equilibrium constant are related by the expression: deltaG'° = -RT ln Keq', For each change in Keq' by one order of magnitude, deltaG'° changes by 5.7 Kjoule/mole.
During starvation the body will break down fats thus releasing large amount of acetyl-CoA. Considering that glucose cannot be synthesized from acetyl-CoA the brain must rely on_______ as an energy source.
Ketone bodies
____ is the substrate concentration at which the reaction velocity is half-maximal. The value of kcat/_____ indicates an enzyme's catalytic efficiency.
Km
For the reaction E + S--> ES-->P the Michaelis-Menten constant, Km, is actually a summary of three terms. What are they? How is Km determined graphically?
Km = (k2 + k-1)/ k1, where k-1 and k1 are the rate constants for the breakdown and association, respectively, of the ES complex and k2 is the rate constant for the breakdown of ES to form E + P. Km can be determined graphically on a plot of V0 vs. [S] by finding the [S] at which V0 = 1/2 Vmax. More conveniently, on a double-reciprocal plot, the x-axis intercept = -1/ Km.
michaelis-menten kinetics
Km = Vmax/2 rectangular hyperbola *see slide 16*
substrate concentration, 1/2 Vmax
Km is a constant, but is also the ___ ___ at ___ ___
michaelis-menten plot
Km is linear first-order: rate is dependent on [S] - S is limiting Vmax 0th-order: rate is independent of [S] - enzyme is saturated with S, catalysis is limiting *Km = [S] when V0 = 1/2 Vmax* *see slide 17*
Kinetic data can be plotted in double-reciprocal form to determine ___ and ____
Km, vmax
For a reaction that can take place with or without catalysis by an enzyme, what would be the effect of the enzyme on the: (a) standard free energy change of the reaction? (b) activation energy of the reaction? (c) initial velocity of the reaction? (d) equilibrium constant of the reaction?
(a) no change; (b) decrease; (c) increase; (d) no change.
Ketogenic:
(converted to FA or ketone bodies) AA degraded to acetyl-CoA
Glucogenic:
(used in gluconeogenesis) AA degraded to pyruvate or TCA intermediate
Enzymes can increase reaction rate up to 10^ ___ to 10^___times.
*7 *19
first order
*A → P* is a ___-___ reaction with units *s^-1* radioactive decay is an example
The elements that are essential for life, and make up over 90% of cellular dry weight include:
*CHNOPS* Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur
first order
*simple ___-___ reactions* display a plot of the reaction rate as a function of reactant concentration that is a *straight line* *see slide 9* if slope= -k you're seeing the disappearance of A if slope= +k you're seeing the appearance of product
Competitive Inhibition will have a ____________ on a line-weaver burk plot.
- -1/akm
A pure noncompetitive inhibition will have a _____________ on a line-weaver burk plot.
- -1/km
What is the y-intercept of the Lineweaver--Burk Plot?
- -1/km
What is the y-intercept of the Lineweaver--Burk Plot?
- 1/Vmax
rule out
kinetics can only ___ ___ various alternative hypotheses, because they don't fit the data
What is the Michaelis-Menten constant?
km
What is the Michaelis--Menten equation?
km= k-1 + k2 (depletion)/k1 (formation)
Vmax
maximal velocity of an enzymatic reaction
Does a spontaneous reaction mean that the reaction will be fast?
no
Uronic:
oxidized at the bottom
irreversible
penicillin is an ____ (so called "suicide" inhibitor
The geometric character of the peptide bond could best be described as
planar and rigid
single-displacement bisubstrate mechanism
plot must indicate increasing second substrate concentration *see slide 30*
Two assumptions that must be made to integrate Michaelis-Menten equation: Assumption of _________ _________ and __________ __________
rapid equilibrium, steady state
A zero-order reaction's rate is dependent on the ______.
rate constant
The proportionality constant is known as the __________ ___________, and is symbolized ____
rate constant, k
k2
rate of product formation of ES is ___ for enzyme-catalyzed reactions
response of enzymatic activity to temperature
rates of enzyme-catalyzed reactions generally increase with increasing temperature (T) however, at temperatures *above 50°to 60°C*, enzymes typically show a *decline in activity* two effects here: 1) enzyme rate typically doubles in rate for every 10º C, as long as the enzyme is stable and active 2) at higher temperatures, the protein becomes unstable and denaturation occurs (loss of structure and function)
Are substrates the reactants or products?
reactants
A graph representing an exergonic reaction will show that the.....
reactants are at a higher level than the products.
__________ inhibitors reduce a enzyme's activity by binding to the substrate-binding site (competitive inhibition), to the enzyme-substrate complex (uncompetitive inhibition), or to both the enzyme and the enzyme-substrate complex (mixed inhibition)
reversible
kcat/KM, apparent _______ order constant of enzyme. "a measure of an enzyme's
second
bisubstrate reactions are classified as __________ (single displacement) or ________ _____ (double displacement). A sequential reaction may proceed by an ordered or random mechanism
sequential, ping pong
Covalent catalysis is ________________.
short-lived
A lead compound for a new drug should bind to its target protein with a very ______.
small Kd
The Lineweaver-Burk plot can be used to:
solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.
The Lineweaver-Burk plot is used to: A) determine the equilibrium constant for an enzymatic reaction. B) extrapolate for the value of reaction rate at infinite enzyme concentration. C) illustrate the effect of temperature on an enzymatic reaction. D) solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration. E) solve, graphically, for the ratio of products to reactants for any starting substrate concentration.
solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.
initial velocity, maximal reaction velocity
the *Michaelis-Menten equation* relates the ___ ___ of a reaction to the ___ ___ ___ and the *Michaelis constant* for a particular enzyme and substrate
Km, Vmax
the effects of pH on enzymes may be *due to effects on ___ or ___ or both*
The term hydrophobic collapse in describing protein folding refers to :
the hydrophobic interactions of non-polar AA side chains sequestering themselves into the water excluded interior of the protein.
Urea cycle occurs in ...
the liver (mito & cytosol)
rate constant (k)
the proportionality constant between the velocity of a chemical reaction and the concentration(s) of the reactant(s)
To some degree, KM measures affinity of substrate and enzyme, true or false.
true
True or false, Km and [S] are same units.
true
True or false, enzymes may be inhibited both reversibly and irreversibly
true
michaelis-menten equations
v = (Vmax [S]) / (Km + [S]) Vmax = k2[Et] Km = (k-1 + k2) / k1
rate law (first-order reaction)
v = k [A]^1 = k [A]
Enzyme needed for nitrogen fixation.
Nitrogenous complex. N2--> NH3
initial velocity simple for michaelis menten=
vo
zero order
when [S] is high, the equation for rate is ___-___ in [S]
Is progress of reaction on the y or x axis?
x axis
Where is [S] concentration plotted on the graph?
x-axis
Is free energy (delta G) on the y or x axis?
y axis
Where is V0 (reaction rate) plotted on the graph?
y-axis
In order to make the hyperbola into a straight line to estimate the Vmax, what is on the y and x axis?
y-axis: 1/V x-axis: 1/[S]
When the enzyme is saturated with substrate, what type of kinetics is observed with respect to substrate?
zero-order
Cells can develop a resistance to drugs by increasing the cellular concentration of the enzyme that that drug inhibits. If a cell increases its concentration of a given enzyme to 10 times the normal amount, which parameters listed below will be increased ten-fold? Km, KI, [S], Vmax, v0 when [S] = Km, and kcat Catalytic efficiency
Only Vmax and v0 are linearly dependent on [E].
Which of the following combines with acetyl CoA to form citrate?
Oxaloacetate
Which of the following is not a type of oxidoreductase a. peroxidase b. hydroxylase c. reductase d. dehydrogenase e. peptidases
Peptidases
What is considered the key reg enzyme in glycolysis?
Phosphofructokinase-1
The basic structure of biological membrane is a consequence of the physical properties of __________.
Phospholipids
A two-substrate enzymatic reaction in which one product is produced before the second substrate binds to the enzyme has a ______ mechanism.
Ping Pong
Which one of the following is not among the six internationally accepted classes of enzymes? A) Hydrolases B) Ligases C) Oxidoreductases D) Polymerases E) Transferases
Polymerases
Level of protein structure for :peptide bonds
Primary
Pumping ions across a membrane to create a gradient requires the expenditure of ATP energy this transport mechanism is:
Primary active transport
double-displacement (ping-pong) reaction
Proceed via formation of a *covalently modified enzyme intermediate*. Reactions conforming to this kinetic pattern are characterized by the fact that the *product* of the enzyme's reaction with A (called P in the above scheme) is *released prior* to reaction of the enzyme with the *second substrate*, B. example: serine proteases *see slide 35*
Level of protein structure for : subunit interactions
Quaternary
Which structure is shown? (6 membered ring with 8 C chain with CH2OH on end)
Retinol
Ribosomes, the protein synthesis complex, are often bound to which organelle?
Rough endoplasmic reticulum
The individual hemoglobin subunits and myoglobin share similar ___________ structure but have different ____________ structure.
Secondary and tertiary; primary
Enzyme reactions that require all the substrate to be present before any product is released are called ___.
Sequential
covalent modification, enzymes most common attacks what amino acids? ____, ____, ____,
Ser, Thr, Tyr
In glycoproteins the carbohydrate is most often linked to threonine, asparagine, or __________.
Serine
What is the difference between general acid-base catalysis and specific acid-base catalysis? (Assume that the solvent is water.)
Specific acid-base catalysis refers to catalysis by the constituents of water; that is, the donation of a proton by the hydronium ion, H3O+ or the acceptance of a proton by the hydroxyl ion OH-. General acid-base catalysis refers to the donation or acceptance of a proton by weak acids and bases other than water.
Which disaccharide is composed of a fructose and glucose molecule?
Sucrose
Increasing the concentration of a classic competitive inhibitor has no effect on the max velocity of an enzyme-substrate reaction.
T
Part of immunoglobulin molecules can be changed in order to bind a variety of antigens while he amino acid sequence of another part does not change
T
Level of protein structure for : variety of interactions between R groups of distant AA's
Tertiary
Give the Michaelis-Menten equation and define each term in it. Does this equation apply to all enzymes? If not, to which kind does it not apply?
The Michaelis-Menten equation is: V0 = Vmax [S]/( Km + [S]), in which V0 is the initial velocity at any given concentration of S, Vmax is the velocity when all enzyme molecules are saturated with S, [S] is the concentration of S, and Km is a constant characteristic for the enzyme. This equation does not apply to enzymes that display sigmoidal V0 vs. [S] curves, but only to those giving hyperbolic kinetic plots.
Which of these statements about enzyme-catalyzed reactions is false? A) At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration. B) If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. C) The rate of a reaction decreases steadily with time as substrate is depleted. D) The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction. E) The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax.
The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction.
On the enzyme hexokinase, ATP reacts with glucose to produce glucose 6-phosphate and ADP five orders of magnitude faster than ATP reacts with H2O to form phosphate and ADP. The intrinsic chemical reactivity of the —OH group in water is about the same as that of the glucose molecule, and water can certainly fit into the active site. Explain this rate differential in two sentences or less.
The binding of glucose to hexokinase induces a conformation change that brings the amino acid residues that facilitate the phosphoryl transfer into position in the active site. Binding of water alone does not induce this conformational change.
When a stong acid is added to a buffer system what reaction occurs to neutralize the acid and resist large changes in pH?
The conjugate base will react with the protons making more of the weak acid
The difference in (standard) free energy content, delta G'°, between substrate S and product P may vary considerably among different reactions. What is the significance of these differences?
The difference in free energy content between substrate (or reactant) and product for each reaction reflects the relative amounts of each compound present at equilibrium. The greater the difference in free energy, the greater the difference in amounts of each compound at equilibrium.
One reason the proximity effect enhances catalysis is because
The effective molarity of reactive substrate groups increases
Explain how a biochemist might discover that a certain enzyme is allosterically regulated.
The enzyme would show kinetics that do not fit the Michaelis-Menten equation; the plot of V vs. [S] would be sigmoidal, not hyperbolic. The enzyme kinetics would be affected by molecules other than the substrate(s).
ordered single-displacement reaction
The leading substrate (A) binds first, followed by B. Reaction between A and B occurs in the ternary complex and is usually followed by an ordered release of the products, P and Q (in either order) *see slide 33*
Why is the Lineweaver-Burk (double reciprocal) plot (see Box 6, p. 206) more useful than the standard V vs. [S] plot in determining kinetic constants for an enzyme? (Your answer should probably show typical plots.)
The plot of V vs. [S] is hyperbolic; maximum velocity is never achieved experimentally, because it is impossible to do experiments at infinitely high [S]. The Lineweaver-Burk transformation of the Michaelis-Menten equation produces a linear plot that can be extrapolated to infinite [S] (where 1/[S] becomes zero), allowing a determination of Vmax.
Sometimes the difference in (standard) free-energy content, delta G'°, between a substrate S and a product P is very large, yet the rate of chemical conversion, S-->P, is quite slow. Why?
The rate of conversion from substrate to product (or the reverse reaction, from product to substrate) does not depend on the free-energy difference between them. The rate of the reaction depends on the activation energy of the reaction delta G'‡, which is the difference between the free-energy content of S (or P) and the reaction transition state.
(Equation) Which of the following is (are) TRUE
The reaction is zero order with respect to [S] if [S] >> [E]
For serine to work effectively as a nucleophile in covalent catalysis in chymotrypsin a nearby amino acid, histidine, must serve as general base catalyst. Briefly describe, in words, how these two amino acids work together.
The serine is a polar hydroxyl, with the oxygen functioning as an electronegative nucleophile. A nearby histidine residue, with pKa about= to 6.0, however, functions as a base to abstract the proton from the serine hydroxyl group. The result is to substantially increase the electronegativity of the serine oxygen, making it a much stronger nucleophile. This, in turn, lowers the activation energy of the covalent catalysis between serine and the carbonyl carbon of the substrate peptide bond.
Penicillin and related antibiotics contain a 4-membered beta-lactam ring. Explain why this feature is important to the mechanism of action of these drugs.
The strained 4-membered ring is easily opened (deltaG << 0); this energy drives the reaction that covalently inactivates the transpeptidase.
Why is a transition-state analog not necessarily the same as a competitive inhibitor?
The structure of a competitive inhibitor may be similar to the structure of the free substrate. Similar structure will mean that the competitive inhibitor can associate with the enzyme at the active site, effectively blocking the normal substrate from binding. A transition-state analog, however, is similar in structure to the transition-state of the reaction catalyzed by the enzyme. Often, a transition-state analog will bind tightly to an enzyme, and it is not easily competed away by substrate.
How does the total enzyme concentration affect turnover number and Vmax?
The turnover number, kcat, is the number of substrate molecules converted to product in a given time by a single enzyme molecule, so turnover number is not affected by the total enzyme concentration, [Et]. For any given reaction, however, Vmax can change because Vmax is the product of turnover number * the total enzyme concentration, or Vmax = kcat [Et].
Write out the equation that describes the mechanism for enzyme action used as a model by Michaelis and Menten. List the important assumptions used by Michaelis and Menten to derive a rate equation for this reaction.
The two equations are E+S<--k1--k-1-->ES<--k2--k-2-->E + p. One assumption is that [P] = 0 so that the rate of the reaction depends exclusively on the breakdown of ES and is not influenced by the reverse reaction; that is, k-2 can be ignored and V0 = k2 [ES]. This condition is possible only if early reaction times are measured; the velocity, therefore, is an initial velocity. A second assumption is that the rate of ES formation equals the rate of ES breakdown; in other words, the reaction is at a steady state. A third assumption is [S] >> [Et], so that total [S], which equals free substrate and enzyme-bound substrate, is essentially equal to [S].
Ribonuclease catalyzes the hydrolysis of ribonucleic acid (RNA). The active site of the enzyme contains two histidine residues (119- positively charged and 112-negatively charged) *The pH-rate profile is bell-shaped, with inflection points at approximately pH 5.8 and pH 6.2. How is the pH-rte profile related to the mechanism for ribonuclease?
The two histidines are acting differently in this mechanism of ribonuclease. For example, Histidine 119 is acting as an acid which makes it electrophilic while Histidine 112 is acting as a base which makes it nucleophilic. This causes them to act differently at different pH conditions. For example, the inflection point (pI) value of Histidine lies between a pH of 6.00 to 9.17, so Histidine 112 will show an inflection point at pH 6.2 while the Histidine 119 will show an inflection point at a slightly low pH of 5.8.
The liver contains the enzyme to drive both glycolysis and gluconeogensis, how are these two opposing pathways modulated in the liver?
There is regulation at the hormonal level, with high blood glucose levels insulin will activate PFK-2 to make F-2,6 bP which stimulates PFK-1 and conversely glucagon inactivates PFK-2 and high levels of F-2,6 bP inhibit fructose 1,6 bisphosphotase in 'neo'. However in class we also focused on the difference in the key regulatory enzymes for these two opposing pathways, reference Figure 8.14 on page 297: In glycolysis: PFK-1 is upregulated by F-2,6-bisphosphate versus the bypass step In glucogeogenesis: fructose-1,6-bisphosphatase is downregulated by F-2,6-bisphosphate These two are regulated by the effector molecule F-2,6-bisphosphate which is an indicator of high blood glucose levels as discussed above
The structure below is which coenzyme? (N+ C-H reactive center)
Thiamine pyrophosphate
Of all the species that enzymes bind, they are thought to bind the most tightly to ________________.
Transition states
The role of very low density lipoprotein is (VLDL)?
Transporting of lipids from liver to tissue
(T/F) Intermediates are more stable and have longer lifetimes than transition states
True
(T/F) Superoxide dismzutase and triosephosphate isomerase are two enzymes that catalyze diffusion-controlled reactions
True
(T/F) The ketohexoses have fewer chiral carbon atoms than the aldohexoses
True
The enzyme may assume the enzymatically inactive T conformation or the catalytically active R form. The conformation of phosphorylase b is allosterically controlled by the effectors AMP, ATP, and G6P is mostly in the T state under physiological conditions. In contrast, the phosphorylated form of the enzyme, phosphorylase a, is unresponsive to these effectors and is mostly in the R state unless there is a high level of glucose. Thus, under usual physiological conditions, the enzymatic activity of glycogen phosphorylase is largely determined by its rate of phosphorylation and dephosphorylation." True or false
True
The difference between uncompetitive and noncompetitive inhibitors is that
Uncompetitive inhibitors bind irreversibly
Excretion of nitrogen in birds-
Uricotelic
Calculate the value of the maximum velocity for an enzyme-catalyzed reaction that follows Michaelis-Menton kinetics if the initial velocity is 6 mM/s at a substrate concentration of 6 mM. The KM for the enzyme system is 2 mM
Vo= Vmax [S]/ (Km + [S]) 6= Vmax (6) / (2+ 6) 8*6= Vmax 6 56= Vmax 6 56=VmAX 8
Did you know that the energy needed to denature a protein is the same as the E needed to disrupt 3 or 4 H bonds?
YES! Because you are a bad bitch!
Assume a first order reaction, the rate of the reaction 2A --> B is dependent on
[A]
small
___ Km means little dissociation (tight binding), e.g. 10^-6 M
bisubstrate reactions
___ ___ can occur by an *ordered* or *random sequential mechanism* or by a *ping pong mechanism*
turnover number (Kcat)
___ ___ defines the activity of one enzyme molecule
time course
___ ___ for a typical enzyme-catalyzed reaction obeying the Michaelis-Menten model for enzyme kinetics the early state of the time course is shown in greater magnification in the bottom graph he *slope* of the blue line is the *initial velocity, ν0* *see slide 15*
bisubstrate
___ reactions may be sequential or single-displacement reactions *is this a typo?? single (sequential) and double (ping pong)?*
enzyme catalyzed
___-___ reactions are more complicated
The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by 1/V0 = Km /(Vmax[S]) + 1/Vmax. To determine Km from a double-reciprocal plot, you would: A) multiply the reciprocal of the x-axis intercept by −1. B) multiply the reciprocal of the y-axis intercept by −1. C) take the reciprocal of the x-axis intercept. D) take the reciprocal of the y-axis intercept. E) take the x-axis intercept where V0 = 1/2 Vmax
a
inhibitors
a *Lineweaver-Burk* plot can be used to present kinetic data and to calculate values for Km and Vmax useful for analysis of ____
Enzyme X exhibits maximum activity at pH = 6.9. X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4. One likely interpretation of this pH activity is that: A) a Glu residue on the enzyme is involved in the reaction. B) a His residue on the enzyme is involved in the reaction. C) the enzyme has a metallic cofactor. D) the enzyme is found in gastric secretions. E) the reaction relies on specific acid-base catalysis.
a His residue on the enzyme is involved in the reaction.
lineweaver-burk plot
a graph of a rearrangement of the Michaelis-Menten equation to a linear form that permits the determination of Km and Vmax also called a double-reciprocal plot *see slide 43* x-intercept = -1/Km tells us about the substrate concentration y-intercept = 1/ Vmax tells us about max velocity
double-displacement reaction
a reaction in which a substrate binds and a product is released in the first stage, and another substrate binds and another product is released in the second stage
sequential reaction
a reaction in which all substrates must combine with the enzyme before a reaction can occur can proceed by an ordered or random mechanism
Enzymes are catalysts: what do they do and not do?
a) increase reaction rates, by decreasing transition state energy, ΔG‡ b) do not change overall thermodynamic parameters: ΔG, ΔH, or ΔS c) rate is affected by temperature (T), pH, [salt]
Which of the following statements about the chemiosmotic theory is correct? a. electron transfer in mitochondria is accompanied by an asymmetric relase of protons on one side of the inner mitochondrial membrane? b. The effect of uncoupling reagents is a consequence of their ability to carry electrons through membranes c. although the energy transductions in mitochondria and in chloroplasts are superficially similar, they have fundamentally different mechanisms d. The membrane ATPase, which plays an important role in other hypotheses for energy coupling, has no significant role in chemiosmotic theory e. All of the above statements are correct
a.
Which of the following statements is true of glycogen synthesis and breakdown? a. Phosphorylation activates the enzyme responsible for breakdown and inactivates the synthetic enzyme b. synthesis is catalyzed by the same enzyme that catalyzes breakdown c. the glycogen molecule "grows" at its reducing end d. the immediate product of glycogen breakdown is free glucose e. Under normal circumstances, glycogen synthesis and glycogen breakdown occur simultaneously and at high rates
a.
Catalytic antibodies, also called ____________, are generated against an antigen that is:
a. abzymes; an analog of the transition-state intermediate in the reaction.
Which of the following cpds Cannot serve as the starting material for the synthesis of glucose via gluconeogenesis in mammals? a. acetate b. pyruvate c. aspartate d. oxaloacetate e. alpha ketoglutarate
a. acetate (Bacteria)
Ketone bodies are normally synthesized from a. acetyl CoA b. glucose c. glycerol d. acetone
a. acetyl CoA
which of the following amino acids would NOT provide a nucleophilic center for covalent catalysis a. alanine b. lysine c. glutamic acid d. serine e. cysteine
a. alanine
the good transition state analog is one which would serve also as an extremely effective: a. competitive inhibitor b. noncompetitive inhibitor c. allosteric inhibitor d. mixed noncompetitive inhibitor e. irreversible inhibitor
a. competitive inhibitor
all are catalytic mechanisms or factors that contribute to the performance of enzymes EXCEPT: a. entropy gain in ES formation b. covalent catalysis c. general acid or base catalysis d. proximity and orientation e. all are true
a. entropy gain in ES formation
Carnitine acyl transferase is an important enzme in the control of: a. fatty acid oxidation b. citric acid cycle c. gluconeogenesis d. glycolysis
a. fatty acid oxidation
Classify the following fatty acids as omega-3, omega-6 or neither: a. linolenate b. oleate c. stearate d. linoleate e. arachidonate
a. omega-3 b. neither c. neither d. omega-6 e. omega-6
in the hydrolysis of p-nitrophenylacetate by chymotrypsin all of the following are correct EXCEPT a. the first product is acetic acid b. an acetyl-enzyme intermediate forms during the mechanism c. attack of a water molecule on the acyl-enzyme intermediate yields the second product d. the active site contains a serine residue, an unprotonated histidine, and an unprotonated aspartate residue at pH 7 prior to binding the substrate
a. the first product is acetic acid
A plot of 1/V vs. 1/[S] for an enzyme catalyzed reaction gave a line with an equation of y = 0.5x + 0.2. The same enzyme with an inhibitor present gave a line with an equation of y = 1.1x + 0.2. Which of the following statements is true?
a. the type of inhibition is competitive
Which of the following lipid types is the least polar: a. triaglycerols b. glycerophosopholipids c. sphingolipids d. gangliosides
a. traiglycerols
When every enzyme molecule in the reaction mixture has its substrate-binding site occupied by substrate, the kinetics become _________-order, and the velocity is ______________.
a. zero; Vmax
initial bond formation in the covalent intermediate in the chymotrypsin catalyzed reaction is between a. serine and carbonyl carbon in peptide backbone b. serine and nitrogen in the peptide backbone c. histidine and the carbonyl carbon in the peptide backbone d. histidine and nitrogen in the peptide backbone e. aspartate and the carbonyl carbon in the peptide backbone
a.( serine and carbonyl carbon in peptide backbone)
A hypothetical enzyme has an effective pKa value of 5. a.) the residue acts a an acid catalyst. b.) the residue acts as a base catalyst.
a.) it is going to have high activity at the beginning of the graph because it is protonated at a low pH. b.) it is going to have high activity at the end of the graph because it is deprotonated at a high pH.
Is fatty acid synthesis an activator or inhibitor of insulin?
activator --> storage hormone
Reversible inhibitors may bind at the ________ site or at some other site
active
Substrates bind to a particular site on the enzyme surface called the _____________________, where catalysis takes place.
active site
catalytic mechanism relates heavily to the ______ _______
active site
Two forms of enzyme control_________ and ____________
activity, availability
The conformational change of an enzyme upon binding of an effector molecule is one example of what form of enzyme regulation?
allosteric regulation
enzyme activity influenced by two things: ____________ affectors and _____________ modification
allosteric, covalent
mixed noncompetitive inhibitor
alters both Km and Vmax
lineweaver-burk plot of mixed noncompetitive inhibition
alters both Km and Vmax different x and y-intercepts intersection of x-axis intercept can be above or below the x-axis *see slide 48*
uncompetitive inhibitor
alters both Km and Vmax with the same slope, Km/Vmax *think parallel lines when you hear same slope*
catalytic efficiency
an enzymes overall ___ ___ is expressed as *kcat/KM*
catalytic efficiency (kcat / Km)
an estimate of "how perfect" the enzyme is is an apparent second-order rate constant it *measures how well the enzyme performs when [S] is low* the *upper limit for kcat/Km is the diffusion limit (approaching ~10^10)*, the rate at which E and S encounter each other by diffusion
To proceed at a visible rate, most reactions require ______________________.
an initial energy input (ex. heat)
value of kinetics
assessment of kinetic parameters using the *Michaelis-Menten equation* and *Lineweaver-Burk double reciprocal plots* allows for: *characterization of enzymes* identification of type and effectiveness of *inhibitors* identification of *bi-substrate mechanisms* with respect to the order of substrate addition and steps in the chemical reaction
enzyme catalyzed reactions
at *low* concentrations of the substrate, *[S]*, the rate is proportional to S, as in a *first-order reaction: v = k [S]* at higher substrate concentrations, the enzyme concentration approaches *zero-order kinetics: v = Vmax* this behavior is a saturation effect rate of formation of ES is *k1*, while rate of dissassociation is *k-1* rate of product formation is *k2* *see slide 12*
low
at ___ concentrations of the substrate, *[S]*, the rate is proportional to S, as in a *first-order reaction: v = k [S]*
zero order kinetics
at higher substrate concentrations, the enzyme concentration approaches *___-___ ___: v = Vmax*
decline
at temperatures *above 50°to 60°C*, enzymes typically show a ___ in activity
In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitorwill alter the: A) curvature of the plot. B) intercept on the l/[S] axis. C) intercept on the l/V axis. D) pK of the plot. E) Vmax.
b
the mechanism of chymotrypsin involves which of the following elements a. deprotonation of an active site Asp residues by His to start the reaction b. formation of an acyl-enzyme intermediate that must be hydrolyzed to complete the reaction c. stabilization of the positively charged His by a Gln residue d. direct deprotonation of water by His to generate a hydroxide ion for initiation of the reaction e. both and b occur
b. (formation of an acyl-enzyme intermediate that must be hydrolyzed to complete the reaction)
if the substrate for an enzyme catalyzed reaction contained a negative charge, which of the following amino acids would most likely be present in the active site to provide electrostatic destabilization of the ES complex a. val b. asp c. arg d. ser e. gln
b. asp
In glycoproteins, the CHO moiety is attached through the amino acid resides a. tryptopha, aspartate or cysteine b. asparagine, serine or threonine c. glycine, alanine or aspartate d. aspartate or glutamate e. glutamine or arginine
b. asparagine serie or threonine
the main property of myoglobin and hemoglobin that makes then an efficient system for oxygen delivery from lungs to muscles is a. hydrophobicity b. different binding affinities for oxygen c. movement of the protein shapes d. cooperativity e. none of the above
b. different binding affinities for oxygen recall: hemoglobin exhibits cooperativity, but myoglobin does not
Chymotrypsin, a serine protease, preferentially cleaves a peptide bond adjoining a bulky non-polar side chain. This is because chymotrypsin's "specificity pocket:" a. contains a sulfhydryl group that forms a disulfide bond with the substrate b. is lined with small hydrophobic side chains, leaving considerable room in the pocket and making it nonpolar c. Contains a negative charge d. is mostly filled with large side chains e. contains a positive charge
b. lined with small hydrophobic side chains, leaving considerable room in the pocket and making it nonpolar
An enzyme's specificity can be due to:
b. molecular recognition based on structural complementarity.
Lysosomal storage diseases occur when mutations cause defects in: a. lysosome formation b. sphingolipid degradation enzymes c. formation of N-acetylgalactosamine derivatives d. sphingolipid biosynthesis enzymes
b. sphingolipid degradation enzymes
The specific site on the enzyme where __________ binds and catalysis occurs is called the _____________ site.
b. substrate; active
NMR is often used for the determination of the ---- of proteins: a. molecular wt. b. tertiary structure c. isolectric point d. pKa
b. tertiary structure
The osmotic pressure of an aqueous solution depends on : a. the chemical nature of the solute b. the molar concentration of the solute c. the hydrophobic effect of the solute d. All of the above e. None of the above
b. the molar concentration of the solute
Which is true about the side chains of residues in an alpha helix? a. they extend above or below the pleats b. they extend radially outward from the helix axis c. the point toward the center of the helix d. they hydrogen bond extensively with each other
b. they extend radially outward from the helix axis
Enzymes have active sites which have the greatest complementarity to the: a. substrate b. transition state c. product d. both substrate and product e. none of above
b. transition state
HIV-1 protease is different from most mammalian aspartic acid proteases in that it has: a. two subunits each with two aspartate active site b. two subunits each contributing an aspartate to the active site c. two active sites on one protein d. two subunits one with an active site, the other with regulatory activity e. none of the above
b. two subunits each contributing an aspartate to the active site
Why does the graph plateau as time continues?
because the majority of substrates are converting into product
Second-order reaction is known as a _____________ reaction
bimolecular
In competitive inhibition, an inhibitor: A) binds at several different sites on an enzyme. B) binds covalently to the enzyme. C) binds only to the ES complex. D) binds reversibly at the active site. E) lowers the characteristic Vmax of the enzyme.
binds reversibly at the active site.
To calculate the turnover number of an enzyme, you need to know: A) the enzyme concentration. B) the initial velocity of the catalyzed reaction at [S] >> Km. C) the initial velocity of the catalyzed reaction at low [S]. D) the Km for the substrate. E) both A and B.
both A and B.
Alderic:
both ends oxidized
For enzymes in which the slowest (rate-limiting) step is the reaction k2 ES → P Km becomes equivalent to: A) kcat. B) the [S] where V0 = Vmax. C) the dissociation constant, Kd, for the ES complex. D) the maximal velocity. E) the turnover number
c
which of the following statements regarding enzymes is true a. stabilization of the transition state must be less than stabilization of ES for catalysis to occur b. an enzyme mechanism is vastly different from the uncatalyzed reaction c. binding of substrate to an enzyme often causes strain thus promoting transition state formation d. a random single displacement mechanisms requires that substrates bind to the enzyme in a specific order e. none of the above
c. (binding of substrate to an enzyme often causes strain thus promoting transition state formation)
because the enzymatic reaction rate is determined by the different in energy between ES and _____ the tighter binding of the substrate, the ____ the rate of reaction a. S, higher b. P, lower c. EX, lower d. EX higher e. S, lower
c. EX lower
Which of the following is true regarding the Briggs and Haldane steady state assumption?
c. The concentration of the enzyme-substrate complex reaches a constant value even in a dynamic system.
Effective HIV1 protease inhibitor should have all the following characteristics EXCEPT a. effective delivery in sufficient quantities to the desired site(s) of action in the organism b. relative specificity for HIV-1 protease c. a backbone- OH group that forms a weak association with the two active site carboxyl groups of protease d. results in inhibiting the production of new virus particles in cells of infected patients e. broad spectrum enough to be effective against mutant viral forms
c. a backbone- OH group that forms a weak association with the two active site carboxyl groups of protease
Linoleate is an essential fatty acid in mammalian diets because mammalian cells a. can use it to synthesize eicosanoids b. synthesize it from arachidonate c. do not have a desaturase that acts beyond the C-9 position d. do not use this acid for biosynthesis
c. do not have a desaturase that acts beyond the c-9 position
The expression Vmax = k2[E]total applies to: a. first order kinetics of an enzyme catalyzed reaction b. second order kinetics of an enzyme-catalyzed reaction c. zero order kinetics of an enzyme-catalyzed reaction d. only the initial part (near time = 0) of an enzyme-catalyzed reaction
c. zero order kinetics -- only enzyme, not substrate, concentration is included
The benefit of measuring the initial rate of a reaction V0 is that at the beginning of a reaction: A) [ES] can be measured accurately. B) changes in [S] are negligible, so [S] can be treated as a constant. C) changes in Km are negligible, so Km can be treated as a constant. D) V0 = Vmax. E) varying [S] has no effect on V0.
changes in [S] are negligible, so [S] can be treated as a constant.
In reversible oxidation of alcohols to aldehydes or ketones, NAD+ acts as a ____________________.
coenzyme
An enzyme inhibitor can be developed for use as a drug through structure-based and or __________ methods. It must then be tested for safety and efficiacy in clinical trials.
combinatorial
Order regularly deals with molecules ________ ________
coming together
The type of enzyme inhibition in which Vmax is unaffected is ______.
competitive inhibition
how much of the free enzyme is occupied by an inhibitor known as
competitive inhibition
inhibitor that binds to the substrate binding site
competitive inhibition
In a first order enzyme-catalyzed reaction, the velocity of the reaction is proportional to the ________, while in a zero order enzyme-catalyzed reaction, the velocity of the reaction is proportional to the ________.
concentration of substrate; amount of enzyme
Enzyme activity may be controlled by _________ ___________
covalent modification
Inactive enzyme precursors are activated by removal of a pro region:
covalent modification
The role of serine at the active site of serine proteases is to act as a ----- catalyst, while the histidine reside serves as a ----- catalyst
covalent; acid-base
The role of serine at the active site of serine proteases is to act as a(n) ________ catalyst, while the histidine residue serves as a(n) ________ catalyst.
covalent; acid-base
Adverse reactions to drugs and drug-drug interactions are often mediated by a _________ _________
cytochrome P450
the mechanism of aspartate protease catalysis is proposed to be a. covalent nucleophilic catalysis b. covalent electrophilic caalysis c. specific base catalysis d. general base-general acid catalysis facilitated by a low barrier hydrogen bond e. all of the above
d. (general base-general acid catalysis facilitated by a low barrier hydrogen bond)
At equilibrium in solution, D-glucose consists of a mixture of its anomers. Which statement most accurately describes the solution. a. The solution consists of approximately equal amt of the alpha and beta anomers b. the straight-chain form is present in high concentration b. the alpha anomer is more stable and is slightly less preferred over the beta anomer c. the alpha anomer is more stable and is slightly preferred d. The beta anomer predominates over the alpha anomer because in the beta anomer all of the hydroxyl groups are equatorial e. none of the above
d. B-anomer predominates
Which of the following statements about starch and glycogen is false? a. both are homopolymers of glucose b. Amylose is unbranched: amylopectin and glycogen contain many alpha 1 --> 6 branches c. Both starch and glycogen are stored intracellularly as granules d. both serve primarily as structural elements in cell walls
d. Both serve primarily as structural elements in cell walls (no, storage)
The assumptions made in the Michaelis Menten equation include: a. that the value of k-2 can be ignored b. that the concentration of the substrate is much greater than the concentration of E (a.k.a enzyme is saturable) c. that the formation and decomposition of the ES is the same for a period of time d. a, b and c e. a and b only
d. all of the above
in the catalytic triad common to many serine proteases, ______ increases the basicity of _____ thus allowing deprotonation of _____ to serve as nucleophile a. ser-his-asp b. his-ser-asp c. ser-his-his d. asp-his-ser e. cys-his-ser
d. asp-his-ser
Sildenafil citrate (Viagra) was developed as an inhibitor of:
d. cGMP phosphodiesterases.
an enzyme catalyzed reaction rate will be increased if the energy level of ES can be increased. which of the following will not increase the energy level of ES a. destabilization of ES by strain caused by non-covalent interactions between E and S b. loss of entropy due to binding of E and S c. destabilization of ES by distortaion d. destabilization of ES by solvation e. destabilization of ES by electrostatic effects
d. destabilization of ES by solvation
A reaction that occurs with every collision between reactant molecules is called a(n) a. rate-det. step b. first order reaction c. saturation point d. diffusion-controlled reaction
d. diffusion-controlled reaction
if the transition state of an enzyme catalyzed reaction contained a positive charge, which of the following amino acids would most likely be present in the cative site to aid in transition state formation a. lys b. val c. asn d. glu e. cys
d. glu
The trivial term for an enzyme that is an ATP-dependent phosphotransferase is a(n):
d. kinase
Which of these amino acid groups would NOT make a good nucleophilic catalyst? a. Amino b. Sulfhydryl c. Imidazole d. methyl e. hydroxyl
d. methyl
Identify the type of reaction that would give the following graph
d. mixed noncompetitively inhibited reaction.
The pH optimum of an enzyme is:
d. occurs when there is optimum secondary and tertiary structure in the active site of the enzyme.
An antibiotic that acts by forming a covalent derivative of the enzyme glycoprotein peptidase is:
d. penicillin.
noncompetitive inhibitor
decreases Vmax with no change in Km
lineweaver-burk plot of pure noncompetitive inhibition
decreases Vmax with no change in Km intersection at the y-intercept is different - tells us there is a different Vmax same x-intercept - tells us that Km is the same cannot alleviate inhibition by adding substrate because it is not binding to the active site *see slide 47*
lineweaver Burk plot also a __________ _________ plot
double recipricol
all are true for the enzyme-transition state complex EXCEPT: a. it is designated as EX+ b. the enzyme stabilized the transition-state complex more than it stabilized the substrate complex c. the enzyme is "designed" to bind the transition-state structure more tightly than the substrate or product d. the energy barrier between ES and EX+ is less than the energy barrier between S and X+ e. all are true
e. all are true
metal ion catalysis include all EXCEPT a. increased acidity of a nucleophile with an ionizable proton b. metal ion requirement to maintain the stable, native state of the enzyme c. metal binding weakly, perhaps only during the catalytic cycle d. electrophilic catalysis stabilizing the increased electron density or negative charge that can develop during a reaction e. all are true
e. all are true
which of the following are relevant to the reaction catalyzed by chorismate mutase a. the reaction invovles a concerted intramolecular rearrangement of chorismate to prephenate during the synthesis of phenylalanine b. the enzyme catalyzed and uncatalyzed reactions follow almost identical routes c. the enzymatic reaction is thought to involve transition state stabilization by 12 electrostatic and hydrogen bond interactions d. the geomtery of the enzyme active site is such that the different in energy between ES and the near attack conformation is less than 1 kJ/mol e. all are true
e. all are true
since enzymes are not rigid molecules but rather flexible proteins which of the following may be attributed to this fact a. active sites are able to conform to the shape of the substrate b. catalytic residues are oriented in such a way to aid in bond breakage and bond formation c. strain is placed upon the substrate while it binds to the enzyme d. near attack conformation are achieved during formation of the transition state during an enzyme catalyzed reaction e. all of the above are correct
e. all of the above are correct
The primary biochemical lesion in homozygotes with familial hypercholesterolemia is: a. loss of feedback inhibition of liver HMG-CoA reductase b. increased production of LDL from HDL c. the loss of alipoprotein B d. the malfuncitoning of acyl-CoA cholesterol acyltransferase (ACAT) e. the functional deficiency of plasma membrane receptors for LDL
e. deficiency of LDL plasma membrane receptors
Humans cannot convert dietary: a. carbohydrate into stored lipid b. amino acids into into stored lipid c. glucose into amino acids d. amino acids into glucose e. fatty acids into glucose
e. fatty acids into glucose (not converted to glucose for energy; undergo B oxidation)
simple molecular processes also known as __________ reactions
elementary
What is unusable energy known as?
entropy (delta S)
Michaelis Menten: E=
enzyme
The main difference between chemical and enzyme kinetics is that ...
enzyme reactions depend on the concentration of the enzyme and its recycling.
pH
enzyme-substrate recognition and catalysis are *greatly dependent on ___*
An update of Fischer's lock-and-key theory of enzyme specificity views the ________ as the lock and ________ as the key.
enzyme; transition state
Most biological catalysts are proteins called _______________________.
enzymes
We study kinetics to discover role of __________ in overall pathway
enzymes
pH
enzymes are usually *active only over a limited range of ___*
inhibited
enzymes may be ___ reversibly or irreversibly
True or false, the differential Michaelis-Menten equation can be integrated directly.
false (cannot!)
True or false, steady states can differentiate between most mechanisms.
false (cannot)
True or false, a complicated enzyme-catalyzed reaction cannot be analyzed in terms of its component elementary reactions.
false (it can!)
Enzyme-catalyzed reactions that are diffusion-controlled reactions can never proceed any fast than the rate determined by random collision rates
false: diffusion controlled reaction --> a reaction that occurs with every collision btwn reactant molecules
For A------->p, the instantaneous rate of appearance of product or dissapearance of reactant, which is called velocity, is v=d[P]/dt=-d[A]/dt=k[A], first order or second order?
first
reversible inhibitors
four kinds: 1. competitive 2. noncompetitive 3. mixed noncompetitive 4. uncompetitive
The activation energy in biochemistry is most commonly called the
free energy of activation (delta G++)
At constant temperature, the rate of an elementary reaction is proportional to the ______ with which the reacting molecules come together.
frequency
Name intermediates in the citric acid cycle that serve as entry points for the carbons from amino acids
fumarate, oxaloacetate, succinyl coA, Alpha- ketoglutarate
The enzymatic activity of __________ __________ is controlled by phosphorylation/dephosphorylation as well as by the influence of allosteric effectors
glycogen phosphorylase
both allosteric and covalent
glycogen phosphorylase
The time for half of the initial reactant present to decompose is known as its
half life
t1/2=
half life
Transition state analogs should
have a dissociation constant of 10-13 M or less. AND bind very tightly to the enzyme
makes a good enzyme
high Kcat and poor Km OR low Kcat and low Km
Most of the known enzymes are ________
hydrolases
Hormone cascade starts...
in hypothalamus
random, single-displacement reaction
in this type of sequential reaction, all possible binary enzyme-substrate and enzyme-product complexes are formed rapidly and reversibly when enzyme is added to a reaction mixture containing A, B, P, and Q conversion of AEB to PEQ is the rate-limiting step in this kind of reaction *see slide 31*
The role of an enzyme in an enzyme-catalyzed reaction is to: A) bind a transition state intermediate, such that it cannot be converted back to substrate. B) ensure that all of the substrate is converted to product. C) ensure that the product is more stable than the substrate. D) increase the rate at which substrate is converted into product. E) make the free-energy change for the reaction more favorable.
increase the rate at which substrate is converted into product.
N-acetylglutamate indicates...
increased glutamate levels
The Michaelis-Menten equation descibes the relationship between _________ _________ ________ and substrate concentration under steady state conditions.
initial reaction velocity
In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the: A) curvature of the plot. B) intercept on the l/[S] axis. C) intercept on the l/V axis. D) pK of the plot. E) Vmax.
intercept on the l/[S] axis.
Michaelis-Menten: ES=__________, enzyme substrate complex.
intermediate
A---->I1----->I2----->P, I1 and I2 are __________ in the reaction?
intermediates
ping-pong (double-displacement) reaction
involves a covalent intermediate
Pennicilin is a reversible or irreversible suicide inhibitor
irreversible
Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is not cleaved by the enzyme. This is an example of what kind of inhibition? A) irreversible B) competitive C) non-competitive D) mixed E) pH inhibition
irreversible
kcat / Km
is an apparent second-order rate constant
Km
is an estimate of the dissociation constant of E from S (like Ka is the acid dissociation constant for HA --> H+ + A-) because it is an estimate of the dissociation constant: *small Km means little dissociation (tight binding), e.g. 10^-6 M large Km means lots of dissociation (weak binding), e.g. 10^-2 M*
rate, or velocity
is the amount of A consumed (or P formed) per unit of time (t) is directly proportional to the concentration of A
rate law
is the mathematical relationship between the reaction rate, or velocity, *v*, and concentration of reactants
rate constant (k)
is the proportionality constant in the rate equation
Vmax for an enzyme-catalyzed reaction: A) generally increases when pH increases. B) increases in the presence of a competitive inhibitor. C) is limited only by the amount of substrate supplied. D) is twice the rate observed when the concentration of substrate is equal to the Km. E) is unchanged in the presence of a uncompetitive inhibitor.
is twice the rate observed when the concentration of substrate is equal to the Km.
Different enzymes that catalyze the same reaction are known as ______.
isozymes
If a reaction is at equilibrium, what is the actual Gibbs free energy change?
it equals zero
Active trypsin formation by the action of enteropeptidase can be viewed as the master activation step because
it is allosterically controlled.
What is the transition state?
it is when the reactants are in the exact condition that the reaction then occurs -ex. pushing the boulder and pushing the boulder. Then right when the boulder is pushed enough, it reaches a state where it has potential to roll down the hill from that point on
Michaelis-Menten: rate constant designated by what letter?
k
What is the reverse rate of the reaction?
k-1
What is the rate of the enzyme-substrate complex formation?
k1
For the simplified representation of an enzyme-catalyzed reaction shown below, the statement "ES is in steady-state" means that: E + S<--k1--k-1-->ES--k2--k-2-->E + P
k1[E][S] = k-1[ES] + k2[ES].
What is the rate of the product forming?
k2
______, also known as turnover number. measured Vmax/[E]t
kcat
second order constant of an enzyme=______/KM
kcat
Cleavage of a C-C bond produces a carbanion that ________ both electrons and a carbocation that ________ both electrons
keeps; loses
Add phosphates to an enzyme, protein
kinases
deductive
kinetic analysis is a ___ reasoning tool
How fast will a reaction occur? answered by thermodynamics or kinetics?
kinetics
cannot
kinetics ___ prove a reaction mechanism
Enzymes that join two substrates and require energy of a nucleoside triphosphate (such as ATP) to do so are called
ligases (aka synthetases)
Double recipricoal plot of equation produces a linear equation.....inverses. this is known as ____________ _____ plot
lineweaver burk
If k1 (formation) is high, km will be....
low
Small values of KM mean that the enzyme becomes saturated at ____ concentrations of S.
low
Enzymes are potent catalysts because they: A) are consumed in the reactions they catalyze. B) are very specific and can prevent the conversion of products back to substrates. C) drive reactions to completion while other catalysts drive reactions to equilibrium. D) increase the equilibrium constants for the reactions they catalyze. E) lower the activation energy for the reactions they catalyze.
lower the activation energy for the reactions they catalyze.
Catalysts, such as enzymes, increase the reaction rate by.....
lowering the activation energy.
reversible inhibitors
may bind at the active site or at some other site
rapid reflux
means the ES complex results in product formation as rapidly as new ES complexes are forming
catalytic efficiency (kcat / Km)
measures how well the enzyme performs when [S] is low linear realationship
Detailed desciption of a chemical reaction in terms of the molecular, atomic or subatomic events is called the reaction ___
mechanism
What is the catalytic mechanism that utilizes metal ions such as zinc to activate bound water through the formation of a nucleophilic hydroxide ion?
metal ion catalysis
free enzyme
michaelis-menten equation assumes that the *ES is in rapid equilibrium with ___ ___ E + S*
enzyme substrate complex
michaelis-menten equation assumes the formation of an *___-___ ___: ES*
In ______, the inhibitor binds to a site involved in both substrate binding and catalysis.
mixed inhibition
inhibitor that binds to both the enzyme and the enzyme-substrate complex
mixed inhibition
Third type inhibition ______ or noncompetitive
mixed, noncompetitive
The reaction order of an elementary reaction corresponds to the ___________ of the reaction, which is the number of molecules that must simultaneously collide to generate a product.
molecularity
Enzymes are undoubtedly the ______________________________.
most important molecular machines.
When an enzyme is inhibited by a molecule that is the end product of its metabolic pathway this is called:
negative feedback inhibitor.
The allosteric enzyme ATCase is regulated by CTP, which binds to the T-state of ATCase. CTP is a:
negative regulator.
Is k affected by the enzyme of a reaction?
no
Is positive delta G spontaneous or nonspontaneous?
nonspontaneous
lineweaver-burk plot of uncompetitive inhibition
note that both intercepts change but the slope, Km/Vmax remains constant in the presence of I alters both Km and Vmax but with the same slope, Km/Vmax *see slide 49*
in the catalytic mechanism of chymotrypsin serine 195 acts as a__________.
nucleophile
first order, molecularity=
one
The binding of reactants or substrates triggers.......
one change in shape of the conformation of the entire protein.
Besides optimum pH of an enzyme, there is also an.....
optimum temperature
single displacement reaction types (2) _________ and ________ bisubstrate
ordered, random
Aldonic:
oxidized at the top
Km Values dependent on _____ and _________
pH and temperature
Which statement is not true about the peptide bond: a. it has partial double bond character b. the peptide bond is longer than the typical C-N bond c. the carbonyl oxygen and the amide hydrogen are most often in a trans config. with respect to one another d. rotation is restricted around the peptide bond
peptide bond: found in peptides or proteins; Amino group of one bonds to carbonyl group of the other b. the peptide bond is longer than the typical C-N bond
A common type of covalent modification of regulatory enzymes involves ______ of serine residues.
phosphorylation
Control of enzyme activity...covalent modification involved ______________ and ________________
phosphorylation, dephosphorylation
double displacement reaction type (1), _____ ______ bisubstrate
ping pong
Site directed mutagenesis is used to study enzymes by..
producing enzymes with different amino acid residues
An enzyme stabilizes the transition state that is bound in the active site. What effect will this have on the energy of the reactants?
raise the energy of the products to be closer to the transition state, but the energy of the transition state is unaltered
competitive inhibitor
raises Km with no change in Vmax
Elementary reactions may be first order, second order, or rarely, third order. In each case, a ______ _______ describes the progress of the reaction as a function of time.
rate equation
k-1
rate of dissassociation of ES is ___ for enzyme-catalyzed reactions
k1
rate of formation of ES is ___ for enzyme-catalyzed reactions
increase
rates of enzyme-catalyzed reactions generally ___ with *increasing temperature (T)*
Michaelis Menten equation describes a shape on graph that is a __________ ____________
rectangular hyperbola
Interactions in which form alpha-helices and beta-sheets give rise to _____ structure while interactions between two subunits constitute ______ structure.
secondary quaternary
enzyme kinetics
seeks to determine the *initial and maximal reaction velocity* (or rate) that enzymes can attain and the *binding affinities* for substrates and inhibitors
lineweaver-burk plot of competitive inhibition
shows lines for no I, [I], and 2[I] raises Km with no change in Vmax only inhibitor in which all of the lines intersect at the y-axis "competing" for active site can be overcome by adding much higher concentration of the substrate - becomes a problem in therapeutics *see slide 44* example: cGMP (substrate) and Viagra (inhibitor)
first order, second order
simple rate equations describe the progress of ___-___ and ___-___ reactions
Bisubstrate reactions are classified as _________ displacement and ____________ displacement
single, double
What is a measure used to identify enzyme purification?
specific activity
target cell:
specific response upon binding @ cognant receptor
Is negative delta G spontaneous or nonspontaneous?
spontaneous
The role of ser-195 in chymotrypsin cleavage of a peptide bond is that of a(n)
strong nucleophile
Michaelis-Menten:S=__________, the initial reactant
substrate
the rate of the reaction varies directly with how often enzyme and ___________ encounter one another in solution.
substrate
The concept of "induced fit" refers to the fact that: A) enzyme specificity is induced by enzyme-substrate binding. B) enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. C) enzyme-substrate binding induces movement along the reaction coordinate to the transition state. D) substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation. E) when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate.
substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
Enzymes bind to specific reactant molecules known as.....
substrates
The steady state assumption, as applied to enzyme kinetics, implies: A) Km = Ks. B) the enzyme is regulated. C) the ES complex is formed and broken down at equivalent rates. D) the Km is equivalent to the cellular substrate concentration. E) the maximum velocity occurs when the enzyme is saturated.
the ES complex is formed and broken down at equivalent rates.
order
the ___ for any reactant is given by its exponent in the rate equation
michaelis menten equation
the ____-____ ____ relates the *initial velocity* of a reaction to the *maximal reaction velocity* and the *Michaelis constant* for a particular enzyme and substrate
kcat/Km
the apparent second-order rate constant for an enzyme-catalyzed reaction it is a measure of an enzyme's catalytic efficiency
turnover number (Kcat)
the catalytic constant for an enzymatic reaction, equivalent to the ratio of the maximal velocity (Vmax) and the enzyme concentration ([E]t)
Kcat
the catalytic constant for an enzymatic reaction, equivalent to the ratio of the maximal velocity (Vmax) and the enzyme concentration ([E]t) also called the *turnover number*
When there are two substrates in a reaction, the reaction is said to be second order if ________.
the reaction is first order with respect to each substrate concentration
What is depletion of a reaction?
the reverse rate (k-1) + the rate of product formation (k2)
catalytic efficiency (kcat / Km)
the upper limit for kcat/Km is the diffusion limit (approaching ~10^10), the rate at which E and S encounter each other by diffusion how fast an enzyme can encounter a substrate
Some reactions are slow because.....
there is an energy barrier between reactants and products
steady-state assumption
there is no change in the concentration of the ES complex (dark rectangle), once the reaction is at a steady-state "equilibrium." however, rapid flux means the ES complex results in product formation as rapidly as new ES complexes are forming *see slide 14*
Will a reaction occur? answered by thermodynamics or kinetics?
thermodynamics
Enzymes are highly specific which means that....
they bind to specific substrates and catalyze particular reactants under certain conditions.
Activation energy is the energy needed to put molecules into the
transition state
2A--->P or A+B---->P, both are examples of second-order reaction true or false
true
Crossing on lineweaver burk characteristic of competitive inhibition, true or false
true
KM values vary widely, true or false?
true
True or false, Kinetics is different than thermodynamics
true
True or false, Michaelis-Menten is first order?
true
True or false, in simple systems, k2 constant is the equivalent of kcat.
true
True or false, most enzyme mechanisms more complex than michaelis menten-but similar.
true
True or false, most enzyme reactions are bisubstrate
true
Various Rate equations are derived from the instantaneous velocity equations (integrating above equation), true or false
true
glycogen phosphorylase control, both allosteric and covalent, true or false
true
True or false, simplifying assumptions must be applied to enable integration of the Michaelis-Menten equation.
true (cannot just be integrated directly)
catalytic constant, kcat also called __________ ________
turnover number
The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the: A) dissociation constant. B) half-saturation constant. C) maximum velocity. D) Michaelis-Menten number. E) turnover number.
turnover number.
ordered
type of single-displacement (sequential) reaction, where a leading substrate binds first, followed by the other substrate
random
type of single-displacement (sequential) reaction, where either substrate may bind first, followed by the other substrate
inhibitor that binds to the enzyme-substrate complex
uncompetitive inhibition
When two different substrates react to form two different products, the rate constants for each separate substrate can be determined by..
varying one substrate at a time, keeping the other in excess.
first order
when [S] is low, the equation for rate is ___-___ in [S]
What is negative feedback inhibitor?
when the product of a pathway binds to the regulatory (allosteric ) enzyme and dow regulates it.
Anomers:
change at the anemic carbon
We study kinetics to discover ___________ analysis
clinical
Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could bewritten as k1 k2E + S ES → E + P k-1 Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by theexpression: A) k1 ([Et] − [ES]). B) k1 ([Et] − [ES])[S]. C) k2 [ES]. D) k-1 [ES] + k2 [ES]. E) k-1 [ES]
d
the Pka's of the side chain group and the alpha carboxyl group of glutamate are 4.1 and 2.1, respectively. Which statement accounts for this difference? a. the side chain has more possible resonance structures b. the alpha carboxyl group has less steric hindrance and is therefore ionized more easily c. the side chain is a diff. functional gorup than the alpha carboxyl group d. the alpha carboxy group is closer ot the alpha amino group than the side chain is
d.
Aspartate proteases display a variety of substrate specificities but normally they are most active in cleavage of peptide bonds a. on the carboxyl side of the basic amino acid b. on the carboxyl side of the aromatic amino acid c. on the carboxyl side of the small, neutral residues d. between two hydrophobic amino acid residues e. none of the above
d. (between two hydrophobic amino acid residues)
For an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. Which of the following would be closest to the value of Km? [S] (mM) Vo(mM/min) 1.0 2.0 4.0 2.8
d. 0.60 mM
the transition state has an estimated life-time of about a. microseconds b. nanoseconds c. 10^-2 seconds d. 10^-14 to 10^-13 seconds e. miliseconds
d. 10^-14 to 10^-13 seconds
If an enzyme has a Vmax of 15 mM/min, what is the velocity if the substrate is present at ¼ of the Km?
d. 3 mM/min
The Henderson-Hasselbach equation can be used to calculate: a. the pH of a solution of an organic acid b. the amount of salt and acid to add to form a specific buffer c. the pKa of a weak acid d. all of the above e. a and c only
d. all of the above
Which of the following is NOT a member of the ETC? a. Cytochrome c oxidase b. Ubiquinone c. NADH Q reductase complex d. Alpha Ketoglutarate dehydrogenase complex e. cytochrome c
d. alpha ketoglutarate dehydrogenase complex
Lysozyme is classified as a: a. oxidoreductase b. phosphorylase c. isomerase d. hydrolase e. transferase
d. hydrolase
organic fluorophosphates are _____ inhibitors of serine proteases such as chymotrypsin a. competitive b. uncompetitive c. noncompetitive d. irreversible e. mixed noncompetitive
d. irreversible
Which of the following statements about the pentose phosphate pathway is incorrect? a. it generates CO2 from the C-1 of glucose b. it involves the conversion of aldohexose to an aldopentose c. it is prominent in adipose tissue d. it requires the participation of oxygen e. it is principally directed toward the generation of NADPH
d. it requires the participation of oxygen Pentose phosphate pathway: pathway in which glucose 6-phosphate is metabolized to generate NADPH and ribose 5- phosphate. It has an oxidative and nonoxidative stage
Which of the following statements is true regarding enzyme pathways? Acting in sequence, enzymes form ____________ and situated at key junctions are specialized ___________ enzymes capable of sensing the momentary metabolic needs and adjusting their ___________ rates accordingly.
d. metabolic pathways are necessary since enzymes usually catalyze only one specific reaction
GTP is formed in which reaction of the citric acid cycle? a. Pyryvate --> acetyl CoA b. isocitrate --> glyoxylate c. alpha ketoglutarate --> succinyl coA d. succinyl coA --> succinate
d. succinyl-CoA --> succinate
Which amino acid residue is the more likely to be found in the interior of a globular protein conformation? a. Lysine b. Arginine c. Glutamic acid d. valine
d. valine all other groups are polar
enzyme availability/amount measured by synthesis minus _______________
degradation
Enzymes differ from other catalysts in that only enzymes: A) are not consumed in the reaction. B) display specificity toward a single reactant. C) fail to influence the equilibrium point of the reaction. D) form an activated complex with the reactants. E) lower the activation energy of the reaction catalyzed.
display specificity toward a single reactant.
lineweaver-burk plots
distinguish different types of inhibition
The number of substrate molecules converted to product in a given unit of time by a single enzymemolecule at saturation is referred to as the: A) dissociation constant. B) half-saturation constant. C) maximum velocity. D) Michaelis-Menten number. E) turnover number
e
Chaperones are proteins which a. renature any denatured proteins b. help cells repair damage due to heat shock c. ue ATP to fold proteins d. assist protein in self-assenbly e. All of the above
e.
all are true for low-barrier hydrogen bonds EXCEPT a. the hydrogen is centered between the two heteroatoms b. the interactions are covalent c. the bond order approaches 0.5 for both O-H interactions d. the barrier that that the hydrogen atom must surmount to exchange oxygens becomes lower e. all are true
e. all are true
transition state analogs are a. approximations of the transition state that bind more tightly than the substrate b. compounds that compete for the active site, but are not necessarily very similar to the substrate c. stable molecules that can not be expected to resemble the true transition state too closely d. stable chemically and structurally similar molecules tot he transition state e. all of the above
e. all of the above
because the pKa is near 7, _____ side chains are often involved in general acid-base catalysis a. cysteine b. aspartate c. glutamate d. lysine e. histidine
e. histidine
Most Fatty acids in our bodies are synthesized as a result of:
excess dietary glucose
Excretion of nitrogen in fish-
excreted directly into surrounding H2O.
Every single enzyme undergoes michaelis menten, true or false.
false
True or false, enzymes can react faster than diffusion can take it.
false (they cannot)
True or false, a first-order elementary reaction is a bimolecular reaction.
false (unimolecular!)
Product binds at a location other than active site Binding (noncovalent) distorts active site This describes what process in enzymes?
feedback inhibition
The reaction velocity at any time point is proportional to the concentration of the reactant A. This is an example of a _________-order reaction
first
When varying the substrate concentration at a fixed concentration of enzyme it is observed that at low concentrations of substrate the reaction is ________, while at high concentrations of substrate the reaction is ________
first order; zero order
The enzyme has an active site which
fits the transition state. AND may contain hydrogen bonds which are covalent-like.
michaelis constant (Km)
for an enzyme that follows the Michaelis-Menten model, Km = (k-1 + k2)/ k1 Km is equal to the substrate concentration at which the reaction velocity is half-maximal
Sphingolipid function?
found in membrane of nervous system
alpha Km=
KMapp