CHE 315 Exam 2

The proteolytic enzyme trypsin is produced in the pancreas as the zymogen trypsinogen. Trypsinogen is cleaved to yield the active form. Trypsin, in turn, activates other pancreatic zymogens. 1. Select every enzyme that is used in the activation of trypsinogen. A. fibrin B. enteropeptidase (enterokinase) C. chymotrypsin D. trypsin 2. Select every pancreatic zymogen that is directly activated by trypsin. A. proelastase B. procarboxypeptidase C. prolipase D. chymotrypsinogen

1. B 2. A, B, C, D

. The mutated form of hemoglobin (hemoglobin S, or HbS) in sickle‑cell anemia results from the replacement of a glutamate residue by a valine residue at position 66 in the β chain of the protein. Normal hemoglobin is designated HbA. Under conditions of low [O2][O2] , HbS aggregates and distorts the red blood cell into a sickle shape. See image of eight aggregated HbS molecules. Sickled red blood cells are relatively inflexible and may clog capillary beds, causing pain and tissue damage. The sickled red blood cells also have a shorter life span, leading to anemia. 1. Which amino acids would be expected to produce a similar sickling effect if substituted for Val at position 6?6? A. lysine B. leucine C. phenylalanine D. arginine E. alanine Sickling occurs in deoxyhemoglobin S but not in oxyhemoglobin S. Oxyhemoglobin has a small, hydrophobic pocket in a β chain region located in the interior of the protein. In deoxyhemoglobin, however, this pocket is located on the surface of the protein. In deoxyhemoglobin S, Val 66 interacts with this surface pocket, leading to aggregation of HbS. 2. Choose two amino acids that would be reasonable candidates for the pocket-Val 66 interaction. A. leucine B. lysine C. phenylalanine D. glutamate E. asparagine 3. How does HbS aggregation occur in sickle‑cell anemia? Place the steps in the correct order. Note that deoxyhemoglobin is in the T state; oxyhemoglobin is in the R state. No aggregation 1. [O2][O2] decreases due to vigorous exercise or high altitude. 2. R state Hb shifts to T state Hb. 3. Val interacts with the pocket of a β chain on another HbS. 4. Additional T state HbS interact with the growing aggregate to form an insoluble fiber. Sickled red blood cell

1. B, E 2. A, C 3. in the right order

the central atom has _____ bonds: ______ to nitrogen atoms in the porphyrin, one to a _____ residue, and one to oxygen

6, 4, histidine

When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until equilibrium is reached, the final mixture contains six times as much glucose 6-phosphate as fructose 6-phosphate. (R = 8.315 J/mol · K; T = 298 K) Calculate DG'° for glucose 6-phosphate ® fructose 6-phosphate

= -RT ln Keq =- 8.315 J/mol K * 298 K * ln 1/6 = +4.4 kJ/mol *(6 times more reactant than product at equilibrium, reverse reaction is thermodynamically favorable)

Enzymes that are activated by specific proteolytic cleavage are called A. zymogens. B. heterozymes. C. allozymes. D. isozymes.

A

Hemoglobin S (HbS), which is an abnormal form of hemoglobin responsible for sickle‑cell anemia, is the result of a mutation in the gene for the β subunit. The mutation found in HbS results in the change of A. a negatively charged amino acid R group to a hydrophobic amino acid R group. B. a hydrophobic amino acid R group to a positively charged amino acid R group. C. a positively charged amino acid R group to a negatively charged amino acid R group. D. a negatively charged amino acid R group to a positively charged amino acid R group.

A

In fetal hemoglobin (HbF), the two β subunits are replaced with two γ subunits. The result is that HbF has a higher affinity for oxygen than the mother's adult hemoglobin (HbA). The greater oxygen affinity of HbF compared with HbA is due to A. the decreased affinity of 2,3‑BPG to the γ subunits of HbF. B. the decreased affinity of the γ subunits for CO2. C. a different mode of binding between the heme ring and the γ globin peptide. D. the γ and β subunits of HbF exhibit a greater degree of cooperativity than the α and β subunits of HbA.

A

Rapidly metabolizing tissues generate protons and carbon dioxide in high concentrations. The result is that the the oxygen‑binding curve of hemoglobin (Y versus pO2) A. shifts to the right, which reflects less saturation of hemoglobin at higher pO2 levels. B. shifts to the left, which reflects more binding of O2 by hemoglobin at lower pO2 levels. C. remains unchanged by the decrease in pH and increase in CO2. D. changes from sigmoidal to hyperbolic because hemoglobin switches to Michaelis-Menten kinetics.

A

Refer to the Biochemistry in Focus section of your text for this chapter to answer this question. Which of the following statements about Ngb-H64Q is true? A. Ngb-H64Q has a higher affinity than hemoglobin for both carbon monoxide and oxygen. However, Ngb-H64Q binds to carbon monoxide with a higher affinity than oxygen. B. Ngb-H64Q has a higher affinity for oxygen than it does for carbon monoxide. C. Ngb-H64Q has a higher affinity than hemoglobin for carbon monoxide, whereas hemoglobin has a higher affinity than Ngb-H64Q for oxygen. D. Ngb-H64Q binds oxygen and carbon monoxide with equal affinity.

A

Suppose that an arginine residue in the active site of an enzyme was mutated to alanine. As expected, the alanine mutant was inactive, suggesting that the arginine residue was critical to the catalytic mechanism. Which mutation is most likely to restore wild‑type level of activity to the alanine mutant? A. A to K B. A to S C. A to Y D. A to E E. A to M

A

Which elastase active site residue forms a covalent bond with the aldehyde inhibitor? A. serine B. histidine C. aspartate

A

What is a zymogen? Explain briefly with an example. Why is it important that protein is produced as a zymogen?

A zymogen is an inactive precursor of an enzyme. An example is the digestive enzyme chymotrypsin, which is produced as the inactive precursor chymotrypsinogen and activated by proteolysis. Active proteases could digest the cells in which they are produced.

What ways do enzymatic catalysts increase the rates of reactions? A. They lower the activation energy of the reaction. B. They promote the formation of a transition state. C. They increase the concentration of reactants. D. They decrease the free energy of the reaction. E. They shift the reaction equilibrium toward the products.

A, B

Which of the following statements describes a dimeric allosteric enzyme following the concerted model? A. The equilibrium between the T state and R state favors the T state. B. The enzyme can exist as an RR dimer. C. The enzyme can exist as an RT dimer. D. The RR form of the enzyme is the most active.

A, B, D

Which five statements about hemoglobin and myoglobin structure are true? A. Both hemoglobin and myoglobin contain a prosthetic group called heme, which contains a central iron atom. B. Heme is composed of an organic protoporphyrin component and a metal atom. C. Hemoglobin and myoglobin are heterotetramers. D. Molecular oxygen binds reversibly to Fe2+Fe2+ in heme. E. By itself, heme is not a good oxygen carrier. It must be part of a larger protein to prevent oxidation of the iron atom. F. Each iron atom can form six coordination bonds. Two of these bonds are formed between iron and oxygen. G. Each hemoglobin molecule can bind four oxygen molecules; each myoglobin can bind only one oxygen molecule.

A, B, D, E, G

Suppose that your Ph.D. mentor asks you to compare the kinetic behavior of the two recently discovered peptidase isozymes PepA and PepB. Your mentor's initial studies identified a pentapeptide substrate called Tide5 that appeared to be able to distinguish the kinetic behaviors of PepA and PepB. All they had time to tell you was this: At low Tide5 concentration, the 𝑉oVo (initial velocity) of PepA was greater than PepB, but at high Tide5 concentration, the reverse was true. Before you start your kinetic assays, you decide it would be wise to ponder this small bit of information. You have no numbers to work with, but does it tell you something about the relative values of 𝐾mKm and 𝑉maxVmax for PepA and PepB? Select the statements that are consistent with the information that you were given. A. The 𝑉maxVmax of PepB is greater. B. The ratio of 𝑉max/𝐾mVmax/Km is larger for PepB. C. The 𝐾mKm of PepB is higher. D. The 𝑉maxVmax of both isozymes could be the same, but the 𝐾mKm values are different. E. The 𝐾mKm of both isozymes could be the same, but the 𝑉maxVmax values are different.

A, C

Hemoglobin is a protein in red blood cells that binds to oxygen. Which physiological changes that naturally occur in the body reduce hemoglobin's affinity for oxygen? A. decrease in pH B. decrease in temperature C. accumulation of nitrogen D. accumulation of carbon dioxide

A, D

choose the type of interaction by which the substrate does NOT bind to the active site of an enzyme A. covalent interactions B. van der Waals forces C. hydrophobic interactions D. hydrogen bonds E. electrostatic interactions

A. covalent interactions

choose the CORRECT statement about enzymes A. enzymes increases the rate of a chemical reaction B. enzymes increase the number of products of a chemical reaction C. enzymes decrease the free energy of reactants D. enzymes decreases the rate of a chemical reaction E. enzymes shift the equilibrium of a chemical reaction

A. enzymes increase the rate of a chemical reaction

what shape does the curve of initial velocity versus substrate concentration for allosteric enzymes have A. sigmoidal B. logarithmic C. parabolic D. hyperbolic E. linear

A. sigmoidal

In a Linweaver Burk plot, the presence of a competitive inhibitor will alter: A. the slope of the curve B. the intercept on 1/V max C. The intercept on 1/[S] D. [S] E. V max

A. the slope of the curve, C. the intercept on 1/[S]

All of the cells in the body need oxygen. Hemoglobin molecules in red blood cells transport oxygen through the bloodstream. Oxygen is loaded onto hemoglobin molecules in the lungs and unloaded from the hemoglobin molecules in the tissues. What drives the loading of oxygen onto hemoglobin molecules in the lungs? A. the high partial pressure of carbon dioxide in the lungs B. the high partial pressure of oxygen in the lungs C. the low partial pressure of oxygen in the lungs D. the low partial pressure of carbon dioxide in the lungs

B

David comes into the emergency room late at night with a cut that will not stop bleeding. His mother, Rose, is worried that he has a bleeding disorder, just like his grandfather. The lab is closed, so the doctor cannot order a specialized coagulation test. However, the hospital does have a sample of blood from a classic hemophiliac. What is the simplest test the doctor could perform using David's blood to determine if it is missing factor VIII activity?A. compare clotting rates between the two blood samples B. combine the samples and check for coagulation C. test the samples for factor VIII mutations using PCR D. determine the factor VIII activity level in Rose's blood

B

Each chain of hemoglobin can be viewed as existing in one of two states: the R (relaxed, high‑affinity) state and the T (tense, low‑affinity) state.What is the relationship of the R and T states to oxygen binding? A. The conversion between the R and T states of hemoglobin takes place only as a result of 2,3‑bisphosphoglycerate binding. B. Oxygen binding induces a change in subunit conformation and affects the equilibrium between the T and R states of hemoglobin. C. Oxygen binds with greater affinity to the R state and, upon binding, converts hemoglobin to the T state. D. Oxygen binding converts hemoglobin from the T state to the R state.

B

Penicillinase, also known as β‑lactamase, is a bacterial enzyme that hydrolyzes and inactivates the antibiotic penicillin. Penicillinase follows simple Michaelis-Menten kinetics and reaches half its maximal rate of 6.8×10−10 µmol⋅min−16.8×10−10 µmol⋅min−1 when the penicillin concentration is 5.2×10−6 M.5.2×10−6 M. What would happen to the initial reaction velocity, 𝑉0,V0, of penicillinase if the penicillin concentration were 10.4×10−6 M?A. 𝑉0 would equal half 𝑉max. B. 𝑉0 would increase towards 𝑉max. C. 𝑉0 would be greater than 𝑉max. D. 𝑉0 would exactly equal 𝑉max.

B

Protein kinases generally regulate the activity of target proteins by transferring a phosphate group from ATP to the target protein. To what amino acid functional groups are these phosphates transferred? A. carboxyl groups B. hydroxyl groups C. amino groups D. hydrophobic groups

B

The difference between the concerted and sequential models of oxygen binding to hemoglobin is A. whether conformational changes occur in the α or β subunits. B. whether the transition between T and R states is an "all‑or‑nothing" event or an intermediate state exists with a mixture of R and T states in the same molecule. C. whether changes in function occur as a result of the presence or absence of regulatory molecules such as 2,3‑BPG. D. whether hemoglobin function is affected by CO2 binding in concert or sequentially with O2.

B

What type of functional group results when a covalent bond forms between the active site residue and the inhibitor?A. acetal B. hemiacetal C. ketal D. hemiketal

B

A double-reciprocal plot of 1/V0 versus 1/[S] for an enzyme in the presence of increasing concentrations of an uncompetitive inhibitor will have lines corresponding to the different inhibitor concentrations that are BEST described by which statement? A) The lines will intersect at the x-axis to the left of the y-axis. B) The lines will cross the y-axis and will be parallel to each other. C) The lines will intersect to the left of the y-axis but above the x-axis. D) The lines will intersect below the x-axis, to the right of the y-axis. E) The lines will be parallel to each other but will not cross the y-axis.

B) The lines will cross the y-axis and will be parallel to each other.

Conversion of CO2 in the blood into the more soluble HCO3- is catalyzed by which enzyme? A) hemoglobinase B) carbonic anhydrase C) bicarbonase D) carbondioxidease E) carbon hydratase

B) carbonic anhydrase

Feedback inhibition is important for the regulation of many metabolic pathways. Which of the statements are examples of feedback inhibition? A. The lac operon is not transcribed when there is no lactose present. B. The beginning of glycolysis is inhibited by high levels of ATP in the cell. C. The production of tryptophan is halted by the presence of excess tryptophan. D. Arsenic binds to pyruvate dehydrogenase and inhibits the enzyme. E. An intermediate of glycolysis activates an enzyme downstream in the pathway.

B, C

Select all the statements that correctly describe the cooperative binding of oxygen to hemoglobin. A. Salt bridges between hemoglogbin subunits allow oxygen to bind tightly. B. The hemoglobin-oxygen binding curve is sigmoidal. C. Hemoglobin consists of four heme‑bound subunits. D. Hemoglobin acts as an oxygen store under anaerobic conditions. E. Hemoglobin always binds oxygen tightly.

B, C

Which of the statements about enzymes are true? A. Nonbiological catalysts and enzymes tend to have a similar degree of reaction specificity. B. A substrate must bind to the active site before catalysis can occur. C. Catalysis occurs at the active site, which usually consists of a crevice on the surface of the enzyme. D. Generally, an enzyme is specific for a particular substrate. For example, thrombin catalyzes the hydrolysis of the peptide bond between Arg and Gly. E. An enzyme yields a specific product, whereas a nonbiological catalyst may produce more than one product with the occurance of side reactions.

B, C, D, E

according to the Michaelis Menten model Km equals the substrate concentration at which the reaction rate is A. a third of its maximal value B. at half of its maximal value C. twice its maximal value D. minimal E. maximal

B. at half of its maximal value

which type of reaction requires an input of energy to proceed A. irreversible reaction B. endergonic reaction C. exergonic reaction D. reversible reaction E. catalyzed reaction

B. endergonic reaction

The allosteric enzyme Quinnipiacase is regulated by Bobcat, which stabilizes the T-state of ATCase when it binds to a regulatory domain. Bobcat is a: A. positive allosteric regulator. B. negative allosteric regulator. C. transition state analog D. competitive inhibitor. E. coenzyme.

B. negative allosteric regulator.

the result of specificity of an enzyme is due to A. exactly matched substrate and coenzyme three dimensional structures B. precise interaction of the substrate with the enzyme C. exactly matched enzyme and substrate two dimensional structures D. precise interaction of the coenzyme with the enzyme E. formation of covalent bonds between the substrate and enzyme

B. precise interactions of the substrate with the enzyme

Carbonic anhydrase contains water coordinated to a Zn(II) in its active site. The pH dependence of the enzyme activity has an apparent pKa near 7.0 that is attributed to the ionization of this bound water molecule.Which of the following is true? A. The pKa near 7.0 indicates that the water freely exchanges with other solvent water. B. The Zn(II) activates the water, raising its pKa and making it more difficult to lose a proton. C. The Zn(II) activates the water, lowering its pKa and making it easier to lose a proton. D. The pKa near 7.0 indicates that there is no significant effect of the Zn(II) on the ability of the bound water molecule to gain or lose a proton.

C

The inhibition of aspartate transcarbamoylase by cytidine triphosphate (CTP) is an example of A. inactivation by phosphorylation. B. competitive inhibition. C. feedback inhibition. D. uncompetitive inhibition.

C

What is the catalytic triad of chymotrypsin, a type of serine protease? A. the enzyme−cofactor−substrate complex B. the enzyme−cofactor−intermediate complex C. the amino acids serine, histidine, and aspartate D. the amino acids cysteine, histidine, and aspartate E. the amino acids serine, histidine, and glutamate

C

Which statement is NOT correct concerning 2,3-bisphosphoglycerate (BPG)? A) It binds at a distance from the heme groups of hemoglobin. B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin. C) It increases the affinity of hemoglobin for oxygen. D) It is an allosteric modulator. E) It is normally found associated with the hemoglobin extracted from red blood cells.

C) It increases the affinity of hemoglobin for oxygen. * (BPG decreases affinity)

What are characteristics of allosteric enzymes? A. They are generally small single subunit proteins. B. They conform to Michaelis-Menten kinetics. C. They may have binding sites for regulatory molecules that are separate from active sites. D. They tend to have a sigmoidal (S‑shaped) curve of 𝑉0V0 vs. [S]. E. They interconvert between a more active form and a less active form.

C, D, E

Which statements about isozymes are true? A. Isozymes are always encoded by the same gene. B. Isozymes catalyze different reactions. C. Isozymes are present in various tissues. D. Isozymes have identical kinetic properties. E. Lactate dehydrogenase is an example. F. Isozymes have different amino acid sequences.

C, E, F

Which statement is FALSE? A. A reaction may not occur at a detectable rate even though it has a favorable equilibrium (i.e. negative ΔG) B. After a reaction, the enzyme involved becomes available to catalyze the reaction again. C. For the reaction S ↔ P, a catalyst shifts the reaction equilibrium to the right (favors products) D. Lowering the temperature of a reaction will lower the reaction rate. E. Substrate binds to an enzyme's active site.

C. For the reaction S ↔ P, a catalyst shifts the reaction equilibrium to the right (favors products)

You are examining the effects of a mutations in the distal histidine of a heme-containing protein, which change the histidine into small, nonpolar amino acids (alanine, valine). Based on your knowledge of the role of heme in hemoglobin and how it is coordinated in the protein, what is the MOST likely effect of the mutation? A. Heme will no longer be bound in the protein. B. The iron in heme will be fully coordinated. C. The iron in heme will be oxidized and/or bound to CO D. The heme will be able to bind to O2 more effectively than it will to CO. E. There will be no effect on the protein structure or function due to this mutation.

C. The iron in heme will be oxidized and/or bound to CO

Treatment of methanol poisoning by using ethanol is an example of what type of enzyme inhibition (both bind at the active site of alcohol dehydrogenase)? A. mixed inhibition B. uncompetitive inhibition C. competitive inhibition D. noncompetitive inhibition E. Irreversible inhibition

C. competitive inhibition

Describe why the concept in the question above is physiologically desirable (or, what would happen without it). 1-3 sentences.

Cells with high metabolic demand will produce carbon dioxide (and potentially lactic acid), lowering pH. These tissues require oxygen, so the Bohr effect helps with the offloading of oxygen from hemoglobin to provide a vital oxygen supply where it is needed

Enzymes that catalyze the same reaction but differ in amino acid sequence are called A. zymogens. B. heterozymes. C. allozymes. D. isozymes.

D

In addition to transporting oxygen from the lungs to the tissues, hemoglobin also plays a minor role in transporting carbon dioxide from the tissues to the lungs. How is this accomplished? A. Carbon dioxide competes for the oxygen‑binding site in the heme ring. B. Carbon dioxide competes for the 2,3‑BPG‑binding site. C. Carbon dioxide reacts with histidines in hemoglobin, resulting in 2,3‑BPG release. D. Carbon dioxide reacts with the amino termini of globin chains to form carbamate.

D

The alteration of enzyme structure on binding of a substrate to an active site is referred to as A. enzyme adaptation. B. enzyme inhibition. C. enzyme denaturation. D. induced fit.

D

The mechanism of chymotrypsin can be viewed as a two‑step process, beginning with acylation of the enzyme active site and followed by a deacylation reaction.The observation of a burst phase in kinetic studies of the hydrolysis of p‑nitrophenyl phosphate by chymotrypsin is due to which of the following? A. A change in the reaction mechanism after the burst phase causes the observed rate reduction. B. The rate of the acylation reaction is slower than the deacylation reaction. C. The rates of acylation and deacylation are essentially equal. D. The rate of the acylation reaction is faster than the deacylation reaction.

D

What does an apoenzyme require to become a holoenzyme? A. a vitamin B. a substrate C. an amino acid D. a cofactor

D

When an allosteric enzyme is directly affected by a molecule that is not its substrate, this effect on the enzyme is called A. a homotropic effect. B. an allosteric effect. C. a competitive effect. D. a heterotropic effect.

D

Which of the following statements best describes how 2,3‑bisphosphoglycerate (2,3‑BPG) reduces hemoglobin's affinity for oxygen? A. 2,3‑BPG binds to the α1β1‑α2β2 dimer interface to stabilize the R state. B. 2,3‑BPG binds to the amino termini of the globin chains to stabilize the R state. C. 2,3‑BPG binds to the heme iron and prevents oxygen binding. D. 2,3‑BPG binds to positively charged Lys and His residues in the center of the hemoglobin tetramer, which stabilizes the T state.

D

You have isolated a new protease that cleaves peptide bonds on the carboxyl side of Asp and Glu. Based on the enzyme's inactivation by DIPF, you suspect that it may utilize a mechanism similar to chymotrypsin.The difference in specificity might be explained by A. the replacement of Ser 195 with a positively charged residue. B. the absence of the S1 binding pocket. C. the presence of a negatively charged residue in the S1 binding pocket. D. the presence of a positively charged residue in the S1 binding pocket.

D

In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (DG'°) of +23.8 kJ/mol. Under what conditions encountered in a normal cell will the free-energy change (DG) be negative, enabling the reaction to proceed spontaneously to the right? A) Under standard conditions, enough energy is released to drive the reaction to the right. B) The reaction will not go to the right spontaneously under any conditions because the DG'° is positive. C) The reaction will proceed spontaneously to the right if there is a high concentration of products relative to the concentration of fructose 1,6-bisphosphate. D) The reaction will proceed spontaneously to the right if there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products. E) None of these conditions is sufficient

D) The reaction will proceed spontaneously to the right if there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.

Which amino acid is NOT capable using its side chain (R group) to participate in general acid-base catalysis? A) Asp B) His C) Ser D) Val E) Lys

D) Val

the turnover number per second of carbonic anhydrase is 600,000. The total number of resulting ions of bicarbonate per 1 minute is: A. 3,600,000 B. 18,000,000 C. 600,000 D. 36,000,000 E. 300,000

D. 36,000,000

The amino acid substitution of Val (V) for Glu (E) in Hemoglobin S results in aggregation of the protein because Val can form _____ interactions between molecules. A. covalent B. disulfide C. hydrogen bonding D. hydrophobic E. ionic

D. hydrophobic

which type of the multiple substrate reaction is shown Enzyme to NADH to pyruvate to lactate to NAD to enzyme A. double displacement reaction B. ordered displacement reaction C. random sequential reaction D. ordered sequential reaction E. double sequential reaction

D. ordered sequential reaction

Penicillin forms a covalent bond with a serine residue at the active site of transpeptidase. What type of inhibitors is it A. affinity label B. bond specific C. reactive substrate analog D. suicide E. group specific

D. suicide

Carbon dioxide is transported in the blood: A) Bound to the iron in heme B) Primarily as a dissolved gas C) Only as bicarbonate ion D) Primarily bound to the iron in heme, and also as bicarbonate ion E) As bicarbonate ion, bound to the N-terminus of hemoglobin, or as dissolved gas

E) As bicarbonate ion, bound to the N-terminus of hemoglobin, or as dissolved gas

Which statement regarding enzyme activity is CORRECT? A) Enzymes bind their substrates better than the transition state. B) Enzymes bind the transition state better than the reaction products, increasing activation energy. C) Enzymes increase activation energy required for the reaction to take place. D) Enzymes bind their substrates better than the transition state and the transition state better than the reaction products. E) Enzymes bind the transition state better than the substrates or reaction products and reduce the activation energy required for the reaction to take place.

E) Enzymes bind the transition state better than the substrates or reaction products and reduce the activation energy required for the reaction to take place.

Myoglobin and the subunits of hemoglobin have: A) no obvious structural relationship. B) very different primary and tertiary structures. C) almost identical primary and tertiary structures. D) almost identical similar primary structures, but different tertiary structures. E) very similar tertiary structures, but different primary structures.

E) very similar tertiary structures, but different primary structures.

the active site of an enzyme A. is a three dimensional cavity, formed by a coenzyme B. consists of unique microenvironment formed by water molecules C. binds to the substrate after a prolonged contact D. occupies a significant part of an enzyme E. binds to the substrate by multiple weak attractions

E. binds to the substrate by multiple weak attractions

To calculate the turnover number (Kcat) of an enzyme, you need to know: A. just the enzyme concentration. B. just the initial velocity of the catalyzed reaction at [S]>>Km. C. Both the enzyme concentration and the initial velocity of the catalyzed reaction at [S]= Km. D. the Km for the substrate. E. both the enzyme concentration and the initial velocity of the catalyzed reaction at [S] >> Km.

E. both the enzyme concentration and the initial velocity of the catalyzed reaction at [S] >> Km.

A system is at equilibrium when A. change in G for the system is positive B change in H for the system is negative C. change in G for the system is negative D. change in H for the system is zero E. change in G for the system is zero

E. change in G for the system is zero

Prosthetic groups are referred to as A. holoenzymes B. apoenzymes C. active sites D. inhibitors E. coenzymes

E. coenzymes

Which term describes an enzyme with its cofactor A. coenzyme B. apoenzyme C. inactive enzyme D. ligase E. holoenzyme

E. holoenzyme

which of the following is TRUE under the following conditions: The enzyme concentration is 5nM, the substrate concentration is 5 mM, and the Km is 5 uM. The enzyme is not saturated with the substrate. True or False

False

Under normal conditions, the central atom of heme is

Fe2+

The enzyme forms several bonds with the tetrahedral intermediate. How does this help accelerate the rate of the reaction (be brief, but specific)?

Lowering the energy of the transition state (which is very much like the tetrahedral intermediate) inversely and exponentially increases the rate of reaction

The change of hemoglobin affinity for oxygen with decreasing pH is known as the

___________Bohr effect__________.

In _______, the central iron atom is displaced 0.4A out of the plane of the porphyrin ring system

deoxyhemoglobin

The prosthetic group of hemoglobin and myoglobin is

heme

The organic ring compound of heme is

porphyrin