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Biochemistry Final

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Compounds that contain a nitrogenous base, a sugar, and a phosphate group are called (a)_________________. Two purines found in DNA are (b)______________ and __________________. A pyrimidine found in all DNA but in only some RNA is (c)_________________. In DNA, the base pair (d)___-___ is held together by three hydrogen bonds; the base pair (e)___-___ has only two such bonds.

(a) nucleotides; (b) adenine and guanine; (c) thymidine; (d) G-C; (e) A-T

Describe three factors that contribute to the high degree of sensitivity of signal transduction systems.

(a) the high affinity of receptors for signal molecules; (b) cooperative binding of signal molecules to receptors; (c) signal amplification by enzyme cascades.

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

A) irreversible

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) multiply the reciprocal of the x-axis intercept by −1.

simple diffusion

A- net movement of an electrically neutral solute is toward the lower concentration

Why are chitin and cellulose hydrophobic, and essentially insoluble in an aqueous media?

A. Because beta-glycosidic linkages are nonpolar and alpha linkages are polar.

From the abbreviated name of the compound Gal(B1->4)Glc, we know that: A. C-4 of glucose is joined to C-1 of galactose by a glycosidic bond. B. The compound is a D-enantiomer C. The galactose residue is at the reducing end D. The glucose is in its pyranose form E. The glucose residue is the B anomer

A. C-4 of glucose is joined to C-1 of galactose by a glycosidic bond

Which group of carbohydrates is unique in that its members are strong anions, containing a significant concentration of carbohydrates and sulfate?

A. Glycoaminoglycans

What term is given to carbohydrates linked at their anomeric carbons? A. Non-reducing sugars B. Glycosides C. Glycans D. Anomers E. Hemiketals

A. Non-reducing sugars

Sanger sequencing was performed on a long sequence of DNA from chloroplasts of a new plant species discovered in the rain forst of Puerto Rico. The X-ray film showed bands in the A, C, and T lanes, but the G lane was blank. What is the most likely explanation for this unexpected result? A. ddG was not added to the reaction tube B. Different template DNA was added to the reaction strand C. The template DNA contained no G D. All 4 ddNTPs were added to that tube E. The template DNA contained no C

A. ddG was not added to the reaction tube

ion transport

ATP is generated in mitochondria and chloroplasts by a mechanism that is essentially _______ __________

How are receptor tyrosine kinases related to cancer?

Abnormal functioning of receptor tyrosine kinases (RTKs) is associated with many types of cancers. For example, patients with breast cancer cells that have excessive levels of a receptor tyrosine kinase called HER2 have a poor prognosis. Using molecular biological techniques, researchers have developed a protein called Herceptin that binds to HER2 on cells and inhibits their growth, thus thwarting further tumor development. (Awesome.) In some clinical studies, treatment with Herceptin improved patient survival rates by more than one-third. One goal of ongoing research into these cell-surface receptors and other cell-signaling proteins is development of additional successful treatments.

irreversible inhibitor

Acetylcholinesterase is an important enzyme in the nervous system. Acetylcholinesterase activity is blocked by the nerve agent sarin gas, which forms a covalent bond with a Ser in the active site of the enzyme. Sarin gas is a(n) a. allosteric effector. b. competitive inhibitor. c. reversible inhibitor. d. irreversible inhibitor.

few GPCRs

Activation of a few ________ leads to the activation of few adenylyl cyclase enzymes

Compare and contrast the modes of action of epinephrine, acting through the β-adrenergic receptor, and of insulin, acting through the insulin receptor.

Adrenergic receptor: Indirectly activates a catalyst (adenylate cyclase), which produces a second messenger (cAMP). Insulin receptor: is itself a catalyst when occupied with insulin; its tyrosine kinase activity phosphorylates and activates another protein kinase, which initiates a cascade of phosphorylations of other proteins.

What is the advantage and disadvantage of direct regulation of transcription by hormones

Advantage: >> immediate physiological response Disadvantage: << amplified signal No GPCR involvement

van der Waals

All of the following are common catalytic reaction mechanisms in enzyme active sites EXCEPT __________ catalysis. a. acid-base b. covalent c. metal ion d. van der Waals

lowering; transition state

An enzyme can increase the rate of a reaction inside a cell by __________ the energy of the __________. a. lowering; transition state b. increasing; product c. lowering; substrate d. increasing; transition state

ANS: The enzyme follows the induced-fit model of enzyme catalysis. Adding the substrate caused the enzyme to change conformation, which caused the crystal to shatter.

An enzyme is crystallized in preparation for X-ray crystallography. The crystal is then soaked in a solution of substrate and the crystal shatters. Propose a reason for this result.

oxidoreductases

An enzyme that requires the coenzyme nicotinamide adenine dinucleotide belongs to which enzyme class? a. transferases b. isomerases c. ligases d. oxidoreductases

Tyr → Phe

An enzyme undergoes a mutation that causes it to lose the ability to be regulated via phosphorylation. Which of the following mutations may lead to this loss of regulation? Assume that the overall structure is not altered by the mutation. a. Ser→Thr b. Thr→Ser c. Tyr → Phe d. Ser→Tyr

A chemical group within the enzyme that has a pKa of around 7 is likely involved in the catalytic mechanism.

An experiment is performed in which the kinetics of an enzyme-catalyzed reaction at different pHs is monitored. It is found that the Km does not change but that the kcat increases as the pH goes above 7. Which of the following is true? a. A chemical group within the enzyme that has a pKa of around 7 is likely involved in the catalytic mechanism. b. A chemical group with a pKa of around 7 must be deprotonated in order for substrate to bind. c. A chemical group with a pKa of around 7 must be positively charged in order for the substrate to bind. d. Protons are acting as positive heterotropic allosteric effectors of this enzyme.

uncompetitive

An inhibitor that binds only to the ES complex and not free enzyme is known as a(n) __________ inhibitor. a. irreversible b. competitive c. uncompetitive d. mixed

What chemical features distinguish a plasmalogen from a common glycerophospholipid?

Ans: (1) The long-chain acyl group attached to C-1 of glycerol is ether-linked in a plasmalogen, but is an ester-linked fatty acyl group in typical glycerophospholipids. (2) There is a double bond between C-1 and C-2 of this fatty acyl chain in plasmalogens, but not in other phospholipids. (See Fig. 10-10, p. 351.)

Circle the fatty acid in each pair that has the higher melting temperature. (a) 18:19 18:29,12 (b) 18:0 18:19 (c) 18:0 16:0

Ans: (a) 18:19 (b) 18:0 (c) 18:0

In cells, fatty acids are stored as triacylglycerols for energy reserves. (a) What is the molecule to which fatty acids are esterified to form triacylglycerols? (b) Define the logic behind cells storing fatty acids in esterified form.

Ans: (a) Three fatty acids are esterified to glycerol. (b) Triacylglycerols are uncharged and insoluble in water. They form lipid droplets within adipocytes, which do not contribute to the osmolarity of the cytosol in those cells, and do not require any water of hydration.

What chemical features distinguish a cerebroside from a ganglioside?

Ans: A cerebroside has a single sugar residue joined to ceramide; a ganglioside has an oligosaccharide joined to ceramide. (See Fig. 10-13, p. 353.)

What are the chemical components of a biological wax, and what is their general structure?

Ans: A wax consists of a long-chain fatty acid in ester linkage with a long-chain fatty alcohol. (See Fig. 10-5, p. 348.)

In one sentence, identify the most obvious structural difference between A-form (Watson-Crick) DNA and Z-form DNA.

Ans: A-form DNA is a right-handed helix; Z-form DNA is a left-handed helix.

Show the basic structure of all glycerophospholipids.

Ans: All glycerophospholipids have two fatty acids in ester linkage with C-1 and C-2 of glycerol; often the fatty acid at C-1 is saturated, and that at C-2 is unsaturated. C-3 of glycerol is joined to an alcohol-containing head group through a phosphodiester linkage, which is negatively charged at neutral pH. (See Fig. 10-9, p. 351.)

Describe the dependence of the melting point of a fatty acid upon (a) chain length and (b) unsaturation; (c) explain these dependencies in molecular terms.

Ans: All other things being equal, (a) the longer the acyl chain, the higher the melting temperature; and (b) the more unsaturation, the lower the melting temperature. (c) The melting temperature is a measure of the thermal energy needed to break the intermolecular interactions that stabilize the "solid" form of a lipid, which depends upon how well the individual lipid molecules fit into the nearly crystalline array of lipids. When a shorter acyl chain lies between two longer chains in a nearly crystalline array of lipid molecules, there is a cavity at the end of the short acyl group that allows freer motion to the neighboring acyl chains. A cis double bond introduces a "kink" into the acyl chain, so that it does not pack as easily with its straighter neighbors.

Write a double-stranded DNA sequence containing a six-nucleotide palindrome.

Ans: Any double-stranded sequence that has the form: 1-2-3-4-5-6-6'-5'-4'-3'-2'-1' 1'-2'-3'-4'-5'-6'-6-5-4-3-2-1 where each number and its prime represent correctly paired bases (A with T, C with G) all along the double-stranded molecule.

How are a nucleoside and a nucleotide similar and how are they different?

Ans: Both have a nitrogenous base and a pentose; nucleotides also have a phosphate group, which nucleosides lack.

Draw the structure of phosphatidylserine in the ionic form it would have at pH 7.

Ans: For this structure, see Fig. 10-8, p. 350. At neutral pH, there is a charge on the phosphate group, and serine is in the zwitterionic form; it has a protonated amino group and an ionized carboxyl group.

Draw the structure of phosphatidylcholine. Circle the part of the molecule that is polar and draw an arrow to the part that is nonpolar.

Ans: For this structure, see Fig. 10-9, p. 351. At neutral pH, there is a negative charge on the phosphate group, and the quaternary amino group of choline carries a fixed positive charge; this entire phosphorylcholine moiety is polar. The acyl chains attached to glycerol are the nonpolar part of the molecule.

Describe briefly how noncovalent interactions contribute to the three-dimensional shapes of RNA molecules.

Ans: Hydrogen-bonding in regions of complementarity within an RNA chain can result in regions of double helix that are stabilized by base-stacking. Breaks in complementary regions can result in loops and bulges that together with the helical regions, can generate a precise three-dimensional structure.

If beeswax, cholesterol, and phosphatidylglycerol were dissolved in chloroform, then subjected to thin-layer chromatography on silica gel using a mixture of chloroform/methanol/water as the developing solvent, which would move fastest?

Ans: In this chromatography, the least polar compound (beeswax) moves fastest and the most polar (phosphatidylglycerol, which has a negative charge on its head group) moves the slowest. (See Fig. 10-24, p. 364.)

Match each of these vitamins with its biological role: Vitamins A, D, E, K. ____ blood clotting ____ vision ____ Ca2+ and phosphate metabolism ____ prevention of oxidative damage

Ans: K; A; D; E

Explain why extraction of lipids from tissues requires organic solvents.

Ans: Lipids are either strongly hydrophobic or amphipathic. Because the solvent in tissues is water, lipids are mainly present in aggregates. This aggregation does not occur in organic solvents; as a result, the lipids are more soluble and thus extractable from the tissues.

What is the effect of a double bond on fatty acid structure?

Ans: Most double bonds in fatty acids are in the cis configuration. This results in a rigid bend in the hydrocarbon chain. (See Fig. 10-1, p. 345.)

Give the structure of phosphatidylethanolamine containing one palmitate and one oleate. Show the ionic form expected at pH 7. How many ester bonds are there in this compound?

Ans: See Fig. 10-9, p. 351 for the phospholipid structure and Table 10-1, p. 344 for the structures of the fatty acids. There are two carboxylate esters and two phosphate esters (one phosphodiester) in the molecule.

Describe briefly what is meant by saying that two DNA strands are complementary.

Ans: The nucleotide sequences of complementary strands are such that wherever an A occurs in one strand, there is a T in the other strand with which it can form a hydrogen-bonded base pair. Wherever a C occurs in one strand, a G occurs in the other. A is the base complementary to T, and C is the base complementary to G.

Show the structure of isoprene; explain what is meant by isoprenoid compounds and give an example.

Ans: The structure is shown on page 361. Isoprenoid compounds contain chains that consist of multiple isoprene units. (See Fig. 10-22, p. 362, for examples.)

Show the structure of sphingosine and indicate the relationship between sphingosine and ceramide.

Ans: The structure of sphingosine is shown in Fig. 10-13, p. 353, which also shows that the attachment of a fatty acyl group to sphingosine in amide linkage converts it to ceramide.

Describe the differences between the glycosphingolipids corresponding to the A, B and O human blood group antigens.

Ans: The type O structure is found in all three glycosphingolipids. In both type A and type B, there is an added sugar; this sugar differs between type A and B.

Explain the cause of hereditary diseases of sphingolipid metabolism, such as Tay-Sachs and Niemann-Pick diseases.

Ans: These diseases are the result of mutations in the genes that code for enzymes of sphingolipid breakdown. The mutant enzyme is defective and unable to catalyze its reaction in the metabolic pathway; this results in the accumulation of the metabolic intermediate that is the substrate for the enzyme. (See Box 10-2, p. 356.)

What do all these compounds have in common: vitamin A, vitamin K, ubiquinone, and dolichol?

Ans: They are all lipids with potent biological activities derived from isoprenoid precursors.

What is the most significant chemical difference between triacylglycerols and glycerophospholipids that leads to their different functions?

Ans: Triacylglycerols are nonpolar hydrophobic molecules that can be stored in specialized nonaqueous cellular compartments. Glycerophospholipids are amphipathic molecules that can serve as structural components of membranes, which have hydrophilic and hydrophobic regions.

Describe three functions of triacylglycerols in mammals and one function in higher plants.

Ans: Triacylglycerols provide mammals with (1) stored fuel, (2) insulation, and (3) a source of metabolic water. In some animals, such as camels and desert rats, the oxidation of stored lipids provides water; in hibernating animals, oxidation of stored lipids generates heat to maintain body temperature (see Chapter 4). In plants, oxidation of the triacylglycerols stored in seeds provides the energy and precursors for biosynthetic processes during germination, before photosynthetic mechanisms become functional.

Match the type of bond with the role below: Bond_type Role (a) phosphodiester ___ links base to pentose in nucleotide (b) N-glycosidic ___ joins adjacent nucleotides in one strand (c) phosphate ester ___ joins complementary nucleotides in two strands (d) hydrogen ___ difference between a nucleoside and a nucleotide

Ans: b; a; d; c

Match the compounds on the left with the important roles they play listed on the right. (Answers are used only once.) (a) prostaglandins ___ blood clotting (b) sphingolipids ___ necessary for sight (c) thromboxanes ___ mediates pain and inflammation (d) vitamin A ___ important component of myelin membranes

Ans: c; d; a; b

Cotransport that moves two compounds in the opposite direction

Antiport

65) Lipid-soluble signal molecules, such as testosterone, cross the membranes of all cells but affect only target cells because A) only target cells retain the appropriate DNA segments. B) intracellular receptors are present only in target cells. C) most cells lack the Y chromosome required. D) only target cells possess the cytosolic enzymes that transduce the testosterone. E) only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.

A compound containing N-acetylneuraminic acid (sialic acid) is: A) cardiolipin. B) ganglioside GM2. C) phosphatidylcholine. D) platelet-activating factor. E) sphingomyelin.

Biological waxes are all: A) trimesters of glycerol and palmitic acid. B) esters of single fatty acids with long-chain alcohols. C) trimesters of glycerol and three long chain saturated fatty acids. D) sphingolipids. E) none of the above.

Consider the transport of glucose into an erythrocyte by facilitated diffusion. When the glucose concentrations are 5 mM on the outside and 0.1 mM on the inside, the free-energy change for glucose uptake into the cell is: (These values may be of use to you: R = 8.315 J/mol•K; T = 298 K; 9 (Faraday constant) = 96,480 J/V; N = 6.022 1023/mol.) A) less than 2 kJ/mol. B) about 10 kJ/mol. C) about 30 kJ/mol. D) about -30 kJoule/mol. E) impossible to calculate without knowledge of the membrane potential.

Fatty acids are a component of: A) carotenes. B) cerebrosides. C) sterols. D) vitamin D. E) vitamin K.

For the process of solute transport, the constant Kt is: A) analogous to Ka for ionization of a weak acid. B) analogous to Km for an enzyme-catalyzed reaction. C) analogous to Vmax for an enzyme reaction D) proportional to the number of molecules of glucose transporter per cell. E) the maximum rate of glucose transport.

In one catalytic cycle, the Na+/K+ ATPase transporter transports: A) 2 Na+ out, 3 K+ in, and converts 1 ATP to ADP + Pi. B) 3 Na+ out, 2 K+ in, and converts 1 ATP to ADP + Pi. C) 3 Na+ in, 2 K+ out, and converts 1 ATP to ADP + Pi. D) 1 Na+ out, 1 K+ in, and converts 1 ATP to ADP + Pi. E) 2 Na+ out, 3 K+ in, and converts 1 ADP + Pi to ATP.

L-selectin is a leukocyte adhesion protein that specifically binds carbohydrate on its extracellular N-terminus. It crosses the plasma membrane once, and the internal carboxyl tail is thought to stimulate secretion. What is the best characterization of this protein? A. Type III membrane protein, integral B. Type I membrane protein, transmembrane C. Type IV membrane protein, integral D. Type II membrane protein, transmembrane E. Type II membrane protein, peripheral

Lipid storage diseases are the result of alterations of what chemical group on membrane lipids? A. Fatty acids B. Carbohydrate C. Sphingosine D. Peptide E. Glycerol

Movement of water across membranes is facilitated by proteins called: A) annexins. B) aquaporins. C) hydropermeases. D) selectins. E) transportins.

Non-steroidal anti-inflammatory drugs (NSAIDS) like aspirin and ibuprofen act by blocking production of: A) biological waxes B) prostaglandins C) sphingolipids D) vitamin D E) none of the above

Nuclear magnetic resonance spectroscopy was performed on a derivative of cortisol, a steroid hormone. What structural feature was not observed in this molecule that would be present in sterols? A. Four six-membered rings in the nucleus rather than three. B. A carbonyl rather than a hydroxyl on the A-ring C. An alkyl chain on the D-ring D. Characteristic alcohol groups on each of the four rings E. An absence of polar groups

The shortest helix segment in a protein that will span a membrane bilayer has about _____ amino acid residues. A) 5 B) 20 C) 50 D) 100 E) 200

Which of the following is a useful consequence of the action of a Na+/K+ ATPase in the plasma membrane? A. Depletes cells of Na+, which can be harmful B. Membrane repolarization C. Draws K+ into cells, contributing to buffering capacity D. Maintains charge equilibrium across the membrane E. Promotes the movement of water into cells

Which of the following is not a fat-soluble vitamin? A) A B) C C) D D) E E) K

Which of the following is not true of sterols? A) Cholesterol is a sterol that is commonly found in mammals. B) They are commonly found in bacterial membranes. C) They are more common in plasma membranes than in intracellular membranes (mitochondria, lysosomes, etc.). D) They are precursors of steroid hormones. E) They have a structure that includes four fused rings.

Which of the following molecules in signaling is not considered a second messenger? A. Calcium B. GTP C. Inositol 1,4,5-trisphosphate D. Diacylglycerol E. Cyclic AMP

Which of the following signaling systems actually moves a molecule across the plasma membrane, as opposed to only a conformational change in the receptor? A. G-protein coupled receptors B. Steroid hormone receptors C. Guanylyl cyclases D. Tyrosine kinase receptors E. Adhesion receptors

Which of the following statements is true of lipids? A) Many contain fatty acids in ester or amide linkage. B) Most are simply polymers of isoprene. C) Testosterone is an important sphingolipid found in myelin. D) They are more soluble in water than in chloroform. E) They play only passive roles as energy-storage molecules.

6) Which of the following is true of synaptic signaling and hormonal signaling? A) Hormonal signaling occurs in animals only. B) Hormonal signaling is important between cells that are at greater distances apart than in synaptic signaling. C) Both act on target cells by a G-protein-signaling pathway. D) Only A and B are true. E) A , B, and C are true.

B Topic: Concept 11.1 Skill: Comprehension

1) In yeast (Saccharomyces cerevisiae), the two sexes are called A) S plus and S minus. B) a and α. C) a and b. D) b and β. E) male and female.

B Topic: Concept 11.1 Skill: Knowledge

3) Which of the following is true of the mating signal transduction pathway in yeast? A) The pathway carries an electrical signal between mating cell types. B) Mating type a secretes a signal called a factor. C) The molecular details of the pathway in yeast and in animals are very different. D) Scientists think the pathway evolved long after multicellular creatures appeared on Earth. E) The signal reception, transduction, and response occur in the nucleus.

B Topic: Concept 11.1 Skill: Knowledge

8) From the perspective of the cell receiving the message, the three stages of cell signaling are A) the paracrine, local, and synaptic stages. B) signal reception, signal transduction, and cellular response. C) signal reception, nucleus disintegration, and new cell generation. D) the alpha, beta, and gamma stages. E) signal reception, cellular response, and cell division.

B Topic: Concept 11.1 Skill: Knowledge

9) The process of transduction usually begins A) when the chemical signal is released from the alpha cell. B) when the signal molecule changes the receptor protein in some way. C) after the target cell divides. D) after the third stage of cell signaling is completed. E) when the hormone is released from the gland into the blood.

B Topic: Concept 11.1 Skill: Knowledge

23) Testosterone functions inside a cell by A) acting as a signal receptor that activates ion-channel proteins. B) binding with a receptor protein that enters the nucleus and activates specific genes. C) acting as a steroid signal receptor that activates ion-channel proteins. D) becoming a second messenger that inhibits adenylyl cyclase. E) coordinating a phosphorylation cascade that increases glycogen metabolism.

B Topic: Concept 11.2 Skill: Comprehension

12) A small molecule that specifically binds to another molecule, usually a larger one A) is called a signal transducer. B) is called a ligand. C) is called a polymer. D) seldom is involved in hormonal signaling. E) usually terminates a signal reception.

B Topic: Concept 11.2 Skill: Knowledge

20) Membrane receptors that attach phosphates to specific animo acids in proteins are A) not found in humans. B) called receptor tyrosine-kinases. C) a class of GTP G-protein signal receptors. D) associated with several bacterial diseases in humans. E) important in yeast mating factors that contain amino acids.

B Topic: Concept 11.2 Skill: Knowledge

49) Which of the following is an incorrect association? A) kinase activity and the addition of a phosphate group B) phosphodiesterase activity and the removal of phosphate groups C) GTPase activity and hydrolysis of GTP to GDP D) phosphorylase activity and the catabolism of glycogen E) adenylyl cyclase activity and the conversion of AMP to cAMP

B Topic: Concept 11.3 Skill: Application

28) Which of the following is (are) true regarding the activity of a protein regulated by phosphorylation? A) It depends mostly on the concentration of inorganic phosphate inside the cell. B) It depends on the balance in the cell between active kinase and active phosphatase molecules. C) It is dependent on the site of attachment of the protein to the plasma membrane. D) Only A and B are true. E) A, B, and C are true.

B Topic: Concept 11.3 Skill: Comprehension

48) Which of the following statements is incorrect? A) When signal molecules bind to receptor tyrosine kinases, the receptors phosphorylate themselves. B) In response to some G-protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3and calcium. C) In most cases, signal molecules interact with the cell at the plasma membrane and never actually enter the cell. D) Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in adenylyl cyclase activity in the absence of an appropriate signal molecule. E) Protein kinase A activation is one possible result of signal molecules binding to G-protein-linked receptors.

B Topic: Concept 11.3 Skill: Comprehension

33) Which of the following is not considered a second messenger? A) cAMP B) GTP C) calcium ions D) diacylglycerol (DAG) E) inositol trisphosphate (IP3)

B Topic: Concept 11.3 Skill: Knowledge

Which of the following deoxyoligonucleotides will hybridize with a DNA containing the sequence (5')AGACTGGTC(3')? A) (5')CTCATTGAG(3') B) (5')GACCAGTCT(3') C) (5')GAGTCAACT(3') D) (5')TCTGACCAG(3') E) (5')TCTGGATCT(3')

B) (5')GACCAGTCT(3')

A novel subclass of thromboxane was discovered in lipids isolated from a newly discovered poison dart from the Amazon valley. What unique structural feature is likely present in these lipids? A) Four conjugated double bonds B) A six membered ring C) A long-chain alcohol bound to a double-ring D) A five membered ring E) An amido group

B) A six membered ring

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 μm/min.

B) At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.

Lipid storage diseases are the result of alterations of what chemical group on membrane lipids? A) Fatty acids B) Carbohydrate C) Sphingosine D) Peptide E) Glycerol

B) Carbohydrate

D-Glucose is called a reducing sugar because it undergoes an oxidation-reduction reaction at the anomeric carbon. One of the products of this reaction is: A) D-galactose. B) D-gluconate. C) D-glucuronate. D) D-ribose. E) muramic acid.

B) D-gluconate.

Which of the following is an epimeric pair? A) D-glucose and D-glucosamine B) D-glucose and D-mannose C) D-glucose and L-glucose D) D-lactose and D-sucrose E) L-mannose and L-fructose

B) D-glucose and D-mannose

Which of the following is an epimeric pair? A) D-glucose and D-glucosamine B) D-glucose and D-mannose C) D-glucose and L-glucose D) D-lactose and D-sucrose E) L-mannose and L-fructose

B) D-glucose and D-mannose

Which of the following is an epimeric pair? A) D-glucose and D-glucosamine B) D-glucose and D-mannose C) D-glucose and L-glucose D) D-lactose and D-sucrose E) L-mannose and L-fructose

B) D-glucose and D-mannose

Which of the following should be considered when looking for a way to increase an enzyme reaction rate? A) Decreasing Ka B) Decreasing Kd between the substrate and enzyme C) Decreasing pO2 D) Increasing Kw E) Any change in nH

B) Decreasing Kd between the substrate and enzyme

Sephadex is a commercially produced branched homopolysaccharide. It contains alpha-glycosidic linkages at carbons 2, 3, 4, and 6. The degree of cross-linking those carbons can be controlled, yielding holes within the molecule of known size. What method can use such a molecule? A) SDS-PAGE B) Gel exclusion chromatography C) Differential centrifugation D) Tandem mass spectroscopy E) Ion exchange chromatography

B) Gel exclusion chromatography ****Based on size

An enzyme accepts H+ from hydronium and transfers it to an amine group of the substrate. The result is an increase in the rate of release of the product. This is an example of which of the following? A) Induced fit B) General acid catalysis C) Covalent catalysis D) Entropy reduction E) Specific acid catalysis

B) General acid catalysis

In a plot of 1/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 of the 1/[S] axis C) Intercept on the 1/V axis D) pK of the plot E) Vmax

B) Intercept of the 1/[S] axis

What function is served by the major groove in DNA?

B) It is a binding site for regulatory proteins

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.

B) It is sometimes used to hold two substrates in the optimal orientation for reaction

A laboratory is studying the binding properties of a glycoprotein on the plasma membrane. What amino acids should they analyze for the presence of branched heteropolysaccharides? A) Ser, Thr, and Tyr B) Ser, Thr, and Asn C) Trp, Tyr, and Asn D) Asp and Glu E) Lys, His, and Arg

B) Ser, Thr, and Asn

When double-stranded DNA is heated at neutral pH, which change does not occur? A) The absorption of ultraviolet (260 nm) light increases. B) The covalent N-glycosidic bond between the base and the pentose breaks. C) The helical structure unwinds. D) The hydrogen bonds between A and T break. E) The viscosity of the solution decreases.

B) The covalent N-glycosidic bond between the base and the pentose breaks.

What chemical feature determines if a sugar is an aldose or a ketose?

B) The position of the carbonyl carbon

Which of the following statements concerning receptor enzymes is correct? A) They are not usually membrane-associated proteins. B) They contain an enzyme activity that acts upon a cytosolic substrate. C) They contain an enzyme activity that acts upon the extracellular ligand. D) They have a ligand-binding site on the cytosolic side of the membrane. E) They have an active site on the extracellular side of the membrane.

B) They contain an enzyme activity that acts upon a cytosolic substrate.

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.

B) a His residue on the enzyme is involved in the reaction

A good transition-state analog: A) binds covalently to the enzyme. B) binds to the enzyme more tightly than the substrate. C) binds very weakly to the enzyme. D) is too unstable to isolate. E) must be almost identical to the substrate.

B) binds to the enzyme more tightly than the substrate.

Steroid hormones are carried on specific carrier proteins because the hormones: A) are too unstable to survive in the blood on their own. B) cannot dissolve readily in the blood because they are too hydrophobic. C) cannot find their target cells without them. D) need them in order to pass through the plasma membrane. E) require subsequent binding to specific receptor proteins in the nucleus.

B) cannot dissolve readily in the blood because they are too hydrophobic.

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.

B) changes in [S] are negligible, so [S] can be treated as a constant.

Compounds that generate nitrous acid (such as nitrites, nitrates, and nitrosamines) change DNA molecules by: A) breakage of phosphodiester bonds. B) deamination of bases. C) depurination. D) formation of thymine dimers. E) transformation of A to T.

B) deamination of bases.

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.

B) display specificity toward a single reactant

Which of the following monosaccharides is not an aldose? A) erythrose B) fructose C) glucose D) glyceraldehyde E) ribose

B) fructose

Which of the following monosaccharides is not an aldose? A) erythrose B) fructose C) glucose D) glyceraldehyde E) ribose

B) fructose

Which of the following monosaccharides is not an aldose? A) erythrose B) fructose C) glucose D) glyceraldehyde E) ribose

B) fructose

The experiment of Avery, MacLeod, and McCarty in which nonvirulent bacteria were made virulent by transformation was significant because it showed that: A) bacteria can undergo transformation. B) genes are composed of DNA only. C) mice are more susceptible to pneumonia than are humans. D) pneumonia can be cured by transformation. E) virulence is determine genetically.

B) genes are composed of DNA only.

The basic structure of a proteoglycan consists of a core protein and a: A) glycolipid. B) glycosaminoglycan. C) lectin. D) lipopolysaccharide. E) peptidoglycan.

B) glycosaminoglycan.

The basic structure of a proteoglycan consists of a core protein and a: A) glycolipid. B) glycosaminoglycan. C) lectin. D) lipopolysaccharide. E) peptidoglycan.

B) glycosaminoglycan.

The basic structure of a proteoglycan consists of a core protein and a: A) glycolipid. B) glycosaminoglycan. C) lectin. D) lipopolysaccharide. E) peptidoglycan.

B) glycosaminoglycan.

In a double-stranded nucleic acid, cytosine typically base-pairs with: A) adenosine. B) guanine. C) inosine. D) thymine. E) uracil.

B) guanine

The DNA oligonucleotide abbreviated pATCGAC: A) has 7 phosphate groups. B) has a hydroxyl at its 3'end. C) has a phosphate on its 3' end. D) has an A at its 3' end. E) violates Chargaff's rules.

B) has a hydroxyl at its 3'end.

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.

B) intercept on the l/[S] axis.

The ion channel that opens in response to acetylcholine is an example of a ____________ signal transduction system. A) G protein B) ligand-gated C) receptor-enzyme D) serpentine receptor E) voltage-gated

B) ligand-gated

Most transduction systems for hormones and sensory stimuli that involve trimeric G proteins have all of the following in common except: A) cyclic nucleotides. B) nuclear receptors. C) receptors that interact with a G protein. D) receptors with multiple transmembrane segments. E) self-inactivation.

B) nuclear receptors.

The force that drives an ion through a membrane channel depends upon: A) the charge on the membrane. B) the difference in electrical potential across the membrane. C) the size of the channel. D) the size of the ion. E) the size of the membrane.

B) the difference in electrical potential across the membrane.

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: A) glucose has more —OH groups per molecule than does water. 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. C) the —OH group of water is attached to an inhibitory H atom, while the glucose —OH group is attached to C. D) water and the second substrate, ATP, compete for the active site resulting in a competitive inhibition of the enzyme. E) water normally will not reach the active site because it is hydrophobic.

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.

The G-protein involved in visual signal transduction is: A) a leukotriene. B) transducin. C) arrestin. D) rhodopsin. E) a GTP receptor.

B) transducin

Sephadex is a commercially produced branched homopolysaccharide. It contains alpha-glycosidic linkages at carbons 2, 3, 4, and 6. The degree of cross-linking at those carbons can be controlled, yielding holes within the molecule of known size. What method can use suck a molecule?

B. Gel exclusion chromatography

Which of the following is a useful consequence of the action of a Na+/K+ ATPase in the plasma membrane? A. Depletes cells of Na+, which can be harmful B. Membrane polarization C. Draws K+ into cells, contributing to buffering capacity D. Maintain charge equilibrium across the membrane E. Promotes movement of water into cells

B. Membrane polarization

Of these 4 fatty acids, which one has the HIGHEST melting point? Why? 12:0 Lauric acid 14:0 Myristic acid 16:0 Palmitic acid 18:0 Stearic acid A. Lauric; due to a higher degree of van der Waals and hydrophobic interactions B. Stearic; due to its 18 double bonds C. Lauric; due to its 12 double bonds D. Stearic, due to a higher degree of van der Waals and hydrophobic interactions E. Myristic; due to closer packing

B. Stearic; due to its 18 double bonds

What chemical feature determines if a sugar is an aldose or a ketose? A. The direction of rotation of polarized light B. The position of the carbonyl carbon C. If the enantiomers resemble glyceraldehyde D. If the epimers differ around configuration around 1 carbon atom E. Contains one carbon or more than one carbon

B. The position of the carbonyl carbon

What chemical feature determines if a sugar is an aldose or a ketose? A. The direction of rotation of polarized light B. The position of the carbonyl carbon C. The number of chiral carbons D. If the enantiomers resemble either glyceraldehyde or dihydroxyacetone E, If the epimers differ in configuration around one carbon or more than one carbon

B. The position of the carbonyl carbon

B. Type I membrane protein, transmembrane

The DNA oligonucleotide abbreviated pATCGAC: A. has seven phosphate groups B. has a hydroxyl at its 3' end C. has a phosphate on its 3' end D. has an A at its 3' end E. violates Chargaff's rule

B. has a hydroxyl at its 3' end

anitporter

Bicarbonate transporter is an ______________

How is a ligand binding similar to the process of allosteric regulation of enzymes?

Binding of a ligand to a receptor changes the shape of the receptor, altering the ability of the receptor to transmit a signal. Binding of an allosteric regulator to an enzyme changes the shape of the enzyme, either promoting or inhibiting enzyme activity.

Explain how the cytokine erythropoetin activates transcription of specific genes essential in blood maturation.

Binding of erythropoetin to its plasma membrane receptor causes the receptor to dimerize. The soluble cytoplasmic protein kinase JAK can now bind to receptor, become activated, and phosphorylate three tyrosine residues on the receptor, some of which in turn are bound by the STAT5 transcription factor, positioning it for phosphorylation by JAK. The phosphorylated STAT5 then dimerizes, facilitating its transport into the nucleus, where it activates transcription of specific genes essential in blood maturation.

Induced-fit

Binding of glucose to hexokinase causes a conformational change in the enzyme. This is an example of the __________ model of enzyme catalysis. a. substrate-induced b. lock and key c. induced-fit d. glove and hand

undergo a nucleophilic attack

Both the substrate and the tetrahedral intermediate, when associated with chymotrypsin, a. contain an oxyanion. b. interact with the oxyanion hole. c. undergo a nucleophilic attack. d. hydrogen bond to Asp102.

How do most intracellular receptors function?

By acting as a transcription factor, the testosterone receptor itself carries out the complete transduction of the signal. Most other intracellular receptors function in the same way, although many of them, such as the thyroid hormone receptor, are already in the nucleus before the signaling molecule reaches them. Interestingly, many of these intracellular receptor proteins are structurally similar, suggesting an evolutionary kinship.

61) Which of the following provides the best evidence that cell-signaling pathways evolved early in the history of life? A) They are seen in "primitive" cells such as yeast. B) Yeast cells signal each other for mating. C) Signal transduction molecules found in distantly related organisms are similar. D) Signals can be sent long distances by cells. E) Most signals are received by cell surface receptors.

62) Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? A) Enzymatic activity was proportional to the amount of calcium added to a cell-free extract. B) Receptor studies indicated that epinephrine was a ligand. C) Glycogen breakdown was observed only when epinephrine was administered to intact cells. D) Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined. E) Epinephrine was known to have different effects on different types of cells.

63) Protein phosphorylation is commonly involved with all of the following except A) regulation of transcription by extracellular signal molecules. B) enzyme activation. C) activation of G-protein-linked receptors. D) activation of receptor tyrosine kinases. E) activation of protein kinase molecules.

66) Signal transduction pathways benefit cells for all of the following reasons except A) they help cells respond to signal molecules that are too large or too polar to cross the plasma membrane. B) they enable different cells to respond appropriately to the same signal. C) they help cells use up phosphate generated by ATP breakdown. D) they can amplify a signal. E) variations in the signal transduction pathways can enhance response specificity.

A ligand-gated ion channel (such as the nicotinic acetylcholine receptor) is: A) a charged lipid in the membrane bilayer that allows ions to pass through. B) a membrane protein that permits a ligand to pass through the membrane only when opened by the appropriate ion. C) a membrane protein that permits an ion to pass through the membrane only when opened by the appropriate ligand. D) a molecule that binds to the membrane thereby allowing ions to pass through. E) always requires a second ligand to close the channel once it is opened.

A process not involving the fusion of two membranes or two regions of the same membrane is: A) endocytosis. B) entry of enveloped viruses into cells. C) entry of glucose into cells. D) exocytosis. E) reproductive budding in yeast

An example of a glycerophospholipid that is involved in cell signaling is: A) arachidonic acid. B) ceramide. C) phosphatidylinositol. D) testosterone. E) vitamin A (retinol).

An integral membrane protein can be extracted with: A) a buffer of alkaline or acid pH. B) a chelating agent that removes divalent cations. C) a solution containing detergent. D) a solution of high ionic strength. E) hot water.

How do both major classes of G-proteins become activated? A. GTP is hydrolyzed to GDP. B. GDP is phosphorylated. C. GDP leaves the G-proteins and GTP binds. D. GDP binds after the alpha subunit dissociates from the delta and gamma subunits. E. A conformational change causes the G-protein to adhere to the inner surface of the plasma membrane.

Integrins are: A) membrane proteins that are involved in ion transport. B) membrane proteins that are involved in sugar transport. C) membrane proteins that mediate cell adhesion. D) proteins of the extracellular matrix that bind to cell surface proteins. E) proteins that are found at the membrane-cytoplasm interface.

Micelles were constructed for delivery of a hydrophobic chemotherapeutic drug. What change would increase the diameter of the micelles? A. Use liposomes instead. B. Increase the concentration of cholesterol. C. Increase the length of the acyl chains used to make them. D. Increase the concentration of polyunsaturated fatty acids. E. Use lipids with head groups having greater polarity.

Self-Quiz Questions 58) Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because A) they are species specific. B) they always lead to the same cellular response. C) they amplify the original signal manyfold. D) they counter the harmful effects of phosphatases. E) the number of molecules used is small and fixed.

The fluidity of the lipid side chains in the interior of a bilayer is generally increased by: A) a decrease in temperature. B) an increase in fatty acyl chain length. C) an increase in the number of double bonds in fatty acids. D) an increase in the percentage of phosphatidyl ethanolamine E) the binding of water to the fatty acyl side chains.

The inner (plasma) membrane of E. coli is about 75% lipid and 25% protein by weight. How many molecules of membrane lipid are there for each molecule of protein? (Assume that the average protein is Mr 50,000 and the average lipid is 750.) A) 1 B) 50 C) 200 D) 10,000 E) 50,000

What sort of carbohydrate (below) is found on glycolipids, one of the glycoconjugates? A. Peptidoglycan B. Glycosaminoglycan C. Branched heteropolysaccharide D. Glycoside E. Lectin

When a bacterium such as E. coli is shifted from a warmer growth temperature to a cooler growth temperature, it compensates by: A) increasing its metabolic rate to generate more heat. B) putting longer-chain fatty acids into its membranes. C) putting more unsaturated fatty acids into its membranes. D) shifting from aerobic to anaerobic metabolism. E) synthesizing thicker membranes to insulate the cell.

Which of the following molecules is not typically highly enriched in microdomains (membrane rafts)? A. Sphingolipids B. Cholesterol C. Lipid-linked proteins containing myristoyl and lauroyl groups on the inner-membrane leaflet D. GPI-linked proteins E. Caveolin

Which of the following would decrease the transition temperature for a mixture of triglycerides and cholesterol? A. Add glycerophospholipids with two (18:0). B. Reduce cholesterol concentration. C. Add triglycerides with two (16:1) and one (21:2) fatty acids. D. Add diacylglyerols with fully saturated fatty acids. E. Add a low concentration of a wax.

Which of these statements about the composition of membranes is true? A) All biological membranes contain cholesterol. B) Free fatty acids are major components of all membranes. C) The inner and outer membranes of mitochondria have different protein compositions. D) The lipid composition of all membranes of eukaryotic cells is essentially the same. E) The lipid:protein ratio varies from about 1:4 to 4:1

Which one of the following statements about membranes is true? A) Most plasma membranes contain more than 70% proteins. B) Sterol lipids are common in bacterial plasma membranes. C) Sterol lipids are common in human cell plasma membranes. D) Sterol lipids are common in plant cell plasma membranes. E) The plasma membranes of all cell types within a particular organism have basically the same lipid and protein composition.

Which vitamin is derived from cholesterol? A) A B) B12 C) D D) E E) K

7) The old saying "one rotten apple spoils the whole barrel" is due to chemical signaling in plants via A) an increased uptake of carbon dioxide during respiration in target cells. B) a local regulator for apple development. C) release of ethylene gas, a plant hormone for ripening. D) an a/α cell signal system in the rotten apple. E) a signal transduction pathway involving glycogen phosphorylase.

C Topic: Concept 11.1 Skill: Comprehension

10) When a cell releases a signal molecule into the environment and a number of cells in the immediate vicinity respond, this type of signaling is A) typical of hormones. B) autocrine signaling. C) paracrine signaling. D) endocrine signaling. E) synaptic signaling.

C Topic: Concept 11.1 Skill: Knowledge

18) G proteins and G-protein-linked receptors A) are found only in animal cells. B) are found only in bacterial cells. C) are thought to have evolved very early, because of their similar structure and function in a wide variety of modern organisms whose common ancestors diverged billions of years ago. D) probably evolved from an adaptation of the citric acid cycle. E) are not widespread in nature and were unimportant in the evolution of eukaryotes.

C Topic: Concept 11.2 Skill: Knowledge

44) Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of A) phosphorylated proteins. B) GTP. C) cAMP. D) adenylyl cyclase. E) activated G proteins.

C Topic: Concept 11.3 Skill: Application

34) Which of the following is the best explanation for the inability of an animal cell to reduce the Ca2+concentration in its cytosol compared with the extracellular fluid? A) blockage of the synaptic signal B) loss of transcription factors C) insufficient ATP levels in the cytoplasm D) low oxygen concentration around the cell E) low levels of protein kinase in the cell

C Topic: Concept 11.3 Skill: Comprehension

36) Which of the following is not true of cell communication systems? A) Cell signaling was an early event in the evolution of life. B) Communicating cells may be far apart or close together. C) Most signal receptors are bound to the outer membrane of the nuclear envelope. D) Protein phosphorylation is a major mechanism of signal transduction. E) In response to a signal, the cell may alter activities by changes in cytosol activity or in transcription of RNA.

C Topic: Concept 11.3 Skill: Comprehension

35) The general name for an enzyme that transfers phosphate groups from ATP to a protein is A) phosphorylase. B) phosphatase. C) protein kinase. D) ATPase. E) protease.

C Topic: Concept 11.3 Skill: Knowledge

38) Which of the following is not part of the phosphorylation cascade model? A) A signal molecule binds to a membrane receptor protein. B) Protein kinase is activated. C) GTP donates a phosphate group to an inactive protein kinase. D) A specific protein is activated via phosphorylation. E) A cellular response is initiated.

C Topic: Concept 11.3 Skill: Knowledge

43) Adenylyl cyclase has the opposite effect of which of the following? A) protein kinase B) protein phosphatase C) phosphodiesterase D) phosphorylase E) GTPase

C Topic: Concept 11.3 Skill: Knowledge

50) A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following? A) lower cytoplasmic levels of cAMP B) an increase in receptor tyrosine kinase activity C) a decrease in transcriptional activity of certain genes D) an increase in cytosolic calcium concentration E) a decrease in G-protein activity

C Topic: Concept 11.4 Skill: Application

Which O-glycosidic bond is commonly found in amylose, amylopectin and glycogen? A) (Beta 1 --> 4) B) (Alpha 1 --> 6) C) (Alpha 1 --> 4) D) (Beta 1 --> 6) E) (Alpha 1 --> 3)

C) (Alpha 1 --> 4)

The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics: V0 Substrate added (μmol/min) (mmol/L) ————————————— 217 0.8 325 2 433 4 488 6 647 1,000 ————————————— The Km for this enzyme is approximately: A) 1 mM. B) 1,000 mM. C) 2 mM. D) 4 mM. E) 6 mM.

C) 2 mM.

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 μmol. 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 μmol) of product to be formed? A) 1.5 min B) 13.5 min C) 27 min D) 3 min E) 6 min

C) 27 min

Which of the following would DECREASE the transition temperature for a mixture of triglycerides and cholesterol?

C) Add triglycerides with two(16:1) and one (21:2) fatty acids.

Nuclear magnetic resonance spectroscopy was performed on a derivative of cortisol, a steroid hormone. What structural feature was NOT observed in this molecule that would be present in sterols? A) Four six-membered rings in the nucleus rather than three. B) A carbonyl rather than a hydroxyl on the A-ring. C) An alykyl chain on the D-ring. D) Characteristic alcohol groups on each of the four rings. E) An absence of polar groups.

C) An alykyl chain on the D-ring.

Which of the following statements about starch and glycogen is false? A) Amylose is unbranched; amylopectin and glycogen contain many (alpha1--> 6) branches. B) Both are homopolymers of glucose. C) Both serve primarily as structural elements in cell walls. D) Both starch and glycogen are stored intracellularly as insoluble granules. E) Glycogen is more extensively branched than starch.

C) Both serve primarily as structural elements in cell walls.

Which of the following statements about starch and glycogen is false? A) Amylose is unbranched; amylopectin and glycogen contain many (α1 → 6) branches. B) Both are homopolymers of glucose. C) Both serve primarily as structural elements in cell walls. D) Both starch and glycogen are stored intracellularly as insoluble granules. E) Glycogen is more extensively branched than starch.

C) Both serve primarily as structural elements in cell walls.

What sort of carbohydrate (below) is found on glycolipids, one of the glycoconjugates? A) Peptidoglycan B) Glycosaminoglycan C) Branched heteropolysaccharide D) Glycoside E) Lectin

C) Branched heteropolysaccharide

Which of the following is not involved in signal transduction by the β-adrenergic receptor pathway? A) ATP B) Cyclic AMP C) Cyclic GMP D) GTP E) All of the above are involved.

C) Cyclic GMP

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.

C) For S → P, a catalyst shifts the reaction equilibrium to the right

Which of the following does not involve cyclic AMP? A) Regulation of glycogen synthesis and breakdown B) Regulation of glycolysis C) Signaling by acetylcholine D) Signaling by epinephrine E) Signaling by glucagon

C) Signaling by acetylcholine

C) Sterol lipids are common in human cell plasma membranes.

Which of the following statements concerning the tautomeric forms of bases such as uracil is correct? A) The all-lactim form contains a ketone group. B) The lactam form contains an alcohol group. C) The lactam form predominates at neutral pH. D) They are geometric isomers. E) They are stereoisomers.

C) The lactam form predominates at neutral pH.

A graduate student carefully heated DNA to about 80 C and then prepared it for electron microscopy. She observed a number of small open loops of DNA. What conclusion did she correctly make from her observation?

C) The open loops contain DNA with high A-T content

Which of the following is not true of all naturally occurring DNA? A) Deoxyribose units are connected by 3',5'-phosphodiester bonds. B) The amount of A always equals the amount of T. C) The ratio A+T/G+C is constant for all natural DNAs. D) The two complementary strands are antiparallel. E) Two hydrogen bonds form between A and T.

C) The ratio A+T/G+C is constant for all natural DNAs.

Which of the following could NOT be part of a reversible enzyme inhibition mechanism? A) An enzyme that performs metal ion catalysis B) The release of a cofactor C) The release of a prosthetic group D) Protonation of amino acid side chains by a single slight change in pH E) Binding of a small molecule to the active site using hydrogen bonds

C) The release of a prosthetic group

Allosteric enzymes:

C) Usually have more than one polypeptide chain

Protein kinase A (PKA) is: A) activated by covalent binding of cyclic AMP. B) affected by cyclic AMP only under unusual circumstances. C) allosterically activated by cyclic AMP. D) competitively inhibited by cyclic AMP. E) noncompetitively inhibited by cyclic AMP.

C) allosterically activated by cyclic AMP.

To possess optical activity, a compound must be: A) a carbohydrate. B) a hexose. C) asymmetric. D) colored. E) D-glucose.

C) asymmetric.

To possess optical activity, a compound must be: A) a carbohydrate. B) a hexose. C) asymmetric. D) colored. E) D-glucose.

C) asymmetric.

To possess optical activity, a compound must be: A) a carbohydrate. B) a hexose. C) asymmetric. D) colored. E) D-glucose.

C) asymmetric.

Double-stranded regions of RNA: A) are less stable than double-stranded regions of DNA. B) can be observed in the laboratory, but probably have no biological relevance. C) can form between two self-complementary regions of the same single strand of RNA. D) do not occur. E) have the two strands arranged in parallel (unlike those of DNA, which are antiparallel).

C) can form between two self-complementary regions of the same single strand of RNA.

Guanyl cyclase receptor enzymes: A) are all membrane-spanning proteins. B) are examples of ligand-gated ion channels. C) catalyze synthesis of a phosphate ester. D) catalyze synthesis of a phosphoric acid anhydride. E) require hydrolysis of ATP in addition to GTP

C) catalyze synthesis of a phosphate ester.

Which of the following monosaccharides is not a carboxylic acid? A) 6-phospho-gluconate B) gluconate C) glucose D) glucuronate E) muramic acid

C) glucose

Which of the following monosaccharides is not a carboxylic acid? A) 6-phospho-gluconate B) gluconate C) glucose D) glucuronate E) muramic acid

C) glucose

Which of the following monosaccharides is not a carboxylic acid? A) 6-phospho-gluconate B) gluconate C) glucose D) glucuronate E) muramic acid

C) glucose

Hemoglobin glycation is a process where_______ is _________ attached to hemoglobin. A) glycerol; covalently B) glucose; enzymatically C) glucose; non-enzymatically D) N-acetyl-galactosamine; enzymatically E) galactose; non-enzymatically

C) glucose; non-enzymatically

The reference compound for naming D and L isomers of sugars is: A) fructose. B) glucose. C) glyceraldehyde. D) ribose. E) sucrose.

C) glyceraldehyde.

The reference compound for naming D and L isomers of sugars is: A) fructose. B) glucose. C) glyceraldehyde. D) ribose. E) sucrose.

C) glyceraldehyde.

The reference compound for naming D and L isomers of sugars is: A) fructose. B) glucose. C) glyceraldehyde. D) ribose. E) sucrose

C) glyceraldehyde.

When the linear form of glucose cyclizes, the product is a(n): A) anhydride. B) glycoside. C) hemiacetal. D) lactone. E) oligosaccharide.

C) hemiacetal.

When the linear form of glucose cyclizes, the product is a(n): A) anhydride. B) glycoside. C) hemiacetal. D) lactone. E) oligosaccharide.

C) hemiacetal.

When the linear form of glucose cyclizes, the product is a(n): A) anhydride. B) glycoside. C) hemiacetal. D) lactone. E) oligosaccharide.

C) hemiacetal.

The effects of acetylcholine on the postsynaptic ion channel are mainly due to: A) cyclic nucleotide synthesis. B) protein cleavage (proteolysis). C) protein conformational changes. D) protein phosphorylation. E) protein synthesis.

C) protein conformational changes.

A transition-state analog: A) is less stable when binding to an enzyme than the normal substrate. B) resembles the active site of general acid-base enzymes. C) resembles the transition-state structure of the normal enzyme-substrate complex. D) stabilizes the transition state for the normal enzyme-substrate complex. E) typically reacts more rapidly with an enzyme than the normal substrate.

C) resembles the transition-state structure of the normal enzyme-substrate complex.

In nucleotides and nucleic acids, syn and anti conformations relate to: A) base stereoisomers. B) rotation around the phosphodiester bond. C) rotation around the sugar-base bond. D) sugar pucker. E) sugar stereoisomers.

C) rotation around the sugar-base bond

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.

C) the ES complex is formed and broken down at equivalent rates.

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) the dissociation constant, Kd, for the ES complex.

Which of the following is true of sphingolipids? A. Phosphatidylcholine is a typical sphingolipid B. They always contain glycerin and fatty acids C. Gangliosides are sphingolipids D. They contain two esterified fatty acids

C. Gangliosides are sphingolipids

C. Increase the length of the acyl chains used to make them.

Which ONE of the following statements is true? A. When ∆G > 0, a reaction is spontaneous B. When ∆G > 0, a reaction will proceed forward, toward products C. When ∆G < 0, a reaction is exergonic D. When ∆G < 0, a reaction is at equilibrium E. Creating bonds requires absorptions of energy by the system (∆H > 0)

C. When ∆G < 0, a reaction is exergonic

The reference compound for naming D and L isomers of sugars is: A.fructose B. glucose C. glyceraldehyde D. ribose E. sucrose

C. glyceraldehyde

Receptor Guanylyl Cyclase (def.)

Catalytic domain that converts GTP to cGMP works thru activation of protein kinase G guanylin receptor is also target of bacteria endotoxin that causes diarrhea

FAST

Cell membranes are permeable to small nonpolar molecules that passively diffuse through the membrane -(FAST/SLOW)

What type of sterol is present in human myelin sheet?

Cholesterol

What type of sterol is present in the mouse liver?

Cholesterol

ANS: forming hydrogen bonds with the oxyanion.

Complete the following statement: The NH groups of Ser195 and Gly193 in chymotrypsin are able to stabilize the intermediate of the reaction by

ANS: By considering the reaction at an early time, when the velocity is the initial velocity (v0), no appreciable product has been generated. Therefore the back reaction, where ES forms from EP with a rate constant k−2, is negligible.

Connect the use of v0 to the ability to treat k−2 as negligible in Michaelis-Menten kinetics.

What are cyclins? What is their role in the regulation of the cell cycle?

Cyclins are regulatory subunits of protein kinases. Cyclin subunits are essential for activation of protein kinase activity. Cyclin levels fluctuate during the cell cycle in response to cellular & extracellular signals. These changes result in changes to activities of cyclin-dependent protein kinases that regulate and control the cell cycle.

59) Binding of a signal molecule to which type of receptor leads directly to a change in the distribution of anions and/or cations on opposite sides of the membrane? A) receptor tyrosine kinase B) G-protein-linked receptor C) phosphorylated receptor tyrosine kinase dimer D) ligand-gated ion channel E) intracellular receptor

According to the current model for HIV infection, which of the following is not involved in the process of membrane fusion? A) A cell surface co-receptor protein B) A cell surface receptor protein C) A viral glycoprotein complex D) The viral chromosome E) The viral envelope

Consider the transport of K+ from the blood (where its concentration is about 4 mM) into an erythrocyte that contains 150 mM K+. The transmembrane potential is about 60 mV, inside negative relative to outside. The free-energy change for this transport process is: (These values may be of use to you: R = 8.315 J/mol.K; T = 298 K; 9 (Faraday constant) = 96,480 J/V; N = 6.022 1023/mol.) A) about 5 J/mol. B) about 15 J/mol. C) about 5 kJ/mol. D) about 15 kJ/mol. E) impossible to calculate with the information given.

G-proteins were initially named because they were found to be GTP-binding proteins, yet they have an active site. What is the enzymatic reaction mechanism? A. Phosphorylation of GDP B. Reduction of GDP C. Formation of a covalent bond between GDP and the alpha subunit D. Hydroylsis of GTP E. G-proteins have no enzyme active site.

Glucose transport into erythrocytes is an example of: A) active transport. B) antiport. C) electrogenic uniport D) facilitated diffusion. E) symport.

How do the features of Vitamins E and K cause them to be in a different cellular location than Vitamins B and C? A. Their mass is too large to move through membrane transporters, unlike Vitamins B and C. B. They are synthesized in endoplasmic reticulum, unlike Vitamins B and C, which are made in cytosol. C. They have receptors on the plasma membrane, whereas Vitamins B and C have nuclear receptors. D. They are hydrophobic, so they are located in membranes rather than in the cytosol, like Vitamins B and C. E. They are negatively charged, and are segregated in the plasma membrane rather than neutral as Vitamins B and C, which are found in many cellular locations

Membrane fusion leading to neurotransmitter release requires the action of: A) cadherins. B) selectins. C) flipases. D) tSNARE and vSNARE. E) none of the above.

The fluidity of a lipid bilayer will be increased by: F) decreasing the number of unsaturated fatty acids. C) decreasing the temperature. G) increasing the length of the alkyl chains. D) increasing the temperature. E) substituting 18:0 (stearic acid) in place of 18:2 (linoleic acid).

The type of membrane transport that uses ion gradients as the energy source is: A) facilitated diffusion B) passive transport. C) primary active transport. D) secondary active transport. E) simple diffusion.

What can be learned from a hydropathy plot of caveolin? A. The protein may have several alpha-helices and at least one beta-strand. B. There is a calcium-binding domain. C. There are three polypeptides in the functional protein. D. The prediction of two membrane-spanning regions. E. It is positively charged at neutral pH.

What would be learned from a Scatchard analysis of cells that were incubated with various concentrations of human growth hormone? A. The hormone stimulated activation of heterotrimeric G-proteins. B. The average number of receptors per cell. C. Receptor number on the membrane increases with increasing hormone concentration. D. The affinity was high. E. Growth hormone increases the expression of new proteins.

Which of the following contains an ether-linked alkyl group? A) Cerebrosides B) Gangliosides C) Phosphatidyl serine D) Platelet-activating factor E) Sphingomyelin

Which of the following elements would likely be found in a protein functioning in signaling through a receptor tyrosine kinase? A. A covalent lipid-link to the membrane B. Beta-barrel motif C. Calcium-binding domain D. SH2 domain E. Transmembrane domain

Which of the following statements about membrane lipids is true? A) Glycerophospholipids are found only in the membranes of plant cells. B) Glycerophospholipids contain fatty acids linked to glycerol through amide bonds. C) Lecithin (phosphatidylcholine), which is used as an emulsifier in margarine and chocolate, is a sphingolipid. D) Some sphingolipids include oligosaccharides in their structure. E) Triacylglycerols are the principal components of erythrocyte membranes.

4) What could happen to the target cells in an animal that lack receptors for local regulators? A) They could compensate by receiving nutrients via an a factor. B) They could develop normally in response to neurotransmitters instead. C) They could divide but never reach full size. D) They would not be able to multiply in response to growth factors from nearby cells. E) Hormones would not be able to interact with target cells.

D Topic: Concept 11.1 Skill: Comprehension

15) Most signal molecules A) bind to specific sites on receptor proteins in a membrane. B) are water-soluble. C) are able to pass through the plasma membrane by active transport. D) A and B only E) A, B, and C

D Topic: Concept 11.2 Skill: Comprehension

19) The ability of a single ligand bound to a receptor protein to trigger several pathways is A) characteristic of the synaptic signal system. B) unique to the yeast mating system. C) rare in animals, but common in bacteria. D) a key difference between the tyrosine-kinase and G-protein-linked receptor systems. E) common to all plasma membrane receptor proteins.