BIOCHEM - Ch7

Kinases usually transfer phosphates from A. ATP. B. inorganic phosphate. C. NADP+/NADPH. D. amino acids.

A. ATP.

The vitamin biotin is involved in this type of reaction: A. Carboxylation reactions B. Decarboxylation reactions C. Redox reactions D. Acyl transfer reactions E. Transamination reactions

A. Carboxylation reactions

The vitamin pantothenic acid is involved in this type of reaction: A. Carboxylation reactions B. Decarboxylation reactions C. Redox reactions D. Acyl transfer reactions E. Transamination reactions

A. Carboxylation reactions

Which of the following is true? A. Caspases are a class of proteases B. Caspases are involved in apoptosis C. Caspases are initially produced as inactive procaspases D. all of these

A. Caspases are a class of proteases

The sequential model for allosteric enzymes was proposed by: A. Koshland B. Pauling C. Pasteur D. Monod, Wyman and Changeux E. All of these

A. Koshland

Redox reactions often use this cofactor: A. Riboflavin B. Lipoic acid C. Pyridoxal D. Thiamine E. Biotin

A. Riboflavin

What happens when a K-acting inhibitor is added to an allosteric enzyme system? A. The apparent KM for the substrate increases. B. The apparent KM for the substrate decreases. C. The apparent Vmax for the substrate increases. D. The apparent Vmax for the substrate decreases.

A. The apparent KM for the substrate increases.

Where do allosteric inhibitors bind on an enzyme? A. They always bind at a site different from the active site. B. They always bind at the active site. C. They can bind at either active site or another site.

A. They always bind at a site different from the active site.

Which of the following is not true about B vitamins? A. They are usually fully active in the form we eat them B. They are usually water soluble C. Niacin and riboflavin are examples D. They are important in many metabolic reactions

A. They are usually fully active in the form we eat them

Enzyme kinetics falls into two general categories, simple saturation and cooperative kinetics. A. True B. False

A. True

Inhibitors which bind covalently to specific amino acids are useful in determining which amino acids are in the active site of an enzyme. A. True B. False

A. True

The term K0.5 is analogous to the KM A. True B. False

A. True

The critical serine residue in the active site of chymotrypsin functions as A. a nucleophile. B. an electrophile. C. a base. D. a methyl donor.

A. a nucleophile.

Labeling the amino acid residues in the active site of an enzyme requires A. a reagent structurally similar to the substrate. B. a highly polar reagent. C. a reagent that contains an aromatic group. D. a reagent that contains a halogen atom.

A. a reagent structurally similar to the substrate.

Kinase reactions describe enzymes which A. add phosphate groups to another molecule. B. oxidize alcohols to aldehydes. C. use NAD+/NADH in their reactions. D. transfer groups from one part of a molecule to another. E. add or remove double bonds in molecules.

A. add phosphate groups to another molecule.

In the concerted model the most active enzyme form will be when A. all subunits are in the R state. B. all subunits are in the T state. C. there is a 50:50 mix of R & T states.

A. all subunits are in the R state.

ATP is a negative allosteric effector for glycogen phosporylase. This is an example of A. feedback inhibition. B. positive cooperativity. C. negative cooperativity. D. competitive inhibition.

A. feedback inhibition.

Zymogens are A. inactive precursors of enzymes which can be activated by the irreversible cleavage of covalent bonds. B. inactive forms of enzymes which require phosphorylation by a kinase to become active. C. allosteric enzymes that are always in the R state. D. allosteric enzymes that are always in the T state.

A. inactive precursors of enzymes which can be activated by the irreversible cleavage of covalent bonds.

A transition-state analog is likely to bind to an enzyme A. more tightly than the substrate. B. less tightly than the substrate. C. about as tightly as the substrate. D. at a site other than the catalytic site.

A. more tightly than the substrate.

Cofactors are A. non-protein in chemical nature. B. always small proteins. C. modified amino acids. D. never required for enzymatic activity.

A. non-protein in chemical nature.

The initial bond formation in the covalent intermediate in the reaction catalyzed by chymotrypsin is between A. serine and the carbonyl carbon in the peptide backbone B. serine and the nitrogen in the peptide backbone C. histidine and the carbonyl carbon in the peptide backbone D. histidine and the nitrogen in the peptide backbone

A. serine and the carbonyl carbon in the peptide backbone

The main distinguishing feature of the concerted model for the behavior of allosteric enzymes is that A. the conformation of all subunits changes simultaneously. B. it applies only to dimeric enzymes. C. it involves three possible conformations for all subunits. D. the T and R conformations exist in roughly equal amounts.

A. the conformation of all subunits changes simultaneously.

In the concerted model for allosteric enzymes A. the relative affinities of substrate for the T and R conformations plays an important role in the cooperativity of the reaction. B. the equilibrium between the T and R conformations plays a minor role. C. the enzymatic activity of the T conformation is considerably higher than that of the R form. D. it is possible to describe the reactions of all allosteric enzymes accurately.

A. the relative affinities of substrate for the T and R conformations plays an important role in the cooperativity of the reaction.

In the concerted model, which state binds the substrate more tightly? A. the relaxed (R) state B. the taut (T) state C. Both states bind equally well.

A. the relaxed (R) state

Homotrophic effects for allosteric enzymes involve A. the same molecule binding to different sites in the enzyme. B. different molecules binding to the same site in an enzyme. C. different molecules binding to different sites in the same enzyme. D. All of these are homotrophic effects.

A. the same molecule binding to different sites in the enzyme.

The active site of chymotrypsin contains all of the following, except: A. Histidine residue. B. A magnesium ion. C. Hydrophobic pocket to bind the substrate. D. Serine residue. E. All of these are in the active site of chymotrypsin.

B. A magnesium ion.

Which of the following is not required in order for an enzyme to display cooperative kinetics? A. Multiple subunits. B. A value for the Michaelis constant, KM. C. Allosteric sites which affect the binding of substrate to the active site. D. Ability to display a Vmax. E. All of these are characteristic of cooperative enzymes.

B. A value for the Michaelis constant, KM.

How do each of these compounds affect the function of ATCase? A. ATP inhibits and CTP activates B. ATP activates and CTP inhibits C. Both ATP and CTP inhibit D. Both ATP and CTP activate

B. ATP activates and CTP inhibits

The amino acids in the active site can be involved in all of these processes, except: A. Binding of the substrate. B. Becoming part of the product of the reaction. C. The actual chemical mechanism for the reaction. D. Binding of some necessary cofactor for the reaction. E. All of these can be functions of the amino acids in the active site

B. Becoming part of the product of the reaction.

Which of the following best describes negative cooperativity? A. Binding of one substrate molecule prevents the enzyme from working at all. B. Binding of one substrate molecule inhibits the binding of a second substrate. C. Binding of one substrate molecule enhances the binding of a second substrate. D. Binding of one substrate molecule inhibits the binding of other effectors.

B. Binding of one substrate molecule inhibits the binding of a second substrate.

B vitamins are often stored in the body. A. True B. False

B. False

Generally speaking, enzymes involved in pathways which generate ATP will be activated by addition of phosphate groups to the enzyme. A. True B. False

B. False

The saturation curve for aspartyl transcarbamylase has a similar shape to the curve for: A. Myoglobin B. Hemoglobin C. Chymotrypsin D. Both hemoglobin and chymotrypsin. E. All of these.

B. Hemoglobin

Acyl transfer reactions often use this cofactor: A. Riboflavin B. Lipoic acid C. Pyridoxal D. Thiamine E. Biotin

B. Lipoic acid

Is the Michaelis-Menten equation useful when studying allosteric enzymes? A. Yes B. No C. Only if the enzyme displays positive cooperativity. D. Only if the enzyme displays negative cooperativity.

B. No

A velocity curve (V vs. [S]) for a typical allosteric enzyme will be A. a rectangular hyperbola. B. a sigmoid curve. C. a straight line. D. a parabola.

B. a sigmoid curve.

Pyridoxal phosphate is required for transfer of A. one-carbon groups B. amino groups C. acyl groups D. aldehyde groups

B. amino groups

Abzymes A. invariably bind to pyridoxal phosphate. B. are antibodies with catalytic activity. C. differ markedly from transition states in enzymatic reactions. D. have proline as part of their structure.

B. are antibodies with catalytic activity.

According to the concerted model of allosteric behavior, an allosteric activator A. favors the taut (tight) form of the enzyme. B. favors the relaxed form of the enzyme. C. can only bind to the enzyme if the substrate is already bound. D. can only bind to the enzyme if the substrate has not already bound.

B. favors the relaxed form of the enzyme.

CTP is a known inhibitor of ATCase, the enzyme that catalyzes the first reaction in the pathway for the synthesis of this compound. This is an example of A. irreversible inhibition B. feedback inhibition C. zymogenic inhibition D. negative cooperativity

B. feedback inhibition

In a comparison of allosteric and non-allosteric enzymes A. it is always possible to define a KM B. it is always possible to define a Vmax C. competitive inhibition is always a possibility D. much of the terminology is completely unchanged

B. it is always possible to define a Vmax

The sequential model for allosteric behavior A. cannot account for reactions that display negative cooperativity. B. postulates binding of substrates and inhibitors by the induced-fit model. C. requires that the conformation of all subunits change simultaneously. D. is mathematically simpler than the concerted model.

B. postulates binding of substrates and inhibitors by the induced-fit model.

Metal ions play an important role in reaction mechanisms because A. they block the active site of enzymes so that inhibitors cannot bind. B. they can act as Lewis acids. C. water is excluded from the active site when metal ions are bound. D. they prevent protein aggregation.

B. they can act as Lewis acids.

Allosteric effectors A. typically bind to the enzyme's active site. B. typically bind at a site unique from the active site. C. bind to the substrate rather than the enzyme. D. only bind to the enzyme-substrate complex.

B. typically bind at a site unique from the active site.

How do each of these compounds affect the function of ATCase? A. ATP is a K effector and CTP is a V effector. B. ATP V effector and CTP K effector. C. Both ATP and CTP are K effectors. D. Both ATP and CTP are V effectors.

C. Both ATP and CTP are K effectors.

Which of the following is not a difference between the concerted model and the sequential model of allosteric enzymes? A. The sequential model allows for different subunits to be in different conformations while the concerted model does not B. Negative cooperativity can be explained by the sequential model but not by the concerted model C. Positive cooperativity can be explained by the sequential model but not by the concerted model D. The sequential model is explained better by considering the induced-fit model of substrate binding, whereas the concerted model focuses on perturbing the equilibrium between the T and R forms.

C. Positive cooperativity can be explained by the sequential model but not by the concerted model

Which of the following is true? A. Phosphorylation always increases enzyme activity B. Kinases often use AMP as a co-substrate in their phosphorylation reactions C. Some enzymes are activated by phosphorylation while others are inhibited D. ADP is the most common substrate for a kinase reaction

C. Some enzymes are activated by phosphorylation while others are inhibited

Which of the following does not apply to the concerted model for subunit behavior: A. Each subunit can exist in a relaxed (R) and taut (T) conformation. B. All subunits will be in either the R or the T conformation at the same time. C. Some subunits can be in the R state while others are in the T state.

C. Some subunits can be in the R state while others are in the T state.

The pH profile of an enzyme can help identify specific amino acids in the active site because: A. all enzymes have a pH optimum B. only the active site amino acids can detect changes in pH C. acidic and basic amino acids are often involved in the active site and pH changes can change their ability to catalyze a reaction D. the pH optimum is always the pI of the most critical amino acid in the active site

C. acidic and basic amino acids are often involved in the active site and pH changes can change their ability to catalyze a reaction

Which of the following is unlikely to occur in binding of a substrate to an enzyme? A. stereospecific interactions. B. hydrogen bonding. C. adsorption to surfaces of metallic catalysts. D. interactions with metal-ions.

C. adsorption to surfaces of metallic catalysts.

In zymogen activation A. only digestive enzymes are involved. B. a conformational change takes place with no alteration of primary structure. C. an inactive protein is converted to an active one by bond cleavage. D. there is aggregation of several enzyme molecules when the substrate binds.

C. an inactive protein is converted to an active one by bond cleavage.

An important step in elucidating the behavior of an enzyme is A. obtaining a crystalline sample of the enzyme. B. insuring that metal ions are always excluded from the enzyme sample. C. determining the active site residues. D. none of these

C. determining the active site residues

How are cofactors bound to their enzymes? A. always covalently B. always non-covalently C. either covalently or non-covalently

C. either covalently or non-covalently

In the concerted model the binding of the first substrate molecule will achieve all except A. facilitation of the binding of other substrate molecules. B. facilitation of the conversion of other subunits to the active state. C. facilitation of the binding of inhibitors to the enzyme. D. All of these are facilitated by the binding of the first substrate molecule. E. None of these answers is correct.

C. facilitation of the binding of inhibitors to the enzyme.

Which of the following amino acid side chains would best serve as a general acid, assuming the protein functions at a pH of 7? A. alanine B. aspartic acid C. lysine D. asparagine

C. lysine

The concerted and sequential models for the behavior of allosteric enzymes differ in A. the conformational change in the enzyme in one model and not in the other. B. the number of predicted binding sites on the enzyme. C. the manner in which changes in quaternary structure take place. D. the response of the enzyme to changes in temperature.

C. the manner in which changes in quaternary structure take place.

In reactions catalyzed by allosteric enzymes A. substrate, activators, and inhibitors all compete for the same binding site on the enzyme. B. there is no distinction between catalytic and regulatory subunits. C. the presence of an activator makes the plot of reaction rate against substrate concentration less cooperative. D. the presence of an inhibitor makes the plot of reaction rate against substrate concentration less cooperative.

C. the presence of an activator makes the plot of reaction rate against substrate concentration less cooperative.

Phosphorylation of enzymes A. has no effect on their catalytic activity. B. does not require ATP. C. usually takes place on serine, threonine, and tyrosine residues. D. is not easily characterized.

C. usually takes place on serine, threonine, and tyrosine residues.

Which of the following can function as coenzymes? A. lead ion, biotin, and lipoic acid. B. copper ion, p-hydroxymercuribenzoate, diisopropylphophofluoridate. C. zinc ion, pyridoxal phosphate, and nicotinamide adenine nucleotides. D. lead ion, p-hydroxymercuribenzoate, diisopropylphophofluoridate.

C. zinc ion, pyridoxal phosphate, and nicotinamide adenine nucleotides.

The concerted model for allosteric behavior was proposed by: A. Koshland B. Pauling C. Pasteur D. Monod, Wyman and Changeux E. All of these

D. Monod, Wyman and Changeux

Which of the following types of amino acids active is least likely to be involved in enzyme catalysis? A. Those with hydrophilic, neutral side-chains. B. Those with negatively charged side-chains. C. Those with positively charge side-chains. D. Those with hydrocarbon side-chains.

D. Those with hydrocarbon side-chains.

Nicotinamide adenine dinucleotide is A. an enzyme inhibitor used in smoking cessation programs. B. an inhibitor of ATP production. C. a coenzyme in reactions that transfer acyl groups. D. a coenzyme in oxidation-reduction reactions.

D. a coenzyme in oxidation-reduction reactions.

The serine in the active site of chymotrypsin functions as A. a Lewis acid. B. a metal ion. C. an electrophile. D. a nucleophile.

D. a nucleophile.

Allosteric enzymes must exhibit which of the following? A. feedback inhibition B. a phosphorylation site C. general acid-base catalysis D. a quaternary structure

D. a quaternary structure

Enzymes that catalyze similar functions will invariably have A. similar overall structures. B. serine in their active sites. C. histidine in their active sites. D. active sites that can catalyze the reactions in question.

D. active sites that can catalyze the reactions in question.

Important mechanisms of enzymatic catalysis include A. nucleophilic reactions B. general acid-base catalysis C. Lewis acid-base catalysis D. all of these

D. all of these

Which of the following enzymes is not a serine protease? A. trypsin B. chymotrypsin C. thrombin D. aspartyl transcarbamylase (ATCase)

D. aspartyl transcarbamylase (ATCase)

Phosphorylation and allosteric control of enzymes. A. are not involved in reactions of carbohydrates. B. play an insignificant role in generating energy. C. are important processes in prokaryotes, but not in eukaryotes. D. can be combined to afford a high degree of control over enzymatic reactions.

D. can be combined to afford a high degree of control over enzymatic reactions.

The behavior of allosteric enzymes A. does not play any role in feedback inhibition in metabolic pathways B. is strongly dependent on the presence of metal ions C. is related to their ability to hydrolyze themselves D. depends on changes in their quaternary structure on binding of substrates or inhibitors

D. depends on changes in their quaternary structure on binding of substrates or inhibitors

Which of the following is true A. Allosteric enzymes are rarely important in the regulation of metabolic pathways. B. Michaelis-Menten kinetics describe the reactions of allosteric enzymes C. Allosteric enzymes have a hyperbolic plot of reaction rate vs. substrate concentration D. none of these is true

D. none of these is true

Which groups of amino acids are likely to be found in the active site of an enzyme? A. leucine, lysine, alanine. B. cysteine, isoleucine, phenylalanine. C. tyrosine, threonine, leucine. D. serine, histidine, aspartate.

D. serine, histidine, aspartate.

Which of the following is a mechanism of regulating enzyme activity? A. Feedback inhibition by product. B. Addition or removal of phosphate groups from of the enzyme. C. Presence of activators. D. Activation of zymogens. E. All of these regulate enzyme activity.

E. All of these regulate enzyme activity.

Which of the following statements about coenzymes is true? A. They are commonly derived from vitamins. B. They bind to the active site region on specific types of enzymes. C. They can be metal ions, such as Zn(II). D. NAD+, FAD and biotin are all examples of coenzymes. E. All of these statements are true.

E. All of these statements are true.