Enzyme Flashcards by Mind Med

The active site of an enzyme is best described as:
A. A rigid, inflexible structure that never changes
B. The region that most directly lowers the activation energy for the reaction
C. The allosteric site on the enzyme
D. The substrate recognition site only

B. The region that most directly lowers the activation energy for the reaction

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Which model currently best explains enzyme-substrate binding?
A. Lock-and-key
B. Induced fit
C. Hand-in-glove
D. Random collision

B. Induced fit

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An example of enzyme specificity highlighted in glucokinase action is:
A. Glucokinase using galactose equally well as glucose
B. Glucokinase phosphorylating only glucose using ATP
C. Glucokinase acting only in acidic conditions
D. Glucokinase being inactivated by glucose

B. Glucokinase phosphorylating only glucose using ATP

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A reaction intermediate lying at the highest energy point with tightest binding to the enzyme is called:
A. Enzyme-product complex
B. Active site
C. Transition-state complex
D. Substrate complex

C. Transition-state complex

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Enzymes accelerate reaction rates by:
A. Changing the net free energy (ΔG) of a reaction
B. Increasing the temperature of the cell
C. Decreasing the activation energy required to reach the transition-state complex
D. Converting all substrate to product

C. Decreasing the activation energy required to reach the transition-state complex

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Which of the following catalysis strategies involves movement of protons?
A. Acid-base catalysis
B. Metal ion catalysis
C. Catalysis by approximation
D. Hydrophobic catalysis

A. Acid-base catalysis

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The functional group in chymotrypsin that acts as a general base catalyst is:
A. Serine
B. Cysteine
C. Histidine
D. Tyrosine

C. Histidine

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Which cofactor forms a covalent bond during catalysis and is often derived from vitamins?
A. NAD+
B. Pyridoxal phosphate (PLP)
C. Iron
D. Calcium

B. Pyridoxal phosphate (PLP)

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The vitamin precursor for coenzyme A (CoA) is:
A. Niacin
B. Pyridoxine
C. Pantothenate
D. Biotin

C. Pantothenate

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A holoenzyme is:
A. The protein part only
B. The small molecule cofactor alone
C. The catalytically active enzyme with all required cofactors/prosthetic groups
D. An inactive enzyme

C. The catalytically active enzyme with all required

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Which statement about reaction energetics is TRUE?
A. Enzymes make nonspontaneous reactions favorable
B. Enzymes can only accelerate exergonic reactions
C. Enzymes decrease the activation energy but not the net ΔG
D. Enzymes are consumed in reactions

C. Enzymes decrease the activation energy but not the net ΔG

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Non-covalently bound cofactors that can be removed from an enzyme are:
A. Prosthetic groups
B. Metal ions
C. Coenzymes
D. Allosteric effectors

C. Coenzymes

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The major role of metal ions in enzyme catalysis is to:
A. Denature the substrate
B. Stabilize developing anions and help bind substrate
C. Hydrolyze proteins
D. Provide kinetic energy

B. Stabilize developing anions and help bind substrate

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In the context of enzyme catalysis, biotin is unique because it:
A. Contains phosphate
B. Functions only in carboxylation reactions and is covalently bound to lysine
C. Participates in oxidation-reduction
D. Is synthesized from pantothenate

B. Functions only in carboxylation reactions and is covalently bound to lysine

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Which enzyme class catalyzes transfer of functional groups other than hydrogen?
A. Oxidoreductases
B. Transferases
C. Ligases
D. Lyases

B. Transferases

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The enzyme that converts L-lactate to pyruvate is a:
A. Hydrolase
B. Oxidoreductase
C. Lyase
D. Ligase

B. Oxidoreductase

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All of the following are activation-transfer coenzymes EXCEPT:
A. Thiamine pyrophosphate (TPP)
B. Pyridoxal phosphate (PLP)
C. NAD+
D. Coenzyme A

C. NAD+

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Which characteristic distinguishes oxidation-reduction coenzymes from activation-transfer coenzymes?
A. They are always prosthetic groups
B. They DO NOT form covalent bonds with the substrate
C. They do not require vitamin precursors
D. Only present in eukaryotic enzymes

B. They DO NOT form covalent bonds with the substrate

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A suicide inhibitor is best described as:
A. An allosteric effector that modulates enzyme activity reversibly
B. Undergoes partial reaction and forms an irreversible covalent bond at the active site
C. A reversible competitive inhibitor
D. A non-protein cofactor

B. Undergoes partial reaction and forms an irreversible covalent bond at the active site

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Which heavy metal inhibits enzymes by replacing essential metals and binding at sulfhydryl groups?
A. Iron
B. Lead
C. Sodium
D. Copper

B. Lead

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Organophosphate poisoning (e.g., malathion) clinically presents with which mechanistic enzyme effect?

A. Increased degradation of acetylcholine
B. Covalent inhibition of acetylcholinesterase at serine in the active site
C. Activation of carboxylase
D. Enhanced tyrosine kinase activity

B. Covalent inhibition of acetylcholinesterase at serine in the active site

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Which is a key feature that distinguishes prosthetic groups from coenzymes?
A. Prosthetic groups always dissociate after the reaction
B. Prosthetic groups are covalently bound and not released until protein degradation
C. Only coenzymes require a metal ion
D. Coenzymes are always vitamin-derived

B. Prosthetic groups are covalently bound and not released until protein degradation

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Allopurinol’s use in gout therapy relates to it being a:
A. Transition-state analog
B. Suicide (mechanism-based) inhibitor of xanthine oxidase
C. Reversible competitive inhibitor for hexokinase
D. Metal ion chelator

B. Suicide (mechanism-based) inhibitor of xanthine oxidase

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What is a diagnostic feature of enzyme-catalyzed reactions compared to non-catalyzed reactions?
A. They make previously impossible reactions possible
B. They shift the equilibrium toward products
C. They increase the rate by lowering the energy barrier—specific for substrate and product
D. They consume the enzyme in each catalytic cycle

C. They increase the rate by lowering the energy barrier—specific for substrate and product

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Deficiency of thiamine (Vit B1) will most directly affect which class of enzyme-catalyzed reaction? A. Glycoside hydrolysis B. Carboxylation reactions C. Decarboxylation and dehydrogenation of alpha-keto acids D. Oxygenation

C. Decarboxylation and dehydrogenation of alpha-keto acids

A patient with acute lead poisoning could manifest with: A. Enhanced enzyme stability B. Neurological toxicity from Ca2+–calmodulin and PKC disruption C. Lowered enzyme specificity D. Hyperglycemia

B. Neurological toxicity from Ca2+–calmodulin and PKC disruption

Which enzyme class catalyzes joining of two molecules with ATP consumption? A. Ligases B. Isomerases C. Hydrolases D. Transferases

A. Ligases

In chymotrypsin catalysis, the residue that acts as a nucleophile is: A. Cysteine B. Histidine C. Arginine D. Serine

D. Serine

Which of the following would most likely result from a mutation in the hinge region far from the active site of glucokinase? A. No effect, since location is not in active site B. Disrupted conformational change, affecting ATP binding and catalysis C. Loss of substrate specificity only D. Spontaneous catalysis without substrate

B. Disrupted conformational change, affecting ATP binding and catalysis

The pH optimum of an enzyme depends primarily on: A. pKa of functional groups at the active site B. Ribosomal pH C. ATP concentration D. Substrate allosteric effects

A. pKa of functional groups at the active site

What is the primary function of enzymes in biochemical reactions? A) They are consumed during the reaction B) They increase the rate of chemical reactions C) They provide energy for the reaction D) They alter the equilibrium of the reaction

B) They increase the rate of chemical reactions

Which of the following best describes the enzyme's active site? A) Binding site for all molecules B) Site where substrate binds and catalysis occurs C) Random region on the enzyme D) Site that is rigid and unchanging

B) Site where substrate binds and catalysis occurs

The lock-and-key and induced-fit models explain what property of enzymes? A) Enzyme specificity B) Enzyme denaturation C) Enzyme inhibition D) Enzyme concentration

A) Enzyme specificity

What is the turnover number (kcat) of an enzyme? A) Number of substrate molecules bound per second B) Number of product molecules formed per second per enzyme molecule C) Substrate concentration at half-maximal velocity D) Enzyme concentration

B) Number of product molecules formed per second per enzyme molecule

Which type of inhibition can be overcome by increasing substrate concentration? A) Competitive inhibition B) Noncompetitive inhibition C) Uncompetitive inhibition D) Irreversible inhibition

A) Competitive inhibition

How do covalent inhibitors typically affect enzyme function? A) They reversibly bind the enzyme B) They permanently inactivate the enzyme by forming strong covalent bonds C) They enhance enzyme activity D) They serve as coenzymes

B) They permanently inactivate the enzyme by forming strong covalent bonds

What is the mechanism of action of organophosphate compounds like malathion? A) Activate acetylcholinesterase B) Inhibit acetylcholinesterase by covalent modification C) Stimulate muscarinic receptors D) Block neurotransmitter release

B) Inhibit acetylcholinesterase by covalent modification

Which coenzyme derived from vitamin B1 is critical for transferring aldehyde groups in metabolism? A) NAD+ B) FAD C) Thiamin pyrophosphate (TPP) D) Coenzyme A

C) Thiamin pyrophosphate (TPP)

What role does NAD+ play in enzymatic reactions? A) Transfers phosphate groups B) Accepts electrons during oxidation reactions C) Donates methyl groups D) Acts as a substrate for proteases

B) Accepts electrons during oxidation reactions

Why are metal ions like Zn2+ important in enzymes like alcohol dehydrogenase? A) They stabilize substrates or intermediates B) They inhibit enzyme activity C) They are consumed in reactions D) They act as substrates

A) They stabilize substrates or intermediates

Which mechanism best describes general acid-base catalysis in enzymes? A) Transfer of electrons B) Transfer of protons between enzyme and substrate C) Formation of covalent intermediates D) Binding of metal cofactors

B) Transfer of protons between enzyme and substrate

What distinguishes the induced-fit model from the lock-and-key model of enzyme-substrate interaction? A) Substrate binding causes conformational changes in the enzyme B) The enzyme is completely rigid C) All substrates bind equally D) Substrate binds non-specifically

A) Substrate binding causes conformational changes in the enzyme

What is the effect of allosteric activators on enzyme kinetics? A) Decrease Vmax B) Increase Km C) Decrease Km and stabilize active form D) Inhibit substrate binding

C) Decrease Km and stabilize active form

Protein kinase A is activated by which second messenger? A) cAMP B) Calcium C) cGMP D) IP3

A) cAMP

What is the main role of zymogens? A) Permanent activation of enzymes B) Enzymes synthesized as inactive precursors C) Enzymes that do not require activation D) Enzymes regulated by allosteric inhibitors

B) Enzymes synthesized as inactive precursors

How does phosphorylation regulate enzyme activity? A) By degrading the enzyme B) Covalent addition of phosphate can alter enzyme conformation and activity C) By increasing enzyme concentration D) By inhibiting substrate binding exclusively

B) Covalent addition of phosphate can alter enzyme conformation and activity

Which molecule regulates muscle glycogen phosphorylase activity as an allosteric activator? A) ATP B) Glucose C) AMP D) NADH

C) AMP

What is the role of calcium-calmodulin in enzyme regulation? A) Directly inhibits enzymes B) Serves as a modulator protein activating target enzymes upon binding calcium C) Degrades zymogens D) Phosphorylates enzymes

B) Serves as a modulator protein activating target enzymes upon binding calcium

What is the function of G proteins in cellular regulation? A) To phosphorylate proteins B) To hydrolyze ATP C) As molecular switches cycling between active (GTP-bound) and inactive (GDP-bound) states D) To bind DNA

C) As molecular switches cycling between active (GTP-bound) and inactive (GDP-bound) states

What happens when protein phosphatases act on a phosphorylated enzyme? A) They activate the enzyme B) They reverse phosphorylation, potentially inactivating or activating enzymes C) They degrade the enzyme D) They add more phosphate groups

B) They reverse phosphorylation, potentially inactivating or activating enzymes

Which of the following is true regarding enzyme kinetics and enzyme concentration? A) Velocity is independent of enzyme concentration B) Velocity doubles if enzyme concentration doubles, at all substrate concentrations C) Enzymes do not saturate D) Substrate concentration does not affect reaction velocity

B) Velocity doubles if enzyme concentration doubles, at all substrate concentrations

What mechanism allows for rapid and amplified cellular responses during hormonal signaling? A) Passive diffusion B) Phosphorylation cascades C) Enzyme degradation D) Protein denaturation

B) Phosphorylation cascades

What is the significance of compartmentation in enzyme regulation? A) Enzymes are randomly distributed B) Organizing enzymes in organelles facilitates substrate channeling and regulation C) Compartmentation inhibits enzyme function D) It only applies to nuclear enzymes

B) Organizing enzymes in organelles facilitates substrate channeling and regulation

How do inhibitory proteins like GAPs regulate G-proteins? A) By preventing signal transduction B) By increasing GTPase activity and terminating signaling C) By blocking GDP binding D) By phosphorylating G-proteins

B) By increasing GTPase activity and terminating signaling

What is the difference between allosteric and active-site enzyme inhibition? A) Allosteric inhibitors bind at the active site B) Active-site inhibitors bind elsewhere C) Allosteric inhibitors bind at different sites, changing enzyme conformation D) Only active-site inhibitors are reversible

C) Allosteric inhibitors bind at different sites, changing enzyme conformation

What type of enzyme regulation involves permanent activation by cleavage of a zymogen? A) Positive feedback B) Allosteric modulation C) Proteolytic activation D) Competitive inhibition

C) Proteolytic activation

Which feature distinguishes competitive from noncompetitive enzyme inhibition? A) Noncompetitive inhibition can be overcome by substrate B) Competitive inhibition is irreversible C) Competitive inhibitors increase Km; noncompetitive inhibitors lower Vmax D) Noncompetitive inhibition raises Km only

C) Competitive inhibitors increase Km; noncompetitive inhibitors lower Vmax

Which type of enzyme regulation rapidly alters the active state using molecules unrelated to substrate or product? A) Simple product inhibition B) Allosteric regulation C) Zymogen activation D) Gene induction

B) Allosteric regulation

What principle underlies pathway feedback regulation? A) The first enzyme is always constitutively active B) The pathway end-product inhibits the rate-limiting enzyme C) All enzymes act at equal rates D) Feedback activation always increases pathway flux

B) The pathway end-product inhibits the rate-limiting enzyme

A patient was born with a mutation in an enzyme that severely affected its ability to bind an activation-transfer coenzyme. As a consequence, which one of the following is most likely to occur? A. The enzyme will be unable to bind the substrate of the reaction. B. The enzyme will be unable to form the transition-state complex. C. The enzyme will normally use a different activation-transfer coenzyme. D. The enzyme will normally substitute the functional group of an active-site amino acid residue for the coenzyme. E. The reaction may be carried out by the free coenzyme, provided the diet carries an adequate amount of its vitamin precursor.

B. The enzyme will be unable to form the transition-state complex.

An individual had a disease-causing mutation in glucokinase in which a proline was substituted for a leucine on a surface helix far from the active site but within the hinge region of the actin fold. This mutation would be expected to have which one of the following effects? A. It would have no effect on the rate of the reaction because it is not in the active site. B. It would have no effect on the rate of the reaction because proline and leucine are both nonpolar amino acids. C. It would have no effect on the number of substrate molecules reaching the transition state. D. It would probably affect the binding of ATP or a subsequent step in the reaction sequence. E. It would probably cause the reaction to proceed through an alternate mechanism.

D. It would probably affect the binding of ATP or a subsequent step in the reaction sequence.

Lysozyme is an important component of the human innate immune system. Lysozyme is an enzyme that cleaves glycosidic linkages in bacterial cell walls. The pH optimum of the purified enzyme is 5.2. There are two acidic residues at the active site of lysozyme (E35 and D52) that are required for enzyme activity. The pKa of E35 is 5.9, whereas the pKa of D52 is 4.5. What are the primary ionization states of these two residues at the pH optimum of the enzyme? A. E35 is protonated; D52 is ionized. B. E35 is protonated; D52 is protonated. C. E35 is ionized; D52 is protonated. D. E25 is ionized; D52 is ionized. E. This cannot be determined from the information provided.

A. E35 is protonated; D52 is ionized. (Correct)

The type of reaction shown fits into which one of the following classifications? A. Group transfer B. Isomerization C. Carbon-carbon bond breaking D. Carbon-carbon bond formation E. Oxidation-reduction

A. Group transfer

The type of enzyme that catalyzes this reaction is which one of the following? A. Kinase B. Dehydrogenase C. Glycosyltransferase (Correct) D. Transaminase E. Isomerase

C. Glycosyltransferase

A patient has accidentally ingested the insecticide malathion, leading to symptoms of an overstimulated autonomic nervous system. Which one of the following best describes malathion in this context? A. Enzyme B. Coenzyme C. Inhibitor D. Cofactor E. Coactivator

C. Inhibitor

Penicillin is an antibiotic used to treat certain infections. It is a transition-state analog and suicide inhibitor. The use of penicillin affects which one of the following in susceptible targets? A. Viral cell wall B. Bacterial cell wall C. Viral nucleus D. Bacterial nucleus E. Protozoan nucleus

B. Bacterial cell wall

Vitamins can act as coenzymes that participate in catalysis by providing functional groups. Therefore, vitamin deficiencies reflect the loss of specific enzyme activities that depend on those coenzymes. Coenzymes are best described by which one of the following? A. In humans, they are always synthesized from vitamins. B. They are proteins. C. They participate in only one reaction, like enzymes. D. They are complex, nonprotein organic molecules. E. They are all carbohydrates.

D. They are complex, nonprotein organic molecules. (Correct)

Many individuals with chronic alcohol abuse disorder develop thiamin deficiency because of a poor diet and an inability to absorb thiamin from the intestine in the presence of ethanol. Which one of the following cofactors, synthesized from a vitamin, or a vitamin itself, exhibits a mechanism of action similar to thiamin? A. NAD+ B. FAD C. Ascorbic acid D. γ-Tocopherol E. CoA

E. CoA

Which one of the following vitamins is the precursor for the correct answer to the previous question? A. Pantothenate B. Niacin C. Pyridoxine (vitamin B6) D. Folate E. Biotin

A. Pantothenate

A patient with glaucoma has been prescribed acetazolamide, a carbonic anhydrase inhibitor. Which one of the following would also lead to a loss of carbonic anhydrase activity? A. Reduce ATP binding to the enzyme B. Reduce NAD+ binding to the enzyme C. Remove the magnesium from the enzyme D. Remove the zinc from the enzyme E. Increase the concentration of carbon dioxide

D. Remove the zinc from the enzyme

A histidine residue is required at the active site of serine proteases for the enzyme to be active. The role of the histidine is as a general base catalyst. If the pKa of this histidine residue is 6.2, at which pH would the enzyme exhibit maximal activity, assuming the rate-limiting step of the enzyme was because of the role of histidine as a general base catalyst? A. 5.2 B. 5.7 C. 6.2 D. 6.7 E. 7.2

E. 7.2

Maple syrup urine disease is due to a mutation in the enzyme branched-chain α-keto acid dehydrogenase, an enzyme that requires TPP along with a number of other cofactors. Some patients who have maple syrup urine disease are responsive to pharmacologic doses of thiamin. The basis for this treatment is that the mutation within the enzyme led to which one of the following? A. Increased the hydrophobicity of the active site B. Increased the affinity of the enzyme for the amino acid substrates C. Decreased the affinity of the enzyme for the amino acid substrates D. Increased the affinity of the enzyme for thiamin E. Decreased the affinity of the enzyme for thiamin

E. Decreased the affinity of the enzyme for thiamin

A patient with a deficiency in pyruvate carboxylase, an enzyme that is covalently linked to biotin in order to catalyze its reaction, is not improved when given pharmacologic doses of biotin. This is most likely a noneffective treatment owing to which one of the following? A. Dietary biotin cannot be modified to the active form of biotin. B. The excess biotin blocks substrate binding to the enzyme. C. The biotin-binding site on the enzyme is altered and can no longer bind biotin. D. The mutated pyruvate carboxylase binds biotin too tightly such that it cannot react with the substrate. E. Carbon dioxide, the substrate for carboxylations, reacts with the excess biotin before the biotin can bind to the enzyme.

C. The biotin-binding site on the enzyme is altered and can no longer bind biotin.

Many drugs work by targeting specific enzymes for inhibition. A major difference between a suicide enzyme inhibitor and a covalent enzyme inhibitor is which one of the following? A. A suicide inhibitor forms a covalent bond with the enzyme, whereas a covalent inhibitor forms a bond with the substrate. B. A suicide inhibitor is also a substrate for the enzyme, whereas a covalent inhibitor is not. C. A covalent inhibitor is a substrate for the enzyme, whereas a suicide inhibitor is not. D. A suicide inhibitor binds to a site outside the active site, whereas a covalent inhibitor binds at the active site. E. A covalent inhibitor binds to a site outside the active site, whereas a suicide inhibitor binds at the active site.

B. A suicide inhibitor is also a substrate for the enzyme, whereas a covalent inhibitor is not.

Salivary amylase is an enzyme that digests dietary starch. Assume that salivary amylase follows Michaelis–Menten kinetics. Which one of the following best describes a characteristic feature of salivary amylase? A. The enzyme velocity is at one-half the maximal rate when 100% of the enzyme molecules contain bound substrate. B. The enzyme velocity is at one-half the maximal rate when 50% of the enzyme molecules contain bound substrate. C. The enzyme velocity is at its maximal rate when 50% of the enzyme molecules contain bound substrate. D. The enzyme velocity is at its maximal rate when all of the substrate molecules in solution are bound by the enzyme. E. The velocity of the reaction is independent of the concentration of enzyme.

B. The enzyme velocity is at one-half the maximal rate when 50% of the enzyme molecules contain bound substrate.

The pancreatic GK of a patient with maturity-onset diabetes of the young (MODY) had a mutation replacing a leucine with a proline. The result was that the Km for glucose was decreased from a normal value of 6 mM to a value of 2.2 mM, and the Vmax was changed from 93 U/mg protein to 0.2 U/mg protein. Which one of the following best describes the patient’s GK compared with the normal enzyme? A. The patient’s enzyme requires a lower concentration of glucose to reach ½Vmax. B. The patient’s enzyme is faster than the normal enzyme at concentrations of glucose <2.2 mM. C. The patient’s enzyme is faster than the normal enzyme at concentrations of glucose >2.2 mM. D. At near-saturating glucose concentration, the patient would need 90 to 100 times more enzyme than normal to achieve normal rates of glucose phosphorylation. E. As blood glucose levels increase after a meal from a fasting value of 5 to 10 mM, the rate of the patient’s enzyme will increase more than the rate of the normal enzyme.

A. The patient’s enzyme requires a lower concentration of glucose to reach ½Vmax.

Methanol (CH3OH) is converted by alcohol dehydrogenases (ADH) to formaldehyde (CH2O), a compound that is highly toxic to humans. Patients who have ingested toxic levels of methanol are sometimes treated with ethanol (CH3CH2OH) to inhibit methanol oxidation by ADH. Which one of the following statements provides the best rationale for this treatment? A. Ethanol is a structural analog of methanol and might therefore be an effective noncompetitive inhibitor. B. Ethanol is a structural analog of methanol that can be expected to compete with methanol for its binding site on the enzyme. C. Ethanol can be expected to alter the Vmax of ADH for the oxidation of methanol to formaldehyde. D. Ethanol is an effective inhibitor of methanol oxidation regardless of the concentration of methanol. E. Ethanol can be expected to inhibit the enzyme by binding to the formaldehyde-binding site on the enzyme, even though it cannot bind at the substrate-binding site for methanol.

B. Ethanol is a structural analog of methanol that can be expected to compete with methanol for its binding site on the enzyme.

A runner’s muscles use glucose as a source of energy. Muscle contains glycogen stores that are degraded into glucose 1-phosphate via glycogen phosphorylase, which is an allosteric enzyme. Assume that an allosteric enzyme has the following kinetic properties: a Vmax of 25 U/mg enzyme and a Km,app of 1.0 mM. These kinetic parameters were then measured in the presence of an allosteric activator. Which one of the following would best describe the findings of that experiment? A. A Vmax of 25 U/mg enzyme and a Km,app of 0.2 mM B. A Vmax of 15 U/mg enzyme with a Km,app of 2.0 mM C. A Vmax of 25 U/mg enzyme with a Km,app of 2.0 mM D. A Vmax of 50 U/mg enzyme with a Km,app of 5.0 mM E. A Vmax of 50 U/mg enzyme with a Km,app of 10.0 mM

A. A Vmax of 25 U/mg enzyme and a Km,app of 0.2 mM

A rate-limiting enzyme catalyzes the first step in the conversion of a toxic metabolite to a urinary excretion product. Which of the following mechanisms for regulating this enzyme would provide the most protection to the body? A. The product of the pathway should be an allosteric inhibitor of the rate-limiting enzyme. B. The product of the pathway should act through gene transcription to decrease synthesis of the enzyme. C. The toxin should act through gene transcription to increase synthesis of the enzyme. D. The enzyme should have a high Km for the toxin. E. The toxin allosterically activates the last enzyme in the pathway.

C. The toxin should act through gene transcription to increase synthesis of the enzyme.

In thyroid hormone production, thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates thyroid-stimulating hormone (TSH) release from the anterior pituitary, which stimulates the thyroid to produce thyroid hormones (triiodothyronine [T3] and thyroxine [T4]). Normal or high levels of thyroid hormone then suppress release of TRH. Which of the following best describes the regulation of this pathway? A. Complementary regulation B. Feedback regulation C. Compartmentation D. Feed-forward regulation E. Negative regulation

B. Feedback regulation

A patient with alcoholic liver disease has profound mental status changes caused by a buildup of ammonia (NH4+) and is suffering from hepatic encephalopathy. The conversion of NH4+ to urea is an example of which one of the following types of pathway regulation? A. Complimentary B. Feedback C. Compartmentation D. Feed-forward E. Negative

D. Feed-forward

Pathway regulation can occur via the expression of tissue-specific isozymes. Glucose metabolism differs in the red blood cell and liver in that the red blood cells need to metabolize glucose, whereas the liver prefers to store glucose. The first step of glucose metabolism requires either GK (liver) or hexokinase I (red blood cell), which are isozymes. Which one of the following best describes these different isozymes and their Km for glucose? A. The Km of hexokinase I is higher than the Km of GK. B. The Km of hexokinase I is lower than the Km of GK. C. The Km of hexokinase I is the same as the Km of GK. D. Hexokinase I is found in liver. E. GK is found in red blood cells.

B. The Km of hexokinase I is lower than the Km of GK.

Which one of the following is true for the inhibitor described in the previous question? A. It increases the apparent Km of the enzyme. B. It decreases the apparent Km of the enzyme. C. It has no effect on the apparent Km of the enzyme. D. It increases the Vmax of the enzyme. E. It decreases the Vmax of the enzyme.

A. It increases the apparent Km of the enzyme.

An antibiotic is developed that is a close structural analog of a substrate of an enzyme that participates in cell wall synthesis in bacteria. This binding of the antibiotic reduces overall enzyme activity, but such activity can be restored if more substrate is added. The binding of the antibiotic to the enzyme is not via a covalent bond, nor does the enzyme alter the structure of the antibiotic. Which one of the following would best describe this antibiotic? A. It is a suicide inhibitor. B. It is an irreversible inhibitor. C. It is a competitive inhibitor. D. It is a noncompetitive inhibitor. E. It is an uncompetitive inhibitor.

C. It is a competitive inhibitor.

A liver cell line has been isolated that has a variant small GTP-binding protein (G-protein), which lacks GTPase activity. The target of this small G-protein is the enzyme phospholipase C, which, when activated by binding to the G-protein, hydrolyzes phosphatidyl inositol bisphosphate into diacylglycerol (DAG) and inositol trisphosphate (IP3). Which one of the following would be expected to occur in the cell line when the variant G-protein binds GTP? A. Continual increased cellular levels of phosphatidyl inositol bisphosphate B. Continual decreased cellular levels of DAG C. Continual increased levels of IP3 D. Continual decreased levels of IP3 E. Continual inactivation of phospholipase C

C. Continual increased levels of IP3

Consider an enzyme, at a concentration of 1.0 μM, in the presence of substrate (at a concentration of 1.0 mM). The velocity of the enzyme-catalyzed reaction under these conditions is 5.0 mM product formed per minute. What is the maximal velocity of the enzyme at this concentration of enzyme, if the Km of the enzyme is 2.0 mM? A. 1.0 mM product formed per minute B. 5 mM product formed per minute C. 10 mM product formed per minute D. 15 mM product formed per minute E. 20 mM product formed per minute

D. 15 mM product formed per minute

Considering the enzyme described in question 12, what is the turnover number of the enzyme (kcat) in terms of reactions catalyzed per minute? A. 1.5 B. 15 C. 150 D. 1500 E. 15,000

E. 15,000

A key metabolic enzyme is regulated by reversible phosphorylation of a serine side chain on the protein. In the absence of phosphorylation, the serine side chain forms noncovalent interactions with the side chains of glutamine and tyrosine. After phosphorylation, the phosphoserine residue on the protein can form a noncovalent interaction with which one of the following amino acid side chains? A. Val B. Phe C. Asp D. Arg E. Leu

D. Arg

A variant enzyme was found in a liver cell line, which catalyzed the reaction of A → B. Enzyme kinetics were done with the wild-type and mutant enzymes, and the following results were obtained. Which one of the following statements is correct in terms of the kinetic properties of these enzymes? A. The variant enzyme has a higher Vmax than the normal enzyme. B. The variant enzyme has a lower Vmax than the normal enzyme. C. The variant enzyme has a higher Km than the normal enzyme. D. The variant enzyme has a lower Km than the normal enzyme. E. The variant enzyme has the same kinetic properties as the normal enzyme.

C. The variant enzyme has a higher Km than the normal enzyme.

The transition state complex is stabilized by what kind of bond?

Covalent

TRUE OR FALSE: The substrate-binding site is a dynamic surface

True

Functional group binding to enzyme A. Covalent B. Noncovalent

B. Noncovalent

Region that is physically separate from the active catalytic site of the enzyme

Allosteric site

This is the difference between the substrate and the transition state complex energy

Activation energy

TRUE OR FALSE: decrease activation energy increases the rate of production

True

This theory states that overall reaction is determined by the number of molecules acquiring the energy

Transition state theory

According to the activation transfer coenzymes, how is biotin bonded with enzymes?

Covalently

Cofactor binding to enzyme A. Covalent B. Noncovalent

B. Noncovalent

TRUE OR FALSE: According to the induced fit model, the substrate undergoes a conformational change to bind to the enzyme

False The ENZYME ADAPTS to the subtrate

According to the lock and key model, what are the reasons for failed substrate binding?

1. Charge repulsion (like repels like) 2. Steric hindrance (slowing or stopping of reaction d/t steric bulk size)

According to the activation transfer coenzymes, how is thiamine bonded with enzymes?

Noncovalently NOTE: with its substrate, it is bonded covalently substrate - covalent enzyme - noncovalent

What kind of bonding do prosthetic groups have with their enzymes

Covalent

Which of the following is described by the Michaelis–Menten equation for enzyme kinetics? a. The linear relationship between substrate concentration and enzyme velocity at all concentrations b. The hyperbolic relationship between substrate concentration and initial reaction velocity c. The irreversible inhibition of enzyme activity d. The relationship between enzyme degradation and synthesis

b. The hyperbolic relationship between substrate concentration and initial reaction velocity

In Michaelis–Menten kinetics, the value of Km represents: a. The enzyme concentration at maximum velocity b. The substrate concentration at which the reaction rate is half of Vmax c. The product concentration at maximum velocity d. The rate at which all enzyme sites are occupied by substrate

b. The substrate concentration at which the reaction rate is half of Vmax

Which parameter does a competitive inhibitor affect in the Michaelis–Menten model? a. Vmax only b. Km only c. Both Km and Vmax d. Neither Km nor Vmax

b. Km only

In a Lineweaver–Burk (double-reciprocal) plot, the presence of a competitive inhibitor: a. Increases the slope and leaves the y-intercept unchanged b. Decreases the slope and increases the y-intercept c. Leaves both slope and intercepts unchanged d. Increases both slope and y-intercept

a. Increases the slope and leaves the y-intercept unchanged

In a graph of velocity (Vi) vs. substrate concentration ([S]), saturation kinetics is indicated by: a. A straight, diagonal line b. A horizontal asymptote as [S] increases c. A vertical line at high substrate concentrations d. An initial decrease followed by a flat line

b. A horizontal asymptote as [S] increases

A decrease in enzyme concentration (with [S] in excess) will: a. Increase Km b. Decrease Vmax c. Increase both Km and Vmax d. Not affect Vmax

b. Decrease Vmax

Km is related to enzyme-substrate affinity in that: a. High Km means high affinity for substrate b. Low Km means high affinity for substrate c. Low Km means no affinity for substrate d. Km is unrelated to affinity

b. Low Km means high affinity for substrate Inverse relationship

Hexokinase and glucokinase have different Km values for glucose. This difference reflects: a. Changes in substrate inhibition b. Tissue-specific regulation of glucose metabolism c. Difference in enzyme degradation rate d. Only their Vmax values

b. Tissue-specific regulation of glucose metabolism

The effect of a noncompetitive inhibitor on an enzyme-catalyzed reaction is best described as: a. Increases both Km and Vmax b. Decreases Vmax, Km unchanged c. Decreases Km, Vmax unchanged d. No change in either Km or Vmax

b. Decreases Vmax, Km unchanged This is because it LOWERS concentration of active enzymes

In the Lineweaver–Burk plot, a noncompetitive inhibitor affects which of the following? a. The x-intercept only b. The y-intercept only c. Both intercepts d. Neither intercept

b. The y-intercept only inhibition increases y-intercept (decreases Vmax), Km unchanged (x-intercept same)

Allosteric regulation is characterized by: a. The substrate always acting as the inhibitor b. Modulation by compounds binding at sites distinct from the active site c. Covalent changes in the enzyme backbone d. Only irreversible inhibition

b. Modulation by compounds binding at sites distinct from the active site

Enzymes regulated by reversible phosphorylation are catalyzed by: a. Allosteric inhibitors b. Protein kinases and protein phosphatases c. Irreversible proteolysis d. Substrate isomerization

b. Protein kinases and protein phosphatases

Zymogen activation (e.g., trypsinogen to trypsin) is controlled by: a. Simple competitive inhibition b. Irreversible proteolytic cleavage c. Covalent acetylation d. Gene induction

b. Irreversible proteolytic cleavage

A sigmoidal (S-shaped) curve in a Vi vs. [S] plot suggests: a. Michaelis–Menten enzyme b. Simple competitive inhibition c. Cooperative or allosteric enzyme d. Noncompetitive inhibition

c. Cooperative or allosteric enzyme

In feedback regulation of metabolic pathways: a. The initial substrate activates its enzyme b. The end product inhibits the rate-limiting enzyme c. All enzymes are equally affected d. Feedback is always at the gene expression level

b. The end product inhibits the rate-limiting enzyme

Feed-forward regulation is seen in which scenario? a. The end product inhibits the pathway b. The starting substrate activates its own disposal pathway c. Decreased necessity for enzyme leads to inhibition d. Allosteric inhibition predominates

b. The starting substrate activates its own disposal pathway

The Lineweaver–Burk plot equation is derived from: a. Michaelis–Menten equation by taking reciprocals b. Direct measurement of reaction end products c. Measuring Km at infinite substrate d. Measuring Vmax at zero substrate

a. Michaelis–Menten equation by taking reciprocals

A key diagnostic difference between competitive and noncompetitive inhibition using graph analysis is: a. Both increase Km b. Both decrease Vmax c. Only competitive inhibition alters Km; noncompetitive only decreases Vmax d. Both leave Km and Vmax unchanged

c. Only competitive inhibition alters Km; noncompetitive only decreases Vmax

Tissue isozymes allow for: a. Redundant regulation b. Pathway specificity and adaptation to tissue function c. Decreased product inhibition d. Only a single type of feedback regulation

b. Pathway specificity and adaptation to tissue function

The principle that the amount of enzyme regulates reaction velocity is best summarized by: a. The reaction always runs at Vmax regardless of enzyme b. The reaction velocity is directly proportional to enzyme concentration (at [S] in excess) c. Velocity is independent of enzyme amount d. Substrate concentration is always rate-limiting

b. The reaction velocity is directly proportional to enzyme concentration (at [S] in excess)

The phosphate group added during phosphorylation of enzymes forms what kind of bond with the amino acid side chain? a. Hydrogen bond b. Covalent bond c. Ionic bond d. Van der Waals interaction

b. Covalent bond

The interaction between an allosteric effector and its regulatory binding site on an enzyme primarily involves which type of bond? a. Covalent bond b. Ionic bond only c. Non-covalent bond d. Peptide bond

c. Non-covalent bond

The activation of zymogens (e.g., conversion of trypsinogen to trypsin) typically involves which type of bond formation or cleavage? a. Formation of non-covalent bonds b. Cleavage of covalent peptide bonds c. Formation of hydrogen bonds d. None; zymogen activation requires no bonds

b. Cleavage of covalent peptide bonds

The association between Ca2+ ions and calmodulin protein is best described by which type of interaction? a. Disulfide bond b. Covalent bond c. Non-covalent bond d. Glycosidic bond

c. Non-covalent bond

The inhibitory binding of a competitive inhibitor to the active site of an enzyme is best characterized as: a. Irreversible covalent bonding b. Reversible non-covalent bonding c. Cleavage of peptide bonds d. Phosphorylation

b. Reversible non-covalent bonding

TRUE OR FALSE: transition state is the rate limiting step in the overall reaction

True

Coenzyme are often derived from which vitamin complex

Dissociates when deficient A. Coenzyme B. Prosthetic group

A. Coenzyme

Stays until degradation A. Coenzyme B. Prosthetic group

B. Prosthetic group

Bond of thiamin to substrate

Covalent

Bond of thiamin to enzyme

Noncovalent

Which cofactor does thiamin attract?

Mg2+

Coenzyme A (CoA/ CoASH) is synthesized from what vitamin?

B5/ pantothenate

Biotin is also known as what vitamin

TRUE OR FALSE: Biotin functions only in carboxylation reactions

True

Forms covalent bonds A.activation transfer coenzymes B.oxidation reduction coenzyme

A.activation transfer coenzymes

Forms noncovalent bonds A.activation transfer coenzymes B.oxidation reduction coenzyme

B.oxidation reduction coenzyme

TRUE OR FALSE: enzymes makes a cofactor ready to react with a substrate

True

What is the optimal reaction temperature for enzymes?

37 degrees celsius 0-37 increase in rxn rate > 37 decrease in rxn rate dt denaturation

Joins substrates without ATP A. Synthase B. Synthetase

A. Synthase

Joins substrates using ATP A. Synthase B. Synthetase

B. Synthetase

TRUE OR FALSE: Glucokinase, found in the liver, can only work in a well fed state

True This is because of its low affinity for glucose

what does an enzyme inhibitor do?

Decreased velocity of a reaction

Enzyme Flashcards

(145 cards)