Enzymes Regulation Questions and Answers

Q: How do competitive inhibitors affect enzyme efficiency?

Correct answer: Raise the Michaelis constantA competitive inhibitor makes the enzyme appear to have less affinity for its substrate, since some active sites are occupied by the inhibitor at any moment. More substrate is therefore needed to reach half-maximal velocity, so \(K_m\) rises. \(V_{max}\) is unchanged, because a high enough substrate concentration still displaces the inhibitor entirely.

Q: How many types of effectors are present?

Correct answer: 2Effectors are of two kinds: positive (activators), which increase the enzyme’s affinity for substrate, and negative (inhibitors), which decrease it. Both act by binding at a regulatory site and shifting the enzyme between its more and less active conformations.

Q: Decreased synthesis of an enzyme is known as

Correct answer: RepressionRepression is a decrease in the synthesis of an enzyme - typically because the end product of its pathway has accumulated and, acting through a repressor protein, shut the gene down. It saves the cell the cost of making an enzyme it does not need.

Q: You have an enzyme solution and you add an inhibitor molecule and observe a marked decrease in enzyme activity. You increase the substrate concentration but this does not lead to any observable increase in enzyme activity. What can you conclude about your inhibitor?

Correct answer: That it is a noncompetitive inhibitorThe diagnostic test is whether extra substrate can overcome the inhibition. A competitive inhibitor competes for the active site, so it can be outcompeted; a noncompetitive inhibitor binds elsewhere and disables the enzyme whatever the substrate concentration. Since more substrate made no difference here, the inhibitor is noncompetitive - and \(V_{max}\) will be found to have fallen while \(K_m\) is unchanged.

Q: What are ribozymes?

Correct answer: RNA acting as enzymesA ribozyme is a molecule of RNA that acts as a catalyst. Its discovery by Cech and Altman overturned the assumption that all enzymes are proteins, and it matters for another reason: the peptidyl transferase activity of the ribosome is itself a ribozyme, so protein synthesis is catalysed by RNA. That is one of the strongest arguments for an early RNA world.

Q: Allosteric enzymes are

Correct answer: larger and more complex than simple enzymeAn allosteric enzyme is larger and more complex than a simple one, because it needs more than an active site: it is built of several polypeptide subunits and carries one or more regulatory sites as well. That extra structure is what allows a modulator to bind at one place and change the shape of the catalytic site elsewhere.

Q: Which of the following statements is incorrect?

Correct answer: Enzymes are inorganic catalystEnzymes are organic catalysts - proteins made by living cells - so that statement is false. The other three are true: they are proteins, they form colloidal solutions because of their size, and they are thermolabile, losing activity as heat denatures them.

Q: The activity of an allosteric enzyme is influenced by

Correct answer: Allosteric modulatorsAn allosteric enzyme is controlled by modulators that bind at its regulatory site - positive ones increasing activity, negative ones decreasing it. The allosteric site and the catalytic site are the places involved; the modulator is what does the influencing.

Q: Plasma represents ______% of total blood volume

Correct answer: 55Blood is about 55% plasma and 45% formed elements - that 45% being the haematocrit, almost all of it red cells. Plasma itself is about 92% water, with plasma proteins, electrolytes, nutrients and waste products dissolved in it.

81.

How do competitive inhibitors affect enzyme efficiency?

A.Raise the maximum rate of the enzymatic reaction
B.Raise the Michaelis constant
C.Lower the Michaelis constant
D.Lower the maximum rate of the enzymatic reaction

Answer: B

Correct answer: Raise the Michaelis constant

A competitive inhibitor makes the enzyme appear to have less affinity for its substrate, since some active sites are occupied by the inhibitor at any moment. More substrate is therefore needed to reach half-maximal velocity, so \(K_m\) rises. \(V_{max}\) is unchanged, because a high enough substrate concentration still displaces the inhibitor entirely.

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82.

How many types of effectors are present?

Answer: A

Correct answer: 2

Effectors are of two kinds: positive (activators), which increase the enzyme’s affinity for substrate, and negative (inhibitors), which decrease it. Both act by binding at a regulatory site and shifting the enzyme between its more and less active conformations.

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83.

Decreased synthesis of an enzyme is known as

A.Transcription
B.Induction
C.Translation
D.Repression

Answer: D

Correct answer: Repression

Repression is a decrease in the synthesis of an enzyme - typically because the end product of its pathway has accumulated and, acting through a repressor protein, shut the gene down. It saves the cell the cost of making an enzyme it does not need.

Discuss in Forum

84.

You have an enzyme solution and you add an inhibitor molecule and observe a marked decrease in enzyme activity. You increase the substrate concentration but this does not lead to any observable increase in enzyme activity. What can you conclude about your inhibitor?

A.That it is a kinase
B.That it is a competitive inhibitor
C.That it is a noncompetitive inhibitor
D.That is it an inorganic inhibitor

Answer: C

Correct answer: That it is a noncompetitive inhibitor

The diagnostic test is whether extra substrate can overcome the inhibition. A competitive inhibitor competes for the active site, so it can be outcompeted; a noncompetitive inhibitor binds elsewhere and disables the enzyme whatever the substrate concentration. Since more substrate made no difference here, the inhibitor is noncompetitive - and \(V_{max}\) will be found to have fallen while \(K_m\) is unchanged.

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85.

What are ribozymes?

A.RNA acting as enzymes
B.Protein acting as enzymes
C.Ribose sugar acting as enzymes
D. Antibodies acting as enzymes

Answer: A

Correct answer: RNA acting as enzymes

A ribozyme is a molecule of RNA that acts as a catalyst. Its discovery by Cech and Altman overturned the assumption that all enzymes are proteins, and it matters for another reason: the peptidyl transferase activity of the ribosome is itself a ribozyme, so protein synthesis is catalysed by RNA. That is one of the strongest arguments for an early RNA world.

Discuss in Forum

86.

Allosteric enzymes are

A.smaller than simple enzymes
B.larger than simple enzymes
C.smaller than simple enzymes but not complex
D.larger and more complex than simple enzyme

Answer: D

Correct answer: larger and more complex than simple enzyme

An allosteric enzyme is larger and more complex than a simple one, because it needs more than an active site: it is built of several polypeptide subunits and carries one or more regulatory sites as well. That extra structure is what allows a modulator to bind at one place and change the shape of the catalytic site elsewhere.

Discuss in Forum

87.

Which of the following statements is incorrect?

A.Enzymes are protein in nature
B.Enzymes are colloidal in nature
C.Enzymes are thermolabile
D.Enzymes are inorganic catalyst

Answer: D

Correct answer: Enzymes are inorganic catalyst

Enzymes are organic catalysts - proteins made by living cells - so that statement is false. The other three are true: they are proteins, they form colloidal solutions because of their size, and they are thermolabile, losing activity as heat denatures them.

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88.

Which of the following is an example of allosteric regulation of enzymes?

A.The non-covalent binding of cAMP to the active site
B.Phosphorylation of an amino acid somewhere other than the active site
C.Phosphorylation of an amino acid in the active site
D.The non-covalent binding of cAMP somewhere other than the active site

Answer: D

Correct answer: The non-covalent binding of cAMP somewhere other than the active site

Allosteric regulation has two requirements, and only this option meets both: the regulator binds away from the active site, and it binds non-covalently, so the effect is readily reversible. Phosphorylation is covalent modification, a different mechanism; and anything binding at the active site is competing with the substrate, not acting allosterically.

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89.

The activity of an allosteric enzyme is influenced by

A.Allosteric modulators
B.Allosteric site
C.Catalytic site
D.None of the above

Answer: A

Correct answer: Allosteric modulators

An allosteric enzyme is controlled by modulators that bind at its regulatory site - positive ones increasing activity, negative ones decreasing it. The allosteric site and the catalytic site are the places involved; the modulator is what does the influencing.

Discuss in Forum

90.

Plasma represents ______% of total blood volume

A.35
B.45
C.55
D.65

Answer: B

Correct answer: 55

Blood is about 55% plasma and 45% formed elements - that 45% being the haematocrit, almost all of it red cells. Plasma itself is about 92% water, with plasma proteins, electrolytes, nutrients and waste products dissolved in it.

Discuss in Forum

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