Enzymes Regulation Questions and Answers

Q: Which bond is not involved in enzyme-substrate interaction?

Correct answer: Disulfide bondsEnzyme-substrate binding is non-covalent and reversible - hydrogen bonds, ionic interactions, van der Waals forces and hydrophobic effects. A disulfide bond is covalent and permanent; disulfides help hold the enzyme’s own structure together, but they do not bind the substrate, which has to be released once the reaction is done.

Q: Lock and Key model is also known as

Correct answer: Template modelThe lock and key model, proposed by Emil Fischer in 1894, is also called the template model: the active site is a rigid shape into which only the right substrate fits. Koshland’s induced fit model succeeded it, allowing the site to change shape as the substrate binds - which explains a good deal that a rigid template cannot.

Q: The fastest enzyme is

Correct answer: carbonic anhydraseCarbonic anhydrase is among the fastest enzymes known, converting up to about a million molecules of CO2 to bicarbonate every second. It has to be: the reaction is uncatalysed far too slow for the blood to carry carbon dioxide from the tissues to the lungs in the few seconds available.

Q: Which enzymes do not require coenzymes for their activity?

Correct answer: The extracellular enzymesExtracellular enzymes - the digestive hydrolases such as amylase, lipase and pepsin - work by simple hydrolysis and need no coenzyme. Coenzymes are required chiefly for the group-transfer and redox reactions of intracellular metabolism, where electrons or chemical groups must be carried from one reaction to another.

Q: The “lock and key” theory of enzyme action was put forward by

Correct answer: FischerEmil Fischer proposed the lock-and-key model in 1894: the substrate fits the active site as a key fits a lock, which explains an enzyme’s specificity. Koshland later refined it into the induced-fit model, in which the site adjusts its shape as the substrate binds - a better account of what actually happens.

Q: Thalassaemia is characterised by

Correct answer: Deficient production of α and β chainsThalassaemia is a quantitative defect: the globin chains that are made are structurally normal, but too few of them are produced - α-chains in α-thalassaemia, β-chains in β-thalassaemia. The unbalanced surplus of the other chain then precipitates and damages the red cell. Sickle cell disease, by contrast, is a qualitative defect: normal quantity, wrong structure.

Q: Uncatalyzed reaction shows ______________ activation energy

Correct answer: HigherAn uncatalysed reaction must surmount the full activation energy barrier, so only the small fraction of molecules with enough energy react and the rate is low. An enzyme lowers that barrier by stabilising the transition state, which is exactly how it speeds the reaction up.

Q: Abzymes are

Correct answer: AntibodiesAbzymes are catalytic antibodies - immunoglobulins raised against a stable analogue of a reaction’s transition state, which then bind and stabilise the real transition state and so catalyse the reaction. They confirm the central idea that catalysis is transition-state stabilisation.

11.

Which bond is not involved in enzyme-substrate interaction?

A.Hydrogen bonds
B. Ionic bonds
C.Disulfide bonds
D.Van der Waals forces of attraction

Answer: C

Correct answer: Disulfide bonds

Enzyme-substrate binding is non-covalent and reversible - hydrogen bonds, ionic interactions, van der Waals forces and hydrophobic effects. A disulfide bond is covalent and permanent; disulfides help hold the enzyme’s own structure together, but they do not bind the substrate, which has to be released once the reaction is done.

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12.

Lock and Key model is also known as

A.Template model
B.Induced fit model
C.Koshland’s model
D.Enzyme-substrate interaction model

Answer: A

Correct answer: Template model

The lock and key model, proposed by Emil Fischer in 1894, is also called the template model: the active site is a rigid shape into which only the right substrate fits. Koshland’s induced fit model succeeded it, allowing the site to change shape as the substrate binds - which explains a good deal that a rigid template cannot.

Discuss in Forum

13.

The fastest enzyme is

A.carbonic anhydrase
B.pepsin
C.DNA polymerase
D.DNA gyrase

Answer: A

Correct answer: carbonic anhydrase

Carbonic anhydrase is among the fastest enzymes known, converting up to about a million molecules of CO₂ to bicarbonate every second. It has to be: the reaction is uncatalysed far too slow for the blood to carry carbon dioxide from the tissues to the lungs in the few seconds available.

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14.

Which enzymes do not require coenzymes for their activity?

A.The extracellular enzymes
B.The intracellular Enzymes
C.The mitochondrial enzymes
D.The Proenzymes

Answer: A

Correct answer: The extracellular enzymes

Extracellular enzymes - the digestive hydrolases such as amylase, lipase and pepsin - work by simple hydrolysis and need no coenzyme. Coenzymes are required chiefly for the group-transfer and redox reactions of intracellular metabolism, where electrons or chemical groups must be carried from one reaction to another.

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15.

The “lock and key” theory of enzyme action was put forward by

A.Koshland
B.Fischer
C.Kuhne
D.Arrhenius

Answer: B

Correct answer: Fischer

Emil Fischer proposed the lock-and-key model in 1894: the substrate fits the active site as a key fits a lock, which explains an enzyme’s specificity. Koshland later refined it into the induced-fit model, in which the site adjusts its shape as the substrate binds - a better account of what actually happens.

Discuss in Forum

16.

Thalassaemia is characterised by

A.Deficient production of α and β chains
B.Defect in the polypeptide chains
C.Normal globin genes
D.All of the above

Answer: A

Correct answer: Deficient production of α and β chains

Thalassaemia is a quantitative defect: the globin chains that are made are structurally normal, but too few of them are produced - α-chains in α-thalassaemia, β-chains in β-thalassaemia. The unbalanced surplus of the other chain then precipitates and damages the red cell. Sickle cell disease, by contrast, is a qualitative defect: normal quantity, wrong structure.

Discuss in Forum

17.

Which of the following takes place due to phosphorylation of isocitrate dehydrogenase?

A.Inhibits the binding of isocitrate at the active site
B.Degrades the enzyme
C.Enhances the substrate-binding affinity
D.No reaction

Answer: A

Correct answer: Inhibits the binding of isocitrate at active site

Phosphorylation of isocitrate dehydrogenase adds a bulky negative phosphate group at the active site, which repels the negatively charged substrate and prevents isocitrate from binding. The enzyme is not degraded, and the change is reversed by a phosphatase - the switch that sends isocitrate into the glyoxylate cycle instead of the TCA cycle.

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18.

Uncatalyzed reaction shows ______________ activation energy

A.Lower
B.Higher
C.Moderate
D.Optimum

Answer: B

Correct answer: Higher

An uncatalysed reaction must surmount the full activation energy barrier, so only the small fraction of molecules with enough energy react and the rate is low. An enzyme lowers that barrier by stabilising the transition state, which is exactly how it speeds the reaction up.

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19.

What are regulatory enzymes?

A.One involved in protein synthesis
B.Those involved in enzyme synthesis
C.Those involved in regulating enzyme activity
D.None of the above

Answer: C

Correct answer: Those involved in regulating enzyme activity

Regulatory enzymes are those whose activity can be turned up or down in response to a signal - by an allosteric modulator, by covalent modification, or by proteolytic activation. They sit at the control points of pathways, and the rest of the enzymes simply follow the flux they set.

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20.

Abzymes are

A.Proteins
B.DNAs
C.RNAs
D.Antibodies

Answer: D

Correct answer: Antibodies

Abzymes are catalytic antibodies - immunoglobulins raised against a stable analogue of a reaction’s transition state, which then bind and stabilise the real transition state and so catalyse the reaction. They confirm the central idea that catalysis is transition-state stabilisation.

Discuss in Forum

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