Question 1

Which of the following best describes the role of Zn$$^{2+} in $$the enzyme alcohol dehydrogenase under normal conditions?

Accepted Answer

It is a cofactor, required for catalytic activity but not covalently bound.

Question 2

Which of the following is NOT one of the six internationally accepted classes of enzymes?

Accepted Answer

Polymerases

Question 3

Enzymes accelerate chemical reactions by:

Accepted Answer

Lowering the activation energy $$\Delta G$$^{\ddagger}$$ for the reaction.

Question 4

Which statement about enzyme specificity is correct?

Accepted Answer

Enzymes are specific and can prevent the conversion of products back to substrates.

Question 5

A competitive inhibitor of an enzyme-catalyzed reaction:

Accepted Answer

Binds at the active site, competing with the substrate.

Question 6

Which of the following statements about the Michaelis-Menten constant $$K_m is $$TRUE?

Accepted Answer

$$K_m is $$the substrate concentration at which the reaction rate is half of $$V_{max}.$$

Question 7

In a Lineweaver-Burk plot, the y-intercept corresponds to:

Accepted Answer

$$1/V_{max}$$

Question 8

If an enzyme-catalyzed reaction has a $$V_{max} of 100$$ $$\mu$$mol/min and a $$K_m of 2 mM$$, what is the initial velocity $$v_0$$ when $$[S] = 2 mM$$?

Accepted Answer

$$v_0 = 50$$ \mu$$mol/min$

Question 9

Which of the following is a consequence of noncompetitive inhibition?

Accepted Answer

$$V_{max}$$ decreases, $$K_m$$ remains unchanged.

Question 10

A metabolic pathway proceeds according to the scheme $$R \rightarrow S \rightarrow T \rightarrow U \rightarrow V \rightarrow W. If $$the last product $$W is a $$negative modulator of $$X$$, which is the most likely regulatory effect?

Accepted Answer

The last product $$W$$ will inhibit the enzyme that catalyzes the first reaction, leading to feedback inhibition.

Question 11

Which of the following statements about allosteric enzymes is TRUE?

Accepted Answer

They usually have more than one polypeptide chain.

Question 12

Which of the following is the best explanation for why glucose is a much better substrate for hexokinase than water?

Accepted Answer

Binding of glucose induces a conformational change in hexokinase that brings catalytic groups into proper orientation.

Question 13

Which of the following is NOT a function of enzymes in biological systems?

Accepted Answer

Increase the equilibrium constant $$K_{eq} of a $$reaction.

Question 14

Which of the following statements about the steady-state assumption in enzyme kinetics is correct?

Accepted Answer

The rate of formation and breakdown of the ES complex are equal.

Question 15

In the reaction $$E + S \xrightleftharpoons[k_{-1}]{k_1$} ES \xrightarrow{k_2$} E + P$$, the rate of breakdown of the enzyme-substrate complex is given by:

Accepted Answer

$$k_{-1}[ES] + k_2$[ES]$$

Question 16

Which of the following is TRUE about the effect of pH on enzyme activity?

Accepted Answer

Enzyme activity is optimal at a specific pH, and deviations can sharply decrease activity.

Question 17

Which of the following is required to calculate the turnover number ($$k_{cat}) of an $$enzyme?

Accepted Answer

The enzyme concentration.

Question 18

Which of the following statements about the effect of substrate concentration on enzyme-catalyzed reactions is correct?

Accepted Answer

At saturating substrate levels, the rate is proportional to enzyme concentration.

Question 19

Which of the following statements about transition-state analogs is correct?

Accepted Answer

They bind more tightly to the enzyme than the substrate.

Question 20

Which of the following is TRUE about allosteric effectors?

Accepted Answer

They bind to a site other than the catalytic site and can increase or decrease enzyme activity.

Enzymes: Structure, Function, and Kinetics – Study Notes

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