Question 1

Which of the following best describes the First Law of Thermodynamics and its relevance to living organisms?

Accepted Answer

Energy cannot be created or destroyed, only transformed or transferred, so organisms must obtain energy from their environment.

Question 2

A chemical reaction has $$G_{initial} = 250\ \mathrm{kcal/mol}$$ and $$G_{final} = 180\ \mathrm{kcal/mol}. $$Calculate $$\Delta G$$ and determine the type of reaction.

Accepted Answer

$$\Delta G = -70\ \mathrm{kcal/mol}$$; exergonic

Question 3

Which of the following statements about exergonic and endergonic reactions is correct?

Accepted Answer

Exergonic reactions have a negative $$\Delta G$$ and increase the stability of the system.

Question 4

A cell needs to drive an endergonic reaction with $$\Delta G = +15\ \mathrm{kcal/mol}. $$ATP hydrolysis under cellular conditions has $$\Delta G = -30\ \mathrm{kcal/mol}. $$What is the net $$\Delta G if $$the reactions are coupled, and will the overall process be spontaneous?

Accepted Answer

Net $$\Delta G = -15\ \mathrm{kcal/mol}$$; the process is spontaneous.

Question 5

Which of the following best explains why enzymes are considered biological catalysts?

Accepted Answer

They lower the activation energy required for a reaction to proceed without being permanently changed.

Question 6

A graph shows the rate of an enzyme-catalyzed reaction peaking at pH 7 and decreasing at both lower and higher pH values. What is the most likely explanation for the decrease in activity at extreme pH values?

Accepted Answer

The enzyme is denatured, altering its active site and reducing its catalytic ability.

Question 7

Which of the following scenarios best illustrates energy coupling in a cell?

Accepted Answer

A spontaneous exergonic reaction is used to drive a nonspontaneous endergonic reaction via ATP hydrolysis.

Question 8

Which of the following is true regarding the effect of enzymes on the transition state of a reaction?

Accepted Answer

Enzymes stabilize the transition state, lowering the activation energy required for the reaction.

Question 9

Which of the following best distinguishes competitive from noncompetitive enzyme inhibition?

Accepted Answer

Competitive inhibitors bind to the active site, while noncompetitive inhibitors bind to a different site on the enzyme.

Question 10

A reaction has $$\Delta G = 0. $$Which of the following statements is correct?

Accepted Answer

The reaction is at equilibrium and no net work can be done.

Question 11

Which of the following best describes the effect of temperature on enzyme activity?

Accepted Answer

Enzyme activity increases with temperature up to an optimal point, then decreases as the enzyme denatures.

Question 12

Which of the following reactions would most likely be coupled to ATP hydrolysis in a cell?

Accepted Answer

An endergonic reaction with $$\Delta G = +20\ \mathrm{kcal/mol}$$

Question 13

Which of the following statements about anabolic and catabolic reactions is correct?

Accepted Answer

Anabolic reactions build complex molecules and are typically endergonic, while catabolic reactions break down molecules and are typically exergonic.

Question 14

If an enzyme-catalyzed reaction is saturated with substrate, which of the following will most likely increase the rate of product formation?

Accepted Answer

Increasing the enzyme concentration.

Question 15

Which of the following best explains why not all enzymes in an organism function at the same optimal pH?

Accepted Answer

Different enzymes are adapted to the specific pH of their cellular environment; for example, pepsin in the stomach works best at low pH.

Question 16

Which of the following is a correct statement about the effect of ATP hydrolysis on endergonic reactions?

Accepted Answer

ATP hydrolysis provides energy, making the overall coupled reaction exergonic and more likely to occur spontaneously.

Question 17

Which of the following best describes the concept of 'induced fit' in enzyme function?

Accepted Answer

The enzyme changes shape slightly to better fit the substrate upon binding.

Question 18

A patient is given a drug that acts as a noncompetitive inhibitor of a key metabolic enzyme. Which of the following is most likely to occur?

Accepted Answer

The drug binds to a site other than the active site, reducing the enzyme's activity regardless of substrate concentration.

Question 19

Which of the following best describes the Second Law of Thermodynamics as it applies to biological systems?

Accepted Answer

Every energy transfer increases the entropy of the universe, so living systems must constantly obtain energy to maintain order.

Energy, Metabolism, and Enzymes: Study Guide for Chapter 8

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