Question 1

Which of the following best describes the role of ATP in cellular metabolism?

Accepted Answer

ATP provides energy by transferring a phosphate group to other molecules, coupling exergonic and endergonic reactions.

Question 2

A scientist measures the free energy change ($$\Delta G) of a $$reaction and finds it to be negative. What does this indicate about the reaction?

Accepted Answer

The reaction is exergonic and thermodynamically favorable.

Question 3

Which of the following statements about enzymes is correct?

Accepted Answer

Enzymes lower the activation energy ($$E_a) $$but do not change the $$\Delta G of a $$reaction.

Question 4

A patient is diagnosed with a genetic mutation that alters a single amino acid in the active site of an enzyme. Which of the following is the most likely consequence?

Accepted Answer

The enzyme's substrate specificity or catalytic efficiency may change, depending on the nature of the mutation.

Question 5

Which scenario best illustrates the concept of feedback inhibition in a metabolic pathway?

Accepted Answer

The end product of a pathway binds to an early enzyme, decreasing its activity and preventing overproduction.

Question 6

In a laboratory experiment, an enzyme-catalyzed reaction is performed at increasing substrate concentrations. The reaction rate increases at first but then levels off, even as more substrate is added. What is the most likely explanation?

Accepted Answer

The active sites of all enzyme molecules are saturated with substrate.

Question 7

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

Accepted Answer

Competitive inhibitors bind to the active site, and their effects can be overcome by increasing substrate concentration; noncompetitive inhibitors bind elsewhere and reduce maximum reaction rate regardless of substrate concentration.

Question 8

A researcher adds a noncompetitive inhibitor to an enzyme-catalyzed reaction. Which of the following graphs best represents the effect on reaction rate as substrate concentration increases?

Accepted Answer

The reaction rate increases but plateaus at a lower maximum rate than without the inhibitor.

Question 9

Which of the following is an example of energy coupling in cells?

Accepted Answer

ATP hydrolysis releases energy that is used to drive the active transport of ions against their concentration gradient.

Question 10

A certain enzyme has an optimal temperature of $$37^\circC. $$What is most likely to happen if the temperature is increased to $$60^\circC$$?

Accepted Answer

The enzyme's structure may be disrupted, leading to decreased activity due to denaturation.

Question 11

Which of the following best explains why cells maintain metabolic pathways far from equilibrium?

Accepted Answer

At equilibrium, the net reaction flux is zero, so no work can be done; continuous input and removal of materials keep pathways running and allow cells to perform work.

Question 12

A mutation causes an enzyme to lose its ability to bind a required zinc ion. What is the most likely effect on the enzyme's activity?

Accepted Answer

The enzyme's activity will decrease or stop, since zinc is an essential inorganic cofactor.

Question 13

Which of the following statements about the ATP cycle is correct?

Accepted Answer

ATP is synthesized from ADP and $$P_i$$ using energy from catabolic reactions, and hydrolyzed to ADP and $$P_i to $$drive cellular work.

Question 14

A metabolic pathway involves several enzymes. If the end product of the pathway accumulates and inhibits the first enzyme, what is this an example of?

Accepted Answer

Feedback inhibition

Question 15

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

Accepted Answer

Changes in pH can alter the ionization of amino acid side chains, affecting enzyme conformation and activity.

Question 16

A researcher observes that the binding of a substrate to one subunit of an enzyme increases the binding affinity of other subunits for the substrate. What is this phenomenon called?

Accepted Answer

Cooperativity

Question 17

Which of the following is true regarding the relationship between free energy, stability, and spontaneous change?

Accepted Answer

Spontaneous changes decrease free energy and increase stability.

Question 18

Which of the following best explains why enzymes are specific for their substrates?

Accepted Answer

The active site of an enzyme has a unique shape and chemical environment that only fits specific substrates, often through induced fit.

Question 19

A cell is exposed to a toxin that acts as a competitive inhibitor for a key metabolic enzyme. Which of the following would most likely reduce the toxin's effect?

Accepted Answer

Increasing the concentration of the substrate.

Question 20

Which of the following is a correct statement about the first and second laws of thermodynamics as they apply to biological systems?

Accepted Answer

The first law states that energy is conserved, and the second law states that total entropy increases in energy transformations.

Enzymes and Energy Transformations in Biological Systems 10/26/26

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