Question 1

Which of the following best explains why the phosphorylation of glucose by ATP is overall a favorable reaction in cells?

Accepted Answer

The hydrolysis of ATP releases more free energy than is required to phosphorylate glucose, making the coupled reaction favorable.

Question 2

Given the following standard free energies of hydrolysis: $$\Delta G$$^{\circ'}$$ for ATP → ADP + P_i$ is -30.5$ kJ/mol, and for glucose + P_i$ → glucose-6-phosphate is +13.8$ kJ/mol. What is the $$\Delta $$G^{\circ'}$$ for the overall reaction: glucose + ATP → glucose-6-phosphate + ADP?

Accepted Answer

$$-16.7 kJ/$$mol

Question 3

Which compound listed in Table 1.1 has the most negative standard free energy of hydrolysis ($$\Delta G$$^{\circ'}$$)?

Accepted Answer

Phosphoenolpyruvate

Question 4

Why does phosphoenolpyruvate (PEP) hydrolysis release so much free energy?

Accepted Answer

The product, pyruvate, rapidly tautomerizes from the enol to the more stable keto form, driving the reaction forward.

Question 5

Which of the following statements about enzyme-catalyzed reactions is correct?

Accepted Answer

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

Question 6

Refer to the free energy diagram for the enzyme-catalyzed phosphorylation of glucose. What is the main effect of the enzyme on the reaction pathway?

Accepted Answer

It decreases the height of the activation energy barrier, allowing the reaction to proceed faster.

Question 7

Which of the following functional groups is responsible for the high-energy character of ATP?

Accepted Answer

Phosphoanhydride

Question 8

During the titration of acetic acid with NaOH, what is the pH at the point where $$[\mathrm{CH_3COOH}] = [\mathrm{CH_3COO^-}]$$?

Accepted Answer

The pH equals the p$$K_a of $$acetic acid, which is 4.76.

Question 9

Which of the following best describes the difference between a nucleotide and a nucleoside?

Accepted Answer

A nucleotide contains a phosphate group, while a nucleoside does not.

Question 10

Which of the following interactions is NOT a major contributor to the stabilization of the DNA double helix?

Accepted Answer

Covalent bonds between base pairs

Question 11

Which of the following best explains why the hydrolysis of ATP to ADP and $$P_i is $$highly exergonic?

Accepted Answer

The products (ADP and $$P_i) $$are stabilized by resonance and charge separation, and there is a relief of electrostatic repulsion.

Question 12

Which of the following best describes the role of coupling reactions in metabolism?

Accepted Answer

They allow energetically unfavorable reactions to proceed by linking them to favorable reactions.

Question 13

Which of the following is a correct statement about the titration curve of glycine?

Accepted Answer

The isoelectric point (pI) is the pH at which glycine has no net charge.

Question 14

Which of the following amino acids contains a side chain that can form a disulfide bond?

Accepted Answer

Cysteine

Question 15

Which of the following best explains the resonance structure of the peptide bond?

Accepted Answer

It gives the C-N bond partial double-bond character, restricting rotation.

Question 16

Which of the following is a property of nonpolar amino acid side chains?

Accepted Answer

They are hydrophobic and often found in the interior of proteins.

Question 17

Which of the following amino acids is most likely to be found at the active site of an enzyme that catalyzes acid-base reactions near physiological pH?

Accepted Answer

Histidine

Question 18

Which of the following best describes the hydrophobic effect in protein folding?

Accepted Answer

It is driven by the increase in entropy of water molecules as hydrophobic groups cluster together.

Coupling Reactions and ATP Hydrolysis in Biochemistry

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