Question 1

Which of the following best explains why water has a much higher boiling point than methane, despite their similar molecular weights?

Accepted Answer

Water forms extensive hydrogen bonds between molecules, requiring more energy to break.

Question 2

Which type of noncovalent interaction is primarily responsible for the specificity of the human growth hormone (hGH) binding to its receptor?

Accepted Answer

Hydrogen bonds and charge-charge interactions

Question 3

Given the following energies for noncovalent interactions: charge-charge (13–17 kJ/mol), hydrogen bond (2–21 kJ/mol), van der Waals (0.4–0.8 kJ/mol), which interaction is most likely to be disrupted by thermal motion at 37°C?

Accepted Answer

Van der Waals interactions

Question 4

Which of the following equations correctly represents the relationship between the acid dissociation constant ($$K_a$$), the concentrations of acid and its conjugate base, and the hydrogen ion concentration?

Accepted Answer

$$K_a = \frac{[H^+][A^-]}{[HA]}$$

Question 5

A solution contains 0.1 M acetic acid ($$pK_a = 4.76) $$and 0.1 M sodium acetate. What is the pH of the solution?

Accepted Answer

pH = 4.76

Question 6

Which of the following best describes the molecular basis for the high heat of vaporization of water compared to ammonia?

Accepted Answer

Water forms more extensive hydrogen bonding networks than ammonia.

Question 7

Which of the following statements about the isoelectric point (pI) of a protein is correct?

Accepted Answer

At the pI, the protein has no net charge.

Question 8

Which of the following best explains why NaCl dissolves readily in water?

Accepted Answer

Water molecules form hydration shells around Na$$^+$$ and Cl$$^-$$ ions, stabilizing them in solution.

Question 9

Which of the following interactions is most distance-dependent, decreasing most rapidly as the distance between molecules increases?

Accepted Answer

Dispersion (van der Waals) interactions

Question 10

Which of the following best describes the role of hydrogen bonds in the structure of DNA?

Accepted Answer

Hydrogen bonds between complementary bases stabilize the double helix.

Question 11

A protein is placed in a solution with pH much lower than its pI. What will be the net charge on the protein?

Accepted Answer

The protein will have a net positive charge.

Question 12

Which of the following best explains why amphipathic molecules form micelles or bilayers in water?

Accepted Answer

Their hydrophobic tails aggregate to minimize contact with water, while hydrophilic heads interact with water.

Question 13

Which of the following is the correct Henderson-Hasselbalch equation for calculating the pH of a buffer solution?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 14

Which of the following best explains why the alpha-helix structure of a protein is stabilized in the absence of water?

Accepted Answer

All internal hydrogen bonds are maintained, preventing disruption by water.

Question 15

Which of the following is a real-life example of a charge-charge interaction?

Accepted Answer

The ionic bond between Na$$^+$$ and Cl$$^- in $$table salt.

Question 16

Which of the following best describes the effect of adding a strong acid to a buffered solution containing equal concentrations of a weak acid and its conjugate base?

Accepted Answer

The pH will decrease slightly, but the buffer will resist large changes.

Question 17

Which of the following best explains why ice is less dense than liquid water?

Accepted Answer

Hydrogen bonds in ice form an open lattice structure, increasing the volume.

Question 18

Which of the following is the strongest noncovalent interaction found in biomolecules?

Accepted Answer

Charge-charge (electrostatic) interaction

Question 19

Which of the following best describes the molecular geometry of a water molecule?

Accepted Answer

Bent geometry with a bond angle of 104.5°

Noncovalent Interactions and Hydrogen Bonding in Biochemistry

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