Question 1

Which of the following best describes a noncovalent interaction in biological systems?

Accepted Answer

A weak, reversible interaction that can be continually broken and reformed.

Question 2

Which equation correctly represents Coulomb’s Law for the force between two charges in a vacuum?

Accepted Answer

$$F = k \frac{q_1$ q_2$}{r^2$}$$

Question 3

In an aqueous environment, the force between two ions is reduced compared to a vacuum. What property of water is primarily responsible for this effect?

Accepted Answer

High dielectric constant

Question 4

Which of the following is NOT a type of noncovalent interaction found in biomolecules?

Accepted Answer

Covalent bond

Question 5

A protein is placed in a solution at a pH equal to its isoelectric point (pI). What is the net charge on the protein?

Accepted Answer

Zero

Question 6

Which of the following best explains why water is an excellent solvent for ionic compounds?

Accepted Answer

Water has a high dielectric constant, which screens electrostatic interactions.

Question 7

Which of the following statements about hydrogen bonds is correct?

Accepted Answer

Hydrogen bonds involve a hydrogen atom covalently bonded to O or N and a lone pair on another O or N.

Question 8

A solution contains 1 M acetic acid (pK$$_a = 4.76) $$and 1 M sodium acetate. What is the pH of the solution?

Accepted Answer

pH = 4.76

Question 9

Which equation is the Henderson-Hasselbalch equation?

Accepted Answer

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

Question 10

Which of the following best describes the hydrophobic effect in aqueous solutions?

Accepted Answer

Water forms ordered clathrate structures around nonpolar molecules, decreasing entropy.

Question 11

A buffer solution is most effective at resisting pH changes when:

Accepted Answer

The pH is close to the pK$$_a of $$the acid in the buffer.

Question 12

Which property of water is primarily responsible for its high boiling point compared to other molecules of similar size?

Accepted Answer

Hydrogen bonding between water molecules

Question 13

Which of the following best describes an amphipathic molecule?

Accepted Answer

A molecule that contains both hydrophilic and hydrophobic regions

Question 14

A solution of glycine (pK$$_1 = 2.3$$, pK$$_2 = 9.6) is $$titrated with NaOH. At what pH is the average net charge of glycine zero?

Accepted Answer

pH = 5.95

Question 15

Which of the following statements about van der Waals interactions is correct?

Accepted Answer

They arise from transient induced dipoles between molecules.

Question 16

During agarose gel electrophoresis, DNA molecules are separated based on which property?

Accepted Answer

Their molecular weight (size)

Question 17

Isoelectric focusing separates proteins based on:

Accepted Answer

Net surface charge (isoelectric point)

Question 18

Which of the following is the correct relationship for the ion product of water at 25°C?

Accepted Answer

$$K_w = [H^+][OH^-]$$

Question 19

A solution has a hydrogen ion concentration of $$1 	imes 10$$^{-5}$$ M. What is its pH?

Accepted Answer

pH = 5

Question 20

Which of the following best explains why proteins are least soluble at their isoelectric point?

Accepted Answer

They have no net charge, reducing electrostatic repulsion and promoting aggregation.

The Chemical Foundation of Life: Weak Interactions in an Aqueous Environment

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