Q: Which of the following is a correct application of the Henderson-Hasselbalch equation for calculating pH?

pH $$= \mathrm{p}K_a + \log\left(\frac{[\text{base}]}{[\text{acid}]}\right)$$

Q: Which equation describes the self-ionization of water, and what is the value of $$K_W at 25$$°C?

$$K_W = [\mathrm{H^+}][\mathrm{OH^-}] = 1.0 \times 10$$^{-14}$$

Question 1

Which of the following statements best explains why water has a high heat of vaporization compared to other small molecules?

Accepted Answer

Water molecules form extensive hydrogen bonding networks, which require significant energy to disrupt during vaporization.

Question 2

A biochemist is preparing a buffer using acetic acid (pKa = 4.76) and sodium acetate. If the desired pH is 5.76, what is the ratio of acetate ion ($$\mathrm{A^-}) to $$acetic acid ($$\mathrm{HA}) $$required? Use the Henderson-Hasselbalch equation.

Accepted Answer

The ratio is $$\frac{[\mathrm{A^-}]}{[\mathrm{HA}]} = 10$$

Question 3

Which amino acid is unique in that its side chain forms a covalent bond with the amino group, resulting in a rigid ring structure?

Accepted Answer

Proline

Question 4

A solution contains 0.2 M glucose and 0.1 M NaCl. What is the total osmolarity of the solution, assuming complete dissociation of NaCl? (Use the Morse equation for osmotic pressure: $$\Pi = iMRT)$$

Accepted Answer

0.4 Osm/L

Question 5

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

Accepted Answer

Hydrophobic molecules aggregate to minimize disruption of water's hydrogen bonding network, increasing the entropy of water.

Question 6

Which amino acid does NOT have an L- or D- enantiomeric form, and why?

Accepted Answer

Glycine, because its side chain is a hydrogen atom, making the alpha carbon achiral.

Question 7

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

Accepted Answer

pH $$= \mathrm{p}K_a + \log\left(\frac{[	ext{base}]}{[	ext{acid}]}ight)$$

Question 8

Which disease is associated with the misfolding of amyloid proteins, resulting in the formation of insoluble fibrils?

Accepted Answer

Alzheimer's disease

Question 9

What is the main driving force for protein folding in aqueous environments?

Accepted Answer

Hydrophobic effect, which causes nonpolar residues to aggregate away from water

Question 10

Which of the following best describes the Miller-Urey experiment and its significance?

Accepted Answer

It demonstrated that amino acids could be synthesized from simple inorganic molecules under prebiotic conditions, disproving vitalism.

Question 11

Which of the following amino acids is most likely to stabilize a cis peptide bond?

Accepted Answer

Proline

Question 12

A protein's secondary structure is primarily stabilized by which type of interaction?

Accepted Answer

Hydrogen bonds between main chain amide and carbonyl groups

Question 13

Which equation describes the self-ionization of water, and what is the value of $$K_W at 25$$°C?

Accepted Answer

$$K_W = [\mathrm{H^+}][\mathrm{OH^-}] = 1.0 	imes 10$$^{-14}$$

Question 14

Which of the following best describes the structure and function of collagen?

Accepted Answer

Collagen is a triple helix composed mainly of glycine, proline, and hydroxyproline, providing structural support in connective tissues.

Question 15

Which of the following is NOT a distinguishing characteristic of living organisms?

Accepted Answer

Ability to form peptide bonds

Question 16

Which of the following best describes the difference between prokaryotes and eukaryotes?

Accepted Answer

Prokaryotes lack a membrane-bound nucleus, while eukaryotes possess one.

Question 17

Which of the following functional groups is present in the side chain of cysteine and is involved in disulfide bond formation?

Accepted Answer

Sulfhydryl ($$\mathrm{-SH})$$

Question 18

A cell is placed in a hypotonic solution. What will happen to the cell?

Accepted Answer

The cell will swell as water enters by osmosis.

Question 19

Which of the following best describes the role of chaperones in protein folding?

Accepted Answer

Chaperones assist proteins in achieving their proper three-dimensional structure, preventing aggregation.

Question 20

Which equation is used to calculate the electrostatic force between two charges in water, and what is the significance of the dielectric constant ($$\varepsilon$$)?

Accepted Answer

$$F = \frac{q_1$ q_2$}{4 \pi \$$varepsilon_0$$ \varepsilon r^2$}$$; a high $$\varepsilon in $$water reduces the force between charges, increasing solubility of ions.

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