Question 1

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

Accepted Answer

Water's polarity and ability to form hydrogen bonds enable it to surround and stabilize both cations and anions.

Question 2

Which of the following molecules is most likely to be amphipathic?

Accepted Answer

Cholesterol

Question 3

A solution is prepared by dissolving 0.01 mol of HCl (a strong acid) in enough water to make 1 L of solution. What is the pH of the solution?

$$\mathrm{pH} = -\log_{10}[\mathrm{H}^+]$$

Accepted Answer

$$\mathrm{pH} = 2$$

Question 4

Which of the following best describes the role of the bicarbonate buffer system in human blood?

Accepted Answer

It maintains blood pH by reversible interconversion of $$\mathrm{CO}_2$$, $$\mathrm{H}_2\mathrm{CO}_3$$, and $$\mathrm{HCO}_3^-.$$

Question 5

Given a weak acid with $$pK_a = 4.75$$, what is the ratio of conjugate base to acid when the pH of the solution is 5.75? Use the Henderson-Hasselbalch equation:

$$\mathrm{pH} = pK_a + \log_{10}\left(\frac{[A^-]}{[HA]}\right)$$

Accepted Answer

10:1

Question 6

Which of the following amino acids would have a net negative charge at pH 7.0?

Accepted Answer

Aspartic acid (Asp, D)

Question 7

A peptide has the sequence Ala-Glu-Lys. At pH 7, what is the net charge of the peptide? (Assume N-terminus and C-terminus are free, and use the following pKa values: $$\alpha-$$COOH = 2.0, $$\alpha-NH$_2 = 9.0$$, Glu side chain = 4.1, Lys side chain = 10.5)

Accepted Answer

0

Question 8

Which of the following best describes the effect of SDS in SDS-PAGE?

Accepted Answer

SDS denatures proteins and imparts a uniform negative charge, allowing separation by size.

Question 9

Which of the following statements about hydrogen bonding in water is FALSE?

Accepted Answer

Hydrogen bonds in water are stronger than covalent bonds.

Question 10

Which of the following best explains why nonpolar molecules are poorly soluble in water?

Accepted Answer

Nonpolar molecules cannot form hydrogen bonds with water, leading to unfavorable entropy changes.

Question 11

A buffer is prepared using acetic acid ($$pK_a = 4.76) $$and sodium acetate. If the buffer solution has a pH of 4.76, what is the ratio of acetate ion to acetic acid?

Accepted Answer

1:1

Question 12

Which of the following best describes the primary structure of DNA?

Accepted Answer

The sequence of nucleotides linked by phosphodiester bonds.

Question 13

Which of the following is TRUE regarding the enthalpic and entropic contributions to DNA stability?

Accepted Answer

Hydrogen bonding and base stacking provide enthalpic stabilization, while DNA unfolding increases entropy.

Question 14

Which of the following best describes the function of restriction enzymes in molecular cloning?

Accepted Answer

They cleave DNA at specific sequences, allowing insertion of foreign DNA.

Question 15

Which of the following amino acids is most likely to be found in the interior of a globular protein?

Accepted Answer

Leucine

Question 16

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? Use the Henderson-Hasselbalch equation.

Accepted Answer

$$4.76$$

Question 17

Which of the following best describes the principle behind size exclusion chromatography?

Accepted Answer

Large molecules elute first because they are excluded from the pores of the resin.

Question 18

Which of the following oligonucleotides would form the most stable DNA duplex (highest melting temperature)?

Accepted Answer

5'-GCGCGC-3'

Question 19

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

Accepted Answer

The weak acid neutralizes the added base, minimizing the change in pH.

Question 20

Which of the following is the correct formula for calculating the isoelectric point ($$pI) of an $$amino acid with two ionizable groups?

Accepted Answer

$$pI = \frac{pK_1$ + pK_2$}{2}$$

Key Concepts in Water Chemistry, Nucleic Acids, and Proteins

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