Question 1

Which of the following statements best describes the isoelectric point (pI) of an amino acid without an ionizable side chain?

Accepted Answer

It is the pH at which the amino acid has no net charge, calculated as $$pI = \frac{pK_1$ + pK_2$}{2}.$$

Question 2

A solution contains glycine at pH 1.0. Which form of glycine predominates at this pH?

Accepted Answer

Cation ($$\mathrm{H_3N^+-CH_2$-COOH})$$

Question 3

Which amino acid is most likely to disrupt an alpha helix due to its unique cyclic structure?

Accepted Answer

Proline

Question 4

Which of the following amino acids contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 5

A peptide bond is formed between which two functional groups of adjacent amino acids?

Accepted Answer

The carboxyl group of one and the amino group of the next

Question 6

Which of the following best explains why proteins fold into specific three-dimensional structures?

Accepted Answer

To minimize hydrophobic interactions with water and maximize stabilizing interactions such as hydrogen bonds, ionic interactions, and disulfide bridges

Question 7

Which method would be most appropriate to separate proteins based on their size?

Accepted Answer

Size exclusion chromatography

Question 8

What is the net charge of histidine at pH 7.59, given its $$pK_1 = 1.82$, pK_2$ = 9.17$$, and $$pK_R = 6.00$$?

Accepted Answer

0

Question 9

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

Accepted Answer

Leucine

Question 10

Which of the following statements about the peptide bond is FALSE?

Accepted Answer

It can freely rotate around the C-N bond.

Question 11

A protein is found to contain several disulfide bonds. Which amino acid is responsible for forming these bonds?

Accepted Answer

Cysteine

Question 12

Which of the following best describes the secondary structure of silk fibroin?

Accepted Answer

Antiparallel beta sheets stabilized by hydrogen bonds and London dispersion forces

Question 13

Which of the following equations correctly calculates the isoelectric point (pI) for aspartate, which has $$pK_1 = 1.88$, pK_2$ = 9.60$$, and $$pK_R = 3.65$$?

Accepted Answer

$$pI = \frac{1.88 + 3.65}{2}$$

Question 14

Which of the following is a function of hemoglobin?

Accepted Answer

Transporting oxygen from the lungs to tissues

Question 15

Which of the following amino acids is NOT chiral?

Accepted Answer

Glycine

Question 16

Which of the following best describes the quaternary structure of a protein?

Accepted Answer

The assembly of multiple polypeptide subunits into a functional protein complex

Question 17

Which of the following amino acids has a positively charged side chain at physiological pH?

Accepted Answer

Lysine

Question 18

Which of the following techniques is most suitable for determining the amino acid sequence of a small peptide?

Accepted Answer

Edman degradation

Question 19

Which of the following interactions is primarily responsible for the stabilization of antiparallel beta sheets?

Accepted Answer

Hydrogen bonds that are linear between strands

Question 20

A mutation replaces a glycine residue with a valine in the interior of a collagen triple helix. What is the most likely consequence?

Accepted Answer

The triple helix will be destabilized because glycine is required at every third position for tight packing.

Amino Acids, Peptides, and Proteins: Structure, Properties, and Function

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