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 electric charge.

Question 2

Given the following pKa values for glycine: $$pK_1 = 2.34$ (carboxyl group) and pK_2$ = 9.60 ($$amino group), calculate the isoelectric point ($$pI) $$for glycine.

Accepted Answer

$$pI = \frac{2.34 + 9.60}{2} = 5.97$$

Question 3

Which amino acid is NOT chiral and why?

Accepted Answer

Glycine, because its R group is a hydrogen atom.

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 two amino acids by which type of reaction?

Accepted Answer

Condensation (dehydration) reaction

Question 6

Which of the following best explains why proline is considered a 'helix breaker' in alpha helices?

Accepted Answer

Its side chain forms a rigid ring that restricts rotation around the N–Cα bond.

Question 7

Which of the following interactions is primarily responsible for stabilizing the tertiary structure of a globular protein?

Accepted Answer

Hydrophobic interactions among nonpolar side chains

Question 8

A protein is found to consist of four polypeptide chains, each with its own tertiary structure. What is the highest level of structure present in this protein?

Accepted Answer

Quaternary structure

Question 9

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

Accepted Answer

Size exclusion chromatography

Question 10

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

Accepted Answer

Leucine

Question 11

A mutation replaces a glycine residue with a proline in the middle of an alpha helix. What is the most likely effect on the protein structure?

Accepted Answer

The alpha helix will be disrupted at the site of mutation.

Question 12

Which of the following best describes the role of disulfide bonds in protein structure?

Accepted Answer

They stabilize the tertiary and quaternary structures by forming covalent links between cysteine residues.

Question 13

Which of the following amino acids has a side chain that can form hydrogen bonds and also participate in disulfide bond formation?

Accepted Answer

Cysteine

Question 14

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

Accepted Answer

It is freely rotatable around the C–N bond.

Question 15

Which of the following best describes the difference between parallel and antiparallel beta sheets?

Accepted Answer

Antiparallel beta sheets have linear hydrogen bonds, making them more stable than parallel beta sheets.

Question 16

Which of the following is a correct statement about the primary structure of a protein?

Accepted Answer

It is the unique sequence of amino acids in a polypeptide chain.

Question 17

Which amino acid is most likely to be found at the turn of a beta sheet due to its small size and flexibility?

Accepted Answer

Glycine

Question 18

A solution of aspartate is titrated with NaOH. Given $$pK_1 = 1.88$, pK_R = 3.65$, and pK_2$ = 9.60$$, what is the isoelectric point ($$pI) of $$aspartate?

Accepted Answer

$$pI = \frac{1.88 + 3.65}{2} = 2.77$$

Question 19

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

Accepted Answer

Edman degradation

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

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