Question 1

Which of the following statements best describes the primary structure of a protein?

Accepted Answer

The covalent bonds linking amino acid residues in a linear sequence.

Question 2

Which of the following amino acids is NOT chiral?

Accepted Answer

Glycine

Question 3

At physiological pH (about 7.4), which form do most amino acids exist in?

Accepted Answer

As a zwitterion with both a negatively charged carboxylate and a positively charged amino group.

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 by which type of reaction?

Accepted Answer

Condensation (dehydration) reaction

Question 6

Which of the following best explains why aromatic amino acids absorb UV light at 270–280 nm?

Accepted Answer

Their side chains contain conjugated double bonds.

Question 7

Calculate the isoelectric point ($$pI) of $$glycine, given $$pK_1 = 2.34$ and pK_2$ = 9.60.$$

Accepted Answer

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

Question 8

Which of the following amino acids can form disulfide bonds?

Accepted Answer

Cysteine

Question 9

A protein is found to have a molecular weight of 44,000 Da. Estimate the number of amino acid residues in this protein.

Accepted Answer

$$\frac{44,000}{110} = 400$$ residues

Question 10

Which of the following statements about the titration curve of glycine is TRUE?

Accepted Answer

It has two buffer regions centered around $$pK_1$$ and $$pK_2.$$

Question 11

Which of the following best describes a conjugated protein?

Accepted Answer

A protein that contains a permanently associated non–amino acid component.

Question 12

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

Accepted Answer

Leucine

Question 13

Which of the following modifications is an example of a post-translational modification of an amino acid?

Accepted Answer

4-hydroxyproline in collagen

Question 14

Which of the following best describes the effect of the chemical environment on the $$pK_a of $$the $$\,\alpha-$$carboxyl group in amino acids?

Accepted Answer

It is more acidic than in simple carboxylic acids due to the electron-withdrawing effect of the $$\,\alpha-$$amino group.

Question 15

Which of the following is TRUE regarding the naming of peptides?

Accepted Answer

The sequence is written from the N-terminal to the C-terminal.

Question 16

Which of the following amino acids has a side chain that can be titrated, affecting the isoelectric point ($$pI) of $$the amino acid?

Accepted Answer

Histidine

Question 17

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

Accepted Answer

The association of two or more polypeptide subunits.

Question 18

Which of the following is a correct statement about the buffer regions of glycine?

Accepted Answer

They are centered around $$pK_1 = 2.34$ and pK_2$ = 9.60.$$

Question 19

Which of the following best explains why proteins can be separated from each other for study?

Accepted Answer

Proteins have distinct chemical and functional properties due to their unique amino acid sequences.

Amino Acids, Peptides, and Proteins: Structure and Properties

Study Guide - Practice Questions