Question 1

Which of the following statements best explains why proteins can have such a wide variety of functions in biological systems?

Accepted Answer

Proteins are polymers made from 20 different amino acids, and their function depends on the specific order of these amino acids.

Question 2

At physiological pH (about 7.4), what is the charge state of a typical amino acid?

Accepted Answer

The amino group is positively charged and the carboxyl group is negatively charged, resulting in a zwitterion.

Question 3

Which of the following amino acids would be classified as hydrophobic (nonpolar)?

Accepted Answer

Valine

Question 4

What type of bond forms between the $$	ext{–NH}_2$$ group of one amino acid and the $$	ext{–COOH}$$ group of another amino acid in a protein?

Accepted Answer

Peptide (amide) bond

Question 5

Which protein function is exemplified by hemoglobin?

Accepted Answer

Transport

Question 6

A tripeptide is composed of the amino acids phenylalanine, cysteine, and alanine. Which amino acid is at the N-terminus if the peptide is written as Phe–Cys–Ala?

Accepted Answer

Phenylalanine

Question 7

Which of the following best describes the process of forming a peptide bond?

Accepted Answer

A condensation reaction where a molecule of water is eliminated as the $$	ext{–NH}_2$$ group of one amino acid reacts with the $$	ext{–COOH}$$ group of another.

Question 8

Which of the following amino acids contains a side chain with an amide group, making it polar and neutral?

Accepted Answer

Glutamine

Question 9

Which of the following is a correct representation of the general structure of an amino acid at physiological pH?

Accepted Answer

$$\mathrm{H_3N^+{-}CHR{-}COO^-}$$

Question 10

Which of the following amino acids would be classified as polar basic?

Accepted Answer

Lysine

Question 11

A mutation changes a nonpolar amino acid in a protein to a polar acidic amino acid. What is the most likely effect on the protein’s structure?

Accepted Answer

The protein may form new ionic interactions, potentially altering its folding and function.

Question 12

Which of the following best describes the difference between a peptide and a protein?

Accepted Answer

Peptides are shorter chains of amino acids, while proteins are very long chains (typically \u003e 100 amino acids).

Question 13

Which of the following is a correct step in drawing the structure of a tripeptide such as Gly–Ser–Met?

Accepted Answer

Remove the O atom from the carboxylate group of the N-terminal amino acid and two H atoms from the ammonium group of the adjacent amino acid to form the peptide bond.

Question 14

Which of the following proteins is classified as a hormone and regulates blood glucose levels?

Accepted Answer

Insulin

Question 15

Which of the following amino acids is most likely to be found on the surface of a protein in an aqueous environment?

Accepted Answer

Glutamate

Question 16

Which of the following is the correct order for naming a tripeptide composed of alanine, glycine, and valine, starting from the N-terminus?

Accepted Answer

Ala–Gly–Val

Question 17

Which of the following is a function of enzymes in the body?

Accepted Answer

Catalyze biochemical reactions such as digestion and cellular metabolism

Question 18

Which of the following amino acids contains a thiol group in its side chain?

Accepted Answer

Cysteine

Question 19

Which of the following statements about the N-terminus and C-terminus of a peptide is correct?

Accepted Answer

The N-terminus is the end with a free amino group, and the C-terminus is the end with a free carboxyl group.

Protein Structure and Function – Chapter 19 Study Notes

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