Question 1

Which of the following statements best describes the general structure of an amino acid found in proteins?

Accepted Answer

It contains a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

Question 2

Which property of proline most significantly affects protein secondary structure?

Accepted Answer

Its rigid imino group restricts rotation around the peptide bond, often disrupting alpha helices.

Question 3

Which amino acid is unique in that it is not chiral?

Accepted Answer

Glycine

Question 4

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

Accepted Answer

Methionine

Question 5

What is the main type of interaction that stabilizes the core of a globular protein composed primarily of nonpolar amino acids?

Accepted Answer

Hydrophobic interactions

Question 6

Which amino acid side chain can form a covalent disulfide bond, and what is the significance of this bond in protein structure?

Accepted Answer

Cysteine; it stabilizes tertiary and quaternary structures by forming covalent links between polypeptide chains.

Question 7

At physiological pH (around 7.4), what is the predominant form of the amino and carboxyl groups in an amino acid?

Accepted Answer

The amino group is protonated ($$\mathrm{NH_3$^+}) $$and the carboxyl group is deprotonated ($$\mathrm{COO^-}).$$

Question 8

Which amino acid is most likely to be found at the active site of an enzyme that catalyzes proton transfer near neutral pH, and why?

Accepted Answer

Histidine, because its side chain has a pKa near physiological pH and can act as a proton donor or acceptor.

Question 9

Which of the following best describes a peptide bond?

Accepted Answer

A covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing water.

Question 10

A mutation in the gene encoding a protein changes a nonpolar amino acid to a charged amino acid in the protein core. What is the most likely effect?

Accepted Answer

The protein may misfold or become unstable due to disruption of hydrophobic interactions.

Question 11

Which of the following amino acids can be phosphorylated during cell signaling?

Accepted Answer

Serine, threonine, and tyrosine

Question 12

Which of the following best explains why proteins from different species can have similar functions but different primary structures?

Accepted Answer

Convergent evolution and functional constraints allow for sequence variability while maintaining overall structure and function.

Question 13

Which amino acid has two chiral centers?

Accepted Answer

Isoleucine

Question 14

A peptide has the sequence Ser-Tyr-Val. How many ionizable groups does this tripeptide have?

Accepted Answer

Four (N-terminus, C-terminus, Ser side chain, Tyr side chain)

Question 15

Which of the following is a real-life example of the importance of protein polymorphism in human health?

Accepted Answer

Polymorphisms in the p53 protein can influence cancer susceptibility.

Question 16

Which amino acid is most likely to be found on the surface of a soluble, globular protein?

Accepted Answer

Glutamine

Question 17

Which of the following best describes the effect of phosphorylation on serine, threonine, or tyrosine residues in proteins?

Accepted Answer

It introduces a negative charge, altering protein conformation and function.

Question 18

Which of the following amino acids is most likely to participate in hydrogen bonding with water due to its side chain?

Accepted Answer

Serine

Question 19

Which of the following best explains why the peptide bond is planar and rigid?

Accepted Answer

It has partial double-bond character due to resonance between the carbonyl and amide nitrogen.

Amino Acids and Peptides: Structure, Properties, and Biological Relevance

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