Question 1

Which of the following best describes the primary structure (1°) of a protein?

Accepted Answer

The sequence of amino acids linked by peptide bonds.

Question 2

Linus Pauling established several principles for secondary structure formation. Which principle is NOT one of them?

Accepted Answer

Side chains must always be hydrophobic.

Question 3

Which of the following correctly identifies the N-terminus of a polypeptide?

Accepted Answer

The end with a free amino group ($$-NH_2$).

Question 4

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

Accepted Answer

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

Question 5

Which property of the peptide bond contributes to its planarity?

Accepted Answer

Partial double-bond character due to resonance.

Question 6

In a polypeptide, the phi ($$\phi) $$and psi ($$\psi) $$angles refer to:

Accepted Answer

The rotation around the N-C$$_\alpha$$ and C$$_\alpha-C $$bonds, respectively.

Question 7

Which of the following is a factor that destabilizes an alpha-helix?

Accepted Answer

Presence of proline residues within the helix.

Question 8

Which statement best distinguishes parallel from anti-parallel beta-sheets?

Accepted Answer

In parallel beta-sheets, the strands run in the same direction; in anti-parallel, they run in opposite directions.

Question 9

Which secondary structure is predominant in collagen?

Accepted Answer

Triple helix.

Question 10

A motif in protein structure is best defined as:

Accepted Answer

A recurring combination of secondary structures with a specific function.

Question 11

Which of the following best describes a domain in a protein?

Accepted Answer

A distinct structural and functional unit that can fold independently.

Question 12

Which statement about globular proteins is correct?

Accepted Answer

Hydrophobic amino acids are generally found in the interior, while hydrophilic amino acids are on the surface.

Question 13

The Anfinsen experiment with ribonuclease A demonstrated that:

Accepted Answer

The primary structure determines the final folded structure of a protein.

Question 14

Which thermodynamic factor is most important in driving protein folding?

Accepted Answer

The hydrophobic effect, which increases entropy of water.

Question 15

Disulfide bonds contribute to protein stability by:

Accepted Answer

Forming covalent links between cysteine residues.

Question 16

The molten globule theory of protein folding suggests that:

Accepted Answer

Proteins pass through a partially folded intermediate with secondary structure but not fully formed tertiary structure.

Question 17

Which of the following is NOT a characteristic of a fibrous protein?

Accepted Answer

Soluble in water.

Question 18

A beta-turn (hairpin turn) in a protein structure is important because:

Accepted Answer

It allows the polypeptide chain to reverse direction.

Question 19

Which level of protein structure is directly stabilized by hydrogen bonds between backbone atoms?

Accepted Answer

Secondary structure (2°).

Question 20

A patient with a mutation that prevents the formation of disulfide bonds in a protein is most likely to experience:

Accepted Answer

Reduced protein stability and increased susceptibility to denaturation.

The Three-Dimensional Structure of Proteins: Principles, Structures, and Folding

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