Question 1

Which statement best explains why peptide bonds are planar and rigid?

Accepted Answer

Because the peptide bond has partial double bond character due to resonance between the carbonyl oxygen and amide nitrogen.

Question 2

Which configuration of the peptide bond is most commonly found in proteins, and why?

Accepted Answer

Trans, because it maximizes steric exclusion between the carbonyl oxygen and amide hydrogen.

Question 3

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

Accepted Answer

The linear sequence of amino acids from the N-terminus to the C-terminus.

Question 4

Which of the following is a consequence of the repeating NCCNCC pattern in the polypeptide main chain?

Accepted Answer

It creates a constant backbone structure, while side chains provide variability.

Question 5

Which statement about secondary structure is correct?

Accepted Answer

Secondary structure is maintained by hydrogen bonds between main-chain amide and carbonyl groups.

Question 6

What is the main difference between parallel and anti-parallel beta sheets?

Accepted Answer

Anti-parallel beta sheets are more stable due to optimal hydrogen bonding geometry.

Question 7

Which amino acid is least likely to be found in an alpha helix, and why?

Accepted Answer

Proline, because its rigid structure disrupts the helix.

Question 8

A protein is found to have a molecular weight of 22,000 Da. Approximately how many amino acids does it contain?

Accepted Answer

Question 9

Which equation would you use to estimate the number of amino acids in a protein given its molecular weight?

Accepted Answer

Divide the molecular weight by the average amino acid residue weight: $$\frac{	ext{Molecular Weight}}{110}$$

Question 10

Which of the following best explains the amphipathic nature of alpha helices?

Accepted Answer

Residues separated by three or four positions in the primary sequence are on the same side of the helix, allowing for distinct polar and non-polar faces.

Question 11

Which of the following is a key stabilizing force in tertiary protein structure?

Accepted Answer

Non-covalent interactions such as hydrogen bonds, ionic interactions, and van der Waals forces.

Question 12

What is the biological significance of quaternary structure in proteins?

Accepted Answer

It enables the association of multiple polypeptide chains, creating unique active sites and dynamic functional combinations.

Question 13

Which post-translational modification is essential for the formation of stabilizing crosslinks in collagen?

Accepted Answer

Hydroxylation of proline and lysine residues.

Question 14

A patient presents with bleeding gums, poor wound healing, and fragile blood vessels. Which biochemical defect is most likely responsible?

Accepted Answer

Deficiency in vitamin C, leading to impaired hydroxylation of collagen residues.

Question 15

Which protein structure is most associated with the mechanical strength of hair, wool, and nails?

Accepted Answer

Keratin, due to its coiled-coil structure stabilized by disulfide bonds.

Question 16

Which of the following is true regarding prion diseases?

Accepted Answer

They result from misfolding of a self-protein into a pathological, infectious conformation.

Question 17

Which of the following best describes the folding funnel model of protein folding?

Accepted Answer

Proteins rapidly collapse into a single, stable, low-energy conformation without sampling all possible states.

Question 18

Which of the following is a common feature of silk that contributes to its strength and flexibility?

Accepted Answer

Fully extended polypeptide chains forming beta sheets stabilized by hydrogen bonds and van der Waals interactions.

Question 19

Which equation best represents the relationship between protein stability and free energy?

Accepted Answer

Protein stability is proportional to the difference in free energy between folded and unfolded states: $$\Delta G = G_{	ext{folded}} - G_{	ext{unfolded}}$$

The Three-Dimensional Structure of Proteins: Study Notes

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