Question 1

Which bonds in the peptide backbone are capable of rotation, allowing for the formation of secondary structures in proteins?

Accepted Answer

The N-C\alpha\ (\phi) and C\alpha\-C (\psi) bonds

Question 2

What is the main reason that proline is rarely found in the middle of an \alpha-helix?

Accepted Answer

Proline's rigid ring structure restricts backbone rotation, disrupting the helix

Question 3

Which of the following statements about the Ramachandran plot is CORRECT?

Accepted Answer

It depicts the sterically allowed regions of dihedral angles for amino acids in a polypeptide chain.

Question 4

In an \alpha-helix, what is the typical hydrogen bonding pattern between backbone atoms?

Accepted Answer

C=O of residue i bonds with N-H of residue i+4

Question 5

Which of the following best describes the orientation of side chains in a \beta-sheet?

Accepted Answer

Side chains alternate above and below the plane of the sheet

Question 6

A protein contains a segment with repeating \phi = -57^\circ\ and \psi = -47^\circ\. What secondary structure is most likely present?

Accepted Answer

Right-handed \alpha-helix

Question 7

Which amino acid is most commonly found in turn regions of proteins due to its small size and flexibility?

Accepted Answer

Glycine

Question 8

What is the main stabilizing force for both \alpha-helices and \beta-sheets in proteins?

Accepted Answer

Hydrogen bonding between backbone amide and carbonyl groups

Question 9

Which of the following statements about parallel and antiparallel \beta-sheets is TRUE?

Accepted Answer

Antiparallel \beta-sheets have linear hydrogen bonds, making them more stable than parallel \beta-sheets.

Question 10

A mutation replaces a glycine with a valine in a \beta-turn. What is the most likely effect on protein structure?

Accepted Answer

The turn may be destabilized due to increased steric hindrance

Question 11

Which of the following best describes a coiled-coil supersecondary structure?

Accepted Answer

Two amphipathic \alpha-helices with hydrophobic residues at i and i+3 positions interact

Question 12

Which of the following amino acids is LEAST likely to be found in an \alpha-helix?

Accepted Answer

Proline

Question 13

What is the pitch (rise per turn) of a right-handed \alpha-helix?

Accepted Answer

$$5.4$$ 	ext{ Å}$

Question 14

Which statement about the planarity of the peptide bond is correct?

Accepted Answer

The peptide bond is planar due to partial double-bond character

Question 15

Which of the following best explains why glycine is allowed in more regions of the Ramachandran plot than other amino acids?

Accepted Answer

Glycine has a small side chain (hydrogen), reducing steric hindrance

Question 16

A segment of a protein has repeating \phi = -139^\circ\ and \psi = 135^\circ\. Which secondary structure is most likely present?

Accepted Answer

Antiparallel \beta-sheet

Question 17

Which of the following is a key feature of \beta-hairpin turns?

Accepted Answer

They are stabilized by a hydrogen bond between the first and fourth residues

Question 18

Which of the following best describes the difference between coil and random coil structures in proteins?

Accepted Answer

Coil refers to any structured region not fitting standard secondary structure, while random coil is unstructured and flexible

Question 19

Which of the following is TRUE regarding the handedness of the \alpha-helix found in proteins?

Accepted Answer

It is right-handed with 3.6 residues per turn

Protein Secondary Structure: Principles, Types, and Structural Features

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