Question 1

Which of the following statements best explains why the peptide bond is planar and exhibits restricted rotation?

Accepted Answer

The peptide bond has partial double-bond character due to resonance, restricting rotation around the C–N bond.

Question 2

A mutation replaces a glycine residue with proline in the middle of an α-helix. What is the most likely effect on the protein structure?

Accepted Answer

The α-helix will be disrupted because proline restricts backbone rotation and cannot form a backbone hydrogen bond.

Question 3

Which equation correctly represents the formation of a peptide bond between two amino acids?

Accepted Answer

$$\mathrm{H_2N{-}$$CHR_1$${-}COOH + H_2N{-}$$CHR_2$${-}COOH \rightarrow H_2N{-}$$CHR_1$${-}CONH{-}$$CHR_2$${-}COOH + H_2O}$$

Question 4

Which of the following best describes the hydrogen bonding pattern in an α-helix?

Accepted Answer

Hydrogen bonds form between the C=O of residue $$i$$ and the N–H of residue $$i+4.$$

Question 5

A protein is denatured by heating. Which of the following statements is TRUE regarding the denaturation process?

Accepted Answer

The secondary, tertiary, and quaternary structures are lost, but the primary structure remains intact.

Question 6

Which of the following is a key difference between parallel and anti-parallel β-sheets?

Accepted Answer

Anti-parallel β-sheets have linear hydrogen bonds, making them more stable than parallel β-sheets.

Question 7

Which of the following best describes the Ramachandran plot?

Accepted Answer

It shows the allowed values of φ (phi) and ψ (psi) backbone dihedral angles for amino acid residues in a protein.

Question 8

Which of the following interactions is primarily responsible for stabilizing the tertiary structure of a protein?

Accepted Answer

Hydrophobic interactions, hydrogen bonds, ionic interactions, and disulfide bonds

Question 9

Which of the following best explains why proteins with exposed hydrophobic surfaces tend to aggregate in solution?

Accepted Answer

Exposed hydrophobic surfaces interact with each other to minimize contact with water, leading to aggregation.

Question 10

Which of the following is TRUE regarding the renaturation of ribonuclease A after denaturation?

Accepted Answer

Renaturation can occur if the primary structure is intact and denaturing conditions are removed gradually.

Question 11

Which of the following is a characteristic feature of the α-helix secondary structure?

Accepted Answer

Right-handed coil with 3.6 residues per turn and a pitch of 5.4 Å

Question 12

Which of the following best describes the role of chaperonins in protein folding?

Accepted Answer

They provide an isolated environment for proper folding of hydrophobic sequences, preventing aggregation.

Question 13

Which of the following is a correct statement about disulfide bonds in proteins?

Accepted Answer

Disulfide bonds form between two cysteine residues, stabilizing tertiary or quaternary structure.

Question 14

Which of the following best describes the difference between integral and peripheral membrane proteins?

Accepted Answer

Integral proteins are embedded within the lipid bilayer, while peripheral proteins are loosely attached to the membrane surface.

Question 15

Which of the following is a common feature of β-turns in proteins?

Accepted Answer

They consist of four amino acids and are stabilized by a hydrogen bond between the C=O of residue $$i$$ and the N–H of residue $$i+3.$$

Question 16

Which of the following best describes the effect of urea on protein structure?

Accepted Answer

Urea disrupts non-covalent interactions, leading to protein denaturation.

Question 17

Which of the following is a real-world example of protein denaturation?

Accepted Answer

The coagulation of egg white proteins when an egg is cooked.

Question 18

Which of the following best describes π–π interactions in protein structure?

Accepted Answer

They are non-covalent interactions between aromatic rings, such as phenylalanine, tyrosine, and tryptophan.

Protein Structure: From Peptide Bonds to Quaternary Organization

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