Question 1

Which of the following best explains why the peptide bond (omega bond) in polypeptides has restricted rotation?

Accepted Answer

Because the peptide bond exhibits resonance, giving it partial double bond character and planarity.

Question 2

In a Ramachandran plot, which factor most directly limits the possible combinations of phi ($$\phi) $$and psi ($$\psi) $$angles in a polypeptide chain?

Accepted Answer

Steric clashes between side chains and backbone atoms.

Question 3

Which of the following correctly describes the hydrogen bonding pattern in an alpha ($$\alpha) $$helix?

Accepted Answer

Each amino acid forms a hydrogen bond with the one four residues ahead in the sequence.

Question 4

Which statement best describes the difference between parallel and antiparallel beta ($$\beta) $$sheets?

Accepted Answer

Antiparallel beta sheets have strands running in opposite directions and typically have more optimal hydrogen bonding geometry.

Question 5

Which torsional angle in a polypeptide backbone is most restricted in its rotation, and why?

Accepted Answer

Omega ($$\omega) $$angle, due to partial double bond character from resonance.

Question 6

Which amino acid is most likely to introduce a kink in an alpha helix, and why?

Accepted Answer

Proline, because its cyclic structure restricts rotation and prevents backbone hydrogen bonding.

Question 7

A polypeptide chain is written from the N-terminus to the C-terminus. Which of the following correctly identifies the chemical groups at these termini?

Accepted Answer

N-terminus: $$-NH_2$; C-terminus: -$$COOH$$

Question 8

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

Accepted Answer

The sequence of amino acids in the polypeptide chain.

Question 9

What is the main stabilizing interaction in beta ($$\beta) $$sheets?

Accepted Answer

Hydrogen bonds between backbone amide and carbonyl groups.

Question 10

Which of the following is NOT a common secondary structure found in proteins?

Accepted Answer

Disulfide bridge

Question 11

A mutation replaces a glycine residue with a bulky tryptophan in a protein. What is the most likely effect on the local phi ($$\phi) $$and psi ($$\psi) $$angles?

Accepted Answer

The angles will be more restricted due to increased steric clashes.

Question 12

Which of the following best describes the information provided by a Ramachandran plot?

Accepted Answer

It displays the allowed and disallowed regions of phi ($$\phi) $$and psi ($$\psi) $$angles due to steric constraints.

Question 13

Which of the following is true regarding the omega ($$\omega) $$bond angle in polypeptides?

Accepted Answer

It is usually found in the trans configuration due to steric hindrance.

Question 14

Which level of protein structure is directly responsible for the overall three-dimensional folding of a single polypeptide chain?

Accepted Answer

Tertiary structure

Question 15

Which of the following statements about proline is correct?

Accepted Answer

Proline's cyclic structure restricts rotation around the phi ($$\phi) $$angle and disrupts alpha helix formation.

Question 16

Which of the following best describes quaternary protein structure?

Accepted Answer

The association of multiple polypeptide chains into a functional protein complex.

Question 17

Which of the following bonds is NOT part of the repeating backbone in a polypeptide chain?

Accepted Answer

Side chain (R group) to alpha-carbon (Cα)

Question 18

Which of the following is a correct application of a Newman projection in protein chemistry?

Accepted Answer

To represent the stereochemistry and steric interactions across the phi ($$\phi) or $$psi ($$\psi) $$bonds in the backbone.

Question 19

Which of the following interactions is NOT typically involved in stabilizing tertiary protein structure?

Accepted Answer

Peptide bonds between amino acids

Amino Acids, Peptides, and Proteins: Structure and Folding

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