Question 1

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

Accepted Answer

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

Question 2

What type of reaction forms a peptide bond between two amino acids?

Accepted Answer

Condensation reaction

Question 3

Which of the following statements about peptide bonds is FALSE?

Accepted Answer

Peptide bonds allow free rotation around the C-N bond

Question 4

A dipeptide is formed from alanine and serine. Which of the following correctly represents the peptide bond formed?

Accepted Answer

$$\mathrm{C=O} - \mathrm{NH}$$

Question 5

Which property of peptide bonds is responsible for the planarity of the protein backbone?

Accepted Answer

Partial double-bond character due to resonance

Question 6

What is the directionality of a polypeptide chain as conventionally written?

Accepted Answer

N-terminal to C-terminal

Question 7

Which of the following best explains why Ala-Ser and Ser-Ala are not the same dipeptide?

Accepted Answer

The sequence of amino acids determines the directionality and properties of the peptide

Question 8

Which of the following is a correct statement about the charges on a tetrapeptide at neutral pH?

Accepted Answer

Only the terminal alpha-amino and alpha-carboxyl groups retain their charges

Question 9

Which of the following best describes the backbone of a polypeptide?

Accepted Answer

A repeating sequence of N-C\alpha-C

Question 10

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

Accepted Answer

It shows the allowed values of phi ($$\phi) $$and psi ($$\psi) $$angles for amino acid residues

Question 11

What is the main stabilizing force in the formation of alpha helices in proteins?

Accepted Answer

Hydrogen bonds between backbone CO and NH groups in the same helix

Question 12

Which of the following is a distinguishing feature of beta-sheets compared to alpha helices?

Accepted Answer

Beta-sheets are stabilized by hydrogen bonds between backbone groups of neighboring strands

Question 13

A mutation replaces a hydrophobic amino acid in the core of a globular protein with a charged amino acid. What is the most likely consequence?

Accepted Answer

The protein may misfold or become unstable due to disruption of the hydrophobic core

Question 14

Which of the following best describes the difference between a motif and a domain in protein structure?

Accepted Answer

A motif is a short region with a recognizable 3D shape, while a domain is a larger, independently folded unit

Question 15

Which of the following forces is NOT primarily responsible for stabilizing tertiary structure in globular proteins?

Accepted Answer

Covalent peptide bonds between backbone atoms

Question 16

Which of the following statements about protein denaturation is TRUE?

Accepted Answer

Denaturation can be caused by extremes of pH, detergents, or chaotropic salts

Question 17

Which of the following is a correct description of quaternary structure?

Accepted Answer

The spatial arrangement of multiple polypeptide subunits in a protein

Question 18

Which of the following best explains why peptide bonds do not ionize as pH changes?

Accepted Answer

The carbonyl and amino groups in the peptide bond are involved in resonance and have no pKa value

Question 19

Which of the following is a consequence of the partial double-bond character of the peptide bond?

Accepted Answer

Restricted rotation around the C-N bond

Question 20

Which of the following best describes the difference between parallel and antiparallel beta-sheets?

Accepted Answer

Antiparallel beta-sheets have linear hydrogen bonds and are more stable than parallel beta-sheets

Protein Structure & Function: Peptide Bonds and Primary Structure

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