Question 1

Which of the following statements best explains why amino acids can act as buffers in physiological pH?

Accepted Answer

Amino acids contain both an amino group and a carboxyl group, allowing them to accept or donate protons depending on the pH.

Question 2

Which post-translational modification is most likely to regulate protein activity by adding a negative charge to the protein?

Accepted Answer

Phosphorylation

Question 3

A peptide bond is formed by which type of chemical reaction?

Accepted Answer

Condensation (dehydration synthesis)

Question 4

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

Accepted Answer

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

Question 5

Which equation correctly represents the Michaelis-Menten relationship for enzyme kinetics?

Accepted Answer

$$v = \frac{V_{max} [S]}{K_m + [S]}$$

Question 6

A mutation causes the replacement of a hydrophobic amino acid with a hydrophilic one in the core of a protein. What is the most likely consequence?

Accepted Answer

The protein may misfold or lose stability due to disruption of hydrophobic interactions.

Question 7

Which of the following is a function of antibodies in the immune response?

Accepted Answer

Binding specifically to antigens to neutralize or mark them for destruction.

Question 8

Which post-translational modification is essential for the stability of collagen fibers?

Accepted Answer

Hydroxylation of proline and lysine residues

Question 9

Hemoglobin exhibits cooperative binding of oxygen. Which of the following best describes this phenomenon?

Accepted Answer

Binding of one oxygen molecule increases the affinity for subsequent oxygen molecules.

Question 10

Which of the following is NOT a typical function of enzymes?

Accepted Answer

Changing the equilibrium constant of a reaction.

Question 11

A patient is diagnosed with scurvy, a disease caused by defective collagen synthesis. Which vitamin deficiency is most likely responsible?

Accepted Answer

Vitamin C

Question 12

Which of the following amino acids can be phosphorylated during post-translational modification?

Accepted Answer

Tyrosine

Question 13

Which of the following best describes the role of the ribosome in protein synthesis?

Accepted Answer

It translates mRNA into a polypeptide chain by facilitating peptide bond formation.

Question 14

Which of the following is a correct statement about the secondary structure of proteins?

Accepted Answer

It consists of alpha helices and beta sheets stabilized by hydrogen bonds.

Question 15

Which of the following is a ribozyme?

Accepted Answer

An RNA molecule that catalyzes a chemical reaction.

Question 16

A researcher is studying the effect of pH on enzyme activity. At very low pH, the enzyme is inactive. What is the most likely explanation?

Accepted Answer

The enzyme is denatured due to disruption of ionic and hydrogen bonds.

Question 17

Which of the following best explains why hemoglobin can transport oxygen efficiently in the blood?

Accepted Answer

Hemoglobin exhibits cooperative binding, allowing efficient oxygen loading and unloading.

Question 18

Which of the following is a consequence of a mutation that disrupts the disulfide bonds in a protein?

Accepted Answer

The protein may lose its tertiary and quaternary structure, leading to loss of function.

Question 19

Which of the following is true about the genetic code?

Accepted Answer

The genetic code is degenerate, meaning multiple codons can encode the same amino acid.

Proteins and Enzymes: Structure, Function, and Catalysis

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