Question 1

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

Accepted Answer

The sequence of amino acids linked by peptide bonds.

Question 2

At a pH of 2, which group on the amino acid glycine is most likely to be ionized?

Accepted Answer

The amino group ($$\mathrm{NH_3$^+}) is $$ionized.

Question 3

Which of the following forces primarily stabilizes the secondary structure of proteins?

Accepted Answer

Hydrogen bonding between backbone atoms.

Question 4

Protein denaturation can be caused by which of the following agents, and what region of the protein is most affected?

Accepted Answer

Heat, affecting secondary and tertiary structure by disrupting hydrogen bonds and hydrophobic interactions.

Question 5

Which of the following is a correct product of the hydrolysis of the peptide Ala-Gly-Ser?

Accepted Answer

Alanine, glycine, and serine as free amino acids.

Question 6

Which statement best describes competitive enzyme inhibition?

Accepted Answer

The inhibitor binds to the active site, preventing substrate binding.

Question 7

An enzyme that catalyzes the transfer of a phosphate group from ATP to another molecule belongs to which major enzyme category?

Accepted Answer

Transferase

Question 8

Which method of enzyme regulation involves the enzyme being synthesized in an inactive form and activated by cleavage?

Accepted Answer

Proenzyme (zymogen) synthesis

Question 9

Which vitamin is water-soluble and what is a consequence of its deficiency?

Accepted Answer

Vitamin C; deficiency leads to scurvy.

Question 10

Which of the following best describes the structure and mode of action of steroid hormones?

Accepted Answer

Steroid hormones are derived from cholesterol and act by entering cells and binding to nuclear receptors.

Question 11

Which step occurs first in the mode of action of epinephrine as a hormone?

Accepted Answer

Epinephrine binds to a cell surface receptor.

Question 12

Which statement about acetylcholine's mode of action is correct?

Accepted Answer

Acetylcholine binds to its receptor, causing ion channels to open and allowing sodium ions to enter the cell.

Question 13

A protein's quaternary structure is stabilized primarily by which interactions?

Accepted Answer

Hydrophobic interactions, hydrogen bonds, and salt bridges between side chains of different polypeptides.

Question 14

Which of the following is an example of feedback control in enzyme regulation?

Accepted Answer

The end product of a metabolic pathway inhibits the first enzyme in the pathway.

Question 15

Which of the following vitamins is fat-soluble and what is a consequence of its excess?

Accepted Answer

Vitamin D; excess can lead to hypercalcemia.

Question 16

Which of the following best describes allosteric control of enzymes?

Accepted Answer

A molecule binds to a site other than the active site, causing a conformational change that affects enzyme activity.

Question 17

Which of the following amino acids would be most likely to be found in the interior of a globular protein due to hydrophobic interactions?

Accepted Answer

Leucine

Question 18

A patient is found to have a deficiency in vitamin B12. Which of the following is a likely consequence?

Accepted Answer

Anemia due to impaired red blood cell formation.

Question 19

Which of the following best describes the effect of uncompetitive inhibition on enzyme kinetics?

Accepted Answer

The inhibitor binds only to the enzyme-substrate complex, decreasing both $$V_{max}$$ and $$K_m.$$

Proteins, Enzymes, Vitamins, and Hormones: Study Guide for Exam #1 (CHEM 123)

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