Question 1

Which of the following statements best explains why glycine is unique among the 20 common amino acids?

Accepted Answer

Glycine is the only amino acid that is not chiral because its alpha carbon is bonded to two hydrogen atoms.

Question 2

A patient with celiac disease experiences inflammation after consuming wheat products. Which property of gluten-derived peptides is most responsible for triggering this immune response?

Accepted Answer

They contain regions rich in proline and glutamine, which are resistant to complete digestion and can be modified to glutamate.

Question 3

Which of the following best describes the isoelectric point ($$pI) of an $$amino acid?

Accepted Answer

The $$pH at $$which the amino acid exists only in its zwitterionic form, with a net charge of zero.

Question 4

Which of the following foods would provide a complete protein source for a vegetarian?

Accepted Answer

Soybeans, because they contain all essential amino acids.

Question 5

Which type of chemical bond is formed between the carboxyl group of one amino acid and the amino group of another during protein synthesis?

Accepted Answer

A peptide bond (amide bond), with the loss of water.

Question 6

A protein’s tertiary structure is stabilized by several interactions. Which of the following is NOT a stabilizing force for tertiary structure?

Accepted Answer

Peptide bonds between amino acids.

Question 7

Which of the following best explains why increasing substrate concentration can reverse the effects of a competitive inhibitor but not a noncompetitive inhibitor?

Accepted Answer

Competitive inhibitors bind to the active site, so more substrate can outcompete the inhibitor; noncompetitive inhibitors bind elsewhere and change the enzyme’s shape.

Question 8

Which of the following statements about enzyme-substrate interactions is correct according to the induced-fit model?

Accepted Answer

The enzyme’s active site changes shape to better fit the substrate upon binding.

Question 9

A patient is prescribed penicillin to treat a bacterial infection. Penicillin acts as an irreversible inhibitor. What does this mean for the bacterial enzymes targeted by penicillin?

Accepted Answer

Penicillin forms a covalent bond with the enzyme, permanently inactivating it.

Question 10

Which of the following best describes the difference between primary and secondary protein structure?

Accepted Answer

Primary structure is the sequence of amino acids; secondary structure is the local folding into alpha helices and beta sheets stabilized by hydrogen bonds.

Question 11

At a pH below the isoelectric point ($$pI) of an $$amino acid, which form predominates?

Accepted Answer

The amino acid is protonated and carries a net positive charge.

Question 12

Which of the following is a real-life consequence of protein misfolding, as seen in Alzheimer’s disease?

Accepted Answer

Beta-amyloid proteins change from alpha-helical to beta-strand structures, forming plaques in the brain.

Question 13

Which of the following best describes a quaternary protein structure?

Accepted Answer

The arrangement and interaction of multiple polypeptide chains to form a functional protein.

Question 14

Which of the following statements about essential amino acids is correct?

Accepted Answer

They cannot be synthesized by the human body and must be obtained from the diet.

Question 15

Which of the following interactions is responsible for the formation of disulfide bonds in proteins?

Accepted Answer

Covalent bonding between the thiol groups of two cysteine residues.

Question 16

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

The active site of the enzyme has a unique shape and chemical environment that only fits specific substrates.

Question 17

A solution contains an amino acid at its isoelectric point ($$pI). $$Which of the following best describes the amino acid’s form in this solution?

Accepted Answer

It exists primarily as a zwitterion, with both a positive and a negative charge but a net charge of zero.

Question 18

Which of the following is a correct statement about the effect of temperature on enzyme activity?

Accepted Answer

Enzyme activity increases with temperature up to an optimum (around 37°C for humans), then decreases as the enzyme denatures.

Question 19

Which of the following best describes a competitive inhibitor?

Accepted Answer

A molecule that resembles the substrate and binds to the enzyme’s active site, preventing substrate binding.

Proteins: Structure, Function, and Enzyme Activity

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