Question 1

Which of the following statements best describes a zwitterion form of an amino acid at its isoelectric point (pI)?

Accepted Answer

It has no net electric charge, with the amino group protonated and the carboxyl group deprotonated.

Question 2

Which equation is used to calculate the pH of a solution containing a weak acid and its conjugate base, such as an amino acid buffer system?

Accepted Answer

$$pH = pK_a + \log \frac{[A^-]}{[HA]}$$

Question 3

A patient with phenylketonuria (PKU) must avoid foods containing which artificial sweetener due to its phenylalanine content?

Accepted Answer

Aspartame

Question 4

Which amino acid is classified as both glucogenic and ketogenic?

Accepted Answer

Tyrosine

Question 5

Which of the following best explains why the peptide bond is rigid and planar?

Accepted Answer

It has partial double bond character due to resonance between the carbonyl oxygen and amide nitrogen.

Question 6

Which of the following amino acids contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 7

During electrophoresis at pH 7, which amino acid will migrate toward the cathode (negative electrode)?

Accepted Answer

Lysine

Question 8

Which coenzyme is required for transamination reactions involving amino acids?

Accepted Answer

Pyridoxal phosphate (PLP)

Question 9

Which of the following is a non-protein amino acid that acts as a major inhibitory neurotransmitter in the central nervous system?

Accepted Answer

GABA (gamma-aminobutyric acid)

Question 10

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

Accepted Answer

They must be obtained from the diet because the body cannot synthesize them.

Question 11

Which post-translational modification is most commonly found on the N-terminal amino acid of eukaryotic proteins and is catalyzed by N-alpha acetyltransferases?

Accepted Answer

N-acetylation

Question 12

Which amino acid is most likely to form disulfide bonds, contributing to protein structure stabilization?

Accepted Answer

Cysteine

Question 13

A solution contains glycine at pH 2.0. Which form of glycine predominates?

Accepted Answer

Cationic form ($$\mathrm{H_3N^+-CH_2$-COOH})$$

Question 14

Which of the following best describes the role of glutathione (GSH) in cells?

Accepted Answer

It serves as a major antioxidant, maintaining proteins in the reduced state and detoxifying peroxides.

Question 15

Which of the following amino acids is classified as a branched-chain amino acid and is associated with Maple Syrup Urine Disease when its metabolism is defective?

Accepted Answer

Leucine

Question 16

Which of the following is true regarding the incorporation of selenocysteine into proteins?

Accepted Answer

It is incorporated at the UGA codon, which is normally a stop codon.

Question 17

Which of the following best describes the process of oxidative deamination?

Accepted Answer

Removal of an amino group as ammonia, converting the amino acid to an alpha-keto acid.

Question 18

Which of the following amino acids is considered conditionally essential, especially in growing children?

Accepted Answer

Arginine

Question 19

Which of the following best explains why plant proteins are considered incomplete proteins?

Accepted Answer

They are deficient in one or more essential amino acids.

Question 20

Which of the following is the correct formula for calculating the isoelectric point (pI) of an amino acid with two ionizable groups?

Accepted Answer

$$pI = \frac{pK_1$ + pK_2$}{2}$$

Amino Acids: Structure, Classification, and Biochemical Roles

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