250+ TOP MCQs on Amino Acids and Answers

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Biochemistry Multiple Choice Questions on “Amino Acids”.

1. Identify the amino acids containing nonpolar, aliphatic R groups.
A. Phenylalanine, tyrosine, and tryptophan
B. Glycine, alanine, leucine
C. Lysine, arginine, histidine
D. Serine, threonine, cysteine
Answer: B
Explanation:
Glycine: H3 N+ – CH2 – COO–
Alanine: H3 N+ – CH(CH3) – COO–
Leucine: H3 N+ – CH(C4 H9) – COO–.

2. The two amino acids having R groups with a negative net charge at pH 7.0 are ___________
A. Aspartate and glutamate
B. Arginine and histidine
C. Cysteine and methionine
D. Proline and valine
Answer: A
Explanation:
Aspartate: H3 N+ – CH( CH2 COO–) – COO–
Glutamate: H3 N+ – CH( C2 H4 COO–) – COO–.

3. If pK1 = 2.34 and pK2 = 9.60, then the isoelectric point pI is?
A. 5.87
B. 5.97
C. 3.67
D. 11.94
Answer: B
Clarification: pI = 1⁄2 (pK1 + pK2) = 1⁄2 (2.34 + 9.60) = 5.97.

4. Which of the following is a true statement?
A. Tryptophan and tyrosine are significantly more polar than phenylalanine
B. Leucine is commonly used as an ingredient in the buffers of SDS page
C. Aspartate is an essential amino acid
D. Lysine is a non-essential amino acid
Answer: A
Clarification: Tryptophan and tyrosine are significantly more polar than phenylalanine because of the tyrosine hydroxyl group and the nitrogen of the tryptophan indole ring.

5. Which among the following is a non-essential amino acid?
A. Serine
B. Threonine
C. Lysine
D. Histidine
Answer: A
Clarification: Serine is one of the 11 non-essential amino acids.

6. Which of the following is an essential amino acid?
A. Cysteine
B. Asparagine
C. Glutamine
D. Phenylalanine
Answer: D
Clarification: Phenylalanine is one of the 9 essential amino acids.

7. Which of the following is an imino acid?
A. Alanine
B. Glycine
C. Proline
D. Serine
Answer: C
Clarification: Proline is secondary amino acid also called as an imino acid as it contains –C = NH – OH group.

8. Which among the following is both glucogenic and ketogenic?
A. Isoleucine
B. Leucine
C. Lysine
D. Histidine
Answer: A
Clarification: Isoleucine produces both glucose and ketone bodies as an energy source.

9. An amino acid that yields acetoacetyl CoA during the catabolism of its carbon skeleton will be considered as __________
A. Glycogenic
B. Ketogenic
C. Both glycogenic and ketogenic
D. Essential
Answer: B
Clarification: In case of Glycogenic amino acids pyruvate metabolites are formed and in case of ketogenic amino acids acetoacyl CoA is formed during the catabolism.

10. Number of chiral centers in isoleucine is?
A. 1
B. 2
C. 3
D. 4
Answer: B
Clarification: H5 C2 – C ̇H(CH3)- C ̇H(NH2) – COOH
The structure clearly shows two chiral centers of isoleucine.

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