This set of Biochemistry Multiple Choice Questions & Answers (MCQs) focuses 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
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
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
Explanation: 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
Explanation: 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?
Explanation: Serine is one of the 11 non-essential amino acids.
6. Which of the following is an essential amino acid?
Explanation: Phenylalanine is one of the 9 essential amino acids.
7. Which of the following is an imino acid?
Explanation: 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?
Explanation: 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
c) Both glycogenic and ketogenic
Explanation: 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
Explanation: H5 C2 – C ̇H(CH3 )- C ̇H(NH2 ) – COOH
The structure clearly shows two chiral centers of isoleucine.
Sanfoundry Global Education & Learning Series – Biochemistry.
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