1. Among the listed amino acids, which one is non-polar?
a) Lysine
b) Serine
c) Histidine
d) Glycine
Explanation: Glycine is a non-polar amino acid because it contains hydrogen atom as its side chain. Lysine, serine, and histidine contain polar groups in their side chain, so they are polar.
2. Find the odd one out.
a) Alanine
b) Valine
c) Leucine
d) Serine
Explanation: Serine would be the odd one out because it is a polar amino acid, whereas alanine, valine, and leucine are non-polar amino acids. Serine is a neutral but polar amino acid. Moreover, it contains a hydroxyl group in its side chain.
3. ______ is also known as ‘helix breaker’.
a) Valine
b) Serine
c) Methionine
d) Proline
Explanation: Proline is also known as ‘helix breaker’. Proline has a fused ring structure due to its side chain. Generally, proline is not present in a helix due to its high steric hindrance. When it is placed in a helix it breaks it.
4. Glycine is the only amino acid that is optically inactive.
a) false
b) true
Explanation: The above statement is true. Glycine contains ‘H’ atom in its side chain; thus, the alpha carbon of glycine is bonded directly to two hydrogen atoms. Hence, it contains an achiral alpha carbon atom. The rest of the amino acids contain side chain groups other than ‘H’ atom, hence they all are optically active. Therefore, glycine is the only optically inactive amino acid.
5. Which of the following amino acid contains benzene ring in it?
a) Glutamine
b) Threonine
c) Histidine
d) Tryptophan
Explanation: Tryptophan is a non-polar aromatic amino acid, as it contains an indole group in its side chain. This indole side chain contains two fused rings one of which is benzene. Hence, tryptophan is the correct answer.
6. Which of the following amino acid is most commonly associated with N-linked glycosylation?
a) Arginine
b) Lysine
c) Aspartic acid
d) Asparagine
Explanation: Asparagine is a neutral but polar amino acid. Asparagine contains an amino group in its side chain. In N-linked glycosylation, glycan binds to this amino group of asparagine. Hence asparagine is the correct answer.
7. _____ is a sulfur-containing amino acid.
a) Alanine
b) Asparagine
c) Tryptophan
d) Methionine
Explanation: Methionine and cysteine are the only sulfur-containing natural amino acids. As there is only methionine in the given options, it is the correct answer. Alanine contains a methyl group as its side chain. Asparagine contains an amide group in its side chain. Tryptophan contains an indole group as its side chain.
8. Which of the following amino acid is not associated with phosphorylation?
a) Tyrosine
b) Threonine
c) Serine
d) Valine
Explanation: Valine is not associated with phosphorylation. Tyrosine, threonine, and serine contain ‘OH’ group in its side chain for phosphorylation whereas valine lacks ‘OH’ group, and thus is not associated with phosphorylation.
9. Which of the following amino acid shows hydrophilic nature?
a) Leucine
b) Glycine
c) Valine
d) Serine
Explanation: Serine shows hydrophilic nature. It contains polar ‘OH’ group in its side chain, hence it is hydrophilic. Thus, serine is neutral but polar. Leucine, glycine, and valine do not have any polar group in their side chain. Hence, they are not hydrophilic.
10. Which of the following amino acid is known to form disulfide cross-links?
a) Glutamine
b) Valine
c) Methionine
d) Cysteine
Explanation: Cysteine contains a sulfhydryl group in its side chain. This sulfhydryl group is reduced to form a disulfide linkage. Glutamine, valine, and methionine do not contain a sulfhydryl group; hence they cannot form disulfide linkage.