This set of Protein Engineering Interview Questions and Answers focuses on “Amino Acids – 2”.
1. The pH at which an amino acid has no net charge on it is known as its isoelectric point (pI).
a) False
b) True
View Answer
Explanation: Amino acids have two or more than two ionizable groups. At low values of pH (acidic), these groups are protonated whereas, at higher values of pH (basic), these groups are deprotonated. There is an intermediate pH value, for which the amino acid will have no net charge. This pH is called its isoelectric point (pI). Hence, the above statement is true.
2. Find the odd one out.
a) Alanine
b) Aspartic acid
c) Serine
d) Glycine
View Answer
Explanation: Glycine contains hydrogen atom as its side chain; therefore, its alpha-carbon is achiral. The rest of the amino acids have side chain groups other than the hydrogen atom, hence contain a chiral carbon atom. Therefore, glycine is the only amino acid that is optically inactive.
3. ______ stereochemical configuration of amino acids is present in proteins.
a) Only D
b) Both D and L
c) Either D or L
d) Only L
View Answer
Explanation: Only the L stereochemical configuration of amino acids is present in proteins. Therefore, the relative configuration around the alpha carbon atoms of all the amino acids is the same. L amino acids can either be dextrorotatory or laevorotatory.
4. The bioluminescent jellyfish Aequorea victoria, has a protein called Green Fluorescent Protein (GFP) that fluoresces with a peak wavelength of ________, under UV or blue light radiation.
a) 808 nm
b) 708 nm
c) 408 nm
d) 508 nm
View Answer
Explanation: The wavelength 508 nm is the correct answer as it lies in the green light spectrum of electromagnetic radiation. The wavelength 808 nm, 708 nm, and 408 nm lie in the infrared region, red light region, and blue light region respectively.
5. Which of the following is the correct sequence of the three consecutive amino acids present in the light-emitting group of green fluorescent protein?
a) Asp-Ser-Glu
b) Ser-Gly-Asn
c) Ser-Thr-Gly
d) Ser-Tyr-Gly
View Answer
Explanation: Ser-Tyr-Gly is the correct sequence. The green fluorescent protein is made up of 238 amino acids. Once this protein is synthesized, these three amino acids undergo spontaneous cyclization and oxidation. The structure thus formed contains a system of double bonds that show conjugation and give this protein its fluorescent property.
6. Among the listed amino acids, which one is non-polar?
a) Lysine
b) Serine
c) Histidine
d) Glycine
View Answer
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.
7. Find the odd one out.
a) Alanine
b) Valine
c) Leucine
d) Serine
View Answer
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.
8. ______ is also known as ‘helix breaker’.
a) Valine
b) Serine
c) Methionine
d) Proline
View Answer
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.
9. Glycine is the only amino acid that is optically inactive.
a) False
b) True
View Answer
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.
10. Which of the following amino acid contains benzene ring in it?
a) Glutamine
b) Threonine
c) Histidine
d) Tryptophan
View Answer
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.
11. Which of the following amino acid is most commonly associated with N-linked glycosylation?
a) Arginine
b) Lysine
c) Aspartic acid
d) Asparagine
View Answer
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.
12. _____ is a sulfur-containing amino acid.
a) Alanine
b) Asparagine
c) Tryptophan
d) Methionine
View Answer
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.
13. Which of the following amino acid is not associated with phosphorylation?
a) Tyrosine
b) Threonine
c) Serine
d) Valine
View Answer
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.
14. Which of the following amino acid shows hydrophilic nature?
a) Leucine
b) Glycine
c) Valine
d) Serine
View Answer
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.
15. Which of the following amino acid is known to form disulfide cross-links?
a) Glutamine
b) Valine
c) Methionine
d) Cysteine
View Answer
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.
Sanfoundry Global Education & Learning Series – Protein Engineering.
To practice all areas of Protein Engineering for Interviews, here is complete set of 1000+ Multiple Choice Questions and Answers.
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