This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Post-Translational Modifications – 1”.
1. Single can encode multiple proteins.
a) False
b) True
View Answer
Explanation: The above statement is true. It is estimated that the human genome comprises between 20,000 and 25,000 genes, while, the total number of proteins in the human proteome is estimated at over 1 million. These estimations demonstrate that single genes encode multiple proteins.
2. Which of the following is not a mechanism that can generate different mRNA transcripts from a single gene?
a) Alternative splicing
b) Transcription initiation at alternative promoters
c) Genetic recombination
d) Recombinant DNA technology
View Answer
Explanation: Recombinant DNA technology is not a mechanism that can generate different mRNA transcripts from a single gene. Alternative splicing, transcription initiation at alternative promoters, and genetic recombination are mechanisms that can generate different mRNA transcripts from a single gene.
3. Which of the following is not a post-translational modification?
a) Lipidation
b) Protein phosphorylation
c) Proteolytic processing
d) DNA methylation
View Answer
Explanation: DNA methylation is not a post-translational modification. It is a biological process in which DNA molecules are methylated. Lipidation, protein phosphorylation, and proteolytic processing are proteolytic processing.
4. In O-linked glycosylation, monosaccharides bind to the hydroxyl group of which of the following amino acids?
a) Histidine or glycine
b) Alanine or tryptophan
c) Aspartic acid or glutamic acid
d) Serine or threonine
View Answer
Explanation: In O-linked glycosylation, monosaccharides bind to the hydroxyl group of Serine or threonine amino acids. It does not bind to alanine, tryptophan, aspartic acid, glutamic acid, histidine, or glycine. O-linked glycosylation takes place entirely in the Golgi complex.
5. The human proteome is dynamic.
a) False
b) True
View Answer
Explanation: The above statement is true. The human proteome is dynamic and changes in response to a legion of stimuli, and post-translational modifications are commonly employed to regulate cellular activity. Post-translational modifications occur at distinct amino acid side chains or peptide linkages, and they are most often mediated by enzymatic activity.
6. Protein phosphorylation cannot occur on which of the following amino acid residues?
a) Serine
b) Threonine
c) Tyrosine
d) Tryptophan
View Answer
Explanation: Protein phosphorylation cannot occur on tryptophan amino acid residues. Protein phosphorylation can occur on serine, threonine, and tyrosine. These amino acid residues contain a hydroxyl group in its side chain. Tryptophan does not contain a hydroxyl group in its side chain.
7. Protein glycosylation does not have significant effects on which of the following?
a) Protein folding
b) Protein distribution
c) Protein stability
d) Protein synthesis
View Answer
Explanation: Protein glycosylation does not have significant effects on protein synthesis. Protein glycosylation can have significant effects on protein folding, protein stability, and protein distribution. There are several types of glycosylations.
8. Find the odd one out.
a) Differential transcription termination
b) Alternative splicing
c) Genetic recombination
d) RNA silencing
View Answer
Explanation: RNA silencing is not a mechanism that can generate different mRNA transcripts from a single gene. Differential transcription termination, alternative splicing, and genetic recombination are mechanisms that can generate different mRNA transcripts from a single gene. Hence, RNA silencing is the odd one out.
9. In N-glycosylation, glycan binds to the amino group of which of the following amino acid?
a) Lysine
b) Arginine
c) Histidine
d) Asparagine
View Answer
Explanation: In N-glycosylation, glycan binds to the amino group of asparagine amino acid residue. It does not bind to lysine, arginine, or histidine. N-glycosylation is also known as N-linked glycosylation. It is a complex biosynthetic process that regulates the maturation of proteins through the secretory pathway.
10. In C-linked glycosylation, mannose binds to which of the following?
a) Hydroxyl group of tyrosine
b) Carboxyl group of glutamic acid
c) The amino group of asparagine
d) Indole ring of tryptophan
View Answer
Explanation: In C-linked glycosylation, mannose binds to the indole ring of tryptophan. It does not bind to the hydroxyl group of tyrosine, carboxyl group of glutamic acid, or amino group of asparagine. Glycans serve a variety of structural and functional roles in the membrane and secreted proteins.
11. Find the odd one out.
a) N-acetylation
b) S-nitrosylation
c) Ubiquitination
d) Polyadenylation
View Answer
Explanation: Polyadenylation is the addition of poly(A) tail to the messenger RNA. Hence, it is not a post-translational modification. N-acetylation, S-nitrosylation, and ubiquitination are post-translational modifications. Therefore, polyadenylation is the odd one out.
12. In phosphoglycosylation, the glycan binds to which of the following amino acids via phosphodiester bond?
a) Methionine
b) Glycine
c) Alanine
d) Serine
View Answer
Explanation: In phosphoglycosylation, the glycan binds to serine amino acids via a phosphodiester bond. It does not bind to glycine, alanine, or methionine. Phosphoglycosylation is one of the several types of protein glycosylations.
13. Protein phosphorylation does not play a critical role in which of the following cellular processes?
a) Cell cycle
b) Cell growth
c) Apoptosis
d) Cell wall synthesis
View Answer
Explanation: Protein phosphorylation does not play a critical role in cell wall synthesis. Protein phosphorylation plays a critical role in the cell cycle, cell growth, apoptosis, and signal transduction pathways. Reversible protein phosphorylation is one of the most important and well-studied post-translational modifications.
14. Which of the following enzymes do not mediate post-translational modifications?
a) Kinases
b) Ligases
c) Phosphatases
d) Helicases
View Answer
Explanation: Helicases class of enzymes do not mediate post-translational modifications. These enzymes catalyze the separation of duplex nucleic acids into single strands. Kinases, ligases, and phosphatases are classes of enzymes that can mediate post-translational modifications.
15. Find the odd one out.
a) Kinases
b) Ligases
c) Transferases
d) Endonucleases
View Answer
Explanation: Endonucleases class of enzymes does not mediate post-translational modifications. These classes of enzymes cleave the phosphodiester bond within a polynucleotide chain. Kinases, ligases, and transferases are classes of enzymes that can mediate post-translational modifications. Hence, endonucleases are the odd one out.
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