This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Translation”.
1. What is the process of synthesis of a polypeptide chain from mRNA known as?
a) Conversion
b) Replication
c) Transcription
d) Translation
View Answer
Explanation: Translation is the process of synthesis of a polypeptide chain from mRNA. First, an mRNA is synthesized from DNA through a process of transcription. This mRNA serves as a template for the synthesis of the polypeptide chain. Replication is the process of duplication of DNA.
2. In which of the following directions does the polypeptide synthesis proceeds?
a) From both N-terminus and C-terminus
b) Either from N-terminus or C-terminus
c) C-terminus to N-terminus
d) N-terminus to C-terminus
View Answer
Explanation: The polypeptide synthesis occurs in the direction from N-terminus to C-terminus. After the first amino acid has been brought to the ribosome, the second amino acid attaches to the carboxyl carbon of the first amino acid. Thus, the first amino acid has an N-terminal free end, and the last amino acid is a C-terminal free end.
3. The ribosome reads mRNA in which of the following direction?
a) Both 3’ → 5’ and 5’ → 3’
b) Either 3’ → 5’ or 5’ → 3’
c) 3’ → 5’ direction only
d) 5’ → 3’ direction only
View Answer
Explanation: Ribosome reads mRNA in the 5’ → 3’ direction only. There is a binding site on the ribosome which has some complementarity to Shine-Dalgarno sequence on the mRNA. This Shine-Dalgarno sequence and the start codon are present on the 5’ side of the mRNA.
4. In prokaryotes and eukaryotes, multiple ribosomes can bind to a single mRNA transcript, and give rise to beads on a string structure. What is this structure called?
a) Monosome
b) Multiribosome
c) Oligosome
d) Polysome
View Answer
Explanation: When multiple ribosomes bind toa single mRNA transcript, they give rise to beads on a string structure known as polysome. Active translation occurs on polysomes.
5. Base pairing between mRNA and which of the following rRNAs help in the selection of translation initiation site?
a) 5.8S rRNA
b) 5S rRNA
c) 28S rRNA
d) 16S rRNA
View Answer
Explanation: The mRNA contains a sequence known as Shine-Dalgarno sequence which is in proximity to the start codon. Base pairing between mRNA and 16S rRNAs help in the selection of translation initiation site. The Shine-Dalgarno sequence pairs to a portion of the 16S rRNA’s 3’ end.
6. Which of the following initiation factor when bound to the 30S subunit blocks the A site, so that only the P site is available for the initiator tRNA to bind to?
a) IF-4
b) IF-2
c) IF-3
d) IF-1
View Answer
Explanation: IF-1 binds to the 30S subunit and blocks the A site so that only the P site is available for the initiator tRNA to bind to. It leaves after the initiator tRNA has attached to its complementary sequence. Now, the 50S ribosomal subunit can bind to the 30S subunit to form a complete 70S ribosome.
7. Which of the following initiation factor bring the initiator tRNA?
a) IF-4
b) IF-3
c) IF-1
d) IF-2
View Answer
Explanation: IF-2 brings the initiator tRNA to the ribosomes. It also carries a molecule of GTP along with it. The initiator tRNA binds to the 30S subunit in the P site.
8. The second and further aminoacyl-tRNAs are brought to the ribosome bound to which of the following protein complex?
a) EF-Ts-ATP
b) EF-Ts-GTP
c) EF-Tu-ATP
d) EF-Tu-GTP
View Answer
Explanation: The aminoacyl-tRNAs are brought to the ribosome bound to EF-Tu-GTP. After its binding to the mRNA GTP hydrolysis releases EF-Tu-GDP. EF-Tu is then recycled with the help of EF-Ts.
9. Which of the following rRNA is intimately involved with the peptidyl transferase activity?
a) 5S rRNA
b) 16S rRNA
c) 28S rRNA
d) 23S rRNA
View Answer
Explanation: 23S rRNA is intimately involved with the peptidyl transferase activity. In this case, the RNA would be acting as a ribozyme. The proteins in the ribosome are the structural units and not catalytic units.
10. With the help of which of the following proteins does the ribosome recognize the stop codon?
a) Cleavage Factors (CF)
b) Elimination Factors (EF)
c) Termination Factors (TF)
d) Release Factors (RF)
View Answer
Explanation: The ribosome recognizes the stop codon with the help of Release Factors (RF). They have shapes mimicking that of tRNA. In E. coli there are three RFs: RF 1, RF 2, and RF 3.
11. Which of the following proteins bind to the ribosome and causes the dissociation of the two ribosomal subunits from mRNA?
a) RF 1
b) RF 2
c) RF 3
d) RRF
View Answer
Explanation: RRF binds to the ribosome on the empty site. A reaction cascade follows this binding and ultimately results in the release of two ribosomal subunits from mRNA. RRF is Ribosome Release Factor.
12. First, the bond between the amino acid and the tRNA in the P site is cleaved, then the peptide bond is formed between the two amino acids.
a) False
b) True
View Answer
Explanation: The above statement is true. First, the bond between the amino acid and the tRNA in the P site is cleaved and then the peptide bond is formed between the two amino acids. This reaction is catalyzed by a peptidyl transferase.
13. The peptidyl transferase center that catalyzes the peptide bond formation is located on the smaller subunit and consists entirely of rRNA.
a) True
b) False
View Answer
Explanation: The peptidyl transferase center that catalyzes the peptide bond formation is located on the larger subunit and consists entirely of rRNA. The ribosome is indeed a ribozyme rather than a conventional protein enzyme.
14. Find the odd one out.
a) Puromycin
b) Streptomycin
c) Chloramphenicol
d) Vancomycin
View Answer
Explanation: Vancomycin is an antibiotic that acts by disrupting the cell wall synthesis. It prevents the formation of the new cell wall by inhibiting peptidoglycan synthesis. Puromycin, streptomycin, and chloramphenicol are antibiotics that act by disrupting protein synthesis.
15. Which of the following antibiotic acts by competitively inhibiting the peptidyl transferase activity of prokaryotic ribosomes?
a) Puromycin
b) Vancomycin
c) Tetracycline
d) Chloramphenicol
View Answer
Explanation: Chloramphenicol is a broad-spectrum antibiotic that acts by competitively inhibiting the peptidyl transferase activity of prokaryotic ribosomes. It binds to the larger subunit, near the A site.
Sanfoundry Global Education & Learning Series – Protein Engineering.
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