This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Elongation and Termination”.
1. Which of the elongation factor binds to amino acyl tRNA?
Explanation: EF-Tu in GTP bound form binds to amino acyl tRNA. It helps to bring the amino acid to the ribosome, and one placed in proper position the GTP hydrolyses.
2. EF-Tu GTP complex is ____________
a) Very unstable
d) Very stable
Explanation: The GTP bound form of EF-Tu is so stable that it needs another factor EF-Ts to break it down and reattach it to another GTP.
3. After the Ef-G cycle the A site_________
a) Houses peptide bound tRNA
b) Amino acid bound tRNA
d) Uncharged trNA
Explanation: The EF-G factor helps in translocation of the ribosome such that the peptide bound tRNA shifts to the P site and A site becomes empty and available to bind another charged tRNA.
4. The E site of the ribosome has a high affinity for___________
a) Peptide bound tRNA
b) Ester linked tRNA
c) Acylated tRNA
d) Deacylated tRNA
Explanation: From the A site and the P site, the tRNA moves to the E site or exit site. Then its tRNA is deacylated as the peptide bond is on the P site tRNA.
5. What is the rate of translation in prokaryotes under adequate conditions?
a) 10 amino acid per second
b) 20 amino acid per second
c) 30 amino acid per second
d) 40 amino acid per second
Explanation: While the ribosome can read about 50-60 nucleotides per second, due to triplet codon the maximum number of amino acids added per second would be : (60/3) = 20 amino acid per second.
6. According to the hybrid state model, if we consider the hybrid state of a tRNA such that its base is bound to the P site of 30S subunit, where will its head be bound?
a) A site of 50S
b) P site of 50S
c) E site of 50S
Explanation: According to hybrid model 1st the head part shifts to the next site in the cycle then the foot part of tRNA bound to 30S subunit shifts along with the input of energy. Thus, according to our question the head should be at E site.
7. If a peptide is 160 amino acids long, How many GTP and ATP molecules does it use for elongation?
a) 318 GTP + 160 ATP
b) 478 GTP + 160 ATP
c) 320 GTP+ 320 ATP
d) 478 GTP+ 320 ATP
Explanation: There are 159 translation steps from initiation to termination. Each step has an input of 2 GTP in form of EF-Tu and Ef-G. For all 160 amino acids we have to charge it with 160 ATP.
8. How many factors play a role in termination of translation?
Explanation: The factors are- RF1-3, RRF and Ef-G respectively. The EF-G factor finally hydrolyses the GTP that leads to final translocation step freeing the ribosome.
9. Which of these factors can recognize the UAA stop codon?
Explanation: RF1 (as well as RF2) can recognize the stop codons at the A site. They can recognize the UAA and UAG stop codons on the mRNA.
10. Binding of RF3.GTP to the ribosome helps in release of the ____________
b) Release factor 1
Explanation: RF3.GTP binds the ribosome after the peptide is already released by the RF1. It hydrolyses to release the RF1 instead.
11. Which factor or factors lead to the ultimate disassembly of the ribosomal complex?
a) RF1 and RF3
b) RF3 and RRF
c) RRF and EF-G
d) RF2 and EF-G
Explanation: The RRF first replaces the RF3 from the termination complex. Then, EF-G translocates the complex for the last time freeing the mRNA, Ribosome, tRNA and the factors.
12. Which factors lead to disassociation of the ribosomal subunits?
a) RRF and Ef-G
b) IF1 and IF2
c) Rf1 and RRF
d) IF-1 and IF-3
Explanation: While the release factor releases the ribosome from the termination complex, in order to keep the ribosome functional the 50S and 30S subunits should be separated. This is maintained by IF1 and IF3 (mainly by IF3) which prevents re-association.
Sanfoundry Global Education & Learning Series – Cytogenetics.
To practice all areas of Cytogenetics, here is complete set of 1000+ Multiple Choice Questions and Answers.