This set of Cytogenetics Questions and Answers for Experienced people focuses on “Ribosome – 2”.
1. The catalytic activity of the ribosome is located in the ______
b) 50S ribosomal rRNA
c) 30S ribosomal rRNA
Explanation: The peptidyl transferase activity of the ribosome is located in the 50S subunit of the ribosome in the rRNA and not in the protein. This has been supported with sound proof.
2. Puromycin is a ribosomal antibiotic. It binds to ________
a) Peptide exit channel
b) 16S rRNA
c) tRNA binding site
d) A site of unassociated 16S rRNA
Explanation: Puromycinis a tRNA analogue that has an amide bond in place of ester bond. This is why when the ribosome transfers the peptide over this; it flees with the peptide and stops the translation.
3. In an experiment you add rifampicin and paramomycin to the ribosome and mRNA mixture. What will inhibit theribosomal translation efficiency and how?
a) Rifampicin will prevent translation initiation
b) Paramomycin will slow down translation
c) Rifampicin will bind irreversibly to the ribosome and inactivate it
d) Paramomycin will increase error rate
Explanation: Paramomycin acts as a ribosomal translation inhibitor while Rifampicin acts on RNA polymerase. Paramomycin actually increases the error rate of the translation thus producing wrong nonfunctional proteins ultimately killing the bacteria.
4. Which antibiotic inhibits peptidyl transfer by blocking the accommodation of aa-tRNA into the peptidyl transferase (A/A) site?
Explanation: While chloramphenicol also blocks the peptidyl transferase activity, tetracycline does so by blocking the A site. Then the A site amino acid can’t interact with the P site one for the reaction to take place.
5. Which of the antibiotic can halt translocation of the ribosome bound to the mRNA?
a) Fusidic acid
Explanation: Fusidic acid inhibits elongation in prokaryotes in a way that it binds to Ef-G-GDP permanently and doesn’t allow the ribosome to fall off.
6. The ribosome slides over the mRNA translating it.
Explanation: The ribosome is a multi protein complex while the mRNA is much smaller. In reality, the mRNA slides past the ribosome in place of the ribosome sliding on it.
7. In an experiment you add streptomycin at low concentration first and then gradually increase the concentration till it completely inhibits peptide formation. What will be its effect at low concentration?
a) No effect
b) Shorter peptide
c) Wrong amino acid incorporation
d) Slower formation
Explanation: Streptomycin interacts with the smaller subunit of the ribosome and prevents the initiation at higher concentration. At lower concentration, it leads to the incorporation of more errors.
8. What will be DNA sequence of Shine and Dalgarno coding region?
a) A/T rich
b) C/G rich
c) A/G rich
d) C/T rich
Explanation: As the Shina and Dalgarno region is purine rich i.e. A/G rich, its corresponding DNA sequence should be pyrimidine rich or C/T rich. This is because a purine base pairs with a pyrimine so a Pyrimidine will code for a purine in RNA.
Sanfoundry Global Education & Learning Series – Cytogenetics.
To practice all areas of Cytogenetics for Experienced people, here is complete set of 1000+ Multiple Choice Questions and Answers.