This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Ribosome as Ribozyme”.
1. In an experiment you grow some cells in a media containing heavy isotopes of C and N. Then you transfer then to a lighter media. If you centrifuge the ribosomes so obtained after an hour how many bands will you expect?
Explanation: You will obtain 4 bands corresponding to heavy 50 and 30S subunit, heavy 50S and light 30S subunit, heavy 30S and light 50S subunit and light 50S and 30S subunit respectively.
2. In an experiment you stall the ribosome with low Mg2+ concentration. Which of the following will then cause the release of the Peptide from the ribosome?
a) Increasing the Mg2+ concentration
b) Adding Urea
c) Adding pyromycin
d) Adding Varomycin
Explanation: Pyromycin will cause the release of peptide with pyromycin at the C terminus. On the other hand urea will simply degrade the pepide.
3. What discovery was stated by Robert Traut and Munro experiment?
a) 30S subunit is binding to IF
b) 50S subunit has peptidy transferase activity
c) rRNA has peptifyl transfer activity
d) Urea prevents peptide bond formation
Explanation: In Robert Traut and Munro experiment puromycin was used as an assay of peptidyl transfer activity. They observed that rRNA was able to transfer the amino acid chain from tRNA on P site to the aminoacyl tRNA on A site.
4. What was the unnatural experimental condition which proved to be a criticism in Robert Traut and Munro experiment?
a) Use of low Mg2+ concentration
b) Use of 33% methanol
c) Use of purified ribosome
d) Use of puromycin
Explanation: The condition of 33% methanol is not usual for a celluar interior. Thus Robert Traut and Munro’s using 33% methanol (or ethanol) to carry out peptidyl transfer activity was criticized.
5. Which of the following was not a protein degrading agent used by Noller in his experiment?
d) Proteinase K
Explanation: In Noller’s experiment ribosomes were strongly treated with protein degrading agents like phenol, SDS etc; but urea was not one of them.
6. You gradually treat ribosome with SDS followed by Proteinase K and the finally extract it with phenol. Which of the options match the result you expect?
a) Ribosome withstands all these treatments and still has peptidyl transferase activity
b) It stands upto SDS treatment
c) It stands no treatment at all
d) It stands upto proteinase K treatment
Explanation: Ribosomes treated by SDS and proteinase K shows a remarkable ability to still carryout peptidyl transfer activity. However, extraction with phenol destroys this activity. This may be because it disturbs some higher order structure.
7. How many proteins were still intact after the treatment of ribosome with SDS and proteinase K?
Explanation: Even after such harsh treatment with SDS and proteinase K, 8 proteins were still retained in the ribosome. If they are removed by phenol treatment the peptidyl transfer activity is lost as they support some tertiary or quaternary structure.
8. What is the distance between the catalytic site and the nearest protein in the ribosome?
a) No distance
b) 10 angestron
c) 50 angestron
d) 100 angestron
Explanation: There is a gap of 50 angestron between the catalytic site of the ribosome and the nearest protein to that point. This ensures that the catalytic activity is due to the rRNA and not any protein as proteins can’t influence a reaction 50 angestron away from it.
9. Tetracyclin is only harmful to prokaryotes.
Explanation: Prokaryotes selectively accumulate tetracycline in their cells by active transport. However, humans don’t do so. Thus, tetracycline selectively inhibits bacterial translation.
10. Aminoglycosides can kill_______________
a) Broad spectrum of prokaryotes
b) Only gram positive bacteria
c) Only anerobic gram positive bacteria
d) Only aerobic gram negative bacteria
Explanation: Aminoglycosides are the group of antibiotic that can kill gram negative bacteria which are aerobic. Some of such antibiotics are Streptomycin, Paramomycin etc.
11. In evolutionary history which of the following rose 1st?
d) Oxygenic mode of respiration
Explanation: RNA was the 1st to arise which served both as information storage and as enzyme namely ribozyme. Later it transferred the activities to more specific molecules namely DNA and protein respectively.
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