One of the cellular events that TOR, a kinase, positively regulates is the rate of rRNA synthesis. TOR regulates the association of a transcription factor to a Pol I subunit. When TOR is inhibited by the drug rapamycin, the transcription factor dissociates from Pol I. A east strain is engineered, which expresses a fusion of the transcription factor and the Pol I subunit. The level of rRNA synthesis is monitored in these cells using pulse labelling following rapamycin addition for the times indicated below. The transcript profile of rRNA observed for the wild type cells is given below:

Identify the pattern expected in the engineered strain.

An eukaryotic cell undergoing mRNA synthesis and processing was incubated with ³²P labelled ATP, with the label at the β-position. Where do you think the radioactive isotope will appear in the mature mRNA?

• ³²P will not appear in the mature mRNA under any circumstances because β and γ phosphates are released during transcription.

• Phosphate groups of the phosphodiester backbone of the mRNA will be uniformly labelled as only α phosphates are released during transcription.

• ³²P will appear at the 5'end of the mRNA if only it has "A" as the first nucleotide.

• No ³²P will appear in the mature mRNA because the 5'-terminal phosphate of an "A" residue will be further removed during the capping process.

Some errors occur during DNA replication that are not corrected by proof reading activity of DNA polymerase. These are corrected by specialized repair pathways. Defect in the activities of some of the following enzymes impair this process.

A. DNA polymerase III and DNA ligase

B. AP endonuclease and DNA glycosidase

C. Mut S and Mut L

D. RecA and RecF

Defect in which of the above enzymes impair the process?

• A, B, and C

• D and B

• A and D

• A and C

Each aminoacyl-tRNA synthetase is precisely able to match an amino acid with the tRNA containing the correct corresponding anticodon. Most organisms have 20 different tRNA synthetase, however some bacteria lack the synthetase for charging the tRNA for glutamine (tRNA^Gln) with its cognate amino acid. How do these bacteria manage to incorporate glutamine in their proteins?

Choose the correct answer.

• Glutamine is not present in the newly synthesized bacterial protein. Post-translational modification converts glutamate to glutamine at the required sites.

• In these bacteria, the aminoacyl tRNA synthetase specific for tRNA glutamate (tRNA^glu) also charges tRNA^gln with glutamine.

• In these bacteria, the aminoacyl tRNA synthetase specific for tRNA^glu also charges tRNA^gln with glutamate. A second enzyme then converts the glutamate of the charged tRNA^gln to glutamine.

• In these bacteria, the aminoacyl tRNA synthetase charges tRNA^glu with either glutamate or glutamine according to their requirement during protein synthesis.

105.

RNA interference is mediated by both siRNA and miRNA. Which one of the following statement about them is NOT true?

• Both siRNA and miRNA are processed by DICER.

• Both siRNA and miRNA usually guide silencing of the same genetic loci from which they originate.

• miRNA is a natural molecule while siRNA is either natural or a synthetic one.

• miRNA, but not siRNA is processed by Drosha.

Error-free repair of double-strand breaks in DNA is accomplished by

• non-homologous end-joining

• base excision repair

• homologous recombination

• mismatch repair

Which of the following are NOT transcribed by RNA Polymerase II?

• miRNA and some snRNA

• miRNA and snoRNA

• mRNA and snoRNA

• tRNA and 5S rRNA

RNA editing, a post-transcriptional process, is achieved with the help of guide RNA (g-RNA). Which one of the following statements about the process is NOT true?

• g-RNA dependent RNA editing happens in the kinetoplast DNA.

• g-RNA is involved in chemical modification of t-RNA.

• This process involves insertion or deletion of uridines.

• Sequences edited once may be re-edited using a second g-RNA

Telomerase, an RNA-protein complex that completed the replication of telomeres during DNA synthesis, is specialized

• RNA dependent DNA polymerase

• DNA dependent DNA polymerase

• DNA dependent RNA polymerase

• RNA dependent RNA polymerase

Consider a short double-stranded linear DNA molecule of 10 complete turns with 10.5 bp/turn. The ends of the DNA molecule are sealed together to make a relaxed circle. This relaxed circle will have a linking number of

• 105

• 20.5

• 10.0

• 10.5