In order to study the transcription factor TFIIH, it was cloned from a large number of human subjects. Surprisingly, the subjects having mutation in TFIIH, also showed defects in their DNA repair system. Given below are the explanations:

A. DNA damage is always associated with transcription inhibition.

B. TFIIH has no role in DNA repair.

C. In mammalian system, TFIIH plays an active role in transcription-coupled DNA repair process.

D. Because of mutation in TFIIH, transcription initiation is inhibited and incompletely synthesized mRNAs remain attached to the template DNA leading to DNA damage. Choose the correct answer.

• A and B

• C only

• B and D

• D only

92.

The 3' end of most eukaryotic mRNAs is defined by the addition of a polyA tail-a processing reaction called polyadenylation. The addition of polyA tail is carried out by the enzyme Poly (A) Polymerase. Given below are few statements about this process:

A. Poly(A) Polymerase is a template independent enzyme.

B. Poly(A) Polymerase catalysts the addition of AMP from dATP to the 3' end of mRNA.

C. Poly (A) Polymerase is a RNA-template dependent enzyme.

D. Poly(A) Polymerase catalyzes the addition of ADP from ATP to the 3'end of mRNA.

E. Poly (A) Polymerase catalyzes the addition of AMP from ATP to the 3'end of mRNA.

F. Poly (A) Polymerase catalyzes the addition of AMP from dADP to the 3'end of mRNA.

Which of the following combination is true?

• B and C

• C and D

• A and E

• C and F

With an intention to identify the genes expressed in an organism at specific stage of development, mRNAs were isolated from the given organism, cDNAs were synthesized, cloned in a suitable vector and sequenced. A few of the cDNA sequences shows no matches with the genomic DNA sequence. Further, it was observed that these were U-rich and found to be in stretches dispersed along the sequence. The following may be possible reasons for appearance of such RNA:

A. Splicing

B. Alternate splicing

C. Trans-splicing

D. Guide RNA mediated introduction of Us involving endonuclease, terminal-U-transferase and RNA ligase.

E. Deaminations converting C to U.

Which of the following is the most appropriate reason/s?

• A and C

• B and D

• C, D and E

• D only

In prokaryotes, the initiator tRNA is first charged with a methionine, followed by the addition of a formyl group to the methionine by the enzyme Met-tRNA transformylase. Given below are several statements in this context.

A. All prokaryotic proteins have formyl methionine at their amino-terminal end. 

B. Deformylase removes the formyl group from the amino-terminal methionine.

C. All prokaryotic proteins have methionine at their amino-terminal end.

D. Aminopeptidases often remove the amino-terminal methionine.

E. Aminopeptidases remove amino-terminal formyl methionine.

Which of the above statement(s) are most likely to be true?

• A only

• B and C

• E only

• B and D

Enlisted below are different types of RNAs produced in the cell (column A) and their functions (column B), but not in the same order.

Column A	Column B
A. Sn RNAs	i. turn off gene expression by directing degradation of selective mRNAs.
B. si RNAs	ii. regulate gene expression by blocking translation of selective mRNAs.
C. mi RNAs	iii. function in a variety of processes including splicing of pre-mRNA.
D. Sno RNAs	iv. used to process and chemically modify rRNAs.

Choose the correct combination.

• A - (iv); B - (ii); C - (i); D - (iii)

• A - (iii); B - (i); C - (ii); D - (iv)

• A - (iv); B - (i); C - (ii); D - (iii)

• A - (iii); B - (ii); C - (i); D - (iv)

The mismatch repair activity of E.coli repairs misincorporated bases which is not removed by the proofreading activity of DNA polymerase. However, while doing so, it has to decide which strand of the DNA is newly synthesized and which one is parental. Mismatch repair system does it by which one of the following ways?

• It recognizes nearby GATC sequence. 

• It recognizes any nearby palindromic sequence.

• It recognizes a specific repetitive sequence.

• It recognizes the hemimethylated GATC sequence nearby.

Although ribonucleotide triphosphates (rNTPs) are present at approximately 10-fold higher concentration than deoxyribonucleoside triphosphates (dNTPs) in the cell, but they are incorporated into DNA at a rate that is more than 1000-fold lower than dNTPS. This is because

• DNA polymerase cannot discriminate between dNTPs and rNTPs. But as soon as rNTPs are incorporated in the DNA chain, they are hydrolyzed due to the presence of 2'-OH group.

• DNA polymerase cannot discriminate between dNTPs and rNTPs. But as soon as rNTPs are incorporated in the DNA chain, they are excised by the proofreading activity of DNA polymerase.

• DNA polymerase efficiently discriminates between rNTPs and dNTPs because its nucleotide-binding pocket cannot accommodate a 2'-OH on the incoming nucleotide.

• DNA polymerase cannot discriminate between rNTPs and dNTPs. Since the rate of transcription in the cell is 10⁶ times faster than replication, it cannot compete with RNA polymerase for rNTPs.

α-Amanitin is a fungal toxin which inhibits eukaryotic RNA polymerases. The three eukaryotic RNA polymerases show differential sensitivity to this toxin. Which one of the following order (higher to lower) is correct in respect of sensitivity towards α-amanitin?

• RNA Pol III > RNA Pol II > RNA Pol I

• RNA Pol II > RNA Pol III > RNA I

• RNA Pol I > RNA Pol III > RNA Pol II

• RNA Pol II > RNA Pol I > RNA Pol III

An antibiotic that resembles the 3' end of a charged tRNA molecule is

• Streptomycin

• Sparsomycin

• Puromycin

• Tetracycline

Which one of the following chemicals is a DNA intercalator?

• 5-Bromouracil

• Ethyl methane sulfonate

• Acridine orange

• UV