The complex responses to different types of DNA damage in both prokaryotes and eukaryotes fall into three main categories:

(i) damage bypass

(ii) damage reversal

(iii) damage removal

Many repair proteins are isolated like

(a) DNA methyltransferase

(b) DNA glycosylase

(c) DNA polymerase IV

Which one of the following represents the correct combination?

• (i) - (a); (ii) - (b); (iii) - (c)

• (i) - (b); (ii) - (c); (iii) - (a)

• (i) - (c); (ii) - (a); (iii) - (b)

• (i) (c); (ii) - (b); (iii) - (a)

In recent years, genome-wide transcription study using high throughput sequence analysis has revealed some novel results that include:

(i) presence of RNA polymerase in both intra-and intergenic regions of the genome.

(ii) existence of non-coding RNAs generated from mRNA coding genes.

(iii) existence of sense and antisense transcripts generated from the promoter and untranslated region of many annotated genes.

Possible interpretation of the above results are:

A. RNA polymerase can loosely bind to any part of the genome but its affinity becomes strong only when it reaches the promoter.

B. Binding of RNA polymerase to non-promoter regions of the genome leads to the generation of various non-coding regulatory RNAs.

C. Non-coding RNAs are generated from mRNA coding genes due to aberrant transcription initiation and termination.

D. Sense and antisense transcripts are generated from the promoter and untranslated regions of protein coding genes by a novel mechanism of bidirectional transcription.

Identify the correct combination of the above interpretations:

• A and B

• B and D

• A and D

• B and C

63.

Aminoacyl tRNA synthetases face two important challenges:

(i) they must recognize the correct set of tRNAs for a particular amino acid.

(ii) they must charge all of these is accepting tRNAs with the correct amino acid.

Both of these processes are carried out with high fidelity by the following possible mechanisms:

A. The discrimination ability resides predominantly at the acceptor stem of the tRNAs.

B. The specificity is contributed by the anticodon loop in tRNAs.

C. The specificity is embedded in the amino acyl synthetase at the 'N' terminus.

D. The specificity is contributed by the variable loop of the tRNA.

Which of the following is correct?

• A and B

• A and C

• B and C

• A and D

The homologous genetic recombination is a DNA repair process referred to as recombination repair. Which one of the following statements is incorrect for recombination repair?

• DNA polymerase III stalls at the site of the damage.

• DNA polymerase III leaves a gap in the daughter strand.

• The gap is filled by recombination between complementary parent strand homologous to daughter strand and the gapped daughter strand.

• Homologous recombination process is catalyzed by topoisomerase II.

During protein synthesis in prokaryotes, the peptidyl transferase activity required for peptide bond formation is due to

• ribosomal protein L26

• 16S ribosomal RNA

• 23S ribosomal RNA

• aminoacyl tRNA

After activation of a promoter by the DNA binding activity of a transcription factor, a co-activator is recruited at the region targeted for transcription which in turn creates a binding site for a chromatin remodeling complex. Which one of the following activities of the co-activator is responsible for the recruitment of chromatin remodeling complex?

• Histone deacetylase activity

• Histone methyl transferase activity

• Histone acetyl transferase activity

• DNA methyl transferase activity

Prior to transcription, chromatin changes from an inactive state to an active state by various factors in a stepwise manner. Which one of the following is involved in the initial step during activation of a chromatin loop?

• HMG 14

• Single stranded DNA-binding protein

• DNA polymerase III

• Topoisomerase I

Virus-induced gene silencing (VIGS) is a process that takes advantage of the RNAi-mediated antiviral defense mechanism. Which one of the following ultimately guides siRNA to degrade the target transcript (mRNA)?

• dsRNA

• ssRNA

• RNA Induced Silencing (RIS) Complex

• dsRNA binding protein

Aminoacyl-tRNA synthetases are very spcific for aminoacylation of tRNAs with the correct cognate amino acids. However, there is a possibility of a mismatch between the tRNA and its cognate amino acid. this error is corrected bythe inherent proof-reading activity of the aminoacyl-tRNA synthetase. In case of two very similar amino acids, namely valine and isoleucine, isoleucyl-tRNA synthetase employs the following possible approaches for an error-free aminoacylation.

A. It removes an incorrect amino acid by hydrolyzing the aminoacyl-AMP linkage following the first reaction step.

B. It is activated for proof-reading activity, leading to breakage of the bond between the wrong amino acid and tRNA.

C. It has an intrinsic ability to recognize the structural difference between amino acids  leading to abortive elimination of the non-cognate amino acid.

D. It gets sequestered in the second step with the wrong amino acid, and that freezes the aminoacylation process.

Which of the following combinations is correct?

• A and B

• A and D

• B and D

• C and D

MicroRNAs (miRNAs) have recently been shown to play a significant role in the fine-tuning of gene expression. Some miRNAs induce gene silencing by binding to mRNAs and inducing by binding to mRNAs and inducing inhibition of translation. On the other hand, there are miRNAs that bind t mRNAs and activate their degradation. The following characteristics can be applicable to the miRNAs that inhibit mRNA translation.

A. miRNA is partially complementary to a region of target mRNA in the 3'UTR.

B. miRNA always base airs with mRNA around an AU-rich sequence.

C. miRNA base pairs with mRNA through 6-7 nucleotides at its 5'end referred to as "seed sequence" as well as few additional bases elsewhere.

D. miRNA is always partially complementary to the 5'UTR of the target mRNA.

Choose the correct option from the following:

• A and B

• A and C

• C and D

• A and D