The following table lists the two major forms of DNA duplexes, the conformation of the base attached to the sugar and the nature of major and minor grooves.

DNA duplex	Properties
A. A form	i. Syn conformation of the base to sugar.
B. B form	ii. Anti conformation of the base to sugar.
	iii. Wide major groove
	iv. Narrow major groove
	v. Wide minor groove
	vi. Narrow minor groove

Which of the following combination correctly depicts the types of DNA duplexes and and their properties (numbered within bracket)?

• A - (i) (iii) (vi); B - (ii) (iii) (vi)

• A - (i) (iii) (vi); B - (ii) (iii) (v)

• A - (ii) (iv) (v); B - (ii) (iii) (vi)

• A - (ii) (iv) (v); B - (i) (iii) (vi)

Imagine the following RNA sequence is translated in the mammalian cytosol and mitochondria.

RNA sequence- AUG AUA CUG UGA CUU AGG CUC UAA

Following are some putative sequences:

Find out the correct combination of peptides made in the cytosol and mitochondria.

• (a) (i)

• (a) (ii)

• (b) (i)

• (b) (ii)

In all organisms, it is critical that replication initiation be tightly controlled to ensure that  chromosome number and cell number remain appropriately balanced. Given below are several statements regarding regulation of replication in E. coli.

A. Hemimethylation and sequestration of oriC (origin of replication) by a protein called SeqA prevents initiation of replication.

B. Availability of DnaA protein is an important requirement for initiation of replication.

C. The ratio of ADP : ATP is important as high level of ADP is required for initiation of replication.

D. Recruitment of Hda protein by sliding clamp inhibits ATP hydrolysis required for initiation of replication.

Which of the above statements are NOT true?

• A and B

• B and C

• C and D

• D and A 

In E. coli, though DNA Polymerase I (Pol I) plays an essential role in the replication process, it is not the major polymerase. Instead, the enzyme responsible for advancement of replication fork is Pol III. From the four DNA structures (A, B, C, and D) given below, students made several interpretations about the shorter arm being extended by Pol I and / orPol III.

Which one of the interpretation written below is correct?

• A will be extended by Pol III but not by Pol I

• Neither B nor C will be extended by either Pol I or Pol III.

• C will be extended by both Pol I and Pol III.

• D will be extended only by Pol I, but not by Pol III.

tRNA genes of a gram positive bacteria were sequenced. While some of the genes possessed sequence corresponding to the -CCA end of the tRNA, others did not. Interestingly, even the genes that lacked the sequence corresponding to the -CCA end of the tRNA were found to code for a functional tRNA. This is because

• the -CCA end in the tRNA is not essential for its function.

• the genes that do not possess sequence corresponding to the -CCA ends of the tRNA are repaired prior to their transcription.

• the -CCA end is added to the tRNA during their maturation.

• the primary transcripts of the genes lacking sequence corresponding to -CCA end are subjected to g-RNA mediated editing prior to their maturation.

It is known that there is a large difference in the DNA content between two organisms with similar developmental complexity. This is due to large differences in the number of

• transposable elements, repetitive DNA and coding sequences

• transposable elements and repetitive DNA

• introns and coding sequences

•  introns and transposable elements 

 In an organism, allele for red eye colour is dominant over the allele for white eye colour. A cross is made between a white eyed male and a red eyed female. In the progeny, all males are red eyed while the females are white eyed. The reciprocal cross leads to all red eyed progeny. Based on the above information which one of the following conclusions is correct?

• This is a sex-limited trait, and the male is the homomorphic sex 

• This is a sex-linked trait, with male being the homomorphic sex

• This is a sex-linked trait, with female being the homomorphic sex

• This is a case of autosomal inheritance, with incomplete penetrance

• expressing luciferase in the presence of heat-stress 

• not expressing luciferase in the presence of heat-stress 

• expressing Iuciferase in the absence of heatstress 

• not expressing luciferase in the absence of heat-stress 

139.

A plasmid with a linking number (Lk) of 200, topological winding (Tw) number of 200 and a writhing number (Wr) of 0 was transformed into E. coli. The plasmid was re-isolated from the culture of the transformant. The re-isolated plasmid was found to possess the same molecular weight as the original plasmid, but it possessed a writhing number of –5. Following statements are made about this observation.

(a) Lk of the re-isolated plasmid would be 195.

(b) Lk of the re-isolated plasmid would remain 200.

(c) Tw of the re-isolated plasmid would remain 200.

(d) Tw of the re-isolated plasmid would be 195.

Which one of the following combinations of the above statements is the correct representation of the facts.

• (a) only

• (a) and (c)

• (a) and (d)

• (d) only

Following statements are being made about the orientation of the N-glycosidic bond between the base and the sugar in the following DNA duplexes.

(a) ‘anti’ for B form DNA duplexes 

(b) ‘syn’ for B form DNA duplexes

(c) ‘anti’ for A form DNA duplexes

(d) ‘syn’ for A form DNA duplexes

Which one of the following combinations of the above statements is correct?

• (a) and (c) 

• (b) and (c)

• (a) and (d) 

• (b) and (d)