Part B-June 2013

CSIR-UGC National Eligibility Test (NET) for Junior Research Fellowship and Lecturer-ship

Part B


This time CSIR does not allow candidates to carry questions with them. We have collected maximum questions from our candidates (memory based).

1.What is the effect of 2, 4 – dinitrophenol on mitochondria ?
The type of interaction between them is
1.   Blocks ATP synthesis without inhibiting electron transport by dissipating the proton gradient.
2.   Blocks electron transport and ATP synthesis by inhibiting ATP – ADP exchange across the inner mitochondrial membrane.
3.   Blocks electron transport and proton pumping at complexes I, II and III.
4.   Interacts directly with ATP synthase and inhibits its activity.

Ans: 1
Expln:- Some chemicals (eg: 2,4-dinitrophenol; DNP) are uncoupling agents; they allow electron transport to proceed without ATP synthesis. They uncouple mitochondria by carrying H+ ions across  the inner mitochondrial membrane and hence dissipate the proton gradient. The energy derived from uncoupled electron transport is released as heat.

2. Which of the following pairs of subcellular compartments is likely to have same pH and electrolyte composition ?
1. Cytosol and lysosomes
2. Cytosol and mitochondrial inter membrane space
3. Cytosol and endosome
4. Mitochondrial matrix and inter membrane space.

Ans:- 2
Expln:- The outer membrane contains many copies of a transport protein called porin which forms large aqueous channels through the lipid bilayer. This membrane thus resembles a sieve that is permeable to all molecules of 5000 daltons or less, including small proteins. Such molecules can enter the intermembrane space, but most of them cannot pass the impermeable inner membrane. Thus, whereas the intermembrane space is chemically equivalent to the cytosol with respect to the small molecules it contains, the matrix contains a highly selected set of these molecules.

3.Origin of replication usually contains
1.   GC rich sequences
2.   both AT and GC rich sequences
3.   no particular stretch of sequences
4.   AT rich sequences

Ans:- 4
Expln:- AT base pairs are more easily separated than GC base pairs.

4. σ- subunit of E. coli RNA polymerase DOES NOT
1. initiate transcription and fall off during elongation
2. increase affinity of the core enzyme to the promoter
3. binds to DNA, independent of the core enzyme
4. ensures specificity of transcription by interacting with the core enzyme.

Ans:- 3
Expln:- Transcription process is catalysed by the enzyme DNA Dependent RNA polymerase. The whole enzyme complex is called holoenzyme. The holoenzyme can be separated into two components. – the core enzyme and the transiently associated sigma factor and ρ(Rho) factor. The core enzyme consists of 4 subunits – two identical (alpha), one beta(ß), and one (ß’)chain.
Sigma factor recognizes the start signal of promoter region. Soon after transcription is initiated, the sigma factor dissociates from the RNA polymerase.
The RNA polymerase is only capable of catalyzing the process of elongation. It associates transiently with initiation-factor (s) and termination factor (?) to initiate and terminate the transcription, respectively. Association with these factors alter the specificity of the RNA polymerase to either initiate or terminate.

5. The part of the embryo from which the ectoderm, mesoderm and endoderm are formed in chick is known as
1.   primitive streak
2.   hypoblast
3.   epiblast
4.   cytotrophoblast

Ans:- 3

Expln:- The embryo develops exclusively from the epiblast. The hypoblast contributes to the formation of extraembryonic membranes. Thus, the fate map of avian embryo is exclusively restricted to the epiblast. In mammals the blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the mass. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus. This is called implantation and it leads to pregnancy.

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