Part B-June 2014

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. Membrane-bound and free ribosomes, are structurally identical, but differ only at a given time in terms of association with
1.   acetylated proteins
2.   glycosylated proteins
3.   phospholipids
4.   nascent proteins
Ans: 4
Expln:- Free ribosomes produce proteins utilized within the cell, while the membrane bound ribosomes produce proteins that are transported out of the cell for secretion, the lysosomes and the membrane formation. Ribosomes are attached to the endoplasmic reticulum through two transmembrane
ribophorins I

2. The dye used in Gram staining is
1. Rhodamine
2. Methylene blue
3. Giemsa
4. Crystal violet
1.   1   2.   2   3.   3   4.   4

Ans:- 4

3. Each origin of replication is activated only once. This is achieved because
1.   pre-replicative complex can only form in G1 and replication can only be initiated when pre-replication complex is disassembled at the beginning of S-phase.
2.   replication can only be initiated when pre-replication complex is intact
3.   replication can only be initiated when unphosphorylated Rb is present
4.   pre-replicative complex can only form in S-phase

Ans:- 1

Expln:- A pre-replication complex (pre-RC) is a protein complex that forms at the origin of replication during the initiation step of DNA replication.

In bacteria, the main component of the pre-RC is DnaA. The archaeal pre-RC is very different from the bacterial pre-RC and can serve as a simplified model of the eukaryotic pre-RC. It is composed of a single origin recognition complex (ORC) protein, Cdc6, and a homohexamer of the mini chromosome maintenance (MCM) protein.

4.Electron microscopes have much higher resolution than any type of light microscope because
1. of their higher magnification
2. the lenses used are of much higher quality
3. of very short wave length of electrons
4. the images are viewed on screen rather than directly using an eye-piece or occular lens
Ans:- 3
5.    Histone acetylase and chromatin remodeling complexes are recruited to specific regions of chromatin by
1.   gene activator proteins
2.   Specific promoter sequence
3.   phosphorylation of histone acetylase
4.   dephosphorylation of chromatin remodeling complexes
Ans:- 1

Expln:- In eukaryotes, DNA is tightly wound into a complex called chromatin. Chromatin not only serves as a way to condense DNA within the cellular nucleus, but also a way to control how that DNA is used. Specific genes are not expressed unless they can be accessed by RNA polymerases and proteins known as transcription factors. Therefore, a cell’s chromatin must “open” in order for gene expression to take place. This process of ‘opening’ is called chromatin remodeling.

The amount of binding between DNA and histones can be altered by a process called acetylation. The addition of the acetyl group to positively charged amino acids such as lysine removes the charge and reduces the affinity with negatively charged DNA. When the histones are deacetylated, the positive charges are restored and the DNA binds more tightly to the histone.

Specific DNA’s binding transcription factors recruit histone acetylases and deacetylases to promoters to activate or repress transcription.

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