Part B-Dec 2015

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. Enzymes accelerate a reaction by which one of the following strategies ?
1.   Decreasing energy required to form the transition state
2.   Increasing kinetic energy of the substrate.
3.   Increasing the free energy difference between substrate and the product.
4.   Increasing the turn over number of enzymes.
Ans: 1
The active site of the enzyme combines with substrate. As a result enzyme – substrate complex is formed. The complex is short lived. During the state where substrate is bound to the enzyme active site, a new structure of the substrate called transition state structure is formed. Very soon, after the expected bond breaking or making is completed, the product is released from the active site. That is, the structure of the substrate is transformed into structure of the products.
For any chemical reaction to take place, old bonds must be brocken before new ones can form. The energy needed to break these bonds, and so set the reaction in motion is the activation energy.
In all reaction there is an energy barrier that has to be overcome in order for the reaction to proceed. This is the energy needed to transform the substrate molecules into the transition state – an unstable chemical form part-way between the substrates and the products. The transition state has the highest free energy of any component in the reaction pathway. Enzymes bring down this energy barriers making the transition of ‘s’ to ‘p’ more easy.[For more details refer Simple Instant Notes].
2.    Glycophorin having one highly hydrophobic domain is able to span a phospholipid bilayer membrane only
1. once
2. twice
3. thrice
4. four times

The firm attachment of integral proteins to membrane is the result of hydrophobic interactions between membrane lipids and hydrophobic domains of the protein. Some proteins like glycophorin have a single hydrophobic sequence in the middle which span the phospholipid bilayer. Others have multiple hydrophobic sequences, each of which is long enough to span the lipid bilayer. One of the best studied membrane – spanning proteins, bacteriorhodopsin, has seven hydrophobic internal sequences and crosses the lipid bilayer seven times. [For more details refer Simple Instant Notes].

3. Which of the following is NOT a second messenger ?
1.   Cyclic GMP
2.   Diacylglycerol
3.   Inositol triphosphate
4.   Phosphatidyl inositol
Ans:- 2

Expln:- When a signal molecule like insulin, epidermal growth factors etc bind to the receptor tyrosine kinase, the phosphodiesteraseenzyme get activated due to the activity of subunit, activated by a transducer G – protein. The activated enzyme phosphodiesterase transforms phosphatidyl inositol biphosphate (PIP3) into two mediators, viz. inositol triphosphate (IP3) and diacylglycerol. IP3 diffuses into the cytoplasm and triggers the release of another messenger Ca2+ from endoplasmic reticulum. Ca2+ bind to calmodulin. Diacylglycerol remains in the cell membrane and activates protein kinase C. Hence phosphatidyl inositolbiphosphate is not a second messenger. Ligand for the second messenger, cyclic GMP are atrial naturetic factor, nitric oxide etc.[For more details refer Simple Instant Notes].

4.    Cytotoxic T cells express
1.   CD8 marker and are class II MHC restricted
2.   CD4 marker and are class I MHC restricted
3.   CD4 marker and are class II MHC restricted
4.   CD8 marker and are class I MHC restricted
Ans:- 4


Class I MHC Class II MHC
1 Encodes a single transmembrane polypeptide called alpha – chain and an extracellular protein called beta – 2 microglobulin. Encodes two alpha – chains and two beta – chains.
2 Class I MHC Class II MHC
3 Class I MHC proteins are expressed in all nucleated cells (hence not in RBC). Expressed only on antigen presenting cells such as macrophages.
3 Cytotoxic T cells (Tc), which has surface antigen CD8 recognise the antigens in association with class I MHC porteins. Helper T cells (Th) which has surface antigen CD4 recognise the antigen in association with class II MHC molecule.
4 Combines with endogenous antigens. (Two common examples of endogenous antigens are viral proteins synthesized within virus infected host cells and unique proteins synthesized by cancerous cells. Combines with exogenous proteins produced outside of the host cell and enters the cell by endocytosis or phagocytosis.

More Questions & Answers Refer Simple Instant Notes