Part C-Dec 2011

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

PREVIOUS SOLVED QUESTIONS – 2011 DECEMBER CSIR – NET EXAM

1.The most important property of any microscope is its power of resolution, which is numerically equivalent to D, the minimum distance between two distinguishable objects. D depends on three parameters namely, the angular aperture, a, the refractive index, N, and wavelength, ?, of the incident light. Below are given few possible options to increase the resolution of the microscope.

A. Decrease the value of ? or increase either N or a to improve the resolution.
B. Moving the objective lens closer to the specimen will decrease sin a and improve the resolution.
C. Using a medium with high refraction index between the specimen and the objective lens to improve the resolution.
D. Increase the wavelength of the incident light to improve the resolution.

Which of the following combination of above statements is correct ?

1. A and C    2. B and C     3.A and D    4.C and D

Ans.   1

Expln:- Resolving power of a microscope depends upon the numerical aperture of the objective lens system and its wavelength. Resolution of a microscope increases as the wavelength decreases, so ultraviolet light allows one to detect objects not seen with visible light. Similarly, the wavelength of light is much larger than the wavelength of electrons….

2.Many cancers carry mutant p53 genes, while some cancers have normal p53 genes. P53 activates p21 (Wafl) which inhibits G1/S-Cdks and phosphorylation of the retinoblastoma protein (Rb). Cancers with normal p53 genes could

1. express non-phosphorylatable form of Rb    2. express high levels of p53-deubiquitinases    3.express inactive forms of G1/ S-cdks    4.express inactive forms of G1/S cyclins

Ans.   3

Expln:- When damage is sensed, the activity of the p53 protein aids in the decision between repair and the induction of cell death (apoptosis).

As a transcription factor, p53 stimulates the transcription of a group of target genes. Among them, p21 is one of the most important. The product of the p21 gene is a negative regulator of cyclin-dependent kinases, enzymes that are critical in the progression of the cell cycle and ultimately cell division. By stimulating the transcription of the p21 gene, p53 prevents ….

3.     Pre-mRNAs are rapidly bound by snRNPs which carry out dual steps of RNA splicing, that removes the intron and joins the upstream and downstream exons.

The following statements describe some facts related to this event

A. Almost all introns begin with GU and end with AG sequences and hence all the GU or AG sequences are spliced out of RNA.
B. U2 RNA recognizes important sequences at the 3’ acceptor end of the intron.
C. The spliceosome uses ATP to carry out accurate removal of intron.
D. An unusual linkage with 2’ OH group of guanosine within the intron form a ‘Lariat’ structure.
Which of the following combinations is correct ?

1. A and B            2. B and C

3.C and D            4.D and A

Ans.   1

4.  Following are some of the statements regarding the effect of CO2 concentration on photosyn thesis in plants

A. With elevated CO2 levels, C3 plants are much more responsive than C4 plants under well watered conditions
B. In C3 plants, increasing intracellular CO2 partial pressure can stimulate photosynthesis only over a narrow range.
C.In C4 plants, CO2 compensation point is nearly zero

Which one of the following combination of above statments is correct ?
1. A and B    2. B and C    3.A and C    4.Only C

Ans.   3

5. Following are some statements regarding plant growth hormones.

A. Ethylene regulates abscission
B. Gibberlins do not play any role in flowering
C.Auxin and cytokinin promote cell division
D.Over expression of cytokinin oxidase would promote root growth
E.ABA inhibits root growth and promotes shoot growth at low water potential
F.ABA promotes leaf senescence independent of ethylene

Which one of the following combination of above statements is correct ?
1. A, C and F    2. B, C and D     3.D, E and F     4.B, D and E

Ans.   1

6.     A monkey undergoes cerebellectomy. After the post-operative recovery, the monkey was given a task to press a bar. The possible observations are:

A. Its hand would overshoot the target while reaching the bar
B. It would be unable to move forelimbs
C.It would show intention tremor while trying to press the bar
D.It would press the bar with mouth instead of hand

Which one of the following is correct ?
1. A and C     2. B only     3.D only     4.B and D

Ans.   1

7.     Maturation-promoting factor (MPF) controls the initiation of mitosis in eukaryotic cells. MPF kinase activity requires cyclin B. Cyclin B is required for chromosome condensation and breakdown of the nuclear envelope into vesicles. Cyclin B degradation is followed by chromosome decondensation, nuclear envelope reformation and exit from mitosis. This requires ubiquitination of a cyclin destruction box motif in cyclin B. RNase-treated Xenopus egg extracts and sperm chromatin were mixed. MPF activity increased with chromosome condensation and nuclear envelope breakdown. However, this was not followed by chromosome decondensation and nuclear envelope reformation because

1. RNase condamination persisted in the system
2. cyclin B was missing from the system
3.ubiquitin ligase had been overexpressed
4.cyclin B lacking the cyclin destruction box had been overexpressed

Ans.   4

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