CSIR UGC NET JRF Life Sciences (June 2013) Answers with Explanation

1. What is the effect of 2-4-dinitrophenol on mitochondria?

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) Blocks ATP synthesis without inhibiting electron transport by dissipating the proton gradient.

Explanation:  2, 4-dinitrophenol (DNP), as a uncoupling agents, are lipid soluble small molecules that can bind H+ ions and transport across membrane. It prevents the formation of proton gradient  therefore no ATP can be made by oxidative phosphorylation.

Reference: Books to Refer-Instant notes Biochemistry

2. A protein has 30% alanine. If all the alanine are replaced by glycine,

1. Helical content will increase

2. Beta sheet content will increase

3. There will be no chage in conformation

4. The alalnine substituted protein will be less structured than the parent protein

Ans: 4. The alalnine substituted protein will be less structured than the parent protein

Explanation: In internal helical positions, alanine is regarded as the most stabilizing residue, whereas glycine, after proline, is the more destabilizing.

Reference: Alpha-helix stabilization by alanine relative to glycine: roles of polar and apolar solvent exposures and of backbone entropy. López-Llano J, Campos LA, Sancho J. Proteins. 2006 Aug 15;64(3):769-78.

3. When you created a fusion between the trp Operon, which encodes the enzymes for tryptophan biosynthesis, under the regulatory control of lac promoter. Under which of the following conditions will tryptophan synthase be induced in the strain that carries the chimeric operator fused operons?

1. Only when both lactose and glucose are absent

2. Only when both lactose and glucose are present

3. Only when lactose is absent and glucose is present

4. Only when lactose is present and glucose is absent

Ans: 4. Only when lactose is present and glucose is absent

Explanation: Lac repressor protein always binds to the operator there by blocking transcription.

In the presence of glucose and lactose, the bacterium will utilize glucose as the primary Carbon source-----à transcription off Lac Operon off

In the presence of lactose alone, Lactose binds to the lac repressor--àtranscription on.

4.Which of the following atomic nuclei cannot be probed by nuclear magnetic resonance spectroscopy?

1. ¹H

2. ³¹P

3. ¹⁸O

4. ¹⁵N

Ans: 3. ¹⁸O

Explanation:

¹H: most commonly used

¹⁵N, ³¹P: used in biochemical studies

¹⁸O: not used

5. In the case of monoclonal antibody production by Hybridoma technology, myeloma cells used lack the enzyme hypoxanthine-guanine phosporibosyl transferase (HGPRT) such that fused cells can only survive when selected on Hypoxanthine-aminopterin-thymidine (HAT). What is the role of Aminopterin in this medium?

1. To be used as cell cycle inhibitor of myeloma cells

2. To block the pathway for nucleotide synthesis

3. To facilitate fusion of myeloid B cells and antibody producing B cells

4. To facilitate production of antibody producing B cells

Ans: 2. To block the pathway for nucleotide synthesis

Explanation: Notes and video on MAB production

6. 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. AT rich sequences

7. The cap binding protein (eIF4E), which is involved in global regulation of translation is highly regulated in eukaryotic cells. In an experiment, a researcher transfected mammalian cells with (eIF4E) gene for its over expression. Due to this the cell will undergo

1.apoptosis

2. neoplastic transformation

3. no change

4. differentiation

Ans: 2. neoplastic transformation

Reference: eIF4E is overexpressed in many epithelial cell cancers, including breast (Kerekatte et al., 1995; Li et al., 1997; Li et al., 1998; Li et al., 2002; McClusky et al., 2005)

8.Bacteriophage T4 infects E.coli and injects its DNA inside the cell. The transcription of viral genes occurs in three stages: immediate early, early and late. All the promoters on viral genome are available, but the control takes place at the level of

1. promoter strength

2. modification of host RNA polymerase

3. synthesis of new polymerases

4. turn over rate of RNA synthesis

Ans: 2. modification of host RNA polymerase
Explanation: reference: T4 early promoter strength probed in vivo with unribosylated and ADP-ribosylated Escherichia coli RNA polymerase: a mutation analysis.

Reference: Nicole Sommer, Vida Salniene, Egle Gineikiene, Rimas Nivinskas and Wolfgang Rüger1

9. Which of the following genes was engineered in the ‘Flavr Savr’ transgenic tomato variety?

1. 1-amino cyclopropane 1- carboxylic acid synthase

2. 1-amino cyclopropane 1- carboxylic acid oxidase

3.Expansin

4.Polygalactouronase

Ans: 4.Polygalactouronase

‘Flavr Savr’ tomato: has increased shelf life by silencing the polygalactouronase gene involved in ripening by anti sense technology.

10. A plot of soil contaminated with diesel oil was inoculated with oyster mushrooms. After 4 weeks, more than 95% of the polycyclic aromatic hydrocarbons had been reduced to non-toxic compounds. The process is called

1. phytoremediation

2. chemoremediation

3. mycoremediation

4. zoo remediation

Ans: 3. mycoremediation

Explanation: Bioremediation is the process of cleaning up or degrading environmental contaminants using biological organisms especially microbes.

Here mushrooms are used. Mushrooms belong to fungi. Therefore myco (fungus)remediation.

Question Source: In an experiment conducted in conjunction with Dr. S. A. Thomas, a major contributor in the bioremediation industry, a plot of soil contaminated with diesel was inoculated with mycelia of oyster mushrooms; traditional bioremediation techniques (bacteria) were used on control plots. After four weeks, more than 95% of many of the PAH (polycyclic aromatic hydrocarbons) had been reduced to non-toxic components in the mycelial-inoculated plots. It appears that the natural microbial community participates with the fungi to break down contaminants, eventually into carbon dioxide and water. Wood-decay fungi are particularly effective in breaking down aromatic pollutants (toxic components of petroleum), as well as chlorinated compounds (certain persistent pesticides; Battelle, 2000).

Reference: Mycoremediation

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