Part B-Dec 2012

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

Part B

PREVIOUS SOLVED QUESTIONS – 2012 December CSIR – NET EXAM

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

1.     With respect to development of any organism, “autonomous specification” would result in which type of development ?
1.   Regulative   2.   Mossaic   3.   Syncytial   4.   Definitive

Ans: 2
Expln:– In developmental biology, the fate of a cell is all the different cell types its descendants can become during normal development. As cell fate becomes restricted following each division in the developmental hierarchy, cells are said to become committed to a certain fate.

In animals, commitment occurs in initially reversible and then permanent. In plants, commitment appears always to be reversible.

The process of commitment can be divided into two stages. They are specification and determination.

An uncommitted cell can be described as naïve, meaning that it has received no instructions directing it along a particular developmental pathway. The fate of a cell is said to be specified if the cell is directed to follow a certain developmental pathway and does so when placed in isolation, which should provide a neutral environment. Specification may occur if a cell inherits a particular cytoplasmic determinant or receives inductive signals from another cell. However, that same cell placed in a different environment, such as in contact with other cells, may be respecifiedby its interaction with those cells. This shows that the commitment at this stage is reversible. The fate of a cell is said to be determined if it cannot be changed, regardless of the cell’s environment. This shows that the commitment has now become irreversible.

There are 3 basic modes of commitments. They are autonomous specification, conditional specification and syncitial specification. If a blastomere is removed from an embryo in its early development, there will be a corresponding defect in the resulting animal. This is because the fate of each blastomere is predetermined in the early embryonic stage itself. This type of specification is shown by annelids, molluscs, ascidiansetc and is known as autonomous specification. Autonomous specification gives rise to a pattern of development referred to as mosaic development.

In a majority of animals including vertebrates and certain invertebrates (echinoderms), when the blastomeres of an early embryo is isolated, they develop into complete embryo. This is because, the fates of blastomeres are not predetermined in the early embryonic period. This type of specification is known as conditioned specification and it give rise to a pattern of development referred to as regulative development.

Many insects also use a third means, known as syncytial specification, to commit cells to their fates. Here, interactions occur not between cells, but between parts of one cell. In Drosophila, for instance the anterior portion of the egg contains an mRNA that encodes aprotein called Bicoid. The posterior most portion of the egg contains an mRNA that encodes a protein called Nanos.

2.     2) In cellular respiration, which of the following processes occur only inside mitochondria and not in the cytoplasm ?

1. Glycolysis and the pentose – phosphate pathway.
2. Glycolysis and the citric acid cycle.
3. The citric acid cycle and oxidative phosphorylation
4. Glycolysis and oxidative phosphorylation

 

(1) II² + III² = I²   (2) II + III = I   (3) II² + III² > I²   (4) II + III < I

Ans:- 3

3.     Which of the following names is appropriate for the sequence 5’ – G/ANNAUG -3’ in a mammalian mRNA ?

1.   Shine-Dalgarno sequence
2.   Kozak sequence
3.   Internal ribosome entry sites
4.   Translation termination site

Ans:- 2

Expln:- The signals that identify initiation codons are different in prokaryotic and eukaryotic cells. Initiation codons in bacterial mRNA are preceded by a specific non-translated leader sequence called the Shine-Dalgarno sequence. This leader sequence seen in the mRNA aligns with a complementary sequence of the 16S ribosomal RNA. However, eukaryotic mRNAs have no leader sequence equivalent to Shine-Dalgarno sequence. Instead the ribosomes recognize the initiation codons by scanning from the 5’ terminus downstream until they encounter an AUG initiation codon. The AUG initiation codon in eukaryotes is embedded in a short sequence called the Kozak sequence. This is called the scanning model for initiation.

The sequences surrounding the AUG initiation codon for cellular mRNAs is important in determining the efficiency of translation. The consensus sequence, G/ANNAUG was identified by Marilyn Kozak, where N is any nucleotide. The mRNAs bearing sequences closest to this are most readily recognized by ribosomes.

 

4.     Which one of the following is responsible for the ejection of milk from mammary glands in mammals ?

1. Oxytocin   2. Prolactin   3. Serotonin   4. Melatonin

Ans:- 1


5.    An enzyme catalyzed reaction was measured in the presence and absence of an inhibitor. For an uncompetitive inhibition.

1.   Only Km is increased
2.   Both Km and Vmax are decreased
3.   onlyVmax is decreased
4.   both Km and Vmaxare not affected

Ans:- 3
Expln:- For experimental measurement of the Michaelis constants reciprocals of enzyme activity and substrate concentration are plotted to yield a straight line. This kind of double reciprocal plot is the Lineweaver-Burk plot. The value of Km from this plot is determined by the extension of line towards the abscissa.

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