CSIR JRF NET Life Sciences Model Question Paper for June 2017 Exam (Set 1/5)

Biosynthesis of purine & pyrimidine

CSIR JRF/NET Life Science Exam
June 2017 (I)
Model Question Paper 1/5
(Practice Questions with Answer Key)

(1). Action of topoisomerase leads to changes in

a.       Linking number of single-stranded linear DNA
b.      Lining number of double stranded linear DNA
c.       Linking number of closed circular single stranded DNA
d.      Linking number of closed circular double stranded DNA

(2). Sarcomas are cancers originating from:

a.       Spleen
b.      Lymph node
c.       Skin
d.      Connective tissue

(3). Receptor mediated endocytosis from plasma membrane requires which one of the following coat proteins

a.       Clathri
b.      Adaptin
c.       Arrestin
d.      Glycophorin

(4). Which of the following compound does not acts as ‘second messenger’ during signaling process?

a.       cAMP
b.      Calcium ions
c.       Inositol 3.4.5 triphosphate
d.      Triacylglycerol

(5). Which of the following peptide is not synthesized on ribosome?

a.       Cyclosporin
b.      Somatotropin
c.       Vasopressin
d.      Oxytocin

(6). If a subcellular fraction from liver tissue exhibits a high level of acid phosphatase activity, it is most likely contain:

a.       Nuclei
b.      Lysosomes
c.       Endoplasmic reticulum
d.      Coated vesicles

(7). Thrombocytopenia or excessive internal bleeding is due to reduced number of:

a.       T cells
b.      B cells
c.       Neutrophils
d.      Platelets

(8). Glyceraldehyde-3—phosphate dehydrogenase, an enzyme of the glycolytic pathway was modified with Iodoacetic acid that resulted in the loss of enzyme activity. This is due to modification of active site residue:

a.       Lysine
b.      Glutamic acid
c.       Cysteine
d.      Cystine

(9). Trypsin is a proteinase enzyme which will cleave a peptide bond in which the amino group is contributed by:

a.       An aromatic amino acid
b.      By proline
c.       An acidic amino acid
d.      A basic amino acid

(10).  A protein has an isoelectric pH of 6.0. It is least soluble at pH:

a.       5.0
b.      6.0
c.       7.0
d.      8.0

(11).  DEAE cellulose is used for the fractionation of :

a.       Acidic proteins
b.      Basic proteins
c.       Basic and neutral proteins
d.      Acidic and basic proteins

(12).  Anti-metabolites are:

a.       Antibodies raised against metabolites
b.      Structural analogues of metabolites
c.       Antimony derivative of metabolites
d.      Enzymes that degrade metabolites

(13).  Thymidylate synthase is an enzyme involved in the synthesis of TMP from:

a.       dUMP
b.      UMP
c.       Thymidine
d.      TDP

(14).  Which of the following inhibitor types is expected to change the Km of an enzyme, but not the Vmax?

a.       Competitive
b.      Non competitive
c.       Uncompetitive
d.      All inhibitors

(15).  An essential building block of phosphatidic acid and phosphatidylcholine is:

a.       Glycerol
b.      Lysine
c.       Cholesterol
d.      Glucose

(16).  Urea is a water soluble excretion product of nitrogen metabolism. How many hydrogen bonds can it donate to the oxygen atom of water?

a.       Three
b.      Four
c.       Six
d.      Two

(17).  The main conclusion from Anfinsen’s work on RNase A was that:

a.       100% enzyme activity corresponds to the native conformation
b.      Urea can reversibly denature protein in vivo
c.       The native conformation of a protein is adopted spontaneously
d.      Mercaptoethanol can reduce disulfide bonds in in vitro

(18).  Glucose-6-phophate inhibits which of the following enzymes

a.       Glucokinase
b.      Hexokinase
c.       Phosphorylase kinase
d.      Fructos-1-6-bisphosphatase

(19).  A polypeptide containing nine lysine residues and seven arginine residues (both are internally located in the polypeptide) is completely digested with trypsin for peptide fractionation and sequencing. How many peptides will the digestion yield?

a.       16
b.      17
c.       18
d.      9

(20).  Diacylglycerol activates:

a.       Protein kinase A
b.      Protein kinase C
c.       MAP kinase
d.      Tyrosine kinase

CSIR JRF NET June 2017 Model Question Papers

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Answer Key with Explanations

(1). Ans. (d). Linking number of closed circular double stranded DNA

Linking number or Lk is a topological feature of a DNA. Lk determines the degree of supercoiling, i.e., the number of times a DNA strand wind in the right handed direction. If the DNA is a covalently closed circular DNA (cccDNA), the linking number cannot be changed until at least one of the stand is split open. In a completely relaxed B DNA, the linking number will be equal to total number of base pairs/10 (Example: if the DNA stand contains 140 base pairs, then the linking number is 140/10 = 14).

Topoisomerases are enzyme which over-wind of unwind DNA during replication or transcription. For the topoisomerase activity, the enzyme first bounds to the DNA and cleave either one or both of the DNA strands. As given in the question, the treatment with topoisomerase in a covalently closed circular DNA can change the linking number of that DNA.

Learn more: Different Types of DNA (A-DNA, B-DNA and Z-DNA)

(2). Ans. (d). Connective tissue

Sarcoma is a type cancer originated from cells of connective tissues (mesenchymal origin, Sarcomas are the rare type of cancer in human. Example: cartilage, fat, muscles. Carcinoma is a type of cancer originated from epithelial cells.

Carcinomas are the most common type of cancers in human. Example: breast, colon, lung, liver, pancreas.

Lymphoma and Leukemia are cancers originated from lymphocytes or white blood cells.

(3). Ans. (a). Clathrin

Receptor Mediated Endocytosis (RME) also called as clathrin mediated endocytosis is a process by which the cell absorbs extracellular materials such as hormones, proteins, or metabolites by the inward budding of the plasma membrane. The inwardly budding of plasma membrane vesicles contains receptors for the specific molecules being transported.

Clathrin: a major protein which forms the coated vesicles in the cells. Clathrins forms triskelion shaped structures.

Adaptins: proteins which facilitate the formation of clathrin coated vesicles.

Arrestins: a family of proteins acting as the regulators of cell signaling through G Protein Coupled Receptors (GPCR).

Glycophorin: they are membrane spanning, heavily glycosylated proteins which are very rich in sialic acid, found on the plasma membrane of RBC.

(4). Ans. (d). Triacylglycerol

Second messenger: they are the molecules released by the cells, as a result of cell signaling pathway, to execute the specific physiological events in the cells.

Important second messengers of the cell are cyclic AMP, cyclic GMP, inositol trisphosphate, diacylglycerol and calcium ions.

(5). Ans. (a). Cyclosporin

Cyclosporin: protenaceous immunosuppressant used during the organ transplantation to prevent the organ rejection by the immunological reactions of the recipient. Cyclosporin is extracted from a fungus called Tolypocladium inflatum. Cyclosporin is not synthesized on ribosome. It is synthesized by a special type of enzyme called cyclosporine synthase.

Somatotropin = Growth Hormone = GH: a protenaceous mitogen that promotes cellular division, growth and development.

Vasopressin = Antidiuretic Hormone = ADH: a peptide hormone

(6). Ans. (b). Lysosomes

Acid phosphatase is considered as the marker protein of lysosomes. This enzyme is stored in the lysosome. The optimum pH of Acid phosphatase is at high acid condition similar to the pH in the lumen of lysosomes.

(7). Ans. (d). Platelets

Thromocytes are better known as platelets.

(8). Ans. (c). Cysteine

Iodoacetic acid: a toxic alkyl halide and it alkylate the cysteine residues in many enzymes and thereby inactivate it.

Iodoacetic acid is an irreversible inhibitor of all cysteine proteinases.

(9). Ans. (d). A basic amino acid

Trypsin hydrolyzes a peptide bond in which the amino group is contributed by a basic amino acid such as lysine, arginine and histidine.

Learn more: Enzyme Specificity with Examples

(10).  Ans. (b). 6.0

Isoelectric pH: pH at with the net charge of the protein (or amino acid) is zero. At isoelectric pH, the protein will not move to any electrode in the electrophoresis. Proteins are LEAST soluble at its isoelectric pH.

pH below PI, the proteins will be cationic.

pH above PI, the proteins will be anionic

pH at PI the net charge of proteins will be zero

(11).  Ans. (a). Acidic proteins

DEAE: Diethylaminoethyl cellulose is a positively charged resin used in ion exchange chromatography. It is positively charged and hence it can bind and retain negatively charged molecules such as nucleic acids or acid proteins.

(12).  Ans. (b). Structural analogues of metabolites

(13).  Ans. (d). dUMP

Learn more: Nucleotide Biosynthesis (De novo and Salvage of Purine and Pyrimidine Biosynthesis)

(14).  Ans. (a). Competitive

(15).  Ans. (a). Glycerol

Phosphatidic acid and phosphatidylcholine (lecithin) are membrane lipids belongs to the class phospholipids.

Learn more: Membrane Lipids: Properties, Structure and Classification

(16).  Ans. (c). Six

Urea is a polar molecule. Urea can completely dissolve in water. It can form six hydrogen bonds when it is dissolved in water. The two amino groups can form four hydrogen bonds and the oxygen atom at the centre can form another two hydrogen bonds. Hence altogether six hydrogen bonds are formed when the urea is completely dissolved in water.

Learn more: Hydrogen Bonds, How Hydrogen Bonds are Formed in Water?

(17).  Ans. (a). 100% enzyme activity corresponds to the native conformation

(18).  Ans. (b) Hexokinase

(19).  Ans. (c). 18

(20).  Ans. (b). Protein kinase C

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