Free Net Life Science Study Materials

CSIR JRF NET Life Sciences Model Question Paper for June 2017 Exam (Set 1/4)


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

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Molecular Biology Tutorials

Similarities and Difference between RNA and DNA- A Comparison Table


difference-between-rna-and-dna

Similarities & Differences between DNA and RNA – A Comparison Table

We wish to suggest a structure for the salt of deoxyribose nucleic acid (DNA).
This structure has novel features which are of considerable biological interest.
Watson & Crick, 1953

DNA and RNA are the two types of nucleic acids (a class of macromolecules in the cells) present in all prokaryotic and eukaryotic organisms. Both are essentially the polymers of nucleotides and have immense role in the storage and expression of genetic information in an organism. DNA and RNA allow the storage of genetic information for long period of time without any changes in the genetic constitution of the organism. The presence of two categories of nucleotides also allows the decoding of genetic information during protein synthesis by the process of transcription and translation. The current post describes the similarities and differences between DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Similarities between DNA and RNA

Ø  Both DNA and RNA can acts as genetic material.

Ø  Both are polymers of nucleotides.

Ø  Both DNA and RNA are linear structures with secondary and super-secondary arrangements.

Ø  Both contain purines and pyrimidines.

Ø  Both DNA and RNA contain pentose sugar.

Ø  In DNA and RNA the adjacent nucleotides are connected by 3’-5’ phosphodiester bonds.

Ø  Both DNA and RNA absorb UV light at 260 nm.

Ø Both DNA and RNA contain hydrogen bonds

Difference between DNA and RNA

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Molecular Biology Tutorials

Difference between Necrosis and Apoptosis: A Comparison Table


necrosis vs apoptosis

Apoptosis vs Necrosis
(Similarities and Differences)

Apoptosis and Necrosis are two types of cell death occur in organisms. The cells undergo death when the cell death becomes necessary as a part of developmental process or they fail to adapt to injuries. Both these types of cell deaths differ in their initial cause and progression of the cell death pathway.

Apoptosis definition (programmed cell death): a physiological process by which unwanted or useless cells are eliminated during the development and other normal biological processes. Often found during tissue homeostasis, embryogenesis, immunological reactions and development of nervous systems. During apoptotic cell death, the cells undergo some characteristic events such as chromatin condensation, nuclear and cytoplasmic aggregation and partitions of cytoplasm and nucleus into membrane bound vesicles called apoptotic bodies containing ribosomes and mitochondria. Apoptotic bodies are recognized and phagocytized by either by macrophages or adjacent cells and thus no inflammatory response are elicited during apoptotic cell death.

Necrosis definition: (accidental cell death) a pathological process occurs when the cells are exposed to serious physical or chemical insults. Occur during pathological infections such as bacterial and fungal infections, hypothermia and hypoxia conditions. The cell and cellular organelles swell and ruptures to release the entire cell content including lysosomal enzymes into the extracellular fluid.  Due to this, necrotic cell deaths are always associated with severe inflammatory response in the surrounding tissues.

The current post describes the similarities and difference between apoptotic and necrotic cell death with a comparison table.

Similarities between Apoptosis and Necrosis

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Molecular Biology Tutorials

Nucleosome Model of Chromosomes in Eukaryotes (Short Notes)


structure of nucleosome short notes

image source: scitable

Nucleosome Model of Chromosome

Does the DNA really need to FOLD inside the nucleus?

A diploid human cell contains approximately 6.4 billion base pairs. These 6.4 billion base pairs are distributed in our 23 pairs (2n = 46) of chromosomes. We know that each chromosome contain a single linear segment of DNA.

According to Watson and Crick model, the distance between each base pair in a DNA double helix is 0.34 nm. Thus, the 6.4 billion base pair will constitute a total length of about 2.2 m DNA strand. The total length of DNA of a single human cell is approximately 2.2 meters long (when all 46 DNA strands are joined end to end).

The size of the nucleus in which the chromatin situated is about 10 µm in diameter. Thus, it is evident that the 2.2 m long DNA should fold several times to fit in the nucleus of 10 µm diameter. The exact nature and pattern of folding of DNA strands in the nucleus disclose the organization of genetic material in the cells.

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Molecular Biology Tutorials

Classification of Chromosomes based on Position of Centromere and Length of Chromosomal Arms


how chromosomes are classified

Classification of Chromosomes Based on Position of Centromere and Length of Arms

Ø  The size and shape of the chromosomes are variable in the different phases of cell cycle.

Ø  Chromosomes in the interphase of cell appear as thin, coiled, elastic and thread-like structures.

Ø  This thread-like stainable interphase chromosome is called chromatin.

Ø  During the mitotic or meiotic cell division, the chromatin materials become thicker in their width and shorter in their length.

Ø  Chromosomes in the metaphase stage of cell division show maximum condensation.

Ø  Each metaphase chromosome contains a centromere (primary constriction).

Ø  The centromere divides the chromosome into two parts called chromosomal arms.

Ø  The small arm of the chromosome is denoted as ‘p’ – arm, whereas the large arm is denoted as the ‘q’ – arm.

Ø  When chromosomes are represented as a karyotype or ideogram, each chromosome is arranged in such a way that the ‘p’ arm is positioned above the centromere and the q arm is represented below the centromere.

Ø  The position of centromere and the relative size of chromosomal arms are used as a criterion for a morphological classification of chromosomes.

Ø  This morphological classification is an important karyotypic feature of an organism.

Classification of chromosome

Ø  Based on the position of centromere and length of chromosomal arms, the chromosomes are classified into 4 groups:

(1).      Telocentric chromosomes

(2).      Acrocentric chromosomes

(3).      Sub-metacentric chromosomes

(4).      Metacentric chromosomes

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