Watson and Crick (1953) proposed DNA was based on
(i) X-ray diffraction studies studies of DNA dne by Wilkins and Franklin
(ii) Chargaff's base equivalence rule
(iii)Griffith's transformation experiment
(iv) Meselson and Stahl's experiment.

Watson and Crick proposed their double helical DNA model based on the X-ray diffraction analysis of ……………..

The double helical model of the DNA was proposed by Watson and Crick based on what data produced by wilkins and Franklin

Which of the following sentence is true or false ? (Symbol is true is T and False is F) (i) Message for the synthesis of a specfic protein is present in DNA (ii) Cytocin base is derivatives of pyrimidine. (iii) beta -2-Deoxy ribose sugar present in DNA. (iv) DNA is the exculusiely repsonsible for maintaining the identity of different species of organism upto 100 years.

Answer the following questions based on Meselson and Stahl's experiment of E. coli : (a) Write the name of the chemical substance used as the only source of nitrogen in the experiment. (b) Why did they allow the synthesis of the light and the heavy DNA molecules in the organism ? (c ) How did they distinguish the heavy DNA molecules from the light DNA molecules? Explain. (d) Write the conclusion the scientists arrived at, at the end of the experiment.

Answer the following questions based on Meselson and Stahl's experiment of E. coli : (a) Write the name of the chemical substance used as the only source of nitrogen in the experiment. (b) Why did they allow the synthesis of the light and the heavy DNA molecules in the organism ? (c ) How did they distinguish the heavy DNA molecules from the light DNA molecules? Explain. (d) Write the conclusion the scientists arrived at, at the end of the experiment.

Go though the following statements (i) Meselson & stahl used cesium chloride density gradient to distinguish heavy DNA molecules from the normal DNA molecules. (ii) In meselson & Stahl experiment the DNA that was extracted from the culture one generation after the transfer from .^(15)N to .^(14)N , was composed of equal amount of hybrid (intermediate) DNA and of light DNA. (iii) In prokaryotes, control the rate of transcriptional initiation is the predominant site for control of gene expression. (iv) In lac operon, the repressor is synthesised only at the time when the level of metabolite is in excess. Find out the correct statements?

The base sequence in one of the strands of DNA is TAGCATGAT (i) Give the base sequence of its complementary strand. (ii) How are these base pairs held together in a DNA molecule? (iii) Explain the base complementarity rules. Name the scientist who framed this rule.