Question

How did the results from twentieth century experiments provide evidence to support claims about the structure of DNA and the process by which it replicates?

Answer 1

• The results from twentieth century experiments provide evidence to support claims about the structure of DNA.In 1953 Watson and Crick based on the X-ray diffraction data proposed a very simple but famous double helical model of DNA.The X-ray diffraction data was produced by Wilkins and Franklin.
• DNA is made of two polynucletide chain and the backbone of DNA is sugar-phosphates.The two chains have anti-parallel polarity and they are coiled in a right-handed fashion.
• In a DNA always purine comes in opposite to pyramidine so it generates uniform distance between the strands of the helix.The pitch of helix is 3.4nm and there are 10bp in each turn.
• The process by which DNA replicates is called a semeconservative DNA replication.The experimental proof was given by Meselson and Stahl in 1958.
• They cultured bacteria in a 15N medium. 15N is a heavy isotope of nitrogen, they then shifted the bacteria to a 14N medium. After one replication cycle, the DNA was all of intermediate density. This shows that its a conservative replication model, which predicts that both heavy density DNA and light density DNA will be present but no intermediate density will be present.It is consistent with the semiconservative replication model which predicts that all DNA molecules will consist of one 15N-labeled DNA strand and one 14N-labeled DNA strand.