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

DNA double helix is the most iconic structure for all biological molecules. Until 1950s, the structure of DNA remained a mystery. The components of DNA we know that A,T,G,C which comes under purines and pyrimidine based dependent on their rings present on them. Techniques for determining the structure of molecules in DNA, known as X-ray crystallography which gives diffraction pattern that gives clues about the molecules structure, which later on, provides a DNA double helix structure. DNA shows anti-paralell orientation which means in a dsDNA molecule, 5' end of one strand allign with the 3'end of its partner. The twisting of DNA right handed double helix gives major and minor grooves which are important binding sites for proteins and regulation of gene activity. Base pairing includes A with T and G with C which are known as complementary base pairs. Although Watson and cricks original model proposed that each base pairs contains 2 hydrogen atoms but we know today that G and C form an additional bonds such as A and T forms with 2 hydrogen bonds whereas G-C pairs form three.

DNA replication process have 4 steps. Step 1 is replication fork formation where dsDNA unzipped by DNA helicase . This enzyme separate strands by forming Y shape known as replication forks. However, replication fork is bi-directional, one strand oriented as a 3'-5' direction which is known as leading strand and the other strand oriented as a 5'-3' known as lagging strand. Replication begins at step two which is primer binding site where RNA primer binds as the starting point for replication, generated by the enzyme DNA primase. Step three is elongation process where DNA polymerase III which is the main replication enzyme binds to the strand at the sites of the primer. Replication proceeds to the leading strand is continuous and replication in lagging strand forms discontinuous called okazaki fragments. Last step known as termination process where exonuclease removes all the RNA primars from the original strand and another exonuclease called DNA ligase joints okazaki fragments. Telomerase catalyzes the synthesis of telomere sequence at the ends of the DNA. In the end replication produces two DNA molecules, each with one strand from parent molecule and one from new strand.