Question

Describe the Watson and Crick model of DNA structure. How did it fit the data provided by Chargaff and the X-ray diffraction pattern?

Answer 1

DNA model given by Watson and Creek in the year of 1953 gave a very detailed study regarding the structure of B DNA which is valid till date and is essentially corroborating with Chargaff's data and Xray diffraction pattern.

Explanation:

The DNA is the most common nucleic acid found in the living organisms as a genetic material. As stated by Watson and Creek, this DNA contains a double helical structure with two sugar phosphate backbones and the nitrogen bases getting projected from it inwards. The backbones are formed of ribose sugar and phosphate and joined together with a phosphodiester bond. The ribose sugar is attached to phosphates at its 3' and 5' Carbon atoms. The nitrogen bases found in DNA are Adenine, Guanine, Thymine and Cytosine. The Adenine has two hydrogen bonds with thymine and guanine has 3 hydrogen bonds with cytosine.

Each full turn of a helix is 34A and each base pair is 3.4A apart. The distance between two strands of DNA is 20A.

Chargaff's rule regarding the equal amount of adenine and thymine as well as guanine and cytosine is matching with this structure. All the other rules also do match with this DNA structure.