Watson and Crick's Model of DNA | Structure of DNA | Article

Watson and Crick's Model of DNA 

Working of Scientists on DNA Structure :

Erwin Chargaff :

In 1951, Erwin Chargaff found that the nitrogenous bases in a DNA show specific ratios. He observed that amount of adenine is always equal to the amount of thymine and amount of guanine is always equal to the amount of cytosine in DNA. This implies that the total purines and total pyrimidines are in 1:1 in any DNA. This conclusion is known as Chargaff's rule.

Maurice Wilkins and Rosalind Franklin : 

In those days the X-ray diffraction analysis of DNA by Maurice Wilkins and Rosalind Franklin was published. They first time claimed that DNA is a duplex (double helix) molecule. The width of duplex is 2nm while the length of each turn is 3.4nm.

James Watson and Francis Crick :

In 1953, on the basis of these observations a graduate student Francis Crick and a research fellow James Watson of Cambridge University proposed a physical model of DNA which is now called Watson and Crick Model of DNA.

Double Helical Structure of DNA Proposed By Watson and Crick's Model of DNA .

According to this model a DNA is made up of two polynucleotide chains which are attached together by base pairs. In order to make base pairing the two polynucleotide chains are opposite in direction i.e., one chain runs from 5' to 3' downward and the other chain runs from 5' to 3' upward. Both chains show a constant width of 2 nm. Therefore, both chains are supposed be antiparallel to each other. The base pairing is very specific i.e., Adenine makes the pair with Thymine and Guanine with Cytosine. The base pairs are held together by the hydrogen bond. There are three hydrogen bonds between Guanine and Cytosine and two hydrogen bonds between Adenine and Thymine. Each turn of the duplex consist of 10 base pairs. Both polynucleotide chains are complementary to each other. There is no restriction of the sequence of nucleotides along the length of a DNA strand. The sequence can vary in countless ways. The sequence is specific for different species, organisms and even individuals.

Watson and Crick's model was groundbreaking and earned them the Nobel Prize in Physiology or Medicine in 1962. It provided a basis for understanding the mechanisms of DNA replication, transcription, and translation, and for exploring the genetic basis of inheritance, disease, and evolution.

Thank you for Reading the article.