Watson and Crick Model of DNA Structure

In this Watson and crick model of DNA structure post we have briefly explained about watson and crick experiment, what is Watson and crick DNA model? and the salient features of watson and crick experiment DNA model.

In Drosophila, Thomas Morgan (1866-1945), the father of modern genetics, discovered that chromosomes contain genes in a sequential order. Barbara McClintock demonstrated gene or mobile gene rearrangement in corn chromosomes in 1931. Working with mutant Neurospora strains, George Beadle proposed the “one enzyme, one gene” concept in 1941.

In 1944, Avery established that DNA is the genetic substance. Hershey demonstrated in 1952 that only the virus’s DNA, not its proteins, enters the host before infection. In 1950, Edwin Chargaff discovered the DNA base pairing rule. Maurice Wilkins’ X-ray crystallographic work on DNA revealed the complexities of DNA structure. Based on these data, James Watson and Francis Crick in 1953 deduced the double helical structure of DNA.

Watson and Crick Experiment DNA Structure

The four deoxyribonucleotides that make up deoxyribonucleic acid are deoxyadenylate (A), deoxyguanylate (G), deoxycytidylate (C), and thymidylate (T). These units are linked together by 3′ to 5′ phosphodiester linkages to form a lengthy chain. The nucleotide is made up of three components: base, sugar, and phosphoric acid. A phosphate group joins the 3′-hydroxyl of one sugar to the 5′-hydroxyl of another sugar.

The importance of the nucleotide sequence of Deoxyribonucleic acid cannot be overstated. The genetic information is encoded in a certain base sequence; if the base is changed, the information is changed as well. The base sequence is always written from the 5′ end to the 3′ end in the case of DNA. The polarity of the Deoxyribonucleic acid  chain is what we call it.

Features of Watson and Crick Experiment DNA Model

Right handed helix

DNA is made up of two polydeoxy ribonucleotide chains that are coiled around each other in a right-handed double helix that looks like a spiral staircase. The handrail is made up of sugar and phosphate groups, with the bases projecting inward representing the stairwell steps. The bases are perpendicular to the helix axis, whereas the sugars are nearly perpendicular to it.

Base pairing rule

The two strands are always complementary to one another. As a result, one strand’s adenine will couple with the opposite strand’s thymine, whereas guanine will couple with cytosine. Chargaff’s rule asserts that the number of purines equals the number of pyrimidines when the bases are paired (A with T; G with C).

Watson and Crick DNA Model

Watson and Crick Experiment DNA Model

Hydrogen bonding

The purine and pyrimidine bases form hydrogen bonds that hold the Deoxyribonucleic acid strands together. Between A and T, there are two hydrogen bonds, but between C and G, there are three hydrogen bonds. As a result, the GC bond is more powerful than the AT bond.


In a DNA molecule, the two strands run antiparallel, meaning one runs in the 5′ to 3′ direction and the other in the 3′ to 5′ direction. This is analogous to dividing a road into two halves, each carrying traffic in the opposing direction.

Other features

During the replication process, each strand of DNA serves as a template for the synthesis of the opposite strand. The spiral has a 3.4 nanometer per turn pitch. Ten base pairs are seen in a single turn. As a result, 0.34 nm separates adjacent bases. 

The helix has a diameter of 1.9 to 2.0 nanometers and a breadth of 1.9 to 2.0 nanometers. A major groove (1.2 nm) and a minor groove (0.6 nm) wind parallel to the phosphodiester backbone along the molecule. Proteins interact with the exposed bases in these grooves.

Further Readings