Question

With the help of a neat and labeled diagram describe Watson and Crick model of DNA.

Answer 1

Hint: DNA is a double helix. By looking at the image below, you will be able to clearly write and understand the structural features of the DNA macromolecule. DNA is the sole carrier of genetic information. In DNA the total number of purines is always equal to the total number of pyrimidines (A+G=T+C).

Complete answer:

The DNA is a large macromolecule. It is also known as the DNA double helix as it contains two strands wound around each other.DNA is made up of nucleotides which consists of a phosphate group, a pentose sugar and a nitrogenous base.

The strands of DNA are composed of the phosphate groups and the pentose sugar lined to one another via phosphodiester bonds.DNA contains four nitrogenous bases which remain attached to the inner sides of the strands. The bases are Adenine, Thymine, Cytosine and Guanine respectively. Adenine pairs with thymine with two hydrogen bonds whereas guanine pairs with cytosine with three hydrogen bonds.

The length of one complete helical turn is about 34 Angstroms however the distance between two consecutive base pairs is about 3.4 Angstroms. One helical turn of the DNA contains about ten base pairs.

The nitrogenous bases of DNA are widely classified as purine and pyrimidine bases.The purine bases are the adenine and guanine and the pyrimidine bases are the cytosine, thymine and uracil respectively which occur in RNA.

In DNA, a purine base always pairs with a pyrimidine. The number of purine bases in DNA is always equal to the pyrimidine bases of DNA. This is known as the Chargaff’s Rule or Chargaff’s Hypothesis.

Note: In an earlier hypothesis known as the RNA world hypothesis, RNA was considered as the genetic material as it had the property of acting both as an enzyme and as a self replicator. However, RNA is a relatively unstable molecule. But RNA was soon replaced by DNA to carry genetic information as it is relatively more stable than RNA in certain conditions. As DNA is the true genetic material, it is also called as the blueprint of life.