Story of DNA

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 Let us introduce DNA first because though it is an important biological molecule, people still don’t understand what actually a DNA is.  

DNA is a hereditary unit of all organism on earth. It inherits characters to its offsprings and makes them adaptive to their environment.


James Watson and Francis Crick together developed the structure of DNA in 1953.  However, it was first observed by Franklin and Wilkins by X-ray diffraction, earlier before Watson and Crick.

Far before the discovery of DNA,  Gregor John Mendel described the fair concept of genetics, in 1843. He was honoured as a father of genetics. 

In early 1928, Frederick Griffith has confirmed that DNA is a basic unit of inheritance. The classical experiment of Griffith was as important as Mendel’s pea plant experiment. Followed by Griffith’s experiment, Phoebus Levene discovered different components involved in the structure of DNA.

Phoebus showed that DNA has four major bases Adenine, Thymine, Cytosine and Guanine and phosphate linked pentose sugar molecule. However, he was unable to explain how the bases are linked with each other.

In 1940, Erwine chargaff postulated a hypothesis, “ Amount of adenine is equal to an amount of thymine and amount of cytosine is equal to an amount of guanine. It was clarify that  A=T and G=C, the hypothesis is now termed as chargaff’s rule.

structure of DNA 2.001
Image represents double stranded helical structure of DNA. Image credit: News medical and life science.


Structurally DNA is made up of  three major parts:

  • Sugar-phosphate
  • Nitrogenous bases
  • Covalent forces

Phosphate is a backbone of DNA. It runs along with the DNA molecule and provides structural support to DNA. Phosphate is attached with pentose sugar at the 5th position of sugar carbon. Hence the phosphate end of DNA is denoted as 5’-P end. The other end of DNA is at the 3rd carbon of sugar molecule with free -OH group, hence it is termed as 3’-OH end. In double-stranded DNA if one strand start with 5’-P than the other end has 3’-OH and vice a versa.

Read the article: Sex determination 


Major 4 bases Adenine, Thymine, Cytosine and Guanine are extensively a part of DNA. Fifth base Uracil is present in RNA instead of Thymine. Adenine and Guanine are purine bases while Cytosine, Thymine and Uracil are pyrimidine bases.

structure of DNA 1.001
The image represents the structure of DNA with phosphate backbone, nitrogenous bases and a pentose sugar. Image credit: News medical and life science.

Covalent forces are an important ingredient in any biochemical molecule. It gives stability to biomolecules and due to covalent bonds, the structure of biomolecules remain intact. Phosphodiester bond between sugar and phosphate provides stability to the backbone of DNA. It is a strong interaction between the 5th carbon of one sugar to the 3rd carbon of another sugar. It creates a ladder-like structure from 5′- P to 3’-OH, from upper to lower.

Another strong bond is present between purine and pyrimidine bases. Three hydrogen bonds between Guanine and Cytosine and two hydrogen bonds between Adenine and Thymine are present between opposite strands. It will join one DNA strand with another strand and creates double-stranded DNA molecule.


DNA is a basic unit of heredity. Triplet codon of DNA codes for particular amino acid, long chain of an amino acid forms a protein. Proteins are complex biological molecules and abundant in nature. Enzymes, Hormones, Receptors, Immunoglobulin and Ligands are different forms of protein which plays a vital role in the survival of life.

Article written by: Tushar Chauhan



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