All articles, Educational articlesDNA story: The structure and function of DNA

DNA story: The structure and function of DNA

 

In this series of articles, we will discuss the history of DNA in addition to the structure and function of it. let us start with the short introduction about DNA,

Deoxyribose Nucleic Acid, DNA is a hereditary unit of all living organism on earth. It inherits characters from one generation to another. 

DNA contains all the information of an organism in the form of triplet codon, this information inherits to offsprings which provide adaptation to all living organism.

History

James Watson and Francis Crick together developed the structure of DNA in 1953.  However, it was first observed by Rosalind Franklin and Wilkins through 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 had confirmed that the DNA is a basic unit of inheritance. The classical experiment of Griffith was as important as Mendel’s pea plant experiments. Followed by Griffith’s experiment, Phoebus Levene discovered different components involved in the structure of DNA. 


Agarose gel electrophoresis is a technique used for separation of DNA. we have covered an entire series on agarose gel electrophoresis. read all articles here,

Role of EtBr in agarose gel electrophoresis

DNA gel loading dye

Agarose gel electrophoresis buffer

Agarose gel electrophoresis


 

Phoebus showed that DNA is made up of nitrogenous bases: Adenine, Thymine, Cytosine and Guanine which is linked with pentose- phosphate-sugar molecule. Although, he was unable to explain how the bases are linked with each other.

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

DNA
The image represents a double-stranded helical structure of DNA. Image credit: News medical and life science.

Structure

Structurally DNA is made up of  three major parts:

  • Sugar-phosphate
  • Nitrogenous bases
  • Covalent forces

 Sugar-Phosphate is a backbone of DNA. It runs along with the length of the DNA molecule and provides structural support to it. Phosphate is attached with a 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 the DNA is attached to the 3rd carbon of sugar molecule with free -OH group. Therefore, it is termed as 3’-OH end. At one end, the DNA molecule starts with 5’-P and end at 3’-OH. similarly, for another strand, it starts with 3′-OH and end at 5′-P in double-stranded DNA.  


Read the article: Sex determination 


 

4 Major bases Adenine, Thymine, Cytosine and Guanine are exclusively a part of the 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.

DNA
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 Play an important role in binding of any biochemical molecule. It provides stability to the biomolecule and due to the covalent bond, the structure of biomolecules remain intact. Phosphodiester bond between sugar and phosphate provides stability to the backbone of the 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 direction.


PCR is an important technique applicable in DNA study, read our collection of PCR articles:

Function of taq DNA polymerase in PCR

Role of MgCl2 in PCR reaction

PCR primer design guidelines


 

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 and creates a double-stranded structure of DNA molecule.

Function

DNA is a basic unit of heredity. Triplet codon of DNA codes for particular amino acid, long chain of amino acid creates 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.

In the next article of this series we will discuss about the function of DNA in depth.

Article written by: Tushar Chauhan

 

 

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