DNA

Almost all organisms contain De-oxy Ribonucleic Acid (DNA)- the carrier of genetic information. It is a very long, thin molecule that is twisted in the shape of a double helix. DNA is responsible for transferring hereditary traits from one generation to another.


Facts About DNA

One gram of DNA molecules holds as much information as 10,00,00,00,00,000 (a trillion) CDs

Each cell in our body contains about two metres of DNA

If all the DNA in all the cells of a single human are stretched out, it would reach the moon and back eight thousand times!

A single human DNA molecule has some 3,00,00,00,000 (three billion) base pairs!


DNA is one of the nucleic acids, information containing molecules in the cell. It guide s the cell(along with RNA) in making new proteins that determine all of our biological traits and gets passed on from one generation to the next.


It is a very long molecule whose basic building blocks are nucleotides. A nucleotide consists of three parts :

Sugar molecule( De oxy ribose sugar)

Phosphate molecule

Nitrogenous base.


The sugar molecule of a nucleotide is bonded with the phosphate group on one side and the nitrogenous base on the other side.

In a DNA , there are two strands that are twisted together like a twisted ladder. This is what is called the double helical structure of the DNA.

The strands of DNA are made of the sugar and phosphate portions of the nucleotides while the middle parts are made of the nitrogenous bases. These nitrogenous bases are held together by hydrogen bonds.


There are four types of nitrogenous bases in SNA. They are :

Adenine

Cytosine

Guanine

Thymine


Adenine and Guanine are double ringed structures where as Cytosine and Thymine are single ringed structure. These get bonded in a particular way. Adenine in one strand attracts only thymine in the other strand forming an A-T pair. Similarly Guanine attracts only Cytosine forming G-C pair.

Water constitutes almost 90% of the cell and the double helical structure can be justified by considering the hydrophilic and hydrophobic nature of the parts of the nucleotides. The sugar and phosphate groups are water loving i.e, hydrophilic where as nitrogenous bases are hydrophobic.

Hydrophilic parts forming the strands and nitrogenous bases forming the middle part is therefore reasonable. Getting twisted further avoids the interaction of water with the hydrophobic middle parts. Thus the twisted ladder structure is justified.,