What is DNA ?

DNA – Structure
Deoxyribose Nucleic Acid
Nucliec acids are polymer of nucleotides.
DNA and RNA are the 02 types of nucleic acids found in living systems. DNA acts as genetic material in most of the organisms.
Genetic Material – A substance that stores genetic information, transfer these to next generation and makes to express itself in the off springs.
Properties
1.    Should self replicate
2.    Can undergo mutations
3.    Must be located in the chromosomes
4.    Must have information to control the synthesis of enzymes and proteins with cell
Structure
DNA is a long polymer of dexoyribonucleotides. Its length is defined as number of nucleotides also called base pairs.
e.g. E. coli has 4.6 x 106 bP
Bacteriophage has 48502bP
Haploid content of human DNA is 43.3 x 109 bP
				Nitrogen base
Nucleotides  -----------------_-----  Pentose Sugar ( Ribose Deoxyribose )
				Phosphate group
					Adenine
			Purines
Nitrogen base					Guanine
					Cytosine
			Pyrimidines
					Thymine
					Uracil
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Base			Nucleoside			Nucleotide			NA
Purines
Aclenine			Adenosine			Adexylate			RNA
			Dexoyadenosine			Deoxyadenylate			DNA
Guanine			Guanosine			guanylate			RNA
			Deoxyguanosine			Deoxyguanyrate			DNA
Pyrimidines
Cytosine			Cytidine			Cytidylate			RNA
			Deoxydytidine			Deoxycytidylate			DNA
Thymine			Thymidine			Thymidylate			DNA
Uracil			Uridine			Uridylate			RNA
Phosphate group is linked to 5' -OH of nucleoside through phosphodiester linkage and corresponding nucleotide is formed.
2 nucleotides are linked through 3'-5' phosphodiester linkage to for dinucleotid. Similarly more nucleotides are joined to form poly nucleotide chain.
This chain has free phosphate mostly at 5' end of sugar and other end of polymer the ribose has free 3' OH group.
Sugar and Phosphate form the backbone of the chain while nitrogenous bases project from the backbone.
Image
DNA was first identified by Friedrich Meisher in 1869 and named "nuclein"
In 1953 James Watson cand Francis Crick based on X ray diffraction data produced by Maurice Wilkins and Rosaline Franklin proposed double
Helix model of the structure of DNA
Chargaff's observation that concentration of thymine was always equat o that of Adenine and concentration of Guanine was equat to Cytosine
In double Helix structure 02 polynucleotide chains are coiled around one another in a spiral with the help of hydrogen bonds between nitrogen
bases of opposite strands. The 2 ploynucleotide chains are complimentry to one another if sequence of bases on 1 strand is know the sequence
on other strand can be predicted.