DNA is deoxy-ribose- sugar which is mainly found in the nucleus of eukaryotic cell, a small amount in mitochondria and chloroplasts. This is long chain of macromolecules of nucleotides with high molecular weights. It is also found in the chloroplast of prokaryotic cell.
A DNA molecule is composed of;
i) pentose sugar-deoxyibose sugar
ii) N-Bases- 1) Purines –a)Adenine (A)
b) Guanine (G)
2) Pyrimidines-a) Cytosine (C)
b) Thymine (T)
DNA is a double helix or double stranded structure. In 1953 Watson and Crick establish the double structure on the basis of X-ray diffraction. According to them DNA is composed of anti-parallel
DNA is a double helix or double stranded structure. In 1953 Watson and Crick establish the double structure on the basis of X-ray diffraction. According to them DNA is composed of anti-parallel
Polynucleotide strands that form a double helix around the central axis.
The strands are made up of alternate band of deoxyribose sugar and phosphate molecules. Each deoxyribose sugar in the strand has one N-base horizontally attached to it at carbon-1. The four N-bases can occur in any possible sequence along the length of a strand. The N-base + deoxyribose sugar + phosphate together form one unit or deoxyribonucletide in the strand. Such many deoxyribosenucleotides are linked with each other in a linear fashion; therefore the resulting strand is described as the polynucleotide strand and DNA molecules as polynucleotide molecule.
The two polynucleotide strands are held together by hydrogen bonds between specific pairs of purines and pyrimidines. Purine of onepolynucleotide chain pairs with pyrimidine of other i.e. adenine (A) with thymine (T) and Guanine (G) with Cytosine(C). A and T are held together by two hydrogen bonds and G and C by three bonds. The sequence of bases in one polynucleotide chain automatically determines the order of bases in the other i.e. the two chains are complementary to each other when adenine occurs in one strand, thymine is present in corresponding position in the opposite strand and vice versa . Similarly, where guanine is present in one strand, the other strand has cytosine opposite to it and vice versa.
The two strands of helix are of opposite polarity. If one chain run in 3' 5' direction (sugar phosphate linkage), then the other in 5' 3’ direction (sugar phosphate linkage) The function of DNA
a) It is a genetic material, hence it carries hereditary information from parents to offspring.
b) DNA has unique property of carbon copies which is essential for transfer of genetic information.
c) It give rise to RNA through transcription process
d) It plays key role in protein synthesis.
e) any changes in the sequence of nitrogen bases due to addition or deletion causes mutation
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