DNA(Deoxyribonucleic Acid) is a double stranded (double helix) polynucleotide. DNA consists of nitrogenous bases both, purines (adenine and guanine) and pyrimidines (cytosine and thyminc), sugar (deoxyribose) and phosphoric acid.
• Uracil (pyrimidine) is not present in DNA.• In DNA the two strands are joined together through out the whole length of the molecule. DNA strands are complementary to cach other but run in opposite directions.The joining between the two strands Always Occurs between purines and pyrimidines and not between purines themselves or pyrimidines themselves.
There is a rule, known as "the pairing rule" according to which adenine always joins thymine through three hydrogen bonds (A=T)) and guanine always join cytosine through three hydrogen bonds(G=C).
A purine and a pyrimidine, which joins together to form DNA, is known as complementary pair of bases. Therefore adenine (A) and thymine (T) form one complementary pair and guanine (G) and cytosine (C) form the another complementary pair.
DNA contains the genetic information that give rise to chemical and physical properties to the living organism. Genes are part of DNA molecule.
The genetic information is contained in one of the two strands of DNA molecule,which is termed as "sense strand". Thus The other strand is known as "anti-sense strand".
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