Question

what is complementary to cytosine

Answer 1

Guanosine(G) is complementary to cytosine(C) and adenine(A) is complementary to thymine(T) in the DNA.

The no of hydrogen bonds formed between guanosine and cytosine is 3. which means this base pair is much stronger than the 2 hydrogen bonds between A and T. There are 2 types of bases in the DNA called purines and pyrimidines. Purines are double ringed cyclic structures, while pyrimidines are single ringed. A and G are purines while T and C are pyrimidines. According to the chargaff base pair rule, always a purine base pairs with a pyrimidine only and the overall number of a purine is always equal to the pyrimidine in the DNA molecule. This means that always a G should pair with C and A with T only. If this base pairing goes wrong by mistake it is corrected by DNA repair mechanisms that remove the wrong base and fit the correct base at the position.Even if these fail then it leads to DNA mutation that can lead to loss of function of the particular gene.According to the watson-crick structure of DNA given in 1953, the DNA is complementary which means that the bases follow chargaff base pair rule. The two strands are antiparallel which means that one strand runs in the 5-->3' direction while the other goes in the 3'---.>5' direction. The DNA strands are held together by weak hydrogen bonds between the bases. The monomer unit of a DNA is called a nucleotide that includes a nitrogenous base+ deoxyribose sugar+ phosphate group.