Question

In DNA, the complementary bases are:
(A)-adenine and thymine; guanine and cytosine
(B)-adenine and thymine; guanine and uracil
(C)-adenine and guanine ;thymine and cytosine
(D)-Uracil and adenine; cytosine and guanine

Answer 1

Hint: In DNA, adenine and thymine, cytosine and guanine are bases and RNA has adenine, Uracil, cytosine and guanine. These bases are complementary to each other because the hydrogen bonds are formed between specific pairs of bases.

Complete step by step answer:
-There are two types of nucleic acids; DNA and RNA
-DNA IS deoxyribonucleic acid and RNA is ribonucleic acid.
-Hydrolysis of DNA and RNA give sugar (Ribose), phosphoric acid and heterocyclic compounds containing nitrogen atoms called bases.
-DNA contains four bases -adenine, guanine, cytosine and thymine.
-RNA contains four bases- adenine, guanine, cytosine and uracil.

Adenine as base

-Base is attached at position 1’ position of sugar which forms nucleoside and phosphoric acid is attached at position 5’ which forms nucleotide.
-nucleotides are linked together by phosphodiester linkage between 5’ and 3’ carbon atoms of ribose sugar.
               

-primary structure of DNA contains sequences of nucleotides in the chain of nucleic acid.
-In secondary structure, two strands of nucleic acids are wound around each other to give double helix structure
-Two strands are held together by hydrogen bonds.
-These bases are complementary to each other because the hydrogen bonds are formed between specific pairs of bases.
-Adenine forms two hydrogen bonds with thymine and cytosine forms three hydrogen bonds.

Note: Adenine always pairs with thymine as they both have OH and NH groups, which can form hydrogen bridges , whereas with other bases it is unfavorable as they are each other’s way. Adenine always pairs with thymine because they form two hydrogen bonds. Guanine and cytosine form three hydrogen bonds.