(a) DNA stands for Deoxyribose Nucleic Acid which is present
in chromosomes.
(b) DNA has a double helical or spiral structure having
nucleotides. Nucleotides comprises of phosphoric acid, deoxyribose sugar and nitrogeneous
bases like adenine, thymine, guanine and cytosine. The nucleotide sequence of
the DNA molecule is called a gene. Genes are present on DNA. Changes in the
genes can alter the characteristics of any organism.
(c) The double helical, spiral structure of DNA was proposed
by James D. Watson and Francis Crick in 1953 for which they were awarded the
Noble prize.
