Purines and pyrimidines are the two categories of nitrogenous bases.
Adenine and guanine are purines. Cytosine, thymine, and uracil are
pyrimidines. In DNA, the bases are adenine (A), thymine (T), guanine
(G), and cytosine (C). In RNA, the bases are adenine, thymine, uracil,
In DNA, the sugar is 2'-deoxyribose. In RNA, the sugar is ribose. Both
ribose and deoxyribose are 5-csrbon sugars. The carbons are numbered
sequentially, to help keep track of where groups are attached. The only
difference between them is that 2'-deoxyribose has one less oxygen atom
attached to the second carbon.
A single phosphate group is PO43-. The phosphorus
atom is the central atom. One atom of oxygen is connected to the
5-carbon in the sugar and to the phosphorus atom. When phosphate groups
link together to form chains, as in ATP (adenosine triphosphate), the
link looks like O-P-O-P-O-P-O, with two additional oxygen atom attached
to each phosphorus, one on either side of the atom.
(Just copied from someone's Blog)