DNA is phosphoric acid + deoxyribose + bases of A, C, G and T. DNA nucleotides are made up of a sugar (deoxyribose), base (adenine, guanine, cytosine, thiamine) and phosphate.
RNA is phosphoric acid +_ ribose + bases of A, C, G and U RNA nucleotides are made up of a sugar (ribose), base (adenine, guanine, cytosine, uracil) and phosphate.
The pentose of each nucleotide unit is bonded through its number 1 carbon atom to the nitrogenous base to form a nucleoside. The pentose is also bonded through its number 5 carbon atoms to phosphoric acid. All three bonded together make a nucleotide. DNA nucleotides are joined together in a condensation reaction which produces water and a covalent bond between the two nucleotides. The DNA double helix is formed by using complementary base pairing (i.e., adenine bonds thymine and cytosine bonds guanine).
The nucleotides are joined to one another like a chain(strand) by covalent bonds between the 3′-hydroxyl group sugar of one nucleotide and the 5′-phosphate group of the next, resulting in an alternating sugar-phosphate backbone. Two such strands running in opposite directions to each other make up DNA.