RNA consists of a 5-carbon sugar, ribose, which is attached to an organic base (either adenine, uracil, cytosine or guanine). There are two biochemical differences between DNA and RNA:
1. the 5-carbon sugar has no hydroxyl group in the 5 position
2. the uracil presence in the RNA which is the non-methylated form of thymine instead of just thymine.
The presence of ribose in RNA makes its structure more flexible than DNA, letting the RNA molecule fold and make bonds within itself which makes the single stranded RNA more than single stranded DNA.