Proteins are not built directly form genes. The working instructions of the genes are made of molecules of ribonucleic acid, or RNA. RNA, like DNA, is a nucleic acid. It differs from DNA in 3 ways. First, RNA consists of a single strand of nucleotides instead of the two strands that form the double helix. Second, RNA contains the five-carbon sugar ribose rather than the sugar deoxyribose. And third, RNA has a nitrogen-containing base called uracil - abbreviated as U - instead of the base thymine found in DNA. Like thymine, uracil is complementary to adenine.
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