RNA consists of ribose nucleotides that are attached by phosphodiester bonds, creating strands of different lengths.The nitrogenous bases in RNA are guanine, cytosine, adenine and uracil (replaces thymine in DNA). Uracil is a pyrimidine that has a similar structure to thymine and binds with adenine through two hydrogen bonds. RNA typically exists in the single-stranded form, but there are some RNA viruses that are double-stranded (e.g. rotaviruses). The bases are always attached together by adding the 5’ phosphate group of one nucleotide onto the 3’ hydroxyl group of the previous nucleotide. On a side note, unlike DNA, the sugar in RNA is ribose instead of deoxyribose.