RNA is very similar to DNA. The differences are 1) the sugar is ribose rather than deoxyribose, 2) the nucleotide Uracil (U) is used instead of Thymine, and 3) RNA is single stranded rather than double stranded. But, the nucleotides in RNA are able to form complementary base pairs A-U (rather than A-T) and C-G which allows the single strand of RNA to form short double stranded regions by looping back on itself.
