Messenger RNA (mRNA) carries the DNA instructions for building the protein, transfer RNA (tRNA) carries the appropriate amino acid to the ribosome, and ribosomal RNA (rRNA) is the major component of a ribosome, the structure that reads codons on the mRNA and assembles amino acids into polypeptides.NA nucleotides contain a sugar called ribose; DNA nucleotides contain a similar sugar called deoxyribose. RNA has the nitrogenous base uracil, which behaves similarly to the thymine in DNA-that is, both uracil and thymine form complementary base pairs with adenine.