RNA

RNA structure is similar to that of DNA, except for the difference in sugar - ribose - instead of deoxyribose and uracil (U) instead of thymine (T). RNA chain lengths varies from one hundred to thousands of nucleotides. Usually RNA molecule is single. It can form double helix DNA–RNA if bases are complementary.

There are several types of RNA:

tRNA (transfer RNA) – transports amino acid to the ribosome where it spots the proper codon (unit of genetic code), tRNA molecules have specified structure

rRNA (ribosomal RNA) – it is ribosome matter, rRNA molecules have specified structure

mRNA (messenger RNA) – it is synthesized on the DNA matrix and carries the DNA message outside nucleus to the ribosomes, mRNA molecules have various structure

snRNA (small nuclear RNA) – it takes part in processing the mRNA into it’s functional form, they catalyze cutting out introns and splicing exons

The final template for protein synthesis is mRNA and thus genetic code usually refers to mRNA. For example codons stop – signifying end of translation are: UAA, UAG and UGA (U – uracil). Codon 5’–AUG–3’ in mRNA was formed on the matrix of 3’–TAC–5’ in DNA. Corresponding tRNA fragment will be 3’–UAC–5’.