RNA STRUCTURE

• RNA is typically single stranded and is made of ribonucleotides that are linked by phosphodiester bonds.

• A ribonucleotide in the RNA chain contains ribose (the pentose sugar), one of the four nitrogenous bases (A, U, G, and C), and a phosphate group.

• The basic components of RNA are the same than for  DNA with two major differences. The pyrimidyne base uracil replace thymine and ribose replace deoxyribose. Adenine and Uracil for a base pair formed by two hydrogen bonds.

Classification of RNA

RNA molecules are classified according to their structure and function.

Transfer RNA, tRNA :

• The tRNA molecule has a distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover.

• One of these hairpin loops contains a sequence called the anticodon, which can recognize and decode an mRNA codon

• the tRNA transfers the appropriate amino acid to the end of the growing amino acid chain.

• Then the tRNAs and ribosome continue to decode the mRNA molecule until the entire sequence is translated into a protein.

Ribosomal RNA, rRNA:

• a ribonucleic acid found in ribosomes, the site of protein synthesis

• only a few types of rRNA exist in cells

• in both prokaryotes and eukaryotes, ribosomes consist of two subunits- one larger than the other (eg. 50S and 30S)

Messenger RNA, mRNA:

• a ribonucleic acid that carries coded genetic information from DNA to ribosomes for the synthesis of proteins

• single stranded

• biosynthesis is directed by information encoded on DNA

• a complementary strand of mRNA is synthesized along one strand of an unwound DNA, starting from the 3’ end