5. Structure of RNA

• RNA molecules are temporary single-stranded molecules used to facilitate protein synthesis.

• Like DNA, the basic unit is a nucleotide.

• However, the components of the nucleotide are different.

Above: Nucleotide of an RNA consists of a ribose sugar, a phosphate group and a nitrogenous base. There are four types of nitrogenous bases present in an RNA, namely adenine, uracil, guanine and cytosine.

• Four types of nucleotides in an RNA are adenine nucleotide, uracil nucleotide, guanine nucleotide and cytosine nucleotide.

Above: Depending on the type of nitrogenous base present, there are four types of nucleotides in an RNA, namely adenine nucleotide, uracil nucleotide, guanine nucleotide and cytosine nucleotide.

• Each RNA molecule consists of one strand and there is no complementary base pairing. As such the ratio of adenine to thymine and guanine to cytosine is not 1:1.

Top: Structure of a RNA molecule

Bottom: Simplified structure of a RNA molecule, showing only the sequence of nitrogenous bases.

• There are three main types of RNA, namely

1: messenger RNA (mRNA): a temporary molecule that contains a specific sequence of nucleotides that code for a specific sequence of amino acids on a polypeptide chain.

2. transfer RNA (tRNA): a temporary molecule that attaches to an amino acid on one end and binds to the complementary sequence of nucleotide codes on the mRNA.

3. ribosomal RNA (rRNA): used to synthesise the ribosomes needed for protein synthesis. This will not be discussed in great depth.