RNA is a type of nucleic acid called ribonucleic acid:

• RNA nucleotides are joined to form a single strand.
• Nucleotides are joined together by a strong covalent bond between the sugar of one nucleotide and the phosphate of the next.

RNA differs from DNA in the following ways:

• RNA is single stranded while DNA is double stranded.
• RNA has a sugar called ribose while DNA has a sugar called deoxyribose.
• RNA has the base uracil while DNA has the base thymine.

Type of RNA

There are three types of RNA involved in gene expression.

mRNA - Messenger RNA is a linear molecule which carries a copy of the gene to be expressed from the nucleus. Every group of three bases (a 'triplet') is described as a codon because each one codes for an amino acid.

tRNA - Transfer RNA has a cloverleaf shape. It is made from a single strand of RNA which folds due to base pairing to form this unusual shape. It has a triplet anti-codon site and an attachment site for a specific amino acid.

rRNA - Ribosomal RNA and proteins form the ribosome. The ribosome is the structure where protein synthesis takes place.