What is a gene?
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule.
For a polypeptide-coding gene, the order of bases determines the order in which amino acids are joined. The resulting amino acid sequence affects the shape and behaviour of the protein and therefore its function.
RNA involved in protein synthesis
RNA molecules have different roles in the production of polypeptides:
- mRNA has a base sequence that is used by ribosomes when a polypeptide chain is assembled.
- tRNA carries amino acids to the ribosome.
- rRNA forms part of the structure of ribosomes.
tRNA and rRNA are functional RNA molecules and can therefore be products encoded by genes.
Exam Tip: For a complete definition of a gene, state both possible outcomes: it codes for the amino acid sequence of a polypeptide or for a functional RNA molecule.