Protein Synthesis (Cambridge (CIE) IGCSE Biology): Revision Note

Transcription & translation: Extended

• Proteins are made by ribosomes with the sequence of amino acids controlled by the sequence of bases contained within DNA (opens in a new tab)

• DNA cannot travel out of the nucleus to the ribosomes (it is far too big to pass through a nuclear pore) so the base code of each gene is transcribed onto an RNA molecule called messenger RNA (mRNA)

• mRNA then moves out of the nucleus and attaches to a ribosome

• The ribosome ‘reads’ the code on the mRNA in groups of three

• Each triplet of bases codes for a specific amino acid

• In this way the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein

• Each tRNA molecule binds to, and carries, a single, specific amino acid from the cytoplasm to the ribosome for the assembly of the amino acid chain

• Once the amino acid chain has been assembled, it is released from the ribosome so it can fold and form the final structure of the protein