Protein synthesis is the making of a protein.
It is carried out by a ribosome.
Protein synthesis involves three distinct stages: transcription; translation; and protein folding
1. Transcription
- Transcription is the making of messenger RNA using a DNA template.
- Enzymes unwind the double helix and separate the two strands by breaking the hydrogen bonds between the bases where the gene is located
- RNA polymerase synthesises messenger RNA (mRNA) using one of the strands of DNA as a template
2. Translation
- Translation is the making of a protein using the code in mRNA.
- mRNA moves to cytoplasm and combines with a ribosome made up of two ribosomal RNA (rRNA) subunits
- A codon (or a ‘triplet’) is a sequence of three bases present on mRNA or DNA.
- Each codon ‘tells’ the ribosome to do one of three things:
- Start making a protein (start codon)
- Add on an amino acid to the growing chain of amino acids
- Stop making the protein and rlease the chain of amino acids (stop codon).
- Transfer RNA (tRNA) is another type of RNA – it is found free-floating in the cytoplasm and is responsible for carrying one amino acid. (Remember amino acids are the building blocks of proteins)
- tRNA has a 3-base (triplet) sequence called the anti-codon that is complementary to a particular codon on the mRNA.
- An anti-codon is a sequence of three bases present on tRNA.
- Each tRNA in turn (with its own amino acid) lines up with the mRNA in the ribosome and an amino acids are joined together by peptide bonds in a long polypeptide line which will form the protein
- This process continues until the stop codon on the mRNA is reached at which point all the translation machinery separates and the protein is released.
3. Protein Folding
- The chain of amino acids leaves the ribosome and is sent to specific areas of the cell where it is packaged and folded into its functional shape.
- It goes and carries out its specific function (e.g. enzyme action)
