Protein Synthesis: Transcription and Translation — AQA GCSE Biology (Separate / Higher)
Genes code for proteins. Protein synthesis is the process of using a gene's DNA sequence to build a protein.
From gene to protein
The sequence of bases in a gene determines the sequence of amino acids in a protein. There are two main stages: transcription and translation.
Transcription
- The DNA of a gene is copied into a molecule of mRNA (messenger RNA).
- mRNA is a smaller molecule that can leave the nucleus and carry the code to the ribosomes.
Translation
- The mRNA attaches to a ribosome.
- Carrier molecules bring specific amino acids in the order coded by the mRNA bases (read in groups of three).
- The amino acids join together to form a chain — the protein.
Folding and function
The chain of amino acids folds into a unique 3D shape, which gives the protein its specific function. Proteins include enzymes, hormones and structural proteins (such as collagen).
Mutations
A change in the DNA base sequence (a mutation) can change the amino acid sequence and therefore the shape and function of the protein. Most mutations have little or no effect, but some can be significant (e.g. changing an enzyme's active site).
Exam tips
- Two stages: transcription (DNA → mRNA) and translation (mRNA → protein at the ribosome).
- The base sequence determines the amino acid sequence.
- Protein folding gives a specific 3D shape for its function.
- A mutation can change the protein's shape (e.g. an enzyme active site).