protein synthesis gcse step by step
Protein Synthesis: Step-by-Step Transcription and Translation in GCSE Biology
Protein synthesis is the biological process by which cells generate new proteins from genetic instructions stored in DNA, occurring in two sequential stages called transcription and translation. Because DNA is too large to leave the nucleus, the cell uses a single-stranded messenger molecule called mRNA to carry the code to the ribosomes.
1. Stage 1: Transcription (Inside the Nucleus):
- DNA Unwinding: The DNA double helix unzips around the specific gene being expressed, exposing the template strand.
- Complementary mRNA Formation: RNA nucleotides pair with the exposed DNA bases via complementary base pairing rules (Cytosine pairs with Guanine, and Adenine pairs with Uracil instead of Thymine).
- Nuclear Exit: The newly formed single-stranded mRNA molecule detaches and moves out of the nucleus through a nuclear pore into the cytoplasm.
2. Stage 2: Translation (At the Ribosome):
- Ribosome Binding: The mRNA strand attaches to a ribosome in the cytoplasm.
- Codon Reading: The ribosome reads the mRNA sequence three bases at a time; each triplet of bases is called a codon, which codes for one specific amino acid.
- tRNA Delivery: Carrier molecules called tRNA (transfer RNA) bring specific amino acids to the ribosome, matching their complementary anticodon to each mRNA codon.
- Peptide Bond Formation: The ribosome links the amino acids together in the correct sequence using peptide bonds, forming a growing polypeptide chain.
- Protein Folding: Once the chain is complete, it detaches from the ribosome and folds into a unique 3D shape to function as an enzyme, hormone, or structural protein.
EXAM INSIGHT / PITFALL: In exam questions comparing DNA and RNA base pairing, always remember that RNA contains Uracil (U) instead of Thymine (T). If the DNA template code is TAC, the corresponding mRNA codon is AUG.