Understanding the Translation Process

Nov 20, 2024

Lecture Notes on Translation Process

Overview

  • Translation Process: Conversion of a gene into a protein.
  • Focus: Big picture understanding of translation and mutations impacting phenotype.

RNA Codons

  • Codons: Three base pair sequences in RNA language.
  • Universal Translation: Nearly all organisms translate UUU to phenylalanine.
  • Codon Table Usage: Helps determine amino acids from codons.
    • First letter determines the row.
    • Second letter determines the column.
    • Third letter specifies the exact amino acid.

Special Codons

  • Stop Codons: UGA, UAA, UAG tell the cell to stop translation.
  • Start Codon: AUG codes for methionine; starts translation.

Mutation Types

1. Silent Mutations

  • Definition: Mutations with no effect on protein produced.
  • Example: GGG in DNA → CCC in mRNA → Proline.
    • Mutating the last base pair to GGA → CCU still results in Proline.
    • Wobble Effect: Flexibility in the third base pair often leads to silent mutations.

2. Missense Mutations

  • Definition: DNA alterations changing the protein produced.
  • Example: GAU (aspartic acid) → GUU (valine) after mutation.
    • Protein function may change but protein still produced.
    • Mutation in start codon can prevent translation.

3. Nonsense Mutations

  • Definition: Mutation leads to a stop codon, truncating protein.
  • Example: ACC (tryptophan) → ATC (stop codon) after mutation.
    • Results in incomplete, often nonfunctional protein.

4. Loss of Stop Mutations

  • Definition: Mutates stop codon, removing stop signal.
  • Example: ATT (stop) → UAC (amino acid) continues protein synthesis.
    • Often results in altered, sometimes nonfunctional proteins.

5. Frameshift Mutations

  • Definition: Insertion or deletion of bases not in multiples of three.
  • Example: Inserting T in GAG shifts reading frame, changes codons.
    • Can lead to nonsense or missense mutations.
    • Three-base insertions/deletions have less impact.

tRNA and Translation

  • tRNA Shape: Clover-shaped with amino acid binding site.
  • Anticodon: Region complementary to the mRNA codon, determining binding amino acid.
  • Ribosome Interaction: tRNA interacts non-covalently with ribosomes.
    • Adds amino acids to the growing polypeptide chain.

Next Steps

  • Further details on translation machinery will be covered in future lectures.