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.