6.3 - Translation (mRNA to protein)

Unit 3: Molecular Genetics

Lesson 6: Protein Synthesis - Translation

Overview of Translation

• Translation: The process where ribosomes create proteins by decoding the mRNA sequence

• Key Components:

  • mRNA

  • tRNA (transfer RNA)

  • rRNA (ribosomal RNA)

  • Ribosomes

  • Amino-acyl tRNA synthetases

Ribosomal Structure

Ribosome Components:

• Large Subunit: Contains the E, P, and A binding sites

  • E Site: Exit site for tRNA

  • P Site: Peptidyl tRNA binding site

  • A Site: Aminoacyl tRNA binding site

• Small Subunit: Provides the platform for mRNA binding and decoding

• Ribosome Composition: Made of rRNA and proteins

  

tRNA Structure

• Structure Features:

  • Amino acids attach to the 3' OH site of tRNA

  • Anticodon: A specific three-nucleotide sequence that pairs with the mRNA codon

• Example mRNA sequence and corresponding tRNA anticodon:

  • mRNA: 5' - AUG - 3'

  • tRNA anticodon: 3' - UAC - 5'

    

Initiation Stage

• mRNA Binding:

  • mRNA binds to the small ribosomal subunit

  • Ribosome recognizes the 5' cap of mRNA

• Codon Recognition:

  • Initiator tRNA (met-tRNA) binds to the start codon (AUG) on the mRNA

• Formation of Active Ribosome:

  • Large subunit joins, completing the initiation complex

  

Elongation Stage

Steps of Elongation:

1. Aminoacyl tRNA Binds:

   • The appropriate aa-tRNA binds to the A site based on codon-anticodon pairing

2. Peptide Bond Formation:

   • A peptide bond forms between the amino acids at the P site and A site

3. Translocation:

   • Ribosome shifts along the mRNA to the next codon

   • The empty tRNA exits from the E site

   • The polypeptide-bearing tRNA moves to the P site

Termination Stage

• Stop Codons:

  • The ribosome reaches a stop codon (UGA, UAG, UAA)

  • Release Factor: A protein that triggers polypeptide release

• Separation of Translation Machinery:

  • The complex disassembles, releasing the newly synthesized protein

Polysomes

• Efficiency of Translation:

  • Multiple ribosomes can translate the same mRNA simultaneously

  • Facilitates rapid synthesis of polypeptides

Post-Translational Modifications

• Processing Steps:

  • Proteins often undergo modifications after translation

  • Involves folding and modifications by molecular chaperones

• Significance of Folding:

  • Proper folding is crucial for protein function

Review : Summary of Translation Process

• Animation and Visual Aids: Understanding of the translation process can be enhanced through visual aids and animations.