Lecture on Translation of RNA to Protein

Overview

• Translation: Process of converting RNA into protein (amino acid language).
• Steps: Initiation, elongation, termination.

Key Players

• mRNA (messenger RNA): The message to be translated.
• rRNA (ribosomal RNA): Location of translation, part of the ribosome.
  • Ribosomes in cells: 80S
  • Ribosomes in bacteria: 70S
• tRNA (transfer RNA): The translator that reads mRNA and brings amino acids.

Types of Ribosomes

• Free Ribosomes: Make proteins for within the cell.
• Fixed Ribosomes: Part of the rough endoplasmic reticulum, make proteins that leave the cell.

Transfer RNA (tRNA)

• Function: Reads a three-letter sequence (codon) and brings an amino acid.
• 61 tRNAs: Correspond to 61 sense codons, bringing 20 unique amino acids.

Process of Translation

Initiation

• Begins at the start codon: AUG (codes for methionine).

Elongation

• mRNA is read in triplets, each triplet is a codon.
• tRNA brings an amino acid, adding to the growing protein chain (polypeptide).
• Peptide bonds form between amino acids.

Termination

• Occurs when the ribosome reaches a stop codon (nonsense codon): UAA, UAG, UGA.
• Translation stops because these codons cannot be read by the machinery.

Genetic Code

• Start Codon: AUG (methionine).
• 61 Sense Codons: Read and translated into amino acids.
• 3 Nonsense/Stop Codons: UAA, UAG, UGA (stop translation).
• 64 Total Codons: Triplets allow for more combinations.
  • Degeneracy: Multiple codons can code for the same amino acid (e.g., CCU, CCC for proline).
  • Allows mutations without affecting the amino acid sequence.

Summary

• Translation is crucial for protein synthesis, converting mRNA into a polypeptide chain.
• Understanding codons and the role of tRNA is key to understanding how proteins are formed from genetic information.

Additional Comments

• Lecture emphasizes the universal nature of the genetic code across living organisms.
• Degeneracy in the genetic code provides resilience against mutations.

Focus on each step and the roles of mRNA, rRNA, and tRNA for a holistic understanding of how proteins are synthesized from RNA.