Overview
This lecture explains the process of translation, where messenger RNA (mRNA) is converted into a protein, covering its steps, key players, and the genetic code.
Steps of Translation
- Translation converts the nucleic acid language (RNA) into the amino acid language (protein).
- The three steps of translation are initiation, elongation, and termination.
- Initiation begins at the start codon (AUG) on the mRNA.
- Elongation involves reading the mRNA three bases (codon) at a time, adding amino acids to the growing polypeptide chain.
- Termination occurs when a stop codon (UAA, UAG, UGA) is reached on the mRNA.
Key Molecules in Translation
- mRNA (messenger RNA) carries the code for the protein.
- rRNA (ribosomal RNA) makes up the ribosome, the site of translation, in large and small subunits.
- Ribosomes in eukaryotes are 80S and in bacteria are 70S.
- tRNA (transfer RNA) acts as the translator, bringing specific amino acids to the ribosome according to the codon sequence.
- Free ribosomes produce proteins for use inside the cell; fixed ribosomes on the rough ER make proteins for export.
The Genetic Code
- A codon is a sequence of three RNA bases coding for an amino acid.
- There are 64 possible codons; of these, 61 are sense codons (code for amino acids), and 3 are stop/nonsense codons.
- Only 20 unique amino acids are used in protein synthesis, so multiple codons can code for the same amino acid.
- The code is degenerate, meaning some mutations in codons do not change the amino acid produced.
Key Terms & Definitions
- Translation — Process of converting mRNA into a protein.
- Codon — Three-base sequence on mRNA that codes for an amino acid.
- Start Codon — AUG; signals the beginning of translation.
- Stop Codon — UAA, UAG, UGA; signals the end of translation.
- Sense Codon — Codon that codes for an amino acid.
- Nonsense Codon — Codon that does not code for an amino acid and stops translation.
- Degeneracy — Redundancy in the genetic code where multiple codons code for the same amino acid.
Action Items / Next Steps
- Review the roles of mRNA, tRNA, and rRNA in translation.
- Study the genetic code chart, focusing on start and stop codons.
- Prepare for upcoming content on genetic mutations and degeneracy.