Overview
This lecture covers the process of translation in protein synthesis, focusing on its definition, the main stages, and detailed steps within the elongation stage.
Definition and Overview of Translation
- Translation converts genetic information in mRNA into a sequence of amino acids, forming a polypeptide (protein).
- It takes place in ribosomes, using tRNA molecules and various enzymes.
Stages of Translation
- There are four main stages: Initiation, Elongation, Translocation (as part of elongation), and Termination.
Initiation
- The small ribosomal subunit binds to mRNA.
- The initiator tRNA pairs with the start codon (AUG) on mRNA.
- The large ribosomal subunit then joins to form the complete ribosome.
Elongation
- Elongation has three main steps: codon recognition, peptide bond formation, and translocation.
- Codon Recognition: tRNA with complementary anticodon pairs with the mRNA codon in the ribosome’s A site.
- Peptide Bond Formation: Ribosomal RNA catalyzes the formation of a peptide bond between the amino group of one amino acid and the carboxyl group of another, joining them in the growing polypeptide chain.
- Translocation: The ribosome moves along the mRNA, shifting the tRNAs and exposing the next codon.
Termination
- The process repeats until a stop codon is reached on mRNA.
- Release factors promote hydrolysis, breaking the bond between the polypeptide and tRNA.
- The completed polypeptide is released, ribosome components dissociate, and the polypeptide may undergo further modification.
Key Terms & Definitions
- Translation — The synthesis of a polypeptide using the genetic information in mRNA.
- mRNA (messenger RNA) — Carries genetic code from DNA to ribosomes.
- tRNA (transfer RNA) — Brings amino acids to ribosomes during translation.
- Ribosome — Cellular structure where protein synthesis occurs.
- Codon — Three-nucleotide sequence in mRNA that specifies an amino acid.
- Peptide Bond — Covalent bond joining amino acids in a protein.
- Initiation — Assembly of the translation components at the start codon.
- Elongation — Addition of amino acids to the growing polypeptide chain.
- Termination — Release of the completed polypeptide and disassembly of the translation machinery.
Action Items / Next Steps
- Review the steps of translation and their order.
- Study diagrams of translation stages.
- Prepare for questions on peptide bond formation and elongation steps.