Chapter 10 - Molecular Biology of the Gene

Bio 100 - Molecular Genetics 6There are 3 important steps in translation: initiation, elongation, and termination1. InitiationThe mRNA molecule binds (5’ end) to a small ribosomal subunitInitiation begins at the area of the start codon (AUG) of m RNAThe first tRNA pairs with the start codon of mRNAA large ribosomal subunit then attaches to the smaller unitThis completes the ribosomal structureIt possess 2 active sites of attachment for tRNA2. ElongationThe ribosome moves down the length of the mRNA (5' ---> 3')It stops at the second and third mRNA codonsTwo tRNAs are then received by these codons, each carrying a specific amino acidThe ribosome moves again, occupying the third and fourth codon, etc.As the ribosome moves past an mRNA codon with a tRNA, the tRNA are released andre-enter the cytoplasms tRNA poolWhen each of the tRNAs with an amino acid are attached to the ribosome, the enzymepeptidyl transferase forges a peptide bond between 2 amino acids3. TerminationThe process continues until the ribosome encounters one of three possible stop codonse.g. UAG, UAA, UGAThe is no tRNA to recognize these codons; instead a release factor will bind to the stopcodonThe last tRNA is released and the polypetide chain is freedThe polypeptides may then go to the ER where further synthesis occurs (e.g. secondary,tertiary structure)Some goes to the cellular organelles e.g. mitochondria and chloroplasts