Translation -- Movie Narrative
Translation is the synthesis of a protein from an mRNA template. This process involves several key molecules including mRNA, the small and large subunits of the ribosome, tRNA, and finally, the release factor. The process is broken into three stages: initiation, elongation, and termination. Let's see the process in action...
Eukaryotic mRNA, the substrate for translation, has a unique 3'-end called the poly-A tail. mRNA also contains codons that will encode specific amino acids.
A methylated cap is found at the 5'-end. Translation initiation begins when the small subunit of the ribosome attaches to the cap and moves to the translation initiation site.
tRNA is another key molecule. It contains an anticodon that is complementary to the mRNA codon to which it binds. The first codon is typically AUG. Attached to the end of tRNA is the corresponding amino acid. Methionine corresponds to the AUG codon.
The large subunit now binds to create the peptidyl (or P) site and the aminoacyl (or A) site. The first tRNA occupies the P-site. The second tRNA enters the A-site and is complementary to the second codon.
The methionine is transferred to the A-site amino acid, the first tRNA exits, the ribosome moves along the mRNA, and the next tRNA enters. These are the basic steps of elongation.
As elongation continues, the growing peptide is continually transferred to the A-site tRNA, the ribosome moves along the mRNA, and new tRNAs enter.
When a stop codon is encountered in the A-site, a release factor enters the A-site and translation is terminated. When termination is reached, the ribosome dissociates, and the newly formed protein is released.