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ELONGATION
The incoming tRNA will bind to the A site (next to where the tRNA with the methionine attached is on the P site). ALL available tRNAs will approach the site and try to attach, but the only tRNA which will successfully attach is the one whose anticodon IS COMPLEMENTARY to the codon of the A site on the mRNA.
Let's say for example that the second tRNA that lands next to the methionine-tRNA is for leucine. The two tRNAs (holding methionine on the P site and leucine on the A site) are now next to each other. What happens next is crucial for the building of proteins.
In order for a protein chain to form, the amino acids must be attached, linked together. The link between amino acids is called a PEPTIDE BOND.
Amino acids continue to be linked until the protein is finished. This special type of bond is formed by the enzyme PEPTIDASE. Once the bond has formed between the two amino acids, the tRNA on the P site leaves and passes its amino acid on to the tRNA on the A site. Now something interesting occurs!
The tRNA with the two amino acids on it is now sitting on the P site (because it is holding the growing protein!). The ribosome slides down three bases (1 codon on the mRNA) exposing a new A site by the action of a TRANSLOCASE! The next appropriate tRNA molecule "lands" bringing its amino acid right next to the tRNA holding the two amino acids. At this point, the process repeats itself: a peptide bond forms between the two amino acid molecules already joined together and the newly brought in amino acid; the tRNA on the P site leaves and the chain of amino acids is passed to the tRNA on the A site by the action of translocase (now this site is called the P site because this tRNA now has the growing protein chains). The ribosome slides down another codon and the procedure repeats itself until the termination event occurs. This hyperlink leads to an overview of the process, and try this hyperlink to see an electron micrograph of the process of translation!
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