Elongation is the term used
to describe the growth of a protein. As amino acids are added together, they
begin to form a peptide chain that will eventually become part of a protein.
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After the first tRNA has attached to the
peptidyl site, a second tRNA enters the complete ribosome and attaches
to its complementary mRNA codon in the aminoacyl site.
With the two tRNA in place, the amino acid from the peptidyl
tRNA, moves and attaches to the tRNA in the aminoacyl site.
No longer bearing an amino acid, the tRNA from the peptidyl
site leaves the ribosome.
The ribosome then moves along the strand of mRNA, and
the former aminoacyl site becomes the new peptidyl site.
A new tRNA, based upon the triplet coding sequence of the mRNA, fills the
new aminoacyl site.
Again, the growing peptide chain of amino acids is transferred
from the petidyl tRNA to the amino acid of the tRNA in the aminoacyl
The ribosome moves along the mRNA again, and another
charged (with its amino acid) tRNA fills the aminoacyl site.
The growing peptide chain is again transferred from the
peptidyl tRNA to the amino acid attached to the tRNA in the aminoacyl
This process of peptide synthesis continues as the ribosome
moves along the mRNA, and the future protein grows longer.