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Specific process of amino acid addition during polypeptide synthesis within cells.
Translation elongation involves first the positioning of the codon adjacent to the A site. The aminoacyl tRNA then diffuses into the A site of the ribosome. If that tRNA's anticodon matches the codon, then this is followed by addition of the associated amino acid to the growing polypetide found in the P site:
peptidyl tRNA + aminoacyl tRNA → tRNA + peptidly tRNA
The resulting peptidyl tRNA containing one additional amino acid is now found in the P site whereas the now peptide-less tRNA has advanced to the E site. See, more generally, elongation (molecular genetics).
Energy is required in the charging of the tRNA by specific aminoacyl-tRNA synthetases. The association of the resulting aminoacyl tRNA with the A site of the ribosome also requires energy (2 GTP). The incrementation of the mRNA through the ribosome, one codon at a time, also is an energy requiring step (1 GTP per one-codon "click" through).
Note that the ribosome moves along the mRNA in the 5' → 3' direction. The mRNA consequently moves through the ribosome in the 3' → 5' direction (that is, the 5' end leads.). This is the same direction of movement of RNA during transcription relative to RNA polymerase, though contrasting translation, the template for transcription is actually read in the 3' → 5' direction owing to the antiparallel nature of the double helix.
This actually can make intuitive sense since the template strand for transcription is the antisense or plus strand whereas the resulting RNA is the sense or minus strand and it therefore is the complementary strand rather than the equivalent of the template strand that is read by ribosomes.
In the days of photography using film, you first generated the negative which was used to form the "positive" or print during film processing. Then, realizing just how primitive your life once was, and since you've lost the negative, you scan the print in order to digitize it – to then post on FaceBook! – going from positive to positive (at least as you perceive the process). The actual information in the photograph, though, was found in the negative, though that negative itself contains the complement to the information the camera sensed in the first place!
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