When proteins are being synthesised, there is a corresponding gene which is encoded in the DNA, this is now transcribed into RNA via transcription. When this is finished it is called mRNA which can be changed before it undergoes the translation process, which results in an amino acid sequence.
These processes take place on the ribosomes. Proteins can be synthesised using the 20 standard amino acids, but additional amino acids can also be en-cooperated. With the amino acid it can only be a part of protein synthesis if the enzyme tRNA synthetases attaches it to the specific transfer RNA. The tRNA is located at the translation site of DNA and RNA to amino acid sequence, this is directed by the genetic code. The structure is L- shaped and binds the amino acid at one end while the corresponding codon attaches to the other.
On the ribosomes there are three binding sites for the tRNAs.
1. The tRNA charged with amino acid goes into A (acceptor site)
2. The tRNA that is attached to the last amino acid in located at P ( peptidyl ) site.
3. The last site being E (exit ) site.
This now leads to a cycle where the polypeptide chain from the P – bound tRNA is transferred to the amino acid in site A. Which forms a new polypeptide bond this catalytic activity is the only one for the ribosomes. There is now an empty tRNA in the P site, which moves to the E site; and the other tRNA moves another chain into the P site. The cycle has now restarted.