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MOLECULAR BIOLOGY Course LowerSixth

CHAPTER V: PROTEIN SYNTHESIS

II. Translation of Genetic Information

From mRNA to Protein:

                  Translation is a mechanism by which the sequences of base in a mRNA molecule is converted into the sequence of amino acid in a polypeptide chain. It occurs in the ribosome.

Molecules of mRNA with the genetic message from DNA bind at the appropriate site of the ribosome. Ribosomes are usually found linked together by strands of mRNA. The complex is known as polyribosome or polysomes.

                     RNA molecules carry the specific amino acid of the protein to be synthesized from the cytoplasm to the ribosome. tRNA is activated using energy in the form of ATP and this is catalyzed by the activating enzyme called amino acyl tRNA synthetase

The anti-cordons of the tRNA molecule form complementary base pairing with the cordon of mRNA that is C and G then A and U and the genetic message is reed.

                  The function of the ribosome is to hold the mRNA, tRNA and enzyme in position until the peptide bonds are formed. These usually starts with the inclusion of two cordons, once the new amino acid has been added to the growing polypeptide chain, the ribosome moves along the mRNA to endorse a new carbon. After handling over the amino acid the tRNA is release until the cytoplasm to be reconverted into a new tRNA amino acid complex and is used again the protein formed on either be an enzyme, a hormone or a structural protein. Polypeptide synthesis is usually indicated by the cordon AUG which codes for the amino acid methionine. Some cordons portuate and other stop (nonsense cordons). Translation usually continues until it comes to a cordon signically stop which is the terminating cordon such as UAA, UGA, and UAG.

par Claude Foumtum