Protein synthesis

After having discussed DNA and the various RNAs, the stage has been set for protein synthesis. The basic reaction of protein synthesis is the controlled formation of a peptide bond between two amino acids. This reaction is repeated many times, as each amino acid in turn is added to the growing polypeptide. Protein synthesis starts when the mRNA binds to a small ribosomal subunit near a AUG sequence in the mRNA. The AUG codon is called start codon, since it codes for the first amino acid (a methionine) to be made of the protein. The AUG codon base-pairs with the anticodon of tRNA carrying methionine. A large ribosomal subunit binds to the complex, and the reactions of protein synthesis itself can begin. The aminoacyl-tRNA to be called for next is determined by the next codon (the next three bases) on the mRNA. Each amino acid is coded for by one or more (up to six) codons. Of course, it would be more straightforward to have each amino acid coded for by only one codon, but nature appears to have chosen a more complex route. The reason for this in part is that there are 20 different amino acids, and 4x4x4=64 different combinations possible in a codon. When the ribosome reaches one of the three codons for which there is no matching tRNA, the ribosome falls off and the synthesized protein is released. The degeneracy of the genetic code for certain amino acids could have a function in regulation of translation; any idea how? The process of protein synthesis has been summarized on pages 34-38 of Molecular Biotechnology, and can also be found on the web at translation (in conjunction with transcription)

Amino acids represent quite a broad spectrum of different chemical structures. The web address http://www.ch.cam.ac.uk/magnus/molecules/amino/ provides the structure of all amino acids. With the generation of a protein with a specific amino acid sequence using essentially the genetic information present in the DNA, the link between genetic and functional information is complete.