nging together of the small ribosomal subunit, the mRNA, and a tRNA complex of the amino-terminal amino acid in the proper orientation. This is followed by association with the large ribosomal subunit to form the initiation complex. A group of proteins known as initiation factors is also required.
Protein synthesis follows in a stepwise elongation to form a polypeptide chain (Devlin, 1997, 727). At each step, ribosomal peptidyltransferase transfers the growing peptide chain from its carrier tRNA to the alpha-amino group of the amino acid residue of the aminoacyl-tRNA specified by the next codon. Transcription of an amino acid chain is ended by a chain-terminating codon (UAG, UAA, or UGA) which does not promote binding of any tRNA, but binds another complex nonribosomal protein releasing factor instead. Translation uses a considerable amount of energy in the conversion of ATP to AMP.
4. When the presence of a specific substrate in the medium initiates the transcription of the structural genes of an operon (the regulatory unit of a set of cluster
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