Fundamentals of Biochemistry - Filippovich, Y. B. 1999

Protein Metabolism
Regulation of Protein Synthesis

Based on the template hypothesis of METABOLISM/35.html">Protein Biosynthesis, F. Jacob and J. Monod (1961) were the first to propose a highly promising model for the Regulation of Protein Synthesis. Adhering to the 'one Gene – one mRNA – one protein' concept, Jacob and Monod linked the central control point of Protein Synthesis to the DNA embedded within The Cell's genetic apparatus. According to their view, the cell's genetic apparatus contains clusters of structural genes known as operons, each responsible for the coordinated synthesis of a group of specific Proteins. The activity of an Operon as an mRNA supplier is controlled by an operator gene, which either permits or prevents the initiation of homologous Transcription of a series of mRNAs on the DNA template. In turn, the function of the operator gene is regulated by a spatially separated regulator gene, which produces the mRNA required to synthesize a repressor protein. It is this repressor protein that, upon binding to the operator gene, blocks its function. Furthermore, the repressor protein itself is subject to allosteric effectors; by binding to the protein, these effectors alter its tertiary Structure in a way that either stimulates or inhibits The formation of the complex between the repressor and the operator gene. Substrates frequently act as such allosteric effectors (as seen in enzyme induction). An accumulating body of evidence also points to the involvement of Hormones and various Other Compounds in controlling mRNA biosynthesis.

This is illustrated in Scheme 4, which also incorporates informosomes, another level at which The regulation of protein biosynthesis takes place:

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Scheme 4. Regulation of protein biosynthesis

This diagram reflects only a fraction of the factors involved in regulating protein synthesis. Such regulation also occurs at the level of metabolites during the activation and transfer of Amino Acids; at the macromolecular level during The biosynthesis of DNA, various types of RNA, and Ribosomes; at the level of subcellular structures (such as polysome assembly and The Role of protein-lipid membranes); at THE CELLULAR LEVEL (including nucleocytoplasmic interactions); at the organ and Organism levels (hormonal regulation); and finally, at the environmental level (for instance, the dependence of Translation fidelity on Temperature).

Fig. 102. Cotranslational protein glycosylation

The lipid-linked oligosaccharide (dolichol pyrophosphate — see Chapter IX) is transferred by glycosyltransferase to the asparagine residue of the protein being synthesized on the ribosome, resulting in the formation of a glycoprotein.