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Mechanisms for the Regulation of Biological Processes

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The regulation of essential biological processes such as metabolism, growth and reproduction is a hallmark of living systems. Cells, the fundamental units of life, employ a variety of mechanisms to achieve this exquisite control, and regulation of the activity of proteins provides a means to fine-tune cellular processes. One of the ways of controlling the activity of proteins is to alter the absolute levels of a protein in a cell. This is achieved either by altering the levels of the mRNA coding for the protein or by altering the stability of the protein in the cellular environment. Transcriptional regulation, along with the presence of microRNAs, is a common mechanism employed by cells to alter the levels of mRNA (1-5). The amount of a protein in the cell is essentially determined by the balance of its rates of synthesis and degradation (6). The stability of a protein can be regulated by different mechanisms including degradation (7, 8), molecular crowding (9), disulfide bond formation, and small molecule binding (10-12).
In addition to controlling the absolute level of a protein, the activity of a protein can also be regulated by covalent modification, interaction with other proteins, or binding of small molecules. Covalent modification of a protein involves the attachment of a functional group resulting in phosphorylation (13, 14), glycosylation (15), or acetylation (16). A protein can also be covalently modified by attachment of another protein resulting in

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