chapter  2
24 Pages

Protein Metabolism: Synthesis and Breakdown on a Cellular Level

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Tissue proteins are constantly being broken down and synthesized simultaneously. Taken together this process is called protein turnover. In muscle, the relative rates of protein synthesis and protein breakdown determine the relative anabolism or catabolism of the tissue. This is commonly referred to as protein balance. Protein balance is equal to the rate of protein synthesis minus the rate of protein breakdown. If the rate of protein synthesis exceeds the rate of protein degradation, the muscle is in a state of positive protein balance and is anabolic. If the rate of protein breakdown exceeds the rate of protein synthesis, then muscle is in a negative protein balance and is catabolic. If the rate of protein synthesis equals the rate of protein breakdown, then the net result is protein balance in which no net growth has occurred. It is important to note that both protein synthesis and protein breakdown are always occurring simultaneously, and it is the relative rates of each that determine the net anabolic or catabolic state of the muscle. In order to maximize muscle mass, athletes will want to increase protein synthesis, limit protein breakdown, or preferably do both. This chapter will describe how protein turnover is regulated and how nutrition, hormones, and exercise affect this metabolic process.