Biochemistry

CHAPTER 8. PROTEIN METABOLISM 8.1 BIOLOGICAL SIGNIFICANCE OF PROTEIN METABOLISM Protein metabolism occupies the main place among the diverse transformations of living matter. Throughout life, a destruction and biosynthesis of cells and tissues occur simultaneously in the body. These opposite, but closely interconnected processes - assimilation and dissimilation - form the basis of life. Therefore, substances necessary for building new cells must constantly provide the body. The main role in this belongs to proteins, since neither carbohydrates nor fats can replace them in the reproduction of the basic structural elements of organs and tissues, as well as in the formation of hormones and enzymes. Due to the fact that proteins are nitrogen-containing substances, one of the methods characterizing the state of protein metabolism in the body can be a determination of nitrogen balance. A healthy person with normal nutrition has a state of protein balance, when the nitrogen intake compensates for its costs. The amount of nitrogen removed exceeds the amount of nitrogen supplied at a negative nitrogen balance. This condition can be observed when digestive system disorders, protein starvation, etc. A positive nitrogen balance occurs in cases where the amount of nitrogen removed is less than supplied. This is characteristic for a growing organism, pregnancy, an increase in the activity of protein biosynthesis (for example, during physical activity). Various amino acids are necessary for the synthesis of proteins in the body. Some of them that form in the body itself are called dispensable. Amino acids that are not synthesized in the human body are called indispensable. They should be used with food regularly. Proteins, which include dispensableand indispensable amino acids in ratios approaching those in the body, are called complete. There are almost no proteins among foods that fully meet these requirements. Mother's milk, chicken eggs are closer to complete proteins. Therefore, in order to fully ensure a healthy organism with complete proteins, various food products of both animal and vegetable origin should be included in the daily diet. For normal human activity, it is necessary to receive such an amount of complete protein that will cover all the body needs. The daily need for protein depends on gender, age, labor intensity, etc. Based on these factors, protein nutrition standards have been developed. Insufficient protein intake leads to disruption of vital processes, poor health, and prolonged protein starvation inevitably ends in death. 158