Protein metabolism, like that of carbohydrates and fats, is controlled largely by hormones rather than by the nervous system. Growth hormone and the male hormone testosterone both have a stimulating effect on protein synthesis, or anabolism. For this reason, they are referred to as anabolic hormones. The protein catabolic hormones of greatest consequence are glucocorticoids. They speed up the hydrolysis of cell proteins to amino acids, their entry into the blood, and their subsequent catabolism. ACTH functions indirectly as a protein catabolic hormone because of its stimulating effect on glucocorticoid secretion.
Thyroid hormone is necessary for and promotes protein anabolism and therefore growth when plenty of carbohydrates and fats are available for energy production. Under different conditions—for example, when the amount of thyroid hormone is excessive or when the energy foods are deficient—this hormone may then promote protein mobilization and catabolism.
12. What is meant by the term essential amino acid?
13. What happens when an amino acid is deaminated?
14. What is the purpose of the process of amino acid deamination?
15. How is protein metabolism controlled?