《aminoacids中国医科大学生物化学课件氨基酸英文课件.ppt

Chapter 7 Amino Acid Metabolism Section 1 Nutritional Function of Proteins § 1.1 The significance of proteins 1. Keep the cells and tissues growing, renewing and mending 2. Take part in some kinds of important physiological activities 3. Oxidation and supply energy § 1.2 The requirements and nutritious value of proteins 1. Nitrogen balance Measuring the amount of intake and losses of total nitrogen can help us to know the general situation of protein metabolism. There are three kinds of conditions: 1) Normal nitrogen balance intake N = losses N 2) Positive nitrogen balance intake N losses N 3) Negative nitrogen balance intake N losses N 2. Physical requirements of proteins Lowest requirement: 30~50g/day Recommend requirement: 80g/day (65kg man) 3. Nutrition value of proteins (1) Essential amino acids : Amino acids that cannot be synthesized by the body and must be obtained from the diet. Eight kinds of essential AAs: Val, Ile, Leu, Phe, Met, Trp, Thr, Lys (2) Non- essential amino acids other 12 kinds of AAs (3) Semi-essential amino acids Tyr←Phe Cys←Met Note: His and Arg are essential AAs for infants and children. (4) Complementary effect of dietary proteins Two or more plant proteins are consumed together which complement each other in essential amino acid content. Section 2 Digestion, Absorption and Putrefaction §2.1 Digestion site: stomach, small intestine enzymes: pepsin Proteolytic enzymes of pancreatic juice Proteolytic enzymes of pancreatic juice §2.2 Absorption §2.3 Putrefaction of proteins Concept: Some undigested proteins and no absorbed products are anaerobic decomposed by the bacteria in intestine. The products are toxic to body except few vitamin and fatty acid. 1. Production of amines 2. Production of ammonia (NH3) Two sources: (1) Metabolism on unabsorbed amino acids (