Digestion of Proteins Lecture Notes PDF

 The roles of proteins in the body Structural Catalytic Transport Regulatory Protective Homeostatic Accumulating  Dynamics of protein metabolism Daily hydrolysis of proteins ~ 400 g. Daily protein synthesis ~ 400 g Daily requirements is ~ 100 g The t...

 The roles of proteins in the body Structural Catalytic Transport Regulatory Protective Homeostatic Accumulating  Dynamics of protein metabolism Daily hydrolysis of proteins ~ 400 g. Daily protein synthesis ~ 400 g Daily requirements is ~ 100 g The time of half- renewal of proteins is 80 days.  Nitrogen balance Nitrogen balance is used as an index of protein metabolism. When more nitrogen is gained than is lost by a patient - positive nitrogen balance (children). In contrast, a "negative nitrogen balance", in which more nitrogen is lost than is gained (elderly people, chronic diseases). Nitrogen balance or nitrogen equilibrium, occurs when nitrogen intake equals nitrogen output (healthy adults). Contents of protein in some food Essential and non-essential amino acids  Examples of food products, lacking some essential amino acids Food product Missing amino acids Plant proteins Proteins of maize lysine Proteins of soybean tryptophan Digestion of proteins  DIGESTION OF DIETARY PROTEINS ⚫ The intake of dietary protein is 50-100 g/day. ⚫ Dietary proteins are denatured on cooking & easily digested. ⚫ The digestion and absorption of proteins is very efficient in healthy humans, hence very little protein (about 5-10 g/day) is lost through feces.  DIGESTION OF DIETARY PROTEINS ⚫Proteolytic enzymes are secreted as inactive zymogens & are converted to active form in the intestinal lumen ⚫Proteolytic enzymes include: ⮚ Endopeptidases  DIGESTION OF DIETARY PROTEINS Endopeptidases: ⚫ Act on peptide bonds inside the protein molecule, the protein becomes successively smaller & smaller units, e.g. Pepsin, Trypsin,  DIGESTION OF DIETARY PROTEINS Exopeptidases: ⚫Act at the peptide bond, at the end region of the chain, e.g. Carboxypeptidase acts on the peptide bond only at the carboxy-terminal end Aminopeptidase, which acts on the peptide bond only at  DIGESTION OF PROTEINS IN THE STOMACH ⚫Gastric juice contains HCl & a protease proenzyme - pepsinogen Hydrochloric acid: ⚫Parietal (oxyntic) cells secrete HCl & pH of the stomach is