PROTEINS.pptx............................

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1. NUTRIENT CLASSIFICATION, SOURCES, DIGESTIONAND ABSORPTION MICHAEL OKUMU

2. PROTEINS The most abundant nutrient in the body accounting for a sixth of the body. Found in muscles, bones and cartilage, the skin and other tissues in the body. Are essential to life because vital parts of the nucleus and protoplasm of every cell is protein

3. COMPOSITION Are large organic compounds Contain carbon, hydrogen oxygen. Also contains 16% nitrogen which is the unique feature of proteins Are more complex than fats and carbohydrates as the size of the molecules are larger and there is a great variation in the units from which it is formed

4. STRUCTURE AND CLASSIFICATION All proteins are built from basic compounds known as amino acids. Amino acids combine to form proteins by means of a peptide bond which joins carboxylic carbon of one amino acid with the nitrogen of the other The resulting peptide has a free carboxyl at one end and a free amino group at the other end permitting addition of other amino acids at the end. Proteins are amphoteric in nature due to the presence of a free acid and a free amino group in their molecule. Polypeptide formed constitute the primary structure of protein

5. STRUCTURE OF PROTEINS The secondary structure of protein formed by linking several polypeptide chains may be helical, pleated or random coil. More complex proteins have a tertiary structure in which a polypeptide chain is wound into a globular form Proteins exist in fibrous and globular forms Fibrous proteins -appear in structure elements – collagen of connective tissue, myosin of muscle tissue and keratin of hair Globular proteins -soluble and occur in tissue fluids- casein, egg albumin, albumins, globulins of blood, plasma and heamoglobin

6. CLASSIFICATION OF PROTEINS Simple proteins-yield only 1 amino acid on hydrolysis. Albumins, globulins, glutelins , prolamins and albuminods Conjugated proteins-combinations of simple proteins with non-protein substances. The combination results in formations essential for the body. Examples Lipoproteins found in blood and plasma Mucoproteins and glycoproteins found in gastric secreations Phosphoproteins found in milk Metalloproteins found in ferritin, hemosidirin

7. CLASSIFICATION OF PROTEINS Derived Proteins-Are proteaoses , peptones and peptides formed in various stages of protein metabolism

8. FUNCTIONS OF PROTEINS Body-building function-Needed for building of new tissues at various levels of development. Maintenance of tissues-Needed to maintain and repair of old tissues throughout the lifespan Regulatory function HB ensures smooth running of the respiratory cycle Proteins such as blood helps regulate body processes Plasma proteins contribute to osmotic pressure Maintain acid-base balance

9. FUNCTIONS OF PROTEINS Proteins as precursors of enzymes, hormones and antibodies-Small amounts of proteins are needed for synthesis of enzymes, hormones and antibodies. Transport of nutrients-Are ideal carriers of nutrients across the cell membranes. Lipoproteins transport triglycerides, cholesterol, phospholipids and fat soluble vitamins across the cell wall. Energy supply-about 6-12% of energy is supplied by products of protein metabolism

10. SOURCES OF PROTEINS Legumes Dals and pulses Milk, cuds Eggs Meat, fish poultry Vegetables-Leafy vegetables, beans and peas, roots, tubers Fruits-vitamin c rich

11. PROTEIN DIGESTION Starts in the stomach where they are hydrolised . Milk is clotted by r enin and acid is added. HCL swells the proteins increasing their surface area , converts the inactive pepsinogen into pepsin , provides the acid medium necessary for the action of pepsin , provides acidic PH for solution of calcium and iron salts. Pepsin digests collagen, the main protein in connective tissue. Pepsin splits proteins to polypeptides . Also digests milk cuds formed by the enzyme renin

12. PROTEIN DIGESTION As soon as chyme enters the duodenum, it stimulates intestinal mucosa to release enterokinase , which converts inactive trypsinogen into active trypsin Trypsin activates chymotrypsin and carboxypolypeptidases . These enzymes breakdown intact protein and with the help of peptidase continue the breakdown until all small polypeptides and amino acids are formed. The last phase of protein digestion occurs in the brush borders. Some intact peptides escape hydrolysis and enter portal circulation

13. PROTEIN DIGESTION Amino acids released are absorbed via active transport. Absorbed amino acids and peptides are transported via the portal vein to the liver to be released into the general circulation At the jejunum, almost all proteins is absorbed. Only 1% is excreted as feaces . Some amino acids which remain in epithelial cells are used for the synthesis of new cells and intestinal enzymes. The endogenous proteins released internally is digested and absorbed from the small intestines along with that ingested in the diet