2. Protein: Amino Acids Chapter 6

3. Major points in chapter 6 What is a protein Factors affecting the shape of a protein Digestion and absorption Roles of proteins in the body Protein quality Protein recommendations Health effects

4. What is a protein? Greek—”to come first” Contains nitrogen Used primarily for regulation and maintenance of the body Can supply energy—4 kcal/g Made of amino acids (at least 100)

5. Amino Acids Body proteins made of 20 different amino acids linked together by condensation reactions and cleaved by hydrolysis Amino acids differ in side chain 9 are essential (see p. 174) 11 are nonessential—can be synthesized by transamination Conditionally essential

8. Levels of protein structure The shape of a protein eventually dictates its function This shape is dependant on the amino acid sequence (primary structure), the kinking and twisting of the chain (secondary structure), the folding of the chain (tertiary structure), and interaction with other proteins (quaternary structure) Hemoglobin example

11. denaturation Changing the shape of a protein It can no longer perform its usual function Example cooking a egg

14. Digestion and absorption of protein Enzymes and HCl in stomach begin process (pepsin) In small intestine Pancreatic enzymes (proteases) polys into 1,2, & 3 amino acid units Intestinal enzymes on villi (peptidases) convert to single amino acids Amino acids are absorbed from the villi into the blood stream Travel to the liver

17. Making proteins We use the amino acids from dietary proteins as building blocks for our own proteins DNA provides the template for the formation of body proteins

18. Roles of protein in the body Vital body constituents Fluid balance Acid/base balance Hormones and enzymes Immune function Transporters Gluconeogenesis energy

20. Nitrogen balance Protein turnover Positive Negative

21. Protein in food Complete proteins provide all of the essential amino acids Animal sources usually complete, plant most have a limiting amino acid except soy Protein quality—ability of a food protein to support growth and maintenance based on digestibility and amino acid content Biological value, PER, chemical score, PDCAAS All based on comparisons to albumin (reference protein) Complementary proteins

22. Protein recommendations 10-35% total kcals 50-175g/day for adults 0.8g/kg of healthy body weight

23. Health effects: too little protein PEM Kwashiorkor Marasmus

25. Health Effects: too much protein Osteoporosis—calcium loss in urine Colon cancer? Red meat Processed foods Kidney disease Heart disease? Animal proteins Homocysteine