WHAT IS PROTEIN?

1. WHAT IS PROTEIN? • Proteins are a sequence of amino acids • Of the 20 amino acids that exist, 9 are essential amino acids, and 11 are non-essential • There are also 4 amino acids that can be considered conditionally essential: arginine, tyrosine, glutamine, and cysteine

2. AMINO ACIDS: Structure • Consist of a central carbon atom bonded to: a hydrogen, a carboxylic acid, an amino group, and an additional side group that is unique to each amino acid

4. AMINO ACIDS: Structure • The side group creates unique characteristics for each amino acid so they differ in: shape, size, composition, electrical charge, and pH.

5. AMINO ACID: Sequence • Amino acids link in specific sequences to form strands of protein • One amino acids is joined to the next by a PEPTIDE bond

7. AMINO ACID: Sequence • Dipeptide – 2 amino acids • Tripeptide – 3 amino acids • Oligopeptides – 4-10 amino acids • Polypeptide – more than 10 amino acids • Proteins in the body and diet are long polypeptides (100s of amino acids)

9. DENATURING of PROTEINS • Acid, alkaline, heat, alcohol, and agitation can disrupt the chemical forces that stabilize proteins and can cause them to lose their shape (denature) • Denaturing of proteins happens during food preparation (cooking, whipping, adding acids) or digestion (in the stomach with hydrochloric acid)

11. PROTEINS: Function Structural Functions: • Collagen – is the most abundant protein in mammals, and gives bone and skin their strength • Keratin – provides structure to hair and nails

13. PROTEIN: Functions ENZYMES • Enzymes are proteins that catalyze chemical reactions without being used up or destroyed in the process • Used in – digestion, releasing of energy from nutrients for fuel, triggering reactions that build muscle and tissue

14. PROTEIN: Functions HORMONES • Hormones are chemical messengers that are made on one part of the body, but act on cells in other parts of the body • Insulin, Glucagon • Antidiuretic Hormone (ADH)

16. PROTEIN: Functions IMMUNE FUNCTION • The Immune Response is a series of steps your body takes to mount an attack against invaders • Antibodies are blood proteins that attack and inactivate bacteria and viruses • Once an antibody has been made for a certain invader, your body can more quickly respond (Immunization)

18. PROTEIN: Functions FLUID BALANCE • Fluids in the body are intracellular or extracellular (interstitial and intravascular) and must remain balanced

20. PROTEIN: Functions FLUID BALANCE • Blood proteins like albumin and globulin help to regulate this balance by remaining in the capillaries and attracting fluid • Edema is the result of fluid imbalance

22. PROTEIN: Functions ACID-BASE BALANCE • Proteins help to maintain a stable pH level in our body fluid by picking up extra hydrogen ions when conditions are acidic, and donating hydrogen ions when conditions are alkaline • Otherwise, the resulting conditions of acidosis or alkalosis could lead to coma or death

24. PROTEIN: Functions TRANSPORT • Lipoproteins (chylomicrons, LDL, HDL) • Albumin transports a variety of nutrients such as calcium, zinc, and Vitamin B6 • Transferrin transports iron (hemoglobin – a protein, contains iron, but it transports oxygen) • Proteins may also acts as channels or pumps across the cell membrane

26. PROTEIN: Functions ENERGY SOURCE • If the diet does not provide enough energy, the body must begin to break down its own protein • The proteins are broken down into individual amino acids, then deaminated, and the remaining carbon, hydrogen, and oxygen compounds are used to make energy or glucose • If the diet contains too much protein, the excess will be converted to glucose, or stored as fat

28. DIGESTION • No digestion of protein takes place in the mouth, it begins in the stomach • Hydrochloric acid denatures protein and also converts pepsinogen to pepsin • Pepsin breaks the protein down into peptides of various lengths and some amino acids • Pepsin completes ~ 10-20% of digestion

30. DIGESTION • Pancreas makes trypsinogen and chymotrypsinogen (proenzymes) in response to protein in the small intestine • They will be activated to trypsin and chymotrypsin (now called proteases) • Proteases break down polypeptides into smaller peptides (very few peptides have been broken down to amino acids at this stage)

31. DIGESTION and ABSORPTION • The intestinal wall produces peptidases which continue to split the remaining polypeptides into tripeptides, dipeptides, and some amino acids • These smaller units are transported into the enterocytes

32. ABSORPTION • In the enterocyte, other peptidases immediately digest everything into single amino acids which are absorbed into the bloodstream • Some amino acids share the same transport system, so if you take in a large amount of one particular amino acid, you may be inhibiting the absorption of others

33. ABSORPTION • Most protein absorption takes place in the duodenum and jejunum • Most amino acids are absorbed into the bloodstream, but some remain in the enterocytes and are used to synthesize enzymes and new cells • >99% of protein enters the bloodstream as amino acids • Absorption of whole protein can cause a severe allergic reaction

34. PROTEINS in the BODY • Amino Acid Pool – amino acids that are available throughout the body (tissues and fluids) for use when needed • Protein Turnover – of the ~ 300 grams of protein synthesized by the body each day, 200 grams are made from recycled amino acids

35. NITROGEN EXCRETION • Amino acid breakdown yields an amino group (containing nitrogen) • This molecule is unstable and is converted to ammonia • Ammonia is toxic, so it is excreted from the cells and sent to the liver, where it is converted to urea and water • The urea is transported to the kidney, where it is filtered from the blood and finally sent to the bladder for excretion in the urine (page 227) • Nitrogen is also lost through hair, skin, GI cells mucus, nails, and body fluids like sweat

37. How Much Protein Do We Need? Adults: 0.8 grams of protein per kilogram of body weight per day Endurance Athletes: 1.2 to 1.4 g/kg/day Heavy Weight Trainers: 1.7 to 1.8 g/kg/day

38. Protein Sources

39. PROTEIN QUALITY • Complete Proteins – proteins that provide all the essential amino acids (most animal proteins) • Incomplete Proteins – proteins that are missing one or more essential amino acids (most plant proteins except soy protein) • Incomplete proteins can be served with a complementary protein to make it complete

41. PROTEIN: Health Effects INSUFFICIENT DIETARY PROTEIN • Protein-Energy Malnutrition (PEM) can occur anywhere in the world, but is most common in developing countries • Kwashiorkor • Marasmus • In industrialized nations, PEM may exist in the elderly population, in the poor, and those with anorexia, cancer, AIDS, or malabsorption syndromes

42. PROTEIN: Health Effects EXCESS DIETARY PROTEIN • May strain the kidneys • May cause mineral losses (especially calcium)* • May increase risk of obesity* • May increase risk of heart disease* • May increase risk of cancer* *only with animal protein

43. VEGETARIANISM • What are the PROS and CONS of vegetarianism?

44. ATKIN’S DIET • How does it work? • What are some of the possible negative consequences?