Protein: Amino Acids
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Protein: Amino Acids Objectives • After reading Chapter 5, class discussion and activities you will be able to: – Describe the role of proteins – Distinguish between complete and incomplete proteins – Identify sources of quality protein – Calculate calories from protein Objectives • Describe protein digestion/absorption • Identify RDA for protein • Discuss health related effects of protein Protein • Essential part of all living cells • Found in animals and plants; Particularly rich in animal foods – meats, poultry, eggs, etc. • Protein is in your skin, hair, nails, muscles, etc. • Made of amino acids – amino acids contain nitrogen, which is necessary for life. Amino Acids p. 163 Fig 5-1 Amino Acids • Nonessential amino acids – Body can synthesize – Over half of the 20 AA • Essential amino acids – Body cannot synthesize – Nine (9) • Conditionally essential amino acids – PhenylalanineTyrosine; New Borns Proteins • Peptide bond – Dipeptide – Tripeptide – Polypeptide Proteins • Dipeptide Proteins • Polypeptide (Example: Insulin) • Protein shape and function • Amino Acid Sequences Proteins • Protein denaturation – Uncoiling & loss of shape – Therefore, loss of function – Caused by heat, acid, mechanical – Examples: cooked egg, egg whites, curdling of milk, separation of foods with milk or egg (syneresis) p. 176 Protein Digestion • Mouth – Mixing, moisturizing • Stomach –HCl –Pepsinogen pepsin •ProenzymeEnzyme Protein Digestion • Small intestine –Proteases •Intestinal and pancreatic –Peptidases Protein Absorption • Carriers – Transport AA into intestinal cells – Used for synthesis and energy • Capillaries – Carried to liver • Absorption misconceptions – Enzyme/amino acid supplements Protein Synthesis • Delivering the instructions –DNA •mRNA- attaches to ribosome –Protein-making machine Protein Synthesis • Sequencing errors Roles of Proteins • Building material: Building blocks of muscles, blood, skin, bones, teeth; protein matrix=collagen –Growth –Maintenance p. 164-168 Roles of Proteins • Enzymes=catalysts p. 165 Fig 5-6 Roles of Proteins • Hormones – Switching Machines Roles of Proteins • Regulation of fluid balance –Edema • Acid-base regulation –Acidosis –Alkalosis • Transport proteins Roles of Proteins • Immunity: Molecular Memory –Antibodies: Giant protein molecules designed to combat –Antigens: Invading foreign proteins (virus) Roles of Proteins • Source of energy – Gluconeogenesis – No storage source=muscle wasting – “Amino acid pool” • Other roles –Fibrinblood clotting –Opsin—light-sensitive pigment Protein Metabolism • Using amino acids to make proteins=CONDENSATION • Using amino acids to make nonessential amino acids Protein Metabolism • Using amino acids to make other compounds –Neurotransmitters • Using amino acids for energy and glucose • Deamination: AA stripped of N – Ammonia produced Protein Metabolism • Protein turnover –Amino acid pool: supply of AA from food/body; collect in cells & blood; ready for use • Nitrogen balance –Positive nitrogen balance –Negative nitrogen balance Protein Quality • High-quality proteins – All essential AA – Animal proteins=complete – Plant proteins=incomplete • Amino acid composition – Limiting amino acid • Digestibility – Animal vs. vegetable Protein Quality • PDCAAS – Protein digestibilitycorrected amino acid score • Reference Protein Protein Quality • Complementary proteins – Two protein foods make up for the lack of certain amino acids in each other when eaten together Food Labels • Quantity of protein • Daily Value –50 g protein •10% of a 2000 kcal diet Nitrogen Balance • Determine adequacy of protein intake • N2 In - N2 Out = Nitrogen Balance – N2 In = Protein Intake as Nitrogen – N2 Out = 24 Hour Urine Collection for N2 + Stool, Insensible Losses • Positive Nitrogen Balance – Body excretes less protein than is taken in (Anabolism) • Negative Nitrogen Balance – Body excretes more protein than is taken in (Catabolism) Protein-Energy Malnutrition (PEM) • Marasmus – Slow developing, chronic PEM – Muscle wasting; no body fat – Pluckable hair; dry skin • Kwashiorkor ?????? • Marasmus-kwashiorkor mix p. 171 Protein-Energy Malnutrition (PEM) • Infections not protein intake –Dysentery • C-Reactive Protein Health Effects • Conditions Associated with Other Nutrients: – Osteoporosis – Calcium – Heart Disease – Fat – Obesity – Fat/CHO – Cancer - Fat Health Effects • Genetic Associated Diseases – Phenylketonuria – Sickle Cell Anemia • Celiac Disease; Sprue • Liver Disease • Kidney Disease Recommended Intakes • RDA –0.8 g/kg/day –10% - 35% of energy intake Objectives • After reading Chapter 5, class discussion and activities you will be able to: – Describe the role of proteins – Distinguish between complete and incomplete proteins – Identify sources of quality protein – Calculate calories from protein Objectives • Describe protein digestion/absorption • Identify RDA for protein • Discuss health related effects of protein
