Chapter 6 Protein Amino Acids Dr Alisha Rovner NTDT200 Fall 2013 Learning Objectives Recognize the chemical structures of amino acids and proteins Summarize protein digestion and absorption Describe how the body makes proteins and uses them to perform various roles Explain the differences between high quality and low quality proteins including notable food sources of each Identify the health benefits of and recommendations for protein The Chemist s View of Proteins Atoms carbon hydrogen oxygen nitrogen Amino acids building blocks of proteins Carbon C Hydrogen H Amino nitrogen containing group NH2 Acid group COOH Side group or side chain The Chemist s View of Proteins More complex than carbohydrates or fats All amino acids share a common structure but they differ in the following Size Shape Electrical charge and Other characteristics because of difference in their side groups Examples of Amino Acids Amino acids consist of a central carbon C with a hydrogen H an amino group NH2 and an acid group COOH The difference is the side group The Chemist s View of Proteins 20 amino acids Essential amino acids amino acids the body cannot make at all or cannot make in sufficient quantity to meet its needs Nonessential amino acids amino acids the body can synthesize Conditionally essential amino acidssometimes a non essential amino acid become essential under certain circumstances eg Tyrosine Amino Acids The Chemist s View of Proteins Cells link amino acids end to end in a variety of sequences to form thousands of proteins Peptide bonds link amino acids Condensation reactions connect amino acids 2 bonded together dipeptide 3 bonded together tripeptide 10 bonded together polypeptide Amino Acid Sequence of Human Insulin Insulin is a relatively small protein made up 51 amino acids The Structure of Hemoglobin The Chemist s View of Proteins Denaturation Change in protein s shape and consequent loss of function Examples of denaturation Hardening of egg white when cooked Curdling of milk when acid added Stiffening of egg white when whipped Protein Digestion Mouth Crushed and moistened Stomach Hydrochloric acid denatures proteins Pepsinogen to pepsin Small intestine Hydrolysis reactions Peptidase enzymes Protein Digestion in the GI Tract Protein Absorption Transport into intestinal cells Uses of amino acids by intestinal cells Unused amino acids transported to liver Enzyme digestion Predigested proteins Protein Synthesis Uniqueness of each person due to small differences in body s proteins Differences determined by amino acid sequences of proteins which in turn are determined by genes Protein synthesis depends on a diet that provides adequate and essential amino acids Sickle Cell Compared with Normal Red Blood Cell Amino acid sequence of normal hemoglobin Val His Leu Thr Pro Glu Glu Amino acid sequence of sickle cell hemoglobin Val His Leu Thr Pro Val Glu Protein Functions in the Body Protein Turnover and Amino Acid Pool Within each cell proteins continually being made and broken down protein turnover When proteins break down they free amino acids which mix with amino acids from dietary protein to form amino acid pool with in cells and circulating blood These amino acids can be used to make body proteins Protein Metabolism Nitrogen balance Nitrogen equilibrium N in N out Positive nitrogen N in N out Body synthesizes more than it degrades Growing infants children adolescent pregnant women Negative nitrogen N in N out Body degrades more than it synthesizes Person who is starving burns infections Protein Quality Two factors that affect protein quality 1 Digestibility Animal proteins high 90 99 Plant proteins 70 90 2 Amino acid composition Essential amino acid consumption Nitrogen containing amino groups Limiting amino acid Protein Quality Reference protein Standard against which to measure the quality of other proteins Quality of protein is determined by comparing it s amino acid composition with the essential amino acid requirements of preschool age children Complementary Proteins Complementary proteins Low quality proteins combined to provide adequate levels of essential amino acids Protein Deficiency Protein energy malnutrition PEM 1 Marasmus Reflects severe deprivation of food over a long period of time Most commonly in children 6 18 months living in poverty severe weight lost and muscle wasting 2 Kwashiorkor Reflects sudden and recent deprivation of food More common in children 18 months 2 years Limbs and abdomen swollen with edema Protein Deficiency Rehabilitation of PEM 1 Rehydration Diarrhea may have caused dramatic fluid and mineral losses that need to be replaced 2 Nutrition Intervention Protein and energy given in small quantities Intake gradually increased Recovery typically better with an initial diet that s relatively low in protein 10 of kcal Health Effects of Protein Heart disease High protein diet may contribute to progression of heart disease Foods rich in animal protein also rich in saturated fat Cancer Protein rich foods don t seem to increase cancer risk Correlation between high intake of red meat and processed meats with colon cancer Health Effects of Protein Osteoporosis When protein intake high calcium excretion Some research suggests animal proteins may be more detrimental than vegetable proteins Weight control High protein diets may be effective because they are low calories Kidney disease High protein diet doesn t cause kidney disease acceleration of kidney deterioration Recommended Intakes of Protein Need for dietary protein Source of essential amino acids Practical source of nitrogen AMDR 10 35 of daily energy intake RDA Adults 0 8 grams kg of body weight day Athletes 1 2 1 7 g kg of body weight day Calculating Protein Intakes To calculate protein needs for a 150 lb person Step 1 Convert lb to kg 150 lb 2 2 lb kg 68 kg Step 2 Multiple kg by 0 8 to get RDA in grams 68 kg x 0 8 g kg 54 g protein From Guidelines to Groceries Protein foods One ounce equals 7 grams of protein USDA Food Patterns Recommended sources Milk and milk products Fruits vegetables and grains Read food labels Protein and Amino Acid Supplements Protein powders Muscle work vs protein supplements Athletic performance Whey protein Impact on kidneys Amino acid supplements Potential risks associated with intake Lysine tryptophan
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