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Chapter 6 Proteins and Amino Acids Important Math Calculations Nitrogen balance = ____ g of nitrogen intake – ___ g of nitrogen output Converting weight in pounds to kilograms: ____ lbs 2.2 = ___ kg Calculating the RDA for protein for adults: ____ weight in kg 0.8 = ___ g protein daily There are several methods of determining protein quality including the following: Chemical score = mg of essential amino acid in food mg of essential amino acid in reference food Protein Efficiency Ratio = weight gain in g protein intake in g Net Protein Utilization = Biological Value = nitrogen retained 100 100 nitrogen intake nitrogen retained 100 100 nitrogen absorbed PDCAAS = chemical score 3% digestibility of the protein Chapter Outline I. Why Is Protein Important? *Many vital compounds are proteins, including enzymes, hormones, transport proteins, and regulation of both acid-base and fluid balance. II. Amino Acids Are the Building Blocks of Proteins (Table 6.1). *Proteins are long chains of amino acids. Amino acids are composed of a central carbon atom bonded to carboxyl, amino, and side groups. A. Amino acids are identified by their side groups. *At least 20 amino acids are important in human nutrition; 9 of these amino acids are considered essential (must come from the diet), while the body can make the other 11 (nonessential) amino acids. B. Protein structure: unique three-dimensional shapes and functions (Figure 6.3). *The amino acid sequence of a protein determines its shape and function. 1. Amino acid sequence 2. Protein shape C. Protein denaturation: destabilizing a protein’s shape (Figure 6.4). *Denaturing of proteins changes their shape and therefore their functional properties. Key terms: wasting, essential amino acid, nonessential amino acid, conditionally essential amino acid, peptide bond, dipeptide, oligopeptide, hemoglobin, hydrophilic amino acids, hydrophobic amino acids, disulfide bridge, denaturation III. Functions of Body Proteins A. Structural and mechanical functions (Figure 6.6) B. Enzymes (Figure 6.7A and Figure 6.7B) C. Hormones (Figure 6.8) D. Immune function E. Fluid balance (Figure 6.10) F. Acid-base balance (Figure 6.11) G. Transport functions H. Source of energy and glucose Key terms: collagen, keratin, motor proteins, antibody, immune response, extracellular fluid, interstitial fluid, intravascular fluid, edema, pH, buffer, acidosis, alkalosis, deamination IV. Protein Digestion and Absorption A. Protein digestion (Figure 6.14). *Protein digestion begins in the stomach through the action of hydrochloric acid and the enzyme pepsin. 1. In the stomach 2. In the small intestine 3. Undigested protein B. Amino acid and peptide absorption (Figure 6.15). *Proteins are completely digested in the small intestine and absorbed by facilitated diffusion and active transport. Key terms: precursor, protease, proenzyme, trypsin/trypsinogen, chymotrypsin/chymotrypsinogen, peptidases, celiac disease, cystic fibrosis V. Proteins in the Body A. Protein synthesis (Figure 6.16) B. The amino acid pool and protein turnover (Figure 6.17) C. Synthesis of nonprotein molecules D. Protein and nitrogen excretion E. Nitrogen balance (Figure 6.18) Key terms: DNA, messenger RNA, ribosomes, transfer RNA, ribosomal RNA, amino acid pool, protein turnover, neurotransmitter, urea, positive nitrogen balance, negative nitrogen balance, nitrogen balance, nitrogen equilibrium VI. Proteins in the Diet. *Dietary protein is found in meats, dairy products, legumes, grains, and vegetables. In general, animal foods contain higher quality protein than what is found in plant foods. A. Recommended intakes of protein. *Protein needs are highest when growth is rapid, such as during infancy, childhood, and adolescence. 1. Adults 2. Other life stages (Table 6.2) 3. Physical stress B. Protein consumption (Table 6.3). *The protein intake of most Americans exceeds their RDA. C. Protein quality 1. Complete proteins 2. Incomplete and complementary proteins (Table 6.4) D. Evaluating protein quality 1. Chemical, or amino acid, scoring 2. Protein efficiency ratio 3. Net protein utilization 4. Biological value 5. Protein digestibility corrected amino acid score E. Estimating your protein intake F. Proteins and amino acids as additives and supplements Key terms: complete protein, incomplete protein, complementary protein, chemical scoring, amino acid scoring, limiting amino acid, protein efficiency ration, net protein utilization, biological value, protein digestibility corrected amino acid score, protein hydrolysate VII. Vegetarian Eating A. Why people become vegetarians B. Types of vegetarians (Table 6.6) C. Health benefits of vegetarian diets D. Health risks of vegetarian diets E. Dietary recommendations for vegetarians VIII. The Health Effects of Too Little or Too Much Protein A. Protein-energy malnutrition (Figure 6.20). *Protein deficiency is most common in developing countries and results in the conditions known as marasmus and kwashiorkor. 1. Kwashiorkor 2. Marasmus 3. Nutritional rehabilitation B. Excess dietary protein (Figure 6.21). *Protein excess is also harmful and may affect risk for osteoporosis, heart disease, and cancer. 1. Kidney function 2. Mineral losses 3. Obesity 4. Heart disease 5. Cancer 6. Gout Key terms: protein-energy malnutrition, kwashiorkor, marasmus, gout Classroom Activities ACTIVITY 1: VEGETARIAN DIETS: FACT OR FALLACY? This activity can be used for both small and large classes. The instructor can put the following statements about vegetarianism on the board, on an overhead transparency, or a PowerPoint slide: 1. Vegetarian diets do not provide enough protein and other essential nutrients. ANSWER: Fallacy. With careful planning, a diet that contains no animal products can be nutritionally complete and can also offer many health benefits. 2. The main reason individuals become vegetarian is because of religion. ANSWER: Fallacy. There are many reasons people become vegetarians such as health reasons, necessity, concern for the environment, a desire to reduce world hunger and make better use of scarce resources, an aversion to eating another living creature, or concerns about cruelty to animals. 3. All vegetarians include no meat in their diet. ANSWER: Fallacy. There are many different types of vegetarians including: semi-vegetarians, pesco-vegetarians, lacto-ovo-vegetarians, lacto-vegetarians, ovo-vegetarians, vegans, and fruitarians. 4. Vegetarian diets usually contain less fat, saturated fat, and cholesterol than nonvegetarian diets. ANSWER: Fact 5. Vegetarians usually weigh less for their height than nonvegetarians. ANSWER: Fact. Vegetarians usually weigh less because their diets provide less energy. Other healthful lifestyle factors may add to this. 6. Semi-vegetarian diets are the most lacking in vital nutrients. ANSWER: Fallacy. Vegan diets are the most restrictive. 7. The vitamin that must be supplemented in vegan diets is vitamin C. ANSWER: Fallacy. Vitamin B12 must be supplemented. 8. Vegetarians may use soy products as a source of complete protein in their diet. ANSWER: Fact 9. Vegans consume more heme iron in their diets than nonheme iron. ANSWER: Fallacy. Plant foods contain a form of iron called nonheme iron that is not as well absorbed as the heme iron in animal foods. The students then have to decide whether the statements are fact or fallacy and explain why. As each statement is analyzed, the instructor can expand on why it is or is not a fact. For smaller classes, this activity works well when students get into groups and discuss all statements presented.