Protein, Amino Acids PDF Fall 2023

11/26/2023 1 PROTEIN: AMINO ACIDS Fall 2023 Dr. Hala Nawaiseh 11/26/2023 2 The Chemist’s View of Proteins Proteins: Compounds composed of carbon, hydrogen, oxygen, and nitrogen atoms, arranged into amino acids linked in a chain...

11/26/2023 1 PROTEIN: AMINO ACIDS Fall 2023 Dr. Hala Nawaiseh 11/26/2023 2 The Chemist’s View of Proteins Proteins: Compounds composed of carbon, hydrogen, oxygen, and nitrogen atoms, arranged into amino acids linked in a chain. Some amino acids also contain sulfur atoms. Nonessential amino acids: Amino acids that the body can make (dispensable amino acids). The body can make all nonessential amino acids, given nitrogen to form the amino group and fragments from carbohydrate or fat to form the rest of the structure. 11/26/2023 3 Amino Acids Essential amino acids Amino acids that the body requires but cannot make, and so must be obtained from the diet (indispensable amino acids). There are nine amino acids that the human body either cannot make at all or cannot make in sufficient quantity to meet its needs. 11/26/2023 4 Amino Acids 11/26/2023 5 Amino Acids Conditionally Essential Amino Acids An amino acid that is normally nonessential, but must be supplied by the diet in special circumstances when the need for it exceeds the body’s ability to make it. Example: the body normally uses the essential amino acid phenylalanine to make tyrosine (a nonessential amino acid). But if the diet fails to supply enough phenylalanine, or if the body cannot make the conversion for some reason (as happens in the inherited disease phenylketonuria, then tyrosine becomes a conditionally essential amino acid. 11/26/2023 6 Examples of Amino Acids 11/26/2023 7 Condensation of Two Amino Acids to Form a Dipeptide Amino Acid Chains Condensation reactions connect amino acids together to form a dipeptide. Peptide bond: A bond that connects the acid end of one amino acid with the amino end of another, forming a link in a protein chain. 11/26/2023 8 Condensation of Two Amino Acids to Form a Dipeptide 11/26/2023 9 Primary Structure—Amino Acid Sequence The primary structure of a protein is determined by the sequence of amino acids. Along a polypeptide chain, each stepping stone would be one of 20 different amino acids. Amino acid sequences within proteins vary. 11/26/2023 10 Secondary Structure—Polypeptide Shapes The secondary structure of proteins is determined not by chemical bonds as between the amino acids but by weak electrical attractions within the polypeptide chain. As positively charged hydrogens attract nearby negatively charged oxygens. These shapes give proteins strength and rigidity. 11/26/2023 11 Tertiary Structure—Polypeptide Tangles The tertiary structure of proteins occurs as long polypeptide chains twist and fold into a variety of complex, tangled shapes. The unique side group of each amino acid gives it characteristics that attract it to, or repel it from, the surrounding fluids and other amino acids. Some amino acid side groups are attracted to water molecules; they are hydrophilic. Other side groups are repelled by water; they are hydrophobic. 11/26/2023 12 Quaternary Structure—Multiple Polypeptide Interactions The quaternary structure of proteins involves the interactions between two or more polypeptides. One molecule of hemoglobin—the large, globular protein molecule that, by the billions, packs the red blood cells and carries oxygen—is made of four associated polypeptide chains, each holding the mineral iron. Figure 6-5 features the primary, secondary, tertiary, and quaternary structures of hemoglobin. 11/26/2023 13 11/26/2023 14 Protein Denaturation When proteins are subjected to heat, acid, or other conditions that disturb their stability, they undergo denaturation. The quaternary, tertiary, and secondary structures are disrupted or destroyed. Consequently, they uncoil and lose their shapes and, as a result, also lose their ability to function. Denaturation is irreversible. Familiar examples of denaturation include the hardening of an egg when it is cooked , the curdling of milk when acid is added, and the stiffening of egg whites when they are whipped. 11/26/2023 15 Digestion and Absorption of Proteins Proteins in foods do not become body proteins directly. Instead, dietary proteins supply the amino acids from which the body makes its own proteins. When a person eats foods containing protein, enzymes break the long polypeptides into short polypeptides, the short polypeptides into tripeptides and dipeptides, and, finally, the tripeptides and dipeptides into individual amino acids. 11/26/2023 16 Digestion and Absorption of Proteins In the Stomach The major event in the stomach is the partial breakdown (hydrolysis) of proteins. Hydrochloric acid: Uncoils (denatures) each protein’s tangled strands so that digestive enzymes can attack the peptide bonds. The hydrochloric acid also converts the inactive form of the enzyme pepsinogen to its active form, pepsin. * Pepsin cleaves proteins into small polypeptides and amino acids. 11/26/2023 17 Digestion and Absorption of Proteins 11/26/2023 18 Digestion and Absorption of Proteins In the Small Intestine When polypeptides enter the small intestine, several pancreatic and intestinal proteases hydrolyze them further into short peptide chains, tripeptides, dipeptides, and amino acids. Then peptidase enzymes on the membrane surfaces of the intestinal cells split most of the dipeptides and tripeptides into single amino acids. Only a few peptides escape digestion and enter the blood intact. 11/26/2023 19 Digestion and Absorption of Proteins 11/26/2023 20 Absorption of Proteins A number of specific carriers transport amino acids (and some dipeptides and tripeptides) into the intestinal cells. Once inside the intestinal cells, amino acids may be used for energy or to synthesize needed compounds. Amino acids that are not used by the intestinal cells are transported across the cell membrane into the surrounding fluid where they enter the capillaries on their way to the liver. 11/26/2023 21 Absorption of Proteins Eating predigested proteins (amino acid supplements) saves the body from having to digest proteins and keeps the digestive system from “overworking.”!!!!!!!! The digestive system handles whole proteins better than predigested ones because it dismantles and absorbs the amino acids at rates that are optimal for the body’s use. 11/26/2023 22 Roles of Proteins 1. As Structural Materials: Proteins form the building blocks of muscles, blood, and skin, it is the major structural component of all the body’s cells. 2. As Enzymes: Digestive enzymes. 11/26/2023 23 Roles of Proteins 4. As Regulators of Fluid Balance Proteins help maintain the body’s fluid balance. Normally, proteins are found primarily within the cells and in the plasma. During times of critical illness or protein malnutrition, however, plasma proteins leak out of the blood vessels into the spaces between the cells. Because proteins attract water, fluid accumulates and causes swelling. Swelling due to an excess of fluid in the tissues is known as edema. 11/26/2023 24 Roles of Proteins 11/26/2023 25 Roles of Proteins 4.As Regulators of Fluid Balance The protein-related causes of edema include: Excessive protein losses caused by inflammation and critical illnesses Inadequate protein synthesis caused by liver disease Inadequate dietary intake of protein. Whatever the cause of edema, the result is the same: a diminished capacity to deliver nutrients and oxygen to the cells and to remove wastes from them. As a consequence, cells fail to function adequately 11/26/2023 26 Protein in Foods Protein Quality The protein quality of the diet determines, in large part, how well children grow and how well adults maintain their health. High-quality proteins provide enough of all the essential amino acids needed to support the body’s work, and low-quality proteins don’t. Two factors influence protein quality: Protein’s digestibility. Amino acid composition. 11/26/2023 27 Protein in Foods Digestibility: Proteins must be digested before they can provide amino acids. Protein digestibility depends on such factors as the protein’s source and the other foods eaten with it. The digestibility of most animal proteins is high (90 to 99 percent). Plant proteins are less digestible (70 to 90 percent for most, but more than 90 percent for soy and other legumes). 11/26/2023 28 Protein in Foods Amino Acid Composition The liver can make any nonessential amino acid that may be in short supply so that the cells can continue linking amino acids into protein strands. If an essential amino acid is missing, though, a cell must dismantle its own proteins to obtain it. Therefore, to prevent protein breakdown in the body, dietary protein must supply at least the nine essential amino acids plus enough nitrogen-containing amino groups and energy for the synthesis of the nonessential ones. 11/26/2023 29 Protein in Foods Reference Protein The quality of a food protein is determined by comparing its amino acid composition with the essential amino acid requirements of preschool-age children. Such a standard is called a reference protein. Limiting amino acid: the essential amino acid found in the shortest supply relative to the amounts needed for protein synthesis in the body. Lysine Methionine Threonine Tryptophan 11/26/2023 30 Protein in Foods High-Quality Proteins A high-quality protein contains all the essential amino acids in relatively the same amounts and proportions that human beings require; it may or may not contain all the nonessential amino acids. Proteins that are low in an essential amino acid cannot, by themselves, support protein synthesis. Foods derived from animals (meat, seafood, poultry, eggs, and milk and milk products) provide high-quality proteins, although gelatin is an exception. 11/26/2023 31 Protein in Foods High-Quality Proteins Proteins from plants (vegetables, nuts, seeds, grains, and legumes) have more diverse amino acid patterns and tend to be limiting in one or more essential amino acids. Some plant proteins are notoriously low quality (for example, corn protein). A few others are high quality (for example, soy protein). 11/26/2023 32 Protein in Foods Complementary Proteins Plant proteins are lower quality than animal proteins, and plants also offer less protein (per weight or measure of food). For this reason, many vegetarians improve the quality of proteins in their diets by combining plant-protein foods that have different but complementary amino acid patterns. This strategy yields complementary proteins that together contain all the essential amino acids in quantities sufficient to support health. The protein quality of the combination is greater than either food alone (see Figure 6-15 and Photo 6-4). 11/26/2023 33 Complementary Proteins 11/26/2023 34 Protein in Foods Some people have long believed that combining plant proteins at every meal is critical to protein nutrition. For most healthy vegetarians, though, it is not necessary to balance amino acids at each meal if protein intake is varied and energy intake is sufficient. Vegetarians can receive all the amino acids they need over the course of a day by eating a variety of whole grains, legumes, seeds, nuts, and vegetables. 11/26/2023 35 Health Effects and Recommended Intakes of Protein Protein Deficiency Protein deficiency develops when the diet consistently supplies too little protein or lacks essential amino acids. When this occurs, the synthesis of body proteins decreases and degradation increases to provide cells with the amino acids they need. The consequences of protein deficiency include slowed growth, impaired brain and kidney functions, poor immunity, and inadequate nutrient absorption. 11/26/2023 36 Health Effects and Recommended Intakes of Protein Heart Disease In the United States and other developed countries, protein is so abundant that problems of excess are more common than deficiency. Depending on the food source, a high-protein diet may contribute to the progression of heart disease. Substituting vegetable protein (legumes and nuts) for animal protein and using low-fat milk, poultry, and fish may improve blood pressure and blood lipids and decrease heart disease mortality. 11/26/2023 37 Health Effects and Recommended Intakes of Protein Heart Disease The amino acid homocysteine is elevated in heart disease, but its role as a risk factor is unclear. Some research suggests that elevated homocysteine is a marker, or free radical oxidation. Lowering homocysteine by using supplements of the B vitamins (particularly folate), however, do not seem to lower the risks of heart attacks, strokes, or sudden death. The amino acid arginine may help protect against heart disease by lowering blood pressure and preventing blood clots. 11/26/2023 38 Health Effects and Recommended Intakes of Protein Cancer Protein does not seem to increase the risk of cancer, but some protein rich foods do. The World Health Organization (WHO) has classified processed meat as a carcinogen, and red meat as a probable carcinogen. In contrast, protein-rich legumes such as soy, fish, and milk may lower the risk of some cancers. For example, soy seems to be associated with a lower risk of breast cancer, but not with endometrial cancer. 11/26/2023 39 Health Effects and Recommended Intakes of Protein Adult Bone Loss (Osteoporosis) When protein intake is high, calcium excretion increases. Whether excess protein depletes the bones of their chief mineral may depend upon the adequacy of calcium in the diet. After all, bones need both protein and calcium for optimal growth. In other words, the problem may reflect too little calcium, not too much protein. In establishing recommendations, the DRI Committee considered protein’s effect on calcium metabolism and bone health, but it did not find sufficient evidence to warrant an adjustment for calcium or a UL for protein. 11/26/2023 40 Health Effects and Recommended Intakes of Protein Importantly, the excess kcalories increased body fat similarly for all groups; the different amounts of dietary protein affected changes in lean body mass. These findings highlight the importance of distinguishing between body weight and body fat. Weight-loss diets that encourage a high-protein, low- carbohydrate diet may be effective, primarily because they are low-kcalorie diets. Furthermore, including sufficient protein at each meal may help with weight loss by providing satiety; feelings of hunger are lower and feelings of fullness are higher on high-protein diets. 11/26/2023 41 Health Effects and Recommended Intakes of Protein Kidney Disease Excretion of the end products of protein metabolism depends, in part, on an adequate fluid intake and healthy kidneys. A high protein intake increases the work of the kidneys, but it does not cause kidney disease. It may, however, accelerate kidney deterioration in people with chronic kidney disease. Restricting dietary protein especially red meat helps slow the progression of kidney disease in people who have this condition. 11/26/2023 42 Recommended Intakes of Protein The body continuously breaks down and loses some protein and it cannot store proteins or amino acids. To replace protein, the body needs dietary protein for two reasons: First, dietary protein is the only source of the essential amino acids. Second, it is the only practical source of nitrogen with which to build the nonessential amino acids and other nitrogen-containing compounds the body needs. 11/26/2023 43 Recommended Intakes of Protein Given recommendations that fat should contribute 20 to 35 percent of total food energy and carbohydrate should contribute 45 to 65 percent, that leaves 10 to 35 percent for protein. In a 2000-kcalorie diet, that represents 200 to 700 kcalories from protein, or 50 to 175 grams. The average intake in the United States is 80 grams per day. Some research suggests that an intake slightly higher than current recommendations may be beneficial, especially for older adults. Furthermore, including moderate amounts (25–35 grams) of high-quality protein at each meal may best support protein synthesis and muscle health. 11/26/2023 44 11/26/2023 45 Health Effects and Recommended Intakes of Protein Protein RDA : The protein RDA for adults is 0.8 gram per kilogram of healthy body weight per day. For infants and children, the RDA is slightly higher. 11/26/2023 46 Health Effects and Recommended Intakes of Protein 11/26/2023 47 From Guidelines to Groceries Protein Foods An ounce of most protein foods delivers about 7 grams of protein. The USDA Food Patterns encourage a variety by sorting protein foods into three. Over a week’s time, the total recommended intake of protein foods should be about: 20 %from seafood. 70 % from meat, poultry, and eggs. 10 % from nuts, seeds, and legumes. 11/26/2023 48 11/26/2023 49 From Guidelines to Groceries Milk and Milk Products The only other food group to provide significant amounts of protein per serving is the milk and milk products group. A serving (a cup) of milk or yogurt provides about 8 grams of protein. Fruits, Vegetables, and Grains Fruits do not contain protein. A serving of vegetables or grains provides 2 or 3 grams of protein, respectively. 11/26/2023 50 Read Food Labels Food labels state the quantity of protein in grams. The “% Daily Value” for protein is not mandatory on all labels but is required whenever a food makes a protein claim or is intended for consumption by children younger than 4 years old. Whenever the Daily Value percentage is declared, researchers must determine the quality of the protein. When a % Daily Value is stated for protein, it reflects both quantity and quality 11/26/2023 51 Read Food Labels Six ounces of grains provide about 18 grams of protein; 2½ cups of vegetables deliver about 10 grams; 3 cups of milk offer 24 grams; and 5½ ounces of protein foods supply 38 grams. This totals 90 grams of protein—higher than the protein RDA for most people. People in the United States typically get more protein than they need. If they have an adequate food intake, they have a more- than-adequate protein intake. The key diet-planning principle to emphasize for protein is moderation. 11/26/2023 52 Protein and Amino Acid Supplements Athletes take protein powders to build muscle. Dieters take them to spare their bodies’ protein while losing weight. Women take them to strengthen their fingernails. People take individual amino acids, too to cure herpes, to make themselves sleep better, to lose weight, and to relieve pain and depression. Like many other magic solutions to health problems, protein and amino acid supplements do not offer miracles. !???????? 11/26/2023 53 Protein and Amino Acid Supplements Protein Powders Because the body builds muscle protein from amino acids, many athletes take protein powders soon after exercising, especially when resistance training, to promote protein synthesis and muscle strength. Whether this enhanced protein synthesis actually builds muscle or improves performance is less clear, but because protein supplements are relatively safe and inexpensive, they remain popular. 11/26/2023 54 Amino Acid Supplements In two cases, recommendations for single amino acid supplements have led to widespread public use: Lysine to prevent or relieve the infections that cause herpes cold sores on the mouth or genital organs. (up to 3 grams per day) when taken in divided doses with meals. Tryptophan to relieve depression and insomnia. up to 5 grams per day. 11/26/2023 55 Protein Deficiency: Protein Deficiency: 1. Kwashiorkor: Insufficient protein disease but not energy. Symptoms of disease appear usually from 12 months old baby to 2 years. Associated with edema in legs and potbelly, changes in the hair and body color, liver enlargement, and low immunity. 11/26/2023 56 Protein Deficiency: Protein Deficiency: 2. Marasmus ( skin and bone baby): Protein and energy deficiency disease. Symptoms of disease appear usually after 6 months of delivery associated with muscle atrophy without edema 11/26/2023 57