Amanda Dornburgh Chapter 6 Problem Set PROTEIN According to Figure 6.1, foods in the Meat, Poultry, Fish, Dry Beans & Nuts Group as well as the Milk, Yogurt and Cheese Group contain the most protein per serving. _____________________ (plant-based food group) is the best overall source of protein. Of the individual plant foods listed, the most concentrated sources of protein are legumes, such as lentils, soybeans, peanuts, black-eyed peas, chickpeas, red beans, pinto beans, kidney beans, and black beans are the most concentrated sources of protein. Protein digestion begins in the stomach, with hydrochloric acid. Hydrochloric acid opens a protein?s folded structure to make them more accessible to enzyme attack. Pepsin is the enzyme that breaks proteins into polypeptides and amino acids. The small intestine breaks polypeptides into smaller peptides, tripeptides, dipeptides, and amino acids through pancreatic protein-digesting enzymes like trypsin and chymotrypsin. Brush border enzymes in the small intestine further break down proteins. Single amino acids and di/tripeptides can be absorbed by the mucosal cells of the small intestine. Inside the mucosal cells, dipeptides and tripeptides are broken down into single amino acids. When amino acids are absorbed, they enter the hepatic portal vein and travel to the liver. The functions of dietary protein in the body are structure and regulation. The two parts of the molecular structure that are found in all amino acids are the carboxylic acid group and the amine group. The chemical composition of amino acids is different from that of carbohydrates and fats because carbohydrates and fats are more efficient energy sources, but amino acids from dietary and body proteins are also used for energy. Each amino acid has a varying side chain, which gives it different properties. The difference between essential and nonessential amino acids are that essential amino acids cannot be made by the body, and therefore must come from the diet, while nonessential amino acids can be made in the body. Most of the nonessential amino acids are made through transamination. These nonessential amino acids are made when an amino group from one amino acid is transferred to a C-compound. There are about 20 amino acids found in proteins: of these 20 amino acids, 9 cannot be made by the body, and are essential. Conditionally essential amino acids are essential only under certain conditions. The sources of the amino acids in this pool are body protein and dietary protein. Amino acids are lost from this pool through deamination, which is usually irreversible. Dipeptides are two amino acids linked with a peptide bond; tripeptides are when 3 amino acids are linked with a peptide bond; polypeptides are when many amino acids are bonded together. An amino acid?s side chain provides proteins with their unique characteristics. Protein synthesis occurs within the cell, and is directed through the blueprint of DNA. Within the nucleus, transcription occurs: transcription is the process of copying the information in DNA to a molecule of mRNA. mRNA then links to the ribosomes, ,which catalyze the peptide bond. Translation is the process of translating the RNA code into the amino acid sequence of a protein. Transfer RNA (tRNA) identifies individual amino acids, and binds to the code on the mRNA. The ribosome complex turns two individual amino acids into a dipeptide. A limiting amino acid is when an essential amino acid is available in the lowest concentration in relation to the body?s needs. Limiting amino acids slow the process of protein synthesis down. Structural proteins are used for structure in the skin and connecting tissue. Skin, hair, and muscle are made largely of protein. The most abundant of the structural proteins is collagen, which is a long fibrous protein. The seven roles for regulatory proteins are (1) enzymes, (2) transporters, (3) defense proteins, (4) contractile/motile proteins, (5) hormones, (6) fluid, (7) pH balance. An example of an enzyme is pepsin ? it catalyzes a reaction through breaking proteins into polypeptides and amino acids. An example of a transporter is hemoglobin: the protein in red blood cells, which picks up oxygen in the lungs and transports it to other organs of the body. An example of a defense protein is skin, which is made up primarily of protein, and is the first barrier against infection and injury. Examples of contractile proteins are actin and myosin, which function in the contraction of muscles. Examples of protein hormones are insulin and glucagon. _____________________________________ (what types of nonprotein molecules) are made from amino acids. Amino acids are used in the synthesis of these molecules because _____________________________________________ Before an amino acid can be used for fuel, it must be deaminated to remove the nitrogen. The nitrogen is converted by the liver into urea? which is excreted in the urine. The carbon skeletons are used to generate ATP in mitochondrion. If your diet contains excess total energy and excess protein, excess amino acids will be converted to glucose or fatty acids. Potential negative implications of consuming a diet that contains a large excess of protein is weight gain, from the conversion of glucose and/or fatty acids. Supplementation with individual amino acids could be problematic to health because unbalanced amino acid intake can disrupt overall amino acid transport. Protein-energy malnutrition is wasting and/or edema, increases one?s susceptibility to infection, and is found primarily in developing countries. The two major types of protein malnutrition are kwashiorkor and marasmus. Kwashiorkor is characterized by an accumulation of fluids in the stomach. There is not enough protein coming in. Protein in the blood is called albumin, which cannot be made without enough dietary protein coming in. Therefore, there is an accumulation of fluids in the stomach, hands, feet, etc. Marasmus is when there is too little energy coming in and not enough protein. It is characterized by almost no lean mass. The typical dietary protein intake for Americans is 15% of energy. The RDA for protein for adult males is 0.8 grams of protein per kilogram of body weight. It is the same for adult females. RDA for protein decreases with life stage. The populations that are at highest risk for deficiency are children in developing countries. Children have the highest RDA for protein, set at 1.52 g/kg of body weight at birth and only decreasing to 1.1 g/kg of body weight by the time a child is 3. When nitrogen output exceeds nitrogen intake, there is a net loss of body protein, which can result in illness. When nitrogen intake exceeds nitrogen output, there is a positive nitrogen balance, when the total body protein increases: this decreases protein breakdown, and occurs during pregnancy. Moderate exercise _______________________ protein needs. Protein quality is a measure of how efficiently a protein in the diet can be used to make body proteins. Foods of animal origin supply essential amino acids in the proper proportions for human use. On the other hand, plant foods contain proteins that don?t provide all the amino acids in the proper proportions required for protein synthesis in humans, and are therefore said to be incomplete. This affects vegetarians, and especially vegans, because they eliminate some or all animal products, which eliminates the intake of essential amino acids. An amino acid score is a measure of protein quality determined by comparing the amount of the limiting amino acid in a food with that in a reference protein. A reference food is ____________________________. The amino acid score is improved when you adjust for digestibility of proteins by adjusting the amino acid score for digestibility. Protein complementation is used for vegetarian diets. It combines proteins from different sources so that they collectively provide the proportions of amino acids required to meet needs.
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