HUN1201 LECTURE NOTES CHAPTER 6 Proteins Crucial Components of All Body Tissues What are proteins Proteins large complex molecules found in cells of all living things Synthesis is controlled by our DNA Contain carbon hydrogen oxygen nitrogen Made from 20 different amino acids How do proteins differ from starch Starch Proteins Amino Acids composed of chains of glucose molecules Composed of chains of amino acids Nine essential amino acids Cannot be produced in sufficient quantities to meet physiological needs Must be obtained from food Nonessential amino acids Can be synthesized in sufficient quantities We do not need to consume them in the diet Non Essential Amino Acids Transamination different acid group and side chain R group Used to make nonessential amino acids Conditionally essential amino acids Nonessential amino acid becomes essential Phenylketonuria PKU The transfer of an amine group from an essential amino acid to a tyrosine becomes a conditionally essential amino acid that must be provided by the diet Phenylalanine tyrosine How are proteins made Proteins are long chains of amino acids Amino acids are connected by peptide bonds Gene expression is the process by which cells use genes to make proteins Gene segment of deoxyribonucleic acid DNA that serves as a template for the synthesis expression of a particular protein Transcription messenger RNA copies the genetic information from DNA Translation the genetic information in RNA is converted into the amino acid sequence of a protein Protein turnover Existing proteins are degraded to provide the building blocks for new proteins Amino acid pool includes amino acids from food and cellular breakdown Protein organization determines function Protein Denaturation Sequential order of the amino acids Spiral shape from twist in amino acid chain Proteins uncoil and lose their shape Damaging substances heat acid base heavy metal alcohol Protein function is lost Denatured enzyme High fever Blood pH out of normal range During digestion Protein in the diet For protein synthesis all essential amino acids must be available to the cell Limiting amino acid Essential amino acid that is missing or in the smallest supply Slows down or halts protein synthesis Inadequate energy consumption Limits protein synthesis Incomplete protein low quality insufficient essential amino acids Does not support growth and health Complete protein high quality sufficient amounts of all nine essential amino acids Derived from animal and soy protein Mutual supplementation combine two or more incomplete protein sources to make a complete protein Complementary proteins two or more foods are combined to supply all nine essential amino acids for a complete protein Protein Digestion Protein digestion begins in the stomach Hydrochloric acid denatures protein strands and activates pepsin Pepsin enzyme breaks down proteins into short polypeptides and amino acids Gastrin hormone controls hydrochloric acid production and pepsin release Digestion continues in the small intestine Pancreatic enzymes proteases complete protein digestion Special sites small intestine transport amino acids dipeptides tripeptides High doses of individual amino acid supplements can lead to amino acid toxicity and deficiencies Protein Quality Methods for estimating protein quality Chemical score Protein digestibility corrected amino acid score PDCAAS Animal protein and many soy products are highly digestible 90 absorption Functions of proteins Cell growth repair maintenance Fluid and electrolyte balance Enzymes and hormones Acid base balance Immune system Energy source Nutrient transport and storage Protein Adequacy Nitrogen balance determines protein needs Positive nitrogen balance Negative nitrogen balance In nitrogen balance RDA for protein RDA 0 8 g per kg body weight per day Recommended percentage of energy is 10 35 of total energy intake Protein needs are higher during growth and development children adolescents and pregnant lactating women Too much protein can be harmful High cholesterol and heart disease Animal protein rich diets are associated with high blood cholesterol levels saturated fat Contribution to bone loss High protein diets increase calcium excretion and possibly lead to bone loss Kidney disease High protein intakes are associated with an increased risk among susceptible individuals People with diabetes have higher rates of kidney disease and may benefit from a lower protein diet Maximum of 2 g of protein per kilogram body weight each day is safe for healthy people Protein sources Meats Milk based products Soy products Legumes Whole grains Nuts Quorn Vegetarian diets Vegetarianism restricting the diet to foods of plant origin People chose vegetarianism for Health benefits Ecological reasons Religious reasons Ethical reasons Concerns over food safety Health benefits of Vegetarianism Lower fat and total energy intake Lower blood pressure Reduced risk of heart disease Fewer digestive problems Reduced risk of some cancers Reduced risk of kidney disease kidney stones and gallstones Challenges of Vegetarian diets Can be low in some nutrients Associated with disordered eating Varied and adequate diet planning Soy and complementary proteins Vegetarian Food Guide Pyramid Special attention to vitamins D B12 and riboflavin B2 minerals zinc and iron Protein energy malnutrition caused by inadequate protein and energy intake Common forms Marasmus Kwashiorkor
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