NTR 109 - Lecture #4

NTR 109 - Lecture #4 - Overview of Protein The body is made...

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Unformatted text preview: Overview of Protein The body is made up of thousands of proteins Contains, carbon, hydrogen, oxygen and nitrogen Proteins are made up of individual amino acids Food sources of protein include both animal and plant sources 1 Functions of Protein Structural component Growth and Maintenance Forms skin, tendons, ligaments, muscles, organs and bones Building material for growth & repair of body tissues Regulates and maintains body functions: hormones (ex. Insulin), antibodies, transport vesicles, cellular "pumps" (transport proteins in cell membrane act as pumps) Provides essential form of nitrogen (in the form of amino acids) 2 3 4 Functions of Protein (cont.) Blood Clotting Fluid and electrolyte balance Transportation Antibodies Provides the netting on which blood clots are built Helps transport substances like lipids, minerals and oxygen around the body Form the immune system, help fight diseases 5 Provides energy 4 Kcal/g Functions of Proteins (cont.) Building blocks of enzymes Enzymes: catalysts that facilitate chemical reactions A + B Slow FAST AB AB + enzyme A + B + enzyme (Enzyme remains unchanged) 6 7 Proteins regulate the amount of fluid within Protein's Role in Fluid and Electrolyte Balance body compartments Proteins attract water Albumin is a blood protein frequently This creates osmotic pressure, which maintains the appropriate quantity of fluid within intercellular spaces measured to determine nutritional status It helps to maintain blood volume 8 Protein's Role in Fluid and Electrolyte Balance (cont.) Edema is the result of low albumin levels in the blood Edema: leakage of fluid into intercellular spaces, causing swelling of body tissues 9 10 11 Protein's Contribution to Acid/Base Balance Blood pH normal range: 7.35 7.45 pH refers to the H+ ion concentration of a solution Proteins act as buffers: pick up H+ in acidic environment, & release H+ in alkaline environments If pH changes too much, the result is either acidosis or alkalosis, which can lead to protein denaturation 12 Acid: donates H+ ions Base: accepts H+ ions Functions of Proteins (cont.) Precursor for hormone synthesis: messenger molecules released in response to changes in the body's internal environment in order to maintain state of homeostasis (equilibrium) Thyroid hormone: regulates metabolism Insulin & Glucagon: maintain glucose homeostasis 13 Functions of Proteins (cont.) Single amino acids are also part of other compounds or can be converted to other compounds Tyrosine is a part of: epinephrine, norepinephrine (chemical messengers); melanin (pigment); thyroxine (hormome) Tryptophan can be converted into serotonin & niacin (vitamin B3) 14 Functions of Proteins (cont.) Immune function Gluconeogenesis Energy yielding (nonpreferred source) 15 Antibodies: blood proteins produced by the immune system in response to antigens (foreign particles such as bacteria, viruses, toxins and food particles that are usually made of protein) Antibodies are antigenspecific The immune system has a molecular memory that enables the development of immunity Provision of Energy Under normal conditions, protein provides very little of the body's energy Energy Protein amine group + C, H, O Urea Glucose There is no special storage form of protein; when used for energy, it is taken directly from body tissues leading to muscle wasting Excess protein in the diet is broken down; nitrogen is excreted and the carbon skeleton stored as glycogen or fat 16 Amino Acid Structure Backbone structure: one carbon atom with both an amine group & an acid group attached Unique side chains: give amino acids their characteristic size, shape, electrical charge and chemical properties 17 Amino Acid Structure NH2 R O C C OH H R group Amine group Acid group 18 Amino Acid Structure 19 Classification of Amino Acids Essential Amino Acids (9) Obtained via the diet Nonessential Amino Acids (11) Produced by the body 20 21 Essential Amino Acids Essential amino acids: amino acids which cannot be made by the body in sufficient quantities or cannot be made at all Conditionally essential amino acids: amino acids which become essential under certain circumstances or conditions Ex: PKU (genetic defect) missing enzyme that converts Phenylalanine Tyrosine 22 Relationship of Essential and NonEssential Amino Acids Example: Phenylalanine Tyrosine (essential nonessential) But in PKU diagnosed individuals: Phenylalanine Tyrosine (essential NOW essential) 23 Dietary Protein Highquality Lowquality complete Allornone principle in protein synthesis Limiting amino acids Complementary proteins 24 incomplete Protein Quality Refers to the completeness of a protein source whether protein contains all of the essential amino acids in proper amounts. Animal protein is usually complete & is considered high quality protein (contains all 9 essential amino acids). Plant protein is generally an incomplete protein source, since it is usually lacking certain amino acids. These are the limiting amino acids. Exception: soy protein When 2 plant sources of protein are combined to achieve a complete source of protein, they are said to be complementary protein sources. Protein from animal sources can be added to any protein meal to complement it. 25 Animal Protein Contribution to our diet Top 5 contributors of protein in U.S. diet: ~70% of our protein intake Beef Poultry Milk White bread Cheese Worldwide, 35% comes from animal sources 26 Plant Protein Provides: Contains no cholesterol Limited saturated fats High fiber Protein, minerals and dietary fiber 27 Health and Plant Proteins Heart healthy Bone health Cancerfighting Better glucose control (good source of fiber) Soy may decrease menopausal symptoms 28 Protein Digestibility Animal protein is more easily digested & absorbed Legumes are high in protein due to their nitrogen fixation ability Grains, Plants > 80% absorbed 60 90% absorbed > 90% absorbed Moist heat cooking methods improve protein digestibility 29 Limiting Amino Acid C is the limiting amino acid in this example CCCCC AAAAAAAA CAR CAR CAR RRRRRR CAR CAR R A A A 30 Complementary Proteins Plant sources of protein, when combined, contain all the essential amino acids Examples Tortilla with beans Beans and rice Hummus and bread 31 Complementary Protein Food 1 Food 2 Combined CC CCCC AAAA AA CAR CAR CAR RRR RRR CAR CAR CAR 32 33 Protein Synthesis DNA contains coded instructions Copies of codes Amino acids added one at a time Requires energy Transferred to the cytoplasm (via mRNA) With aid of transfer RNA (tRNA) 34 35 Protein Synthesis Protein synthesis is a result of gene expression DNA in nucleus of the cell contains the blueprint for every human protein mRNA Translation In cytoplasm (ribosomes) Transcription DNA In nucleus protein 36 Protein Organization Order of amino acids in a protein determines its ultimate shape Protein's final shape determines its function in the body 37 Protein Structure Amino acids are linked together to form proteins via peptide bonds These bonds are formed between the amine group of one amino acid and the acid group of another amino acid The linking of amino acids via peptide bonds is a protein's primary structure 38 39 Protein Structure (cont.) Weak interactions between nearby side chains of the amino acids on the protein strand cause the protein strand to form coils or sheets This is a protein's secondary structure 40 41 Protein Structure (cont.) The tertiary structure of a protein is caused by stronger interactions between amino acid side groups that are farther apart on the protein strand that cause the protein molecule to fold and loop Examples include: covalent bonds between sulfurcontaining groups, hydrophobic orientations and electrostatic interactions between charged amino acid residues 42 43 Protein Structure (cont.) Some proteins must join together with other polypeptide chains in order to become functional This is called quaternary structure Each polypeptide strand is called a subunit of the protein Some proteins also require a vitamin or mineral in order to become activated Hemoglobin is an example of both of these (made of 4 subunits with an iron atom in the center) 44 45 46 Digestion of Protein in the Stomach Denatured: permanent change in structure or shape By cooking and acid in the stomach Causes of protein denaturation: Thermal: heat Chemical: acid, base Mechanical: crushing, whipping Gastrin Pepsin Stimulates the release of acid and pepsin, which cleave peptide bonds Breaks down proteins 47 Denaturation of Proteins Heat/acid/alkaline/enzymes Results in alteration of the protein's 3dimensional structure 48 49 Digestion of Protein in the Small Intestine Release of CCK Pancreatic enzymes: Peptones peptides amino acids Small peptides and amino acids Trypsin, among others, into the duodenum Ready for absorption 50 51 Site of digestion Absorption of Protein in the Small Intestine Many different amino acid transport mechanisms Active absorption Amino acids are sent to the liver Via portal vein Microvilli surface and within absorptive cells of the small intestine Amino acids are absorbed via amino acid carrier proteins These are specific for certain amino acids 52 Protein Turnover Breakdown and synthesis Responds to change Amino acids can be recycled 53 Metabolism of Amino Acids 54 RDA for Protein Promotes equilibrium protein losses equal protein intake 0.8 gm of protein / kg of healthy body weight 154 lb. = 70 kg 2.2 kg/lb. 70 kg x 0.8 g protein = 56 g protein kg healthy body wt 55 RDA for Protein Increased by ~1015 gm /day for pregnancy Endurance athletes Provide about 810% of total calories May need 1.2 1.7 g/kg healthy weight Most of us eat more than the RDA for protein Excess protein cannot be stored as protein 56 57 58 Nitrogen Balance Compares N excretion to N intake from food When N in = N out When N in > N out Nitrogen balance = zero When N in < N out Positive nitrogen balance (example: growth, pregnancy) Negative nitrogen balance (example: sickness) 59 60 Protein Wasting Amino acids can be: In the last two instances, protein is "wasted" in a sense, since it is not used to build protein or make other Ncontaining compounds. This occurs under the following circumstances: inadequate energy intake excess intake of single amino acid excess protein intake intake of low quality protein incorporated into protein being synthesized converted/incorporated into another compound converted into another amino acid used for energy stored as glycogen or fat 61 Prevention of Protein Wasting In order to prevent dietary protein wasting, the following 3 conditions must be met: 1.Quantity adequate protein intake 2.Quality proper intake/amount of essential amino acids 3.Adequate carbohydrate & fat intake 62 PEM: ProteinEnergy Malnutrition Rare in U.S. (usually occurs in underdeveloped countries) 2 Forms: 1. Marasmus chronic inadequate intake of energy (calories) & protein Distinguishing features: severely underweight, muscle wasting, loss of body fat stores, dry/wrinkled skin, apathy, infections. Affects infants to toddlers. 1. Kwashiorkor protein deficiency of firstborn after weaned from breast milk Distinguishing features: edema; retain some fat stores, fatty liver, skin lesions, loss of pigmentation in skin/hair, sadness, irritability, loss of appetite. Affects toddlers to young children. 63 64 65 Treatment of PEM IV's (Intravenous Fluids) Electrolyte replacement (sodium and potassium) Low fat, high carbohydrate, high protein foods Skim milk Fat introduced later protein is needed to transport fat around the body (protein must be replaced before fat can be introduced) 66 PEM in the U.S. Homeless Eating Disorders Drug and alcohol addicts Poverty formula dilution 67 Reasons for PEM Loss of food producing land Water shortages Water pollution War Global warming, droughts and floods 68 High Protein/Low Carbohydrate Diets Zone, Atkins, Sugar Busters Theory: Too many carbohydrates lead to increased insulin, which increases fat stores Diet is high in fat and protein, low in carbohydrates 69 High Protein Diet (cont.) Low Carbohydrate Intake (example 20 g/day) Glycogen is depleted blood glucose Body uses glycogen stores to maintain blood glucose Protein is broken down Fat is broken down Breakdown of muscle tissue Most amino acids can be used to make glucose Used as an energy source Produces Ketones (build up of ketones in the body is dangerous) 70 High Protein Diet (cont.) Weight loss Initial weight loss = water and glycogen stores Muscle loss Fat loss (seems like a good thing, but the body produces ketones when fat is burned without carbohydrate available) 71 Is a HighProtein Diet Harmful? Can negatively affect health of heart, kidneys and bones Low in plant foods, which are the main source of fiber, vitamins & phytochemicals Protein sources are often high in saturated fat and cholesterol, which can increase CVD risk Excessive intake of processed red meat is linked with colon cancer Excess protein can overwork/burden the kidneys & liver Very high protein intakes can cause calcium to be excreted in the urine, which can accelerate adult bone loss 72 High Protein Diet (cont.) Side effects Bad breath Constipation Ketones released in breath Low fiber diet Ketones Fatigue, irritability 73 High Protein Diet (cont.) What happens when you go off the diet? Many put the weight back on How long can you stay on it? Diet is very restrictive; may be difficult to stay on long term 74 75 Vegetarian Diets Why become a vegetarian? Some common reasons are: Religion Animal rights Health Environmental causes Preference 76 Types of Vegetarianism 1. "Far" vegetarian: no red meat; will eat poultry, fish, eggs, milk, grains, fruits and vegetables 2. Lactoovo vegetarian: no meat but includes dairy products and eggs 3. Lactovegetarian: includes dairy products; no meat or eggs 4. Ovovegetarian: includes eggs; no milk products or meat 5. Vegan: most restrictive and includes only food from plant sources; absolutely no animal products 77 5 main types: Types of Vegetarianism 78 Benefits of Vegetarianism risk of CVD, Diabetes (Type II) Rarely obese Low in saturated fat High in fiber and antioxidants More likely to exercise Less likely to drink, smoke and abuse drugs 79 Nutrient Concerns for Vegetarians Protein need for complementary protein sources Certain vitamins & minerals: Calcium vitamin D vitamin B12 Iron Zinc Mainly from Animal Sources Concerns for infants and children 80 81 The Vegetarian Diet Pyramid 82 Often taken by athletes to build muscle Protein supplements vs. protein foods Protein and Amino Acid Supplements Less digestible More expensive Potentially dangerous 83 Protein and Amino Acid Supplements (cont.) Increased risk for amino acid deficiency (compete for absorption) Risk of toxicity (could cause liver or kidney If a supplement contains a mega dose of one amino acid it may block the absorption of other amino acids damage) No good research supports safety 84 85 Food Allergies and Intolerances Food allergies have increased by 18% from 1997 to 2007 Cause 150200 deaths each year 11 million Americans are affected 86 Definitions: Allergies Immune response to a foreign protein (allergen) Intolerance Inability to digest a certain food component Food Sensitivity A mild reaction to a substance in a food Anaphylactic shock A severe allergic response that can be fatal 87 Symptoms of Food Allergies: Coughing Sneezing Nausea Vomiting Diarrhea Hives Other rashes 88 Common Foods Nuts Milk Shellfish Eggs Soybeans Wheat Fish 89 Theories Early introduction of solid food in infancy Prior to 6 months the GI tract is immature Allows undigested proteins to be absorbed Increases allergy risk Hygiene Hypothesis Heavy use of antibiotics, hand sanitizers, etc Immune system not challenged 90 Diagnosis History Physical Exam Skin Test Elimination Diet Blood Test 91 2006 Food Allergen Labeling and Consumer Protection Act Manufacturers must clearly identify presence of major food allergens 80% of children outgrow allergies by the age of 3 92 Prevention Solid food introduction after 6 months of age Cow's milk introduction after 12 months Egg (Whites) introduction after 24 months Fish and other seafood introduction after 36 months 93 Intolerances Lactose bloating, nausea, diarrhea Sulfites, MSG sweating, vomiting, headache Treatment Avoidance In some cases just limit intake 94 ...
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