Nutrition Notes.docx

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Danny M.Pincivero

Bioenergetics Metabolism - Sum of all chemical reactions that occur in the body Anabolic reactions - Synthesis of molecules Catabolic reactions - Breakdown of molecules Bioenergetics - Converting food (carbs, proteins, fats) to energy Protein Synthesis - DNA contains information to produce proteins - Transcription produces mRNA - mRNA leaves nucleus and binds to ribosome - Amino acids are carried to the ribosome by tRNA - In translation, mRNA is used to determine the arrangement of amino acids in the polypeptide chain Endergonic Reactions - Require energy to be added - Endothermic Exergonic Reactions - Release energy (transfer to mechanical/chemical AND thermal) - Exothermic Oxidation - Removing an electron Reduction - Addition of electron - Oxidation and reduction are always paired - Often involves the transfer of hydrogen atoms rather than free electrons o Hydrogen atom contains one electron o A molecule that loses a hydrogen also loses an electron and therefore is oxidized Enzyme - Catalysts that regulate the speed of reactions - Lower the activation energy - Factors: temperature, pH Where do we get our energy? - Energy “substrates” o Carbs, fats, proteins How do we get energy out of the substrates? - Depends on: - Substrate availability - Enzyme dynamics - Nervous system demand - Metabolic “backup” Energy for muscle activity - Formation of ATP o Phosphocreatine (PCr) breakdown o Degradation of glucose o Oxidative formation of ATP - Anaerobic pathways o Do not involve oxygen o PC breakdown and glycolysis - Aerobic pathways o Require oxygen o Oxidative phosphorylation Creatine - Non-essential dietary element (meat & fish) - Greek derivative, kreas, meaning flesh - Humans: made in 2 step process (liver and kidney) - Found mostly in skeletal muscle, heart, spermatozoa, retinal cells - Important for ATP re-synthesis for high intensity/velocity muscle contraction through creatine phosphate (phosphocreatine, PCr, CrP) - CP contains energy in phosphate bond Creatine biosynthesis - 2 step process o Step 1: Kidney: Arginine + glycine o Step 2: Liver: Guanidinoacetate + methionine How does it make ATP PCr + ADP  ATP + Cr ATP  ADP + P + E (thermal/chemical)  Reverse reaction when we run out of creatine phosphate Creatine kinase - 381 amino acid sequence Creatine Phophate Usage During Exercise Creatine Phophate Supplementation - Increase the muscle’s stores of CP, extends high intensity exercise and speeds muscle recovery Types: - Creatine monohydrate - Creatine anhydrous - CP - Creational-O-phosphate Creatine Supplement Forms - Holds one molecule of water (creatine monohydrate) - Drying of creatine monohydrate yields creatine anhydrous - Creatine salts created by combining and a strong acid (pyruvic acid, malic acid, citric acid) Creatine content - Creatine anhydrous (100%) - Creatine monohydrate (88%) - Creatine malate (75%) - Creatine citrate (66%) Creatine solubility in water - Greater solubility with creatine salts than creatine monohydrate Creatine stability - Creatine monohydrate most stable o Takes long time to degrade, long shelf life - Creatine degrades in warm, acidic water o Should be consumed immediately after dissolving in water Bioavailability - Absorb creatine from small intestine into blood - Uptake creatine into muscle tissue Creatine solubility in water - Greater solubility with creatine salts than creatine monohydrate - Dietary creatine intestinal absorption close to 100% - Muscle tissue uptake stimulated by insulin Creatine dosage st - 1 4-6 days o 20g/day o Loading phase - 5g/day (maintenance phase) - Takes 2-3 days for tissue creatine accumulation Creatine and phosphate performance - 5-20% improvement in short-term exercise Side effects - Increased weight gain (water retention in muscle) - Nausea, vomiting, diarrhea - Increased urinary creatine and creatinine (related to kidney inflammation) - Altered fluid balance (dehydration) - Negative feedback from exergenous supply (decrease natural production) Glucose - Blood sugar ‘broken down’ called glycolysis Glycogen - Storage form of glucose in liver and muscle o Synthesized by enzyme of glycogen synthase Glycogenolysis - Break down of glycogen to glucose Frutose - ~50% glucose - ~25% lactate - Minor  fatty acids  very low density lipoprotein (VLDP) o Carbohydrate needs are met Glycogen - Cleaved into individual glucose units o In muscle, myophosphorylase (activated by epinephrine) followed by phophoglucomutase. Saves 1 ATP o In liver, phosphorylase (activated by glucagon) followed by glucose-6-phosphatase (allows glucose to enter the blood) Glycolysis/Glcogenolysis - Originally called Embden-Meyerhof Pathway - Exists both as anaerobic and aerobic pathways - Purpose: re-synthesize ATP Glycolysis: pathway start at glucose Glycogenolysis: pathway start at glycogen Metabolic pathway yield: - 4 substrate level ATP (gross) - Reducing equivalents (2NADH + H+) - Pyruvic acid (and lactic acid) Metabolic Pathway Cost: - 1 ATP (from muscle glycogen) - 2 ATP (from muscle glucose) - 2NAD The Kreb’s Cycle (TCA/ citric acid cycle) Pathway yield: - 1ATP - 2 CO2 - 3 NADH + H+ - 1 FADH2 - Add in 1 more NADH + H+ for pyruvate conversion Pathway Cost: - Pyruvate Oxidative Phosphorylation Cost: - NADH + H+ - FADH2 - O2 Yield: - 2ATP per FADH2 - 3ATP per NADH + H+ So, from 1 glucose molecule we get 24 ATP Fat as an energy substrate Adipocyte: fat cell 4 roles: - Building block of phospholipid and glycolipids - Protein modification by attaching to fatty acids - Fuel - Derivatives serves as hormones and intracellular messengers Make ATP from fatty acids - Mobilization: adipocyte - Activation: muscle cell o Carnitine, surface of mitochondria - B-oxidation Protein as an Energy Substrate - Amino acids are assembled in various combinations in 4 levels of structures (primary, secondary, tertiary, quartenary) - Gluconeogenesis - Conversion to metabolic intermediates Incremental Exercise - Oxygen uptake increases linearly until maximal oxygen uptake (VO2) is reached - No further increase in VO2 with increasing work rate VO2 Max - Physiological ceiling for delivery of O2 to muscle - Affected by genetics and training - Quantified: volume of gas per unit time Physiological factors influencing VO2 Max - Maximum ability of cardiorespiratory system to deliver oxygen to the muscle - Ability of muscles to use oxygen and produce ATP aerobically Lactate Threshold - Abrupt/non-linear increase in blood lactate - Reasons: o Low muscle oxygen (hypoxia) o Accelerated glycolysis o NADH produced faster that it is shuttled into mitochondria o Excess NADH in cytoplasm converts pyruvic acid to lactic acid o LDH isozyme in fast fibres promotes lactic acid formation o Reduced rate of lactate removal from the blood - Fast Twitch Fibres: favours pyruvate  L.A - Slow Twitch Fibres: favours LA  pyruvate - LDH: lactate dehydrogenase - Recruitment of FT muscle fibres o LDH isozyme in fast fibres promotes lactic acid formation Exercise and Fuel Selection Incremental Exercise - Low intensity exercise (<30% VO2 max) o Fats are primary fuel - High intensity exercise (>70% VO2 max) o Carbs are primary fuel - Crossover concept o Describes the shift from fat to carbs metabolism as exercise intensity increases o Due to:  Recruitment of fast muscle fibres  Increasing blood levels of epinephrine Prolonged, low-intensity exercise - Shift from carbohydrate metabolism toward fat metabolism - Due to increased rate of lipolysis o Breakdown of triglycerides  glycerol + FFA o By enzymes called lipases o Stimulated by rising blood levels of epinephrine Carbohydrates - Hydrate of carbon - Manufactured by plants Storage form of glucose - Animal: glycogen - Plants: starch (amylopectin and amylose) & fibre Fibre: Non-digestible carbohydrates (in plants) Soluble fibre - Dissolves in hot water - Forms a gel in GI system - Slow gastric/intestinal motility - Fuller feeling, absorbs FA’s - Decreases CV disease, CHOL - Oat, bran, dried beans, nuts Insoluble fibre - Does not dissolve in hot water - Absorbs water INTO GI system - Speeds intestinal motility - Decreases absorption time - Decreases Type II DM - Can lead to nutrient deficiencies - Vegetables, fruit skins Function of Carbs - Burned for energy - Ribose and deoxyribose sugars - Structure and strength of plants - Linked to proteins and lipids Glycoprotein: covalent link between protein and a carbohydrate monomer Glycolipid: forms myelin around neuron axons Forms of Carbohydrates - Monosaccharides o Simple form of CHO o Contain 3-9 carbon atoms - Sugar alcohols o Derived from monosaccharides o Used as a sweetener Carbohydrate Digestion Fibre Mouth: - Mechanical action of the mouth crushes and tears fibre in food and mixes it with saliva to moisten it for swallowing Stomach - Fibre is not digested, and it delays gastric emptying Small Intestine - Fibre is not digested and it delays absorption of other nutrients Large Intestine - Most fibre passes intact through the digestive tract to the large intestine - Bacterial enzymes digest fibre - Some fibre (bacterial enzymes) short-chain fatty-acids, gas - Fibre holds wter, regulates bowel activity, and binds substances such as bile, cholesterol, and some minerals, carrying them out of the body Starch Mouth and Salivary Glands - Salivary glands secrete saliva into the mouth to moisten the food. The salivary enzymes amylase begin digestion - Starch  (amylase) small polysaccharides, maltose Stomach - Stomach acid inactivates salivary enzymes, halting starch digestion Small Intestine and Pancreas - The pancreas produces an amylase that is released through the pancreatic duct into the small intestine - Starch  (pancreatic amylase) small polysaccharides, maltose - Then disaccharidase enzymes on the surface of the small intestine cells hydrolyze the disaccharides into monosaccharides - Maltose  (maltase) glucose + glucose - Sucrose  (sucrose) fructose + glucose - Lactose  (lactase) galactose + glucose - Intestinal cells absorb these monosaccharides Disaccharides - Sucrose, lactose, maltose Oligosaccharides - 3-9 CHO monomers - Considered to be a complex carb Polysaccharides - Dietary form: starch o Vegetables and fruits o Grains: wheat, corn, oats, barley, rice o Legumes: peas, beans, lentils, soy o Tubers: potatoes, yams, cassava (toxic raw) Why do we need to eat carbs? - Energy needs o Fuel source for neurons (only uses glucose except during starvation- can uptake protein) o Red blood cells only use glucose o Need CHO to metabolize other fuels- fats burn in a flame of carbs) - Ketone bodies o Major source of production is the liver (inside mitochondrion) o Heart and renal cortex cells: ketone bodies are used as fuel o Accumulate from protein and fat metabolism - Starvation and diabetes o Brain neurons use ketone bodies (water soluble) – converted to Acetyl CoA o High levels of ketone bodies in blood reduces adipocyte lipolysis- increases reliance and carbs for energy o Type 1:  Accumulation of ketones  Increased lipolysis  No insulin - Pregnancy o Fetus and placenta feed on glucose o Gestational diabeted: elevated blood glucose during pregnancy - Spares muscle protein degradation for energy o Glucose must be synthesized from muscle protein
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