01:377:370 Lecture 3: Biochemistry Macromolecules and Energetics

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Exercise Science and Sport Studies
Professor Pellegrino

Biochemistry Macromolecules & Energetics Digestion: • Eating sends signals throughout body o Gastric emptying from stomach ▪ Can be affected by many factors: volume of stomach, temperature of substance, carbonation of substance o Absorption in small intestine o Water absorption in large intestine o Gastric distress from large intestine ▪ Microbiota receive undigested food Biochemistry: • Enzymes increase reaction rates • Feedback- via probability and inhibition • Glycolysis o ADP o AMP o Phosphate o NAD+ o Glucose • Reverse glycolysis o ATP o NADH o H+ o Pyruvate o Acetyl CoA • Redox reactions- paired reactions that underlie energy metabolism o Reduced molecule accepts electrons o Oxidized molecule donates electrons o NAD+ and FAD+ serve as major electron acceptors and oxidizers ▪ NAD+ becomes NADH + H+ ▪ FAD+ becomes FADH2 Metabolic processes- use sugars, lipids, and proteins to build more complex compounds (anabolism) or break them down to release energy (catabolism) • Sugars and starches  monosaccharides  glucose • Lipids  glycerol + fatty acids • Protein  amino acids Anabolic Reactions- build up or transform • Glucose + glucose (uses energy)  glycogen • Glycerol + fatty acids (uses energy)  triglycerides • Amino acid + amino acid (uses energy)  protein Catabolic Reactions- break down • Glycogen  glucose (yields energy) • Triglycerides  glycerol + fatty acids (yields energy) • Protein  amino acids (yields energy) ATP- storage compound for available energy • Energy originates from catabolism of organic substrates o Energy from food used to attach a phosphate group to ADP  ATP o ATP captures and stores this energy o Energy from ATP is released when phosphate bond is broken o This energy fuels the body’s work • Cells hydrolyze the high energy bonds between the 3 phosphate of ATP for energy • Don’t store a lot of ATP- too heavy, make it as need it Energy Processing • Organic foods o CHO glycolysis (carbs) ▪ Somewhat limited in body ▪ Broken down quickly o FAT beta oxidation (fats) ▪ Abundant in body ▪ Broken down slowly o PRO De/Trans animation (proteins) ▪ Broken down slowly ▪ Inefficient (costs energy to break down) ▪ Ketones- used in emergency situations • Good when limited or with adaptation • Not really a food • Mainly made in liver o Alcohol (ADH) ▪ Good source of energy ▪ Good in isolation ▪ Poor systemically • PCr (CK) –single phosphate bonded to creatine o Fast o Immediate and for mobility Carbohydrates • All carbohydrates break down into glucose and are used in glycolysis o Quick limited energy = 2 ATP/glucose in glycolysis ▪ Can go to pyruvate or lactate • Aerobic (slow glycolysis) o Products = pyruvate/NADH into mitochondria o On to TCA and ETC for aerobic energy o 15x more ATP • Anaerobic (fast glycolysis) o Product = lactate ▪ Lactate is a mobile interconvertible substrate- can be converted into glycogen for later use (limited) or fat for storage (unlimited) o Only 2 ATP/glucose o Very quick ▪ Used for a quick power lift or sprint Fats • Fatty acid chains can be modified and product used o Triglyceride dissociates from glycerol for energy o Glycerol used for gluconeogenesis- making of new glucose o Beta oxidation of fatty acid chain for acetyl CoA (TCA) ▪ Requires oxygen ▪ Slow • Can be stored in intramuscular triglycerides (IMTG) or fat cells o Requires movement of fat through body or lipolysis for later use • Extremely abundant Proteins • Generally ignored for energy consumption o Use less than 5-15% of proteins during exercise • Break down o CHO skeleton converted to pyruvate or ketones for energy o Urea used for disposal of amine (NH3) • No storage of proteins Carbs vs. Fats vs. Proteins • Carbs o Low storage o Fast digestion o Fast metabolism (glycolysis and oxidative phosphorylation) o Lactate o High CO2/O2 ratio o All fiber types • Fats o High storage o Slow digestion o Slow metabolism (oxidative phosphorylation) o Slow delivery o Low CO2/O2 ratio o Type I fibers • Proteins o No storage o Slow digestion o Slow inefficient metabolism (deanimation and NH3 removal, glycolysis and/or oxidative phosphorylation) o Moderate CO2/O2 ratio Phosphocreatine (PCr)- energy reservoir • PCr hydrolysis and adenylate kinase reaction generate: o Phosphate o AMP o ADP • By-products stimulate o Glycogenolysis/glycolysis o Oxidative phosphorylation • Stored higher in power/strength athletes o Need energy quickly • Anaerobic resynthesis of ATP o PCr hydrolyzed by enzyme creatine kinase (CK) o ADP phosphorylated to ATP o High levels of ADP for this reaction o Reaches max energy yield in less than 10 seconds • Creatine may be phosphorylated back to PCr o Cells store 4-6 times more PCr than ATP • Adenylate kinase reaction can assist in ATP regeneration: 2ADP  ATP + AMP Important Reactions: Creatine kinase reaction: ADP + PCr  ATP + Cr Adenylate kinase reaction: 2ADP  ATP + AMP Glycolysis- breaking down glucose • Location: o Cytosol • Function: o CHO breakdown for fast energy o Begins with glucose or glycogen ▪ Use 2 ATP ▪ End product = pyruvate + 2ATP + 2NADH o Immediate energy for 60-90 seconds (slower than PCr) • Anaerobic energy process o Produces ATP and ATP-potential compound (NADHx2) ▪ 1 NADH = 2 or 3 ATP • 3 rate-limiting enzymes o Hexokinase- uses ATP o PFK- uses ATP o Pyruvate kinase- yields ATP • GLUT-1 o In resting muscle cell- transports glucose • GLUT-4 o During exercise and in response to hormonal signaling- transports glucose to muscle cell o Sensitive to hormones o Exercise without hormone increases GLUT-4 Hexokinase- works on glucose molecule to create glucose-6-phosphate Phosphorylase- breaks down glycogen into glucose-6-phosphate • Epinephrine stimulates reaction- increases rate to produce energy by increasing rate to break down glycogen Phosphofructo-kinase- breaks down fructose-6-phosphate to create fructose 1,6-diphosphate • Glucagon stimulates reaction- increases rate of glucose breakdown Lactate dehydrogenase- lactate  pyruvate Regulation of Glycolysis: • 3 rate-limiting enzymes- important when starting with free glucose o Hexokinase ▪ GK in liver o PFK ▪ PFK 1 ▪ PFK 2- reversible enzyme that converts fructose-2, 6-biphosphate • Fructose-2, 6-biphosphate increases flux through PFK 1 via allosteric binding  flux through glycolysis • Increases rate of PFK 1 o Pyruvate kinase and lactate dehydrogenase ▪ CP and ATP • GLUT-4 transporters bring glucose into cell o Responds ▪ Insulin (following high CHO meal) ▪ Physical activity independent of insulin • Dependent on available glycogen (from glycogenesis) o Glucose  G 6-P  glycogen (using glycogen synthase) Glucagon- released when blood sugar is low • Increases glycolytic flux o Non-muscle tissue: Slow metabolism nd ▪ Glucagon stimulates 2 messenger system (cAMP) to activate protein kinase A ▪ Protein kinase A phosphorylates PFK 2 ▪ Lowers fructose-2, 6-biphosphate  slows glycolysis ▪ Glucose made more available to be released from cell into blood  increase blood sugar o Muscle tissue: Fast metabolism (high energy need) ▪ PFK becomes activated and the reverse slowed ▪ Increases rate of glycolysis Insulin- released when blood sugar is high Fasting state • Don’t eat  blood sugar drops • Start breaking down glycogen stores into glucose and releasing glucose into blood for delivery through the body (increasing blood glucose) • Liver = main site of glucose mobilization • Pancreas releases glucagon  slows glycolysis in the liver  allows glucose not being broken down to be stored as glycogen or released into the bloodstream Exercise • Muscles initially take up much glu
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