Chapter 2.pptx

CHAPTER 2 FUEL FOR EXERCISE: BIOENERGETICS AND MUSCLE METABOLISM  Energy substrates Controlling the rate of energy production Storing energy: high-energy phosphates CHAPTER 2 The basic energy systems OVERVIEW Interaction of t...

CHAPTER 2 FUEL FOR EXERCISE: BIOENERGETICS AND MUSCLE METABOLISM  Energy substrates Controlling the rate of energy production Storing energy: high-energy phosphates CHAPTER 2 The basic energy systems OVERVIEW Interaction of the energy systems The crossover concept The oxidative capacity of muscle TERMINOLOGY Substrates (or macronutrients) Fuel sources from which we make energy (adenosine triphosphate [ATP]) Carbohydrate, fat, and protein Bioenergetics Conversion of substrates into energy Cellular-level process Metabolism: chemical reactions in the body MEASURING ENERGY RELEASE  Can be calculated from heat produced  1 calorie (cal) = heat energy required to raise 1 g of water from 14.5 °C to 15.5 °C  1,000 cal = 1 kcal = 1 Calorie (dietary)  Carbohydrate, fat, protein Composed of which elements: Energy from chemical bonds in food stored in high-energy compound ATP SUBSTRATE Resting: 50% carbohydrate, S: FUEL 50% fat FOR Exercise (short): more EXERCISE carbohydrate Exercise (long): carbohydrate, fat CARBOHYDRATE All carbohydrate converted to glucose Extra glucose stored as 4.1 kcal/g (~2,500 kcal Primary ATP substrate glycogen in liver, stored in body) for muscles, brain muscles Glycogen converted back to glucose when needed to make more ATP Glycogen stores limited (2,500 kcal); dietary carbohydrate needed in order to replenish Muscle stores: Liver stores: FAT Efficient 9.4 kcal/g substrate, 70,000+ kcal stored in body even efficient in lean individuals storage Energy substrate Yields high net ATP but slow ATP production for Must be broken down into free prolonged, fatty acids (FFAs) and glycerol less intense Only FFAs are used to make ATP exercise TABLE 2.1 PROTEIN  Energy substrate during starvation  Possibly ~5% of energy expended during exercise under normal conditions  4.1 kcal/g  Some AAs are converted into glucose (gluconeogenesis)  Some AAs are converted into FFAs (lipogenesis)  For energy storage  For cellular energy substrate FIGURE 2.1  Energy is derived from the three substrates (macronutrients) in the diet  Energy currency in the cells is in the form of ATP  Carbohydrate and protein provide ~ 4.1 kcal/gram; 9.4 kcal/gram for fat REVIEW  Fat is stored as triglycerides— breaks down into glycerol and free fatty acids  Carbohydrate is stored in the liver and the muscle for a total of 2,500 kcals ENZYMES AND THE PRODUCTION OF ENERGY   Energy released at CONTROLLING controlled rate based on availability of primary RATE OF substrate ENERGY  Mass action effect PRODUCTION  Substrate availability affects metabolic rate BY SUBSTRATE AVAILABILITY  More available substrate =  Excess of given substrate = CONTROLLING RATE OF ENERGY PRODUCTION BY ENZYME ACTIVITY  Energy released at controlled rate based on enzyme activity in metabolic pathway  Enzymes  Do not start chemical reactions or set ATP yield  Do facilitate breakdown (catabolism) of substrates  Lower the activation energy for a chemical reactions  End with the suffix –ase  Dependent on the rate limiting step for speed of metabolism  ATP broken down by ATPase FIGURE 2.2 CONTROLLING RATE OF ENERGY PRODUCTION BY ENZYME ACTIVITY Specific enzyme(s) required for each step in a biochemical pathway More enzyme activity = more product Can create bottleneck at an early step Rate-limiting Activity is influenced by negative enzyme feedback Slows overall reaction, prevents runaway reaction ANIMATION 2.3  ATP stored in small amounts until needed Breakdown of ATP to release energy ATP + water + ATPase  ADP + Pi + energy ADP is a lower-energy compound that is less useful Synthesis of ATP from by-products ADP + Pi + energy  ATP (via phosphorylation) Can occur in either absence or presence of O 2 STORING ENERGY: HIGH-ENERGY PHOSPHATES FIGURE 2.4 BIOENERGETICS: BASIC ENERGY SYSTEMS  Limited ATP storage  Constant synthesis of new ATP  Three (four) ATP synthesis pathways:  ATP-PCR  Glycolysis  Kreb’s Cycle + electron transport chain REVIEW  Enzymes control the rate of metabolism and energy production  Enzymes speed up the rate of the overall reaction by lowering the initial activation energy  Enzymes can be inhibited by negative feedback of subsequent pathway by- products  ATP is generated through three (four) primary energy systems: ATP-PCr, glycolysis, Kreb’s cycle + electron transport chain ATP-PCr AND GLYCOLYSIS ATP-PCR SYSTEM  Anaerobic, substrate-level metabolism  ATP yield: 1 mol ATP/1 mol PCr  Duration: 3 to 15 s  Because ATP stores are very limited, this pathway is used to reassemble ATP quickly ATP-PCR SYSTEM  Phosphocreatine (PCr): ATP recycling  PCr + creatine kinase  Cr + Pi + energy  PCr energy cannot be used for cellular work  PCr energy can be used to reassemble ATP  Replenishes ATP stores during rest  Recycles ATP during exercise until used up (~3-15 s maximal exercise) FIGURE 2.6 ANIMATION 2.5 CONTROL OF ATP-PCR SYSTEM: CREATINE KINASE (CK) PCr breakdown catalyzed by creatine kinase (CK) CK controls rate of ATP production Negative feedback system When ATP levels  (ADP ), CK activity  When ATP levels , CK activity  GLYCOLYTIC SYSTEM In the cytoplasm!  Anaerobic  ATP yield: 2 to 3 mol ATP / 1 mol substrate  Duration: 15 s to 2 min  Breakdown of glucose via glycolysis  What location in the cell does GLYCOLYTIC SYSTEM  Uses glucose or glycogen as its substrate  Some proteins can be converted into pyruvate which can lead to new glucose production  Must convert to glucose-6- phosphate  Costs 1 ATP for glucose, 0 ATP for glycogen  Pathway starts with glucose-6- phosphate, ends with pyruvic acid  10 to 12 enzymatic reactions total  All steps occur in cytoplasm  ATP yield:  Glucose:  Glycogen: GLYCOLYTIC SYSTEM  Cons  Low ATP yield, inefficient use of substrate  In the absence of oxygen, what is created?  Pros  Allows muscles to contract when O2 limited  Permits shorter-term, higher- intensity exercise than oxidative metabolism can sustain   Phosphofructokinase (PFK) GLYCOLYTIC  Rate-limiting enzyme regulated by negative feedback SYSTEM  ATP ( ADP)   PFK activity  ATP   PFK activity  Also regulated by products of Krebs cycle  Glycolysis lasts approximately how long in maximal exercise?  Need another pathway for longer durations   ATP-PCr—anaerobic quick energy source but expended quickly—one to one conversion used for immediate response from stimulus  Glycolysis breaks down glucose or glycogen down into pyruvic acid— anaerobic REVIEW  In absence of oxygen pyruvic acid is converted to lactic acid—cellular fermentation  In the presence of oxygen pyruvate is converted into acetyl CoA and enters the Kreb’s cycle  Yields 2 or 3 ATP for glucose and glycogen, respectively KREB’S CYCLE AND THE ELECTRON TRANSPORT CHAIN OXIDATIVE SYSTEM In the MITOCHONDRIA!  Aerobic = REQUIRES OXYGEN  ATP yield dependent on substrate  32 to 33 ATP/one glucose  100+ ATP/ one free fatty acid (FFA)  Duration: steady supply for hours  Most complex of three bioenergetic systems  Mitochondria  Density within mitochondria is determined by demand; location is determined by oxygen diffusion  Minimize excess oxygen to prevent creating reactive oxygen species (ROS)  Distribution is nonuniform to maintain OXIDATIVE oxygen delivery and thereby maintain high metabolic rates SYSTEM FIGURE 2.8 OXIDATION OF CARBOHYDRATE: GLYCOLYSIS REVISITED  Glycolysis can occur with or without O2  ATP yield is same as for aerobic or anaerobic glycolysis  General steps are same as for anaerobic glycolysis  In the presence of oxygen, pyruvic acid is converted to what intermediate to enter the Kreb’s cycle? OXIDATION OF CARBOHYDRATE: KREBS CYCLE  1 molecule glucose  2 acetyl-CoA  1 molecule glucose  2 complete Krebs cycles  1 molecule glucose  double ATP yield  2 acetyl-CoA  2 GTP  2 ATP  Also produced: NADH, FADH, H+  Too many H+ in the cell = too acidic How does acidification of the muscle effect the function?  H+ moved to electron transport chain FIGURE 2.9 Rate limitin g step OXIDATION OF CARBOHYDRATE: ELECTRON TRANSPORT CHAIN  H+, electrons are carried to electron transport chain via NADH, FADH2 molecules.  H+, electrons travel down the chain  H+ combines with O2 (neutralized, forms H2O)  Electrons + O2 help form ATP  There are 2.5 ATP per NADH and 1.5 ATP per FADH2 OXIDATION OF CARBOHYDRATE: ENERGY YIELD  1 glucose = 32 ATP  1 glycogen = 33 ATP  Breakdown of net totals  Glycolysis = +2 (or +3) ATP  Kreb’s cycle and electron transport chain:  GTP from Krebs cycle = +2 ATP  10 NADH = +25 ATP  2 FADH2 = +3 ATP FIGURE 2.11 ANIMATION 2.12 REVIEW  The Kreb’s cycle and electron transport chain occur in the mitochondria of the cell  Kreb’s cycle + electron transport chain requires oxygen and is more efficient— creates 32 or 33 ATP from one glucose and glycogen, respectively  The products of metabolism are H2O, CO2, and ATP  The most energy is produced in the electronic transport chain (28 of the 32 ATP) THE OXIDATION OF FAT AND PROTEINS AND THE UTILIZATION OF LACTATE Triglyceride Rate of FFA s: major fat entry into energy muscle: source dependent Broken down on to 1 glycerol + concentrati on gradient 3 FFAs Lipolysis, OXIDATION carried out by lipases OF FAT Yield: 3 to 4 Slower than times more glucose ATP than oxidation glucose β-OXIDATION OF FAT  Process of converting FFAs to acetyl-CoA before entering Krebs cycle  Up-front expenditure of 2 ATP  Number of steps dependent on number of carbons on FFA  16-carbon FFA yields 8 acetyl-CoA  In comparison, 1 glucose yields 2 acetyl-CoA  Fat oxidation requires more O now, yields far more ATP later 2  Fat cannot enter the glycolytic system—MUST BE AEROBICALLY METABOLIZED! OXIDATION OF FAT: KREBS CYCLE, ELECTRON TRANSPORT CHAIN Acetyl-CoA enters Krebs cycle Then follows same path as glucose oxidation Different FFAs have different number of carbons Yield different numbers of acetyl-CoA molecules  ATP yield differs for different FFAs  Example: For palmitic acid (16 C), net yield is TABLE 2.2 OXIDATION OF PROTEIN  Rarely used as a substrate (starvation)  Different AA are converted to:  Pyruvate—glucogenic AA—synthesize glucose— gluconeogenesis  Acetyl CoA—ketogenic AA—enter the Kreb’s cycle  Oxaloacetate and other Kreb’s cycle intermediates  Energy yield not easy to determine  Nitrogen presence is unique  Nitrogen excretion requires ATP expenditure  How is nitrogen excreted from the body?  Because it is generally minimal, estimates ignore protein metabolism  Lactate produced in cytoplasm can Lactate is an be taken up by important fuel mitochondria of during exercise the same muscle fiber and oxidized Lactate can be Muscles can use transported via LACTATE MCP transporters lactate in three ways: to another cell and UTILIZATION oxidized there (lactate shuttle) Lactate can recirculate back to the liver and be reconverted to pyruvate and then to glucose through gluconeogenesis  Negative feedback regulates Krebs cycle  Isocitrate dehydrogenase is a rate-limiting enzyme  Functions as PFK does for glycolysis  Regulates electron transport chain  Is inhibited by ATP, activated by ADP CONTROL OF OXIDATIVE PHOSPHORYLATION: NEGATIVE FEEDBACK FIGURE 2.13 REVIEW  Fat oxidation begins with the β-oxidation of FFAs and follows the same path as carbohydrate oxidation producing acetyl CoA  The energy yield is much higher for fat than for carbohydrate—more carbon, but less oxygen—slower process than metabolism of carbohydrate  Because fat oxidation requires the input of more oxygen than carbohydrate, during high-intensity exercise, carbohydrate is the preferred energy source  When carbohydrate stores are depleted and fat because the primary fuel source, the athlete’s performance will slow  Protein contributes relatively little to energy production and is generally ignored  Despite lactic acid’s reputation of causing muscle soreness, it is an important fuel source during exercise THE INTERACTION OF ENERGY SYSTEMS IN ACTIVITY AND TRAINING INTERACTION OF ENERGY SYSTEMS  All three systems interact for all activities  No single system contributes 100%  But one system often dominates for a given task  Cooperation increases during transition periods FIGURE 2.14A & B TABLE 2.3 CROSSOVER CONCEPT  At rest and exercise below 60% VO2max, lipids serve as the primary substrate  During high intensity (above 75% VO2max), carbohydrates serve as the primary substrate  The crossover point is the intersection, which is affected by exercise intensity and endurance training FIGURE 2.15 OXIDATIVE CAPACITY OF MUSCLE  Not all muscles exhibit maximal oxidative capabilities  Oxidative capacity is determined by multiple factors:  Enzyme activity  Fiber type composition, endurance training  O2 availability versus O2 need  ENZYME ACTIVITY  Not all muscles exhibit optimal activity of oxidative enzymes  Enzyme activity predicts oxidative potential  Representative enzymes include succinate dehydrogenase and citrate synthase  Levels differ in endurance-trained versus untrained individuals FIBER TYPE COMPOSITION AND ENDURANCE TRAINING Type I fibers: greater oxidative capacity—What are some differences between Type I and Type II fibers Endurance training—What are some of the adaptations occur due to endurance training?  ATP demand increases with intensity Inof Rate response, increases occur in: O2 delivery by oxidative ATP production O2 intake at lungs the heart and vessels OXYGEN NEEDS OF O2 storage is limited—use it or lose it MUSCLE O2 levels entering and leaving lungs enable accurate estimate of O2 use in muscle REVIEW  No activity is 100% one energy system  There is an inverse relationship between speed of ATP product and the length of time the system is available  Oxidative capacity is determined by muscle fiber type, endurance training, and oxidative enzyme availability  Endurance training increases vasculature, mitochondria development, enzyme availability among others