Exercise Physiology Exam I Notes

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Rutgers University
Exercise Science and Sport Studies
Sara Campbell

1 PHYSIOLOGY OF EXERCISE CHAPTER 5: INTRODUCTION TO ENERGY TRANSFER I. Energy- the capacity for work ■ first law of thermodynamics- the body does not produce, consume, or use up energy, rather it transforms energy from one form to another ○ physiology- being the continual dynamic changes that occur within the human body ■ three types of energy 1. potential energy 2. kinetic energy 3. heat energy ■ energy releasing and conserving reactions: a cyclic process ○ exergonic- energy releasing reaction (ex breakdown of adenosine triphosphate for the use of mechanical work) ○ endergonic- energy absorption or storage (ex food intake in the form of carbohydrates, fats, and proteins are stored for future use during an exergonic reaction) II. biological work within the human body ■ mechanical work- muscular contractions ■ chemical work- biological chemical pathways (ex make and breakdown of ATP) ■ transport work III. factors that affect biological work A. enzymes- proteins that act as catalysts to biological reactions ○ are substrate specific and only function under specific environmental conditions (*neutral pH and stable temperature) ○ how do enzymes work i) substrate matches the active site of an enzyme ii) substrate + enzyme forms a substrate-enzyme complex (lock and key; initiates a reaction) iii) enzyme-substrate complex splits to yield product iv) enzyme is now available for interaction with another substrate B. coenzymes- (helpers) non-protein organic substances that act to “turn on” enzymes ○ require less specificity than enzymes because they act to help not initiate a reaction ○ can be vitamins, minerals, or other non-protein molecules ○ example- B vitamins C. enzyme inhibitors- (hinderers) particles that resemble normal substrate and bind to the enzyme blocking its active site ○ non- competitive inhibitors bind to a site other than the active site altering an enzyme's structure V. hydrolysis and condensation reactions: basis for digestion and synthesis ■ hydrolysis- catabolizes carbohydrates, lipids and proteins into simpler forms the body can easily absorb; splits chemical bonds by adding H+ and OH- (H20) to the reaction ○ figure 5.9 ie digestion of starches and disaccharides to monosaccharides, proteins to AA, and lipids to glycerol and fatty acids V. redox reactions- process of both reduction and oxidation ■ oxidation reaction- process of transferring/ losing electrons 2 ■ reduction reaction- process of gaining electrons VI. electron transport chain (ETC)- example of a redox reaction important to exercise which occurs in the mitochondria ■ aerobic process in which the NADH and FADH2 produced during glycolysis, β-oxidation, and other catabolic processes are oxidized thus releasing energy in the form of ATP ■ carrier molecules transfer oxidized hydrogen atoms and their removed electrons for delivery to oxygen ■ ETC described and simplifie ○ http://www.dbriers.com/tutorials/2012/04/the-electron-transport-chain-simplified/ CHAPTER 6: ENERGY TRANSFER IN THE BODY I. adenosine triphosphate ■ storage form of energy ■ powers all cellular reactions ■ energy is stored within the phosphate bonds ○ the greatest potential energy is stored within the third phosphate ■ chemical reaction: ATP + H2O *ATPase* → ADP + Pi ■ ATPase breaks down ATP which releases energy II. metabolism- the sum of all chemical activity and reactions that occur within the body ■ anabolism- synthesizing molecules from smaller components; *the building in metabolism which stores energy (endergonic); ex muscle building ■ catabolism- the breakdown of molecules into simpler substances; *the breakdown in metabolism which releases energy (exergonic) III. ATP is limited- cells contain a small quantity of ATP and must resynthesize it at its rate of use ■ aerobic and anaerobic processes are used to resynthesize ATP (depending on activity) ■ aerobic- performed in the mitochondria in the presence of oxygen ■ anaerobic- performed in the cytosol without presence of oxygen at the cellular level ■ one ATP molecule provides enough energy for two seconds of physical activity/work ■ figure 6.4 contributors to the anaerobic and aerobic resynthesis of ATP citric acid cycle/ respiratory chain *aerobic glycolysis *anaerobic MITOCHONDRIA CYTOSOL ○ fatty acids ○ phosphocreatine ○ pyruvate from glucose ○ glucose/ glycogen ○ some deaminated amino acids ○ glycerol ○ some deaminated amino acids IV. anaerobic ATP resynthesis: phosphocreatine (PCr) *first to occur ■ some energy for ATP resynthesis comes directly from the splitting of a phosphate from PCr ■ PCr is another high energy phosphate (like ATP) ■ reaction works in both directions ■ cells store roughly six times more PCr than ATP due to its free energy ■ need based reaction ■ by-products of these reactions will activate other metabolic pathways ■ Pcr is the first to occur when the breakdown of ATP releases a phosphate 3 ■ the reaction does not require oxygen and reaches a maximal energy yield for about 6-10 seconds of mechanical work ATP → ADP + Pi + Energy PCr + ADP → Cr + ATP ■ figure 6.5: ATP and PCr provide anaerobic sources of phosphate- bond energy; the energy resulting from the hydrolysis of PCr rebonds ADP + Pi to form ATP ■ temporary increases in ADP within the muscles contractile unit during exercise shift the creatine kinase reaction toward PCr hydrolysis and ATP production ■ PCr serves as a reservoir of high energy phosphate bonds V. aerobic ATP resynthesis: cellular oxidation ■ oxidation- refers to the “burning” of carbohydrates, fats, and proteins, from the diet for energy ■ cellular oxidation- an oxidation-reduction reaction (redox reaction) which constitutes the biomechanical mechanism that underlies energy metabolism ○ this process will continually provide hydrogen atoms for ATP production ■ carrier molecules in the mitochondria remove electrons from hydrogen (oxidation) and and eventually pass them to oxygen (reduction) cellular oxidation: electron transport ■ dehydrogenase enzymes- enzymes that catalyze hydrogens release from the nutrient substrate which is then transferred to acceptor molecules ■ NAD and FAD- energy transfer molecules which accept pairs of electrons from hydrogen; coenzymes to dehydrogenase ○ nicotinamide adenine dinucleotide (NAD+)- gains hydrogen as well as two electrons and is reduced to NADH ○ flavin adenine dinucleotide (FAD)- accepts two hydrogens as well as electron pairs and is reduced to FADH2 ○ NADH and FADH2 provide high energy transfer potential ○ B vitam based ■ cytochromes- a series of membrane bound hemoproteins (iron-based) electron carriers dispersed on the inner membranes of the mitochondria which help move the electrons carried by NADH and FAHD2 ■ figure 6.7A: the ETC removes electrons from hydrogens for ultimate delivery to oxygen ○ in the redox reaction one FAD in ETC makes two ATP ○ one NAD makes three ATP cellular oxidation: oxidative phosphorylation and ETC coupling (figure 6.8) ■ energy releasing reactions of the electron transport create a proton (H+) gradient across the inner mitochondrial membrane ■ this leads to a net flow of protons to provide the coupling mechanism to drive ATP synthesis ○ stored energy of the proton gradient plus the inner mitochondrial membrane potential provide the electrochemical basis for coupling electron transport to oxidative phosphorylation to form ATP 4 oxidative phosphorylation ■ synthesizes ATP by transferring electrons from NADH to FADH2 to oxygen ■ governed by: ○ proton gradient of the stored energy ○ inner mitochondrial membrane potential ■ 90% of ATP resynthesis occurs in the ETC by oxidative reactions coupled with phosphorylation ■ P:O ratio (phosphate bonds: oxygen atoms) governs the number of ATP able to be produced ○ P:O ratio for NAD is three (3 ATP can be produced) ○ P:O ratio for FAD is two (2 ATP can be produced) ○ low ratios of ATP will turn on the system, high ratios will slow/turn off system understanding oxygens role summary: what is needed for continuous ATP resynthesis? 1. reducing agents in the form of NADH or FADH2 2. presence of an oxidizing agent in the tissue oxygen 3. sufficient concentration of enzymes and mitochondria ■ aerobic metabolism- is the energy generating reactions in which oxygen serves as the final electron acceptor, in addition to serving as a regulator for the capacity to produce ATP, therefore without oxygen you can not sustain exercise ■ oxygen is the final electron acceptor- combines with H+ and forms water ■ higher concentration of H+ ions lowers pH; lower concentration of H+ raises pH V. energy release from food- macronutrient use for energy metabolism ■ macronutrients/ substrates (fuel) ○ proteins → amino acids ○ carbohydrates → simple sugars ○ fats → glycerol + fatty acids ■ process of energy release ○ stage 1: macronutrient digestion, absorption, and assimilation into useful form ○ stage 2: degradation of subunits into acetyl- CoA ○ stage 3: oxidation of acetyl-CoA to CO2 and H2O ■ macronutrient fuel sources that supply substrates for regenerating ATP (figure 6.10) ○ the liver produces a rich source of AA and glucose ○ adipocytes generate large quantities of energy rich fatty acid molecules ○ the bloodstream delivers these components to the muscle cell ○ most of the cells energy production takes place within the mitochondria ○ mitochondrial proteins carry out their roles in oxidative phosphorylation ○ the intramuscular energy sources consist of the high energy phosphates ATP and PCr, triglycerides, glycogen and amino acids VI. energy from carbohydrates ■ CHO supplies energy for cellular work in the form of either glucose or glycogen ○ glycogen is the storage form of glucose ■ generates ATP anaerobically (no oxygen, occurs in cytosol) ■ light to moderate exercise only uses ⅓ CHO ■ process of regeneration is called glycolysis (predominant pathway for breakdown of CHO) 5 ■ carbs are the main macronutrient in exercise; carb metabolism influences metabolism of other substrates especially during exercise VII. glycolysis ■ occurs in the cytoplasm of the cell ■ crucial for exercise lasting up to 90 seconds for ATP resynthesis ■ phosphofructokinase (PFK) is critical to regulating glycolysis ■ two three-carbon molecules are then moved through the remainder of the glycolytic reactions to eventually become pyruvate (figure 6.11)- a series of 10 enzymatically controlled chemical reactions that creates two molecules of pyruvate from the anaerobic breakdown of glucose. lactate forms when NADH oxidation does not keep pace with its formation in glycolysis. three important enzymes- rate limiting because break down glucose 1. hexokinase: converts glucose to glucose 6-phosphate 2. phosphorylase: converts glycogen to glucose 6-phosphate 3. phosphofructo-kinase (PFK): converts fructose 6-phosphate to fructose 1, 6-diphosphate; rate limiting step, allows glycolysis to proceed and break down into three molecules ■ glycogenolysis- breakdown of glycogen ■ gluconeogenesis- creation of new glucose from a non CHO source; from protein AA breakdown, lactate, glycerol, and pyruvate ■ glycogen phosphorylase- to maintain blood glucose this enzyme breaks down glycogen in the liver only; less glycogen is stored in the liver than muscle so it wont last long ■ more efficient to use glycogen already in the muscles (1:3 ATP) ■ make less energy with blood glucose, required energy to be broken down and to enter the cell (1:2 ATP) regulation of glycolysis is dependent upon 1. the concentration of key glycolytic enzymes 2. levels of the substrate fructose 1, 6 diphosphate 3. oxygen because when its levels are high it will inhibit glycolysis 4. glucose entry into the cell- via GLUT-4 (glucose transporter 4) ○ located on the cell membrane ○ stimulated by physical activity and insulin ○ allows glucose entry into the sarcoplasm (muscle cytoplasm) for ATP resynthesis VI. lactate formation during glycolysis ■ lactate formation is greatest during high intensity exercise because? ○ when oxygen is low the ETC cannot process all NADH hydrogen ions ○ unprocessed hydrogen ions can combine with pyruvate to form lactate via lactate dehydrogenase ○ H+ ion accumulation at the end of glycolysis lowers pH because there is no oxygen to accept them (acidic); pH changes the enzymes and causes them to stop working, critical enzymes no longer make ATP anaerobically; lactate forms ■ muscle soreness ○ high intensity exercise causes tears in muscles ○ chest pain occurs because muscles are working with a lack of oxygen and ATP 6 as well as an improper pH ■ what happens to lactate after it is formed? ○ lactate shuttle- (70-80%) lactate is moved to different tissues that use it as energy (brain) ○ cori cycle- (20-30%) in the lover glucose is synthesized from the lactate released by active muscles and helps to maintain carbohydrate reserves VII. aerobic resynthesis (figure 6.14) ■ phase 1: in the mitochondria the citric acid cycle generates hydrogen atoms during acetyl-CoA breakdown ■ phase 2: significant quantities of ATP regenerate when these hydrogens oxidize via the aerobic process of electron transport-oxidative phosphorylation citric acid cycle (krebs) ■ anaerobic glycolysis is insufficient in making ATP ■ the pyruvate route will allow more ATP resynthesis from glucose ■ pyruvate dehydrogenase with the addition of coenzyme A results in acetyl-CoA ■ acetyl-CoA can enter the citric acid cycle which can generate 3 NAD and 1 FAD ■ acetyl-CoA turns on the krebs cycle ■ beta oxidation breaks down fats added to acetyl-CoA ■ one cycle makes 1 ATP but makes a lot of NAD (3) AND FAD (1) ○ 3 ATP : 1 NAD ○ 2 ATP: 1 FAD VIII. energy release from fat ■ three sources 1. triglycerides within the muscle 2. circulating triglycerides 3. circulating free fatty acids ■ figure 6.17: fat metabolism and fat use ○ hormone sensitive lipase (HSL) stimulates triglyceride breakdown into its glycerol and fatty acid components ○ the blood transports free fatty acids (FFAs) released from the adipocytes and bound to plasma albumin ○ triglycerides stored within the muscle fiber also degrade to glycerol and fatty acids to provide energy ■ two major enzymes 1. hormone sensitive lipase 2. lipoprotein lipase- breaks down triglycerides into glycerol and fatty acid components ■ lipolysis- lipid/fat breakdown ■ when insulin concentration is high it blocks enzyme action and promotes fat storage instead of metabolic breakdown to release triglycerides and make ATP beta oxidation (figure 6.18)- breakdown of a triglyceride molecule into glycerol and fatty acid components ■ glycerol enters the energy pathways during glycolysis ■ fatty acids prepare to enter the citric acid cycle through 𝞫- oxidation 7 ■ the ETC accepts hydrogens released during glycolysis, 𝞫-oxidation, and citric acid cycle metabolism ■ glycerol provides the carbon skeleton from which you can make glucose ■ one molecule of glucose is 6C catabolism of glycerol and FAs ■ fate of glycerol ○ converted to pyruvate ○ gluconeogenesis due to carbon skeleton ■ beta-oxidation ○ fatty acids transform to acetyl-CoA in the mitochondria ○ cleaves two carbons ○ this can enter the krebs cycle ○ must have presence of oxygen slower rate of energy release from fat ■ rate is slower for fats that for CHO ■ CHO oxidation helps maintain fat oxidation ○ glycolytic production of pyruvate maintains substrate to allow for beta-oxidation to continue ■ CHO depletion inhibits exercise performance ■ less “bang for buck” when using fats compared to CHO (low P:O ratio, fats make more ATP but it is easier to make ATP from CHO) IX. protein as fuel ■ during prolonged exercise cortisol is high and can stimulate AA use ■ also occurs during starvation mode ■ only 5% of the time will protein ever be used as fuel deamination versus transmission ■ nitrogen removal occurring in the liver and muscle so entry into krebs cycle is possible ■ transferring an amino acid group to create glutamine ○ this frees up the carbon skeleton to enter the krebs cycle glucogenic ■ may be used to form intermediates for gluconeogenesis ■ may be used to form: ○ pyruvate ○ oxaloacetate ○ malate ketogenic ■ used to form: ○ acetyl-CoA ○ acetoacetate ■ can’t be used to synthesize glucose, but can form TG or used in Krebs cycle CHAPTER 7: ENERGY FOR PHYSICALACTIVITY 8 I. supply and demand: how do we supply energy when our body demands it? ■ the human body possesses three different energy systems 1. immediate energy system 2. short term energy system 3. long term energy system II. immediate energy system: ATP-PCr system ■ anaerobic system ■ best suited for very short duration exercises (ex 100 m dash, 25m swim, weightlifting) ■ energy is provided by intramuscular high energy phosphates ○ ATP and phosphocreatine (PCr) ■ this system only provides enough energy for 2-3 seconds of work (ATP alone) and 6-10 seconds if both ATP and PCr are used ○ there is 6x the amount of PCr as there is ATP ■ virtually every sport uses this system ○ examples- fast break in basketball, vault in gymnastics, home run*, football play, golf swing* ■ fuels powerful and high force output activities II. short term energy: the lactic acid system ■ anaerobic system ■ supplies energy for short periods of time, up to 2 or 3 minutes maximum ■ resynthesis of ATP to sustain exercise for this 2-3 minutes comes from anaerobic glycolysis ■ limited glycogen stores ■ lactate production is rapid and large ■ high intensity exercise therefore cannot be sustained ■ ex intervals III. lactate accumulation during exercise (figure 7.2) ■ lactate threshold- point at which one begins to produce lactate at a rate higher than the body can remove it, results in accumulation of lactic acid in muscles ■ accumulation of lactic acid lowers pH and interferes with ATP production ■ training may move lactate more efficiently and raise threshold ○ represented as percentages of maximum oxygen consumption (VO2max) ■ VO2 max- max amount of oxygen a person can circulate and use during exercise ○ 55-60%: light exercise, aerobic (ex brisk walk) ○ 60-80%: moderate exercise, aerobic (ex jog) ○ >80%: high intensity exercise, anaerobic ■ factors related to lactate threshold ○ low tissue oxygen ○ reliance on glycolysis ○ activation of fast twitch muscle fibers ○ reduced lactate removal IV. lactate producing capacity *increases with anaerobic training ■ sprint/ power athletes can achieve 20-30% higher blood lactate levels compared to untrained individuals ■ mechanisms 9 ○ improved motivation ○ increase in intramuscular glycogen stores used to make ATP ○ increased glycolytic enzymes to break down muscle glycogen ○ increased ability to recruit type II fibers (fast twitch) V. long term energy: the aerobic system ■ aerobic meaning that oxygen must be present for metabolism to proce
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