Bioenergetics
Components of a typical cell
Cellular Structures Cell membrane –semi-permeable –encloses internal components of cell –regulates flux of metabolites and nutrients Nucleus –contains genetic material (DNA) –regulates protein production Cytoplasm –fluid portion of the cell which contains organelles, enzymes etc.
Mitochondria “power station” for the cell All “aerobic” respiration takes place within the mitochondria “anaerobic” glycolysis occurs in the cytoplasm
ATP Generation The purpose of glycolysis and aerobic respiration is to produce ATP All of the systems we study in Exercise Physiology relate to ATP production
ATP as universal energy donor that drives energy needs of cells
Breakdown of glucose to CO2 + H2O via cellular oxidation releases energy (Big Picture)
The First Step
Glycolysis: part 1
glycolysis: part 2
Substrate Level Phosphorylation
Production of Lactate
Fate of Glucose (Glycolysis) glucose is broken down to pyruvate pyruvate can then enter the Krebs Cycle (aerobic) or pyruvate can form lactate (lactic acid) –anaerobic, feel the burn
The Krebs Cycle
pyruvate enters the Krebs from glycolysis fatty acids also enter the Krebs cycle together pyruvate and fatty acids drive the Krebs to produce a lot of ATP
Krebs in Detail
Electrons enter respiratory chain from glycolysis and Krebs
Electron transport
Electron transport 1
Electron transport 2
Chemiosmotic theory of aerobic ATP production
Movement of protons across membrane and electrons along ETC
A high proton gradient enables ATP to be generated
Movement of protons through ATPase generates ATP
ATP tally from breakdown of 1 glucose molecule
Putting it together Glycolysis occurs in the cytosol Glycolysis feeds the Krebs cycle Krebs occurs in the mitochondria
Energy Transformation Exergonic vs. endergonic rxns –exergonic produces energy –endergonic requires energy input Coupled rxns –by coupling exergonic rxn, energy can run endergonic rxn
Coupling exergonic and endergonic reactions
The energy systems Anaerobic vs aerobic systems Anaerobic (non-oxidative) –ATP-PC (Phosphocreatine or phosphagen) PC + ADP => ATP + C –Glycolysis breakdown of glucose to form 2 pyruvate or lactate Aerobic –Krebs Cycle (TCA or oxidative phosphorylation)
The Phosphocreatine (PC) System
Phosphogen Reactions PCr + ADP + H + ATP + Cr Creatine Kinase ADP + ADP ATP + AMP Adenylate Kinase Determines Energy State of Cell –Hi [ATP] = lo [ADP],[ AMP], [Pi] –Low [ATP]= Hi [ADP, [AMP], [Pi]
Phosphagen System as Bioenergetic Regulator Phosphagen system produces ATP at high rate to maintain energy state Results in metabolites (AMP, Pi, ADP) which stimulate metabolism Elevations in AMP and decrease in [ATP]/[ADP] ratio stimulate metabolism
Enzymes –necessary for almost all biological processes –lower Energy of Activation –work in a “lock and key” type of mechanism –very sensitive to temperature and pH remember body temp regulated in narrow range
Enzymes catalyze reactions by lowering energy of activation
Lock and Key model of enzyme action
Take Home Message enzymes catalyze reactions by bringing the reactants into close proximity this means less energy is required to activate the reaction
Fuels for Exercise Carbohydrates Fats Proteins
Carbohydrates-”A quick fix” Simple sugars –glucose, fructose, sucrose, maltose Complex carbs (polysaccharides) –starch, cellulose, glycogen –storage form of glucose is glycogen Glycogenolysis –process by which glycogen is broken down into glucose for use by the body
Fats-”Energy for the long haul” More efficient storage form of energy than CHO (9 kcal/gram vs 4 kcal/gram) Kinds of fats –fatty acids, triglycerides, phospholipids, steroids Fatty acids and triglycerides are used for energy Phospholipids and steroids are used for structural and regulatory purposes
Proteins-”The building blocks” Composed of sub-units called amino acids Primarily used for structural purposes (muscle tissue, tendons, ligaments) Also serve as enzymes Can be used for energy (4 kcal/gram), but not readily
Metabolism of Proteins, Carbohydrates and Fats