Bioenergetics Components of a typical cell Cellular Structures

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

ADP and ATP structures

ATP as universal energy donor that drives energy needs of cells

Breakdown of glucose to CO 2 + H 2 O via cellular oxidation releases energy (Big Picture)

The First Step

Glycolysis: part 1

glycolysis: part 2

Glycolysis Yields Potential and Direct Energy • The glycolytic process yields NADH from NAD+ – NADH transported into mitochondria to produce ATP in electron transport • Glycolysis also yields ATP directly by “substrate level phosphorylation”

Substrate Level Phosphorylation

Production of Lactate

Why Produce 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

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 • Animation of Electron transport in Mitochondria. htm

A high proton gradient enables ATP to be generated

Movement of protons through ATPase generates ATP • Animation of ATP synthesis in Mitochondria. htm

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

Pathways of Catabolism

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

Phosphagen System as Bioenergetic Regulator • Phosphagen system produces ATP at high rate to maintain energy state

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 p. H • 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