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

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

MetabolicProcess

High energyproducts

ATP fromoxidative

phosphorylation

ATP subtotal

Glycolysis 2ATP2 NADH

--6

2 (if anaerobic)8 (if aerobic)

Pyruvic acid toacetyl-CoA

2 NADH 6 14

Krebs Cycle 2 GTP6 NADH2 FADH

--184

163438

Grand Total 38 ATP

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 + AMPAdenylate 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