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
Metabolic
Process
High energy
products
ATP from
oxidative
phosphorylation
ATP subtotal
Glycolysis
2ATP
2 NADH
-6
2 (if anaerobic)
8 (if aerobic)
Pyruvic acid to
acetyl-CoA
2 NADH
6
14
Krebs Cycle
2 GTP
6 NADH
2 FADH
-18
4
Grand Total
16
34
38
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 + 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