Download Energy Transfer

ENERGY TRANSFER
ADENOSINE TRIPHOSPHATE
THE ENERGY CURRENCY
• The energy in food does not transfer directly to the
cells for biologic work. Rather, energy from
macronutrient oxidation is harvested and funneled
through ATP.
• The energy donor - energy receiver role of ATP
represents the body’s two main energy transforming
activities.
1.
2.
Extract potential energy from food and conserve it within
the bonds of ATP.
Extract and transfer the chemical energy in ATP to power
biologic work.
ATP STRUCTURE
A LIMITED CURRENCY
• Cells store only a small quantity of ATP and must
therefore continually resynthesize it at its rate of use.
• ATP is a relatively heavy molecule and the average
sedentary person resynthesizes enough ATP in one
day to equal ~ 75% their body weight.
• The body stores ~ 80-100 g of ATP at any time.
• Costs about 80 kg of ATP to run a marathon in 2.5
hrs.
HARNESSING ATP’S POTENTIAL
ENERGY
• ATP hydrolysis:
 ATP + H2O
ATPase
ADP + Pi = 7.3 kcal/mol
• ATP Resynthesis:
 PCr + ADP
 2 ADP
creatine kinase
adenylate kinase
Cr ATP
ATP + AMP
ATP RESYNTHESIS
• Cells are very sensitive to a decrease in the ATP:ADP
ratio.
• Signal the enzymes involved in ATP resynthesis to kick in.
• Phosphocreatine (PCr) – The energy reservoir.
• Anaerobic resynthesis of ATP from ADP
• Creatine can later be phosphorylated back to PCr
• Cells store ~ 4-6 times more PCr than ATP
IMPORTANT BY-PRODUCTS
• ATP hydrolysis and resynthesis generate as byproducts:
• Pi
• AMP
• ADP
• These by-products stimulate:
• Glycogenolysis
• Glycolysis
• Respiratory pathways of mitochondria
CELLULAR OXIDATION
• There is not enough stored ATP to fuel all of your
body’s processes.
• Your body must oxidize stored macronutrients so
that mitochondria can synthesize more ATP.
• ATP is synthesized by coupling of electron transport
and oxidative phosphorylation in the electron
transport chain.
ENERGY RELEASE FROM FOOD
• Macronutrient catabolism serves one crucial
purpose – to phosphorylate ADP to re-form ATP.
• 3 broad stages:
1.
2.
3.
Digestion, absorption, and assimilation of relatively large
food macromolecules into small subunits.
Within the cytosol, AA’s, glucose, fatty acids, and
glycerol units are degraded into acetyl-CoA
Within the mitochondria, acetyl-CoA degrades to CO2
and H2O with considerable ATP resynthesis.
CITRIC ACID CYCLE
• AKA Krebs cycle, tricarboxylic acid cycle.
• A complex sequence of metabolic events that
degrades acetyl-CoA to carbon dioxide and
hydrogen atoms.
• The hydrogen atoms are then oxidized during the
electron transport chain.
CITRIC ACID CYCLE
ELECTRON TRANSPORT CHAIN
• Iron-rich carrier
molecules
transport electrons
via redox
reactions.
• Oxygen is the final
electron acceptor.
• This process is
responsible for >
90% of ATP
synthesis.
NADH + H+ + 3 ADP + 3 Pi + ½ O2 = NAD+ + H20 + 3 ATP
ENERGY TRANSFER FROM FOOD
• Liver releases glucose and deaminated amino
acids into the bloodstream.
• Adipose tissue releases fatty acids into the
bloodstream.
• Within the cytosol, glucose, AA’s and fatty acids get
turned into acetyl-CoA.
• Acetyl-CoA enters the citric acid cycle and
produces NADH and H+ ions.
• Hydrogen ions enter the ETC and resynthesize ADP
into ATP.