BIOENERGETICS

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BIOENERGETICS
Tehran University of Medical Sciences (TUMS)
How we make ATP
Power plant of cells
Dr. Parvin Pasalar
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Objectives

• To understand the differences between
  Thermodynamics and Bioenergetics
• To know the two Thermodynamics laws (energy
  exchange)
• To understand how the energy of food stuffs are
  released
• To understand how the energy of food stuffs are
  converted into the ATP Substrate level
  Oxidative ATP synthesis
• To predict and calculate the degree of
  possibility of a given reaction
• To describe Chemiosmotic theory of ATP synthesis
• To describe the function of ETC complexes (I, II,
  III IV)
• To write 4 sentences about the mechanism of
  Fo-FI function
• To know coupling reaction and the roles of
  uncouplers
• To know and name 4 types of oxidative
  phosphorylation poisons

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Biomedical importance of BIOENERGETICS
Oxidation/ Reduction

• In human , an amount of ATP approximately equal
  to the body weight is formed and broken down
  every 24 hrs.
• Brown fat
• Thyroid hormones and Uncouplers
• Oxygen toxicity and Free radicals
• Many drugs, pollutants and chemical carcinogens(
  Xenobioticts) are metabolized by cytochrome P450
  system
• Some poisons are inhibitors of oxidative
  phosphorylation
• Phosphagens such as creatine-P

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Extraction and packaging of the energy from food
stuffs Why and how we make ATP?

• O2 ? CO2 H2O

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Which Energy Currency
Gold coin OR
OR glucose OR ATP
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Energy

• Definition Capacity to perform work.
• Types
• 1- Kinetic Energy in the process of
• doing work or Energy of motion.
• Example Heat, Light
• 2- Potential Energy content of
• a matter, because of its arrangement or
• position
• Example Chemical energy
• of a gas or food,
• Water behind a dam

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Thermodynamics/ Bioenergetics

• The study of energy transformations that occur in
  a collection of matter is called Thermodynamics.
• The Thermodynamics in living organisms is called
  Bioenergetics.
• In other words, Bioenergetics is the study of
  energy in living systems
• Living systems Environments Organisms

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First second Laws of Thermodynamics

• First Law Energy cannot be created or destroyed,
  but only converted to other forms.
• This means that the amount of energy in the
  universe is constant

• Second Law All energy transformations are
  inefficient because every reaction results in an
  increase in entropy and the loss of usable energy
  (free energy) as heat.

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SA
SB
HA
HB
GA
GB
A
B

• IF
• H Enthalpy the total heat of a system
• G Free energy the amount of usable energy in a
  system that can be used to perform a work.
• S Entropy the amount of disorder in a system.
  In most but not all cases it is heat.
• Then somehow
• ?G GB-GA
• ?H HB-HA
• ?S SB-SA

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Gibbs equation

• ?G ?H - T?S
• Gibbs equation in living organisms
• ?G ?E - T?S
• The relationship between the value of ?G and the
  spontaneity of a reaction
• Endergonic Reactions have ?G
• Exergonic Reactions have ?G -
• At equilibrium state have ?G 0

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?G OR ?Go OR ?Go, Which one is more important?

• ?G Free energy difference of a system in any
  condition.
• ?Go Free energy difference of a system in
  standard condition ( 25Co and one atmosphere
  pressure.
• ?Go Free energy difference of a system in
  standard condition at pH 7.
• NEVER FORGET THAT
• ?G determines the feasibility of a reaction not
  ?Go or ?Go

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Cellular Metabolism

• The sum total of the chemical activities of all
  cells is called Cellular Metabolism.
• Anabolic Pathways (Endergonic reactions)
• Those that consume energy to build complicated
  molecules from simpler compounds such as
  Protein, Glycogen lipid synthesis.
• Catabolic Pathways (Exergonic reactions)
• Those that release energy by breaking down
  complex molecules into simpler compounds such as
  glycolysis.

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Most energy from fuel (food) obtained through
oxidative processes

• oxidation
• Gain of Oxygen
• Loss of Hydrogen
• Loss of electrons
• Reduction
• Gain of Hydrogen
• Gain of electron
• Loss of Oxygen

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E Reduction Potential (Redox)

• Redox potential measures of the tendency of
  oxidant to gain electrons, to become reduced, it
  is a potential energy.
• Electrons move from compounds with lower
  reduction potential (more negative ) to compounds
  with higher reduction potential ( more positive).
• Reductant ? oxidant e-
• Oxidant e- ? reductant
• DH D
• AH A

Oxidation and reduction must occur simultaneously
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?E Reduction Potential Difference

• ?E EA - ED
• ?E Redox difference of a system in any
  condition.
• ?Eo Redox difference of a system in standard
  condition ( 25Co and one atmosphere pressure).
• ?Eo Redox difference of a system in standard
  condition at pH 7
• NEVER FORGET THAT
• ?E determines the feasibility of a reaction not
  ?Eo or ?Eo.
• and
• The more positive the reduction potential
  difference is, the easier the redox reaction

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Can we predict the amount of energy that can be
released from an oxidation-reduction reaction?

• ?Gº? -nF ?Eº?
• Where n the number of transferred electron
  (1,2,3)
• F the Faraday constant that is 96.5 kJ/volt
• E measured in volts
• G measured in KCal or KJ
• In other words energy (work) can be derived from
  the transfer of electrons and an electron
  transfer system (ETS) Or
• Oxidation of foods can be used to synthesize ATP.

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Standard Reduction Potential (Eº) of some
biologically important compounds
Oxidant Reductant n Eº, v NAD
NADH 2
-0.32 acetaldehyde ethanol
2 -0.20 pyruvate lactate
2 -0.19 oxaloacetate
malate 2 -0.17 1/2 O22H
H2O 2 0.82

• Oxidants can oxidize every compound with less
  positive voltage (above it in Table)
• Reductants can reduce every compound with a
  less negative voltage (below it in Table).

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The enzymes and coenzymes that are responsible
for Oxidation and reduction in living organisms
1- Dehydrogenases (loss of Hydrogen) 2- Oxidases
(electron transfer to molecular oxygen) 3-
Oxygenases(gain of Oxygen ) 4- Cytochromes
(electron transfer ) 5- Fe S centers (electron
transfer ) 6- CoQ ubiquinone (Hydrogen
transfer )
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Electron Transport Chain (ETC)

• Electrons move from a carrier with low redox
  potential toward carriers with higher redox.
• Electrons can move through a chain of donors and
  acceptors.
• In the electron transport chain, electrons flow
  down a gradient.

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Different ways to make ATP
ADP P ATP

• Phosphorylation is
• Mechanisms of phosphorylation
• 1- Photophosphorylation (chlorophyll /
  light-absorbing pigments)
• 6CO2 6H2O C6H12O6 6O2 ATP
• 2- Substrate-level phosphorylation (in cytosol)
• D P ADP D ATP
• 3-Oxidative phosphorylation (across inner
  mitochondrial membrane)

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Up to now you have combined your physico-chemical
knowledge to understand the basis of ATP synthesis

• So lets run into the second part !
• Fasten your belt!

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Oxidative phosphorylation
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oxidative phosphorylation
substrate level phosphorylation
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• Most energy from food obtained through stepwise
  anaerobic oxidative processes to yield NADH or
  FADH2 (reducing equivalent).
• Then
• NADH or FADH2 aerobically oxidized ( in ETC ).
• This energy is used to synthesize
• ATP (phosphorylation).

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• But how the energy of ETC
• (oxidation) is used to
• synthesize ATP (phosphorylation)
• The coupling of oxidation phosphorylation.

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Chemiosmotic Theory
Peter Mitchell
A proton gradient is generated with energy from
electron transport by the vectorial transport of
protons (proton pumping) by Complexes I, III, IV
from the matrix to intermembrane space of the
mitochondrion.
 
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Mitochondrion or the power house of cell

• Outer membrane
• permeable to small molecules
• Inner membrane
• Impermeable to small molecules.
• Cristae increase area
• IT contains
• Electron transport system (ETC) and ATP synthase
  complex embedded
• Integrity required for coupling ETC to ATP
  synthesis
• Matrix contains Krebs cycle enzymes,
  ß-oxidation enzymes also ATP, ADP, NAD, NADH2,
  Mg2, etc

The size (1-2µ) The number 1-1000s in each
cell
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Chemiosmotic Theory
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ETC electron transport chain
Ubiquinone and cytochrome c are mobile carriers.
They ferry electrons from one complex to the next
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• NADH dehydrogenase (NADH Q reductase)
• Huge protein
• 25 pp
• FMN, Fe-S
• Electron ? UQ

• Iron-Sulfur Centers
• Transfer of electrons in variety of proteins such
  as NADH and succinate dehydrogenase

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Complex II Succinate Q Recuctase (Succinate
dehydrogenase) Is the only membrane bound enzyme
in the TCA cylce and contains ? FAD, Fe-S II ?
electrons ? UQ
Coenzyme Q Ubiquinone ?a lipid in inner
membrane ? carries electrons ? polyisoprene tail
? moves freely within membrane
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Complex III Cyt C reductase
Cytochromes - proteins in ETC ?electron
transferring proteins that contain a heme or
heme-like prosthetic group! ?Heme based on
porphyrins with iron in center, usually as
Fe(II), and is tightly bound at sides, sometimes
covalently ?Contrast heme in cytochromes
hemoglobin
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Complex IV (Cytochrome C oxidase)
Cyto oxidase Contains a, a3, and CuA, CuB The
detail of this electron transfer in Complex IV is
not known It also functions as a proton pump
Cu(II) ? Cu(I)
e- from cyt c to a
Heme A and Cu act together to transfer electrons
to oxygen
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Membrane potential 140 mV pH gradient 60
mV Total proton motive force 200 mV
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ATP Synthase (F0 - F1 complex)

• F0-F1

FI
F0
F0 Oligomycin sensitive Fragment
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ATP synthesis at F1 results from repetitive
comformational changes as ? rotates
? Rotates 1/3
turn- energy for ATP release
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Uncoupling Protein
The coupling of oxidation (to make Proton
gradient) and phosphorylation ( ADPP) is needed
for ATP synthesis. Thermogenin is a proton
carrier located at inner mitochondrial membrane.

This uncoupling protein produced in brown
adipose tissue of newborn mammals, and
hibernating mammals for cold adaptation.
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Uncoupling Protein

• The uncoupling protein blocks development of a H
  electrochemical gradient, thereby stimulating
  respiration. DG of respiration is dissipated as
  heat.
• This "non-shivering thermogenesis" is costly in
  terms of respiratory energy unavailable for ATP
  synthesis, but provides valuable warming of the
  organism.
• The gene is activated by thyroid hormone
• Different level of the hormone in different
  season and areas

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Poisons of Oxidative Phosphorylation

• 1- OXIDATION (ETC) inhibitors.
• 2- PHOSPHORYLATION inhbitors.
• 3- Uncouplers.
• 4- ATP/ADP transporter (tanslocators) inhibitors.

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ETC inhibitors
HCN, CO, H2S
Rotenone, amytal
Antimycin A Dimercaprol
Malonate

• Complex 1 Rotenone and Barbiturates such as
  amobarbital and amytal inhibit NDAH- DH. They are
  fatal at sufficient dosage.
• 2- Complex 2 Malonate is competitive inhibitor
  of Suc- DH
• 2- Complex 3 Antimycin A and Dimercaprol inhibit
  cyt C reductase.
• 3- Complex 4 Classic poisons HCN, CO, H2S arrest
  respiration by inhibiting cyt oxidase.
• Note all the components of the respiratory chain
  before the block become reduced, all the
  components
• downstream become oxidized.

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ATP Synthase and ATP/ADP translocator inhibitors

• The antibiotic Oligomycin completely blocks F0 (
  Oligomycin sensitive Fragment) the flow of H
  through the F0 directly inhibiting ox-phos.
• Atractyloside ATP/ADP translocator.

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Uncoupling reagents (uncouplers)

• Uncouplers are lipid-soluble weak acids. E.g., H
  can dissociate from the OH group of the uncoupler
  dinitrophenol.
• Uncouplers dissolve in the membrane and function
  as carriers for H.

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How is the energy yield in living cells

• It is very efficient process
• Recall living cells efficiency is 42, compared
  to about 3 efficiency when burning oil or
  gasoline.
• BUT HOW?
• Separating carbohydrates, lipids, etc. from
  oxygen to optimize recover of energy. In other
  words first they are anaerobically oxidized to
  yield NADH and FADH2,
• And then
• Stepwise aerobic oxidation of NADH and FADH2
  through ETC
• And then
• ATP synthesis by electrochemical energy.

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Summary

1. Oxidative Phosphorylation is carried out by
   respiratory assemblies that are located in the
   inner membrane...
2. Respiratory assemblies contain numerous electron
   carriers, Such as cytochromes.
3. When electrons are transferred, H are pumped
   out.
4. ATP is formed when H flow back to the
   mitochondria.
5. Oxidation and phosphorylation are COUPLED
6. The oxidation of NADH ? 3 ATP, and FADH2 ? 2 ATP

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Have a nice ATP consumption !