Parvin Pasalar1

• BIOENERGETICS BIOENERGETICS

How we make ATPHow we make ATP

Power plant of cellsPower plant of cells

Dr. Parvin Pasalar

Tehran University of Medical Sciences (TUMS)

Parvin Pasalar2

• 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

Objectives:

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Biomedical importance of BIOENERGETICS & Oxidation/ BIOENERGETICS & Oxidation/

ReductionReduction• 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+ ATP

energy

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Which Energy Currency

OR glucose OR ATP

Gold coin OR

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Energy• Definition:Definition: CapacityCapacity to performperform workwork.. • Types:Types: 1- Kinetic: 1- Kinetic: Energy in the process of Energy in the process of

doing work or Energy of motion.doing work or Energy of motion.

• Example: Example: Heat, LightHeat, Light

2- Potential: 2- Potential: Energy content of Energy content of

a matter, because of it’s arrangement ora matter, because of it’s arrangement or position position

Example: Example: Chemical energyChemical energy

of a gas or food,of a gas or food,Water behind a dam Water behind a dam

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Thermodynamics/ Thermodynamics/ BioenergeticsBioenergetics • The studystudy of energyenergy transformationstransformations that

occur in a collection of matter collection of matter is called is called Thermodynamics.Thermodynamics.

• The Thermodynamics in living organisms is The Thermodynamics in living organisms is called called BioenergeticsBioenergetics..

• In other words, BioenergeticsBioenergetics is the study of energyenergy in living systemsliving systems

• Living systemsLiving systems = = Environments + Organisms Organisms

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First & second Laws of Thermodynamics First & second Laws of Thermodynamics

• First Law: Energy cannot be createdcreated or or destroyeddestroyed, but only convertedconverted to other forms.

This means that the amount of energy in the universeuniverse is is constantconstant

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

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• IF:IF:• H = Enthalpy= H = Enthalpy= the total heat of a system• G = Free energy= G = Free energy= the amount of usable energy in a

system that can be used to perform a work.• S =Entropy = 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

HASA

GB

HB

SB

GA

A B

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Gibbs equationGibbs equation• ∆G = ∆H - T∆S• Gibbs equation in living organismsGibbs equation in living organisms

• ∆G = ∆E - T∆S• The relationship between the value of ∆G and the The relationship between the value of ∆G and the

spontaneity of a reaction:spontaneity of a reaction:

• Endergonic Reactions have: Endergonic Reactions have: ∆∆GG ++• Exergonic Reactions have Exergonic Reactions have : :∆∆G -G -

• At equilibrium state have: At equilibrium state have: ∆∆GG = = 00

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∆G OR ∆Go OR ∆Go’, Which one is Which one is

more important?more important? • ∆G = Free energy difference of a system in = Free energy difference of a system in

any conditionany condition..• ∆Go = Free energy difference of a system in = Free energy difference of a system in

standard conditionstandard condition ( ( 25C25Co and and one one atmosphereatmosphere pressure. pressure.

• ∆Go’ = Free energy difference of a system in = Free energy difference of a system in standard condition at standard condition at pH = 7pH = 7..

• NEVER FORGET THAT :NEVER FORGET THAT :• ∆G determines the feasibility of a reaction

not ∆Go or ∆Go’

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Cellular MetabolismCellular Metabolism• The sum totalsum total of the chemical activitieschemical activities of all

cells is called Cellular Metabolismcells is called Cellular Metabolism.

• Anabolic PathwaysAnabolic Pathways (Endergonic reactions): (Endergonic reactions):

Those that consume energyconsume energy to buildbuild complicated molecules from simpler compounds such as: Protein, Glycogen & lipid synthesis.

• Catabolic Pathways Catabolic Pathways (Exergonic reactions):(Exergonic reactions):

Those that release energyrelease energy by breaking downbreaking down complex molecules into simpler compounds such as glycolysis.

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• oxidation :

* Gain of Oxygen

* Loss of Hydrogen

* Loss of electrons• Reduction:

* Gain of Hydrogen

* Gain of electron

* Loss of Oxygen

Most energy from fuel (food) obtained through oxidative processes:

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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

D:H D

AH A

Oxidation and reductionmust occur simultaneously

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E =Reduction Potential Difference E= EA - ED • ∆E = Redox difference of a system in = Redox difference of a system in any conditionany condition..

• ∆Eo = Redox difference of a system in = Redox difference of a system in standard conditionstandard condition ( ( 25C25Co and and one atmosphereone atmosphere pressure). pressure).

• ∆Eo’ = Redox difference of a system in standard condition = Redox difference of a system in standard condition at at pH = 7pH = 7

• NEVER FORGET THAT :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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Oxidant Reductant n Eº, vNAD+ NADH 2 -0.32acetaldehyde ethanol 2 -0.20pyruvate lactate 2 -0.19oxaloacetate malate 2 -0.171/2 O2+2H+ H2O 2 +0.82

Standard Reduction Potential (Eº) of some biologically important compounds

• 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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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 )

The enzymes and coenzymes that are responsible for Oxidation and reduction in living organisms

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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

• 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 let’s run into the second part !

• Fasten your belt!

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substrate level phosphorylation

oxidative 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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Peter Mitchell

Chemiosmotic Theory

A proton gradient is generated with energy from electron transport by the vectorial transport of protons (protonpumping) by Complexes I, III, IV from the matrix tointermembrane space of the mitochondrion.

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• 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, β-oxidation

enzymes; also ATP, ADP, NAD, NADH2, Mg2+, etc

Mitochondrion or the power house of cell

The size : (1-2μ) The number: 1-1000s in each cell

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Chemiosmotic Theory

Parvin Pasalar29Ubiquinone and cytochrome c are mobile carriers. They ferry electrons from one complex to the next

ETC= electron transport chain

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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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2H+ + 2 e-

Coenzyme Q

Coenzyme Q

Coenzyme Q = Ubiquinonea lipid in inner membrane carries electrons polyisoprene tail moves freely within membrane

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

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Cytochromes - proteins in ETCelectron transferring proteins that contain a heme or heme-like prosthetic group!

Heme based on porphyrins with iron in center, usuallyas Fe(II), and is tightlybound at sides, sometimes covalently

Contrast heme

in cytochromes & hemoglobin

Complex III= Cyt C reductase

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Complex IV (Cytochrome C oxidase)

Heme A and Cu act together totransfer electrons to oxygen

e- from cyt c to a

Cyto oxidaseContains a, a3, and CuA, CuB

The detail of this electron transfer in Complex IV is not knownIt also functions as a proton pump

Cu(II) Cu(I)

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Membrane potential = 140 mVpH gradient = 60 mVTotal proton motive force = 200 mV

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•F0-F1

ATP Synthase (F0 - F1 complex)

F0

FI

F0 = Oligomycin sensitive Fragment

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ATP synthesis at F1 results fromrepetitive comformational changesas rotates

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The coupling of oxidation (to make Proton gradient) and phosphorylation ( ADP+P) is needed for ATP synthesis.*Thermogenin is a proton carrier located at inner mitochondrial membrane. *

Uncoupling Protein

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

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Uncoupling ProteinThe uncoupling protein blocks development of a H+ electrochemical gradient, thereby stimulating respiration. G 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 inhibitorsRotenone, amytal

Antimycin A

Dimercaprol

HCN, CO, H2S

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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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+.

OH

NO2

NO2

2,4-dinitrophenol

Uncoupling reagents (uncouplers)

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It is very efficient processIt 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.

How is the energy yield in living How is the energy yield in living cells cells

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Summary1. 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 !