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BI/CH 422/622 on 2/22/
OUTLINE:
GlycogenolysisGlycolysis Other sugarsPasteur: Anaerobic vs Aerobic Fermentations Pyruvate (^) pyruvate dehydrogenase (ox-decarbox; S-ester) Krebs’ CycleHow did he figure it out? Overview8 Steps Citrate Synthase (C–C)Aconitase ( = , -OH) Isocitrate dehydrogenase (ox-decarbox; =O)Ketoglutarate dehydrogenase (ox-decarbox; S-ester) Succinyl-CoA synthetaseSuccinate dehydrogenase (sub-level phos)( = ) FumaraseMalate dehydrogenase ( -OH) (=O) EnergeticsRegulation Summary Oxidative Phosphorylation EnergeticsMitochondria TransportElectron transport Discovery Four Complexes
Exam-1 material Exam-2 material
Oxidative
Phosphorylation
Oxidative Phosphorylation
- Function of electron-transport chain in mitochondria…... make water (finish the reaction: C 6 H 12 O 6 + 6O 2 à 6CO 2 + 6H 2 O )
- Building up the proton-motive force
- Synthesis of ATP in mitochondria, chloroplasts, & bacteria
Learning goals:
- Fuels for the cell, in the form of reduced carbon
compounds (sugars), have been burned to carbon
dioxide.
- Electrons from reduced fuels are transferred to
cofactors, which get reduced as NADH or FADH 2.
- In oxidative phosphorylation, energy from NADH
and FADH 2 is used to make ATP. …... But how?
6O 2 6H 2 O
Glycogenolysis
Glycolysis
Pyruvate Oxidation
Krebs' Cycle
Oxidative
Phosphorylation
Oxidative Phosphorylation
Energy of the reduced cofactors
Oxidative Phosphorylation
Is there enough energy in NADH & FADH 2 to drive the synthesis of ATP? Each ATP synthesis is about +7.3 kcal/mol (opposite of hydrolysis) We can do this calculation two ways:
- Calculate the D E °’^ needed to get 1 ATP made: compare to D E °’^ of NADHàO (^2)
- Calculate the D G °^ ’^ for the NADHàO 2 : compare to the D G °^ ’^ for ATP synthesis
D G °^ ’^ = –n F D E °^ ’
D E °’^ = E °’^ ( reduction ) – E °’^ ( oxidation )
= +0.82 V – (–0.32 V)
= +1.14 V
7.2 times more energy in 2e– going from NADH to oxygen than needed to drive the synthesis of ATP
D G °’^ of NADHà ½ O 2 DG °’^ of ATP
D G °^ ’^ = –52.6 kcal/mol D G °^ ’^ = +7.3 kcal/mol
= –(2)(23.06V-1kcalmol -1)(+1.14V)
6.5 times more energy in 2egoing from FADH – than needed to drive the^2 to oxygen synthesis of ATP
Structure of Mitochondria
Oxidative Phosphorylation
Double membrane leads to fourdistinct compartments:
- Outer membrane:– relatively porous membrane; allows passage of metabolites
- Intermembrane space (IMS):– similar environment to cytosol
- higher proton concentration(lower pH)
- Inner membrane– relatively impermeable, with
- proton gradient across itlocation of electron transport
- chain complexesConvolutions called cristae serve to increase the surface area.
- Matrix– location of the citric acid cycle and parts of lipid and amino-acidmetabolism
- lower proton concentration(higher pH)
+++++
cow artery endothelial cell
cow heart muscle
cow liver
D! ≈ –0.06 V
- These translocases cost the membrane potential, which must be restored; costs 25% of Electron Transport.
- These translocases require energy from both the electrochemical gradient across inner mitochondrial membrane plus the proton gradient. Together they are called the Proton Motive Force.
- What generates this gradient?
- How much energy does it take to pump H +^ out?
Oxidative Phosphorylation
D! ≈ –0.06 V
This antiporter works muchlike GLUT1. The import of ADP and export of ATP isfavored by 1) the [ATP] concentrations, and 2) thecharge difference.
0
This symporter has to combatthe charge difference of P to a more negative space, but its i^ going favored by the overwhelminghigh [H +] and [P i ] on the outside.
14% of protein in theinner membrane is the ADP/ATP translocase
Energy required to pump a single proton against a pH gradient
[H +in]
[H +out ] H +in ⇌ H +out
D
So, if its more negative And, if its more positive
As a consequence, it will take ~3 protons per ATP.
Oxidative Phosphorylation
D G^ ’^ = RT ln ____[H^ + z F D"
pHin ≈ 7.
pHout ≈ 6.
ln[H +]out = 2.3log[H +]out = -2.3 pH (^) out ln(1/[H +]in) = 2.3-log[H +]in = +2.3 pH (^) in
= RT2.3(pH (^) in – pH (^) out ) = 5.9(7.5 – 6.75) = 5.9(0.75) = 4.4 kJ/mol = 1.0 kcal/mol
= z F D" = (+1)(96480) D" = (+1)(96480)(+0.06) = 5.8 kJ/mol = 1.4 kcal/mol
Switch the sign herebecause reaction is opposite that of transport
D G^ ’^ = 1.0 + 1.4 = 2.4 kcal/mol
+++++
Top
Bottom
D" ≈ –0.06 V
- When it was realized that isolated mitochondria are capable of respiration (oxygen consumption when provided fuels), biochemists began purifying them and their components.
- The first things purified were redox compounds and small stable proteins: - – NADHflavin mononucleotide (FMN) - flavin adenine dinucleotide (FAD)(bound to protein; flavoproteins) - iron-sulfur clusters - – Coenzyme Q (Ubiquinol)cytochromes a , b , or c
- Once purified, they were analyzed by mea-
suring their E °’.
- Order of transfer of electrons is dependent
on E °’^ :
Electron Transport Electron-Transport Chain Complexes Contain a Series of Electron Carriers
Big Drop! FAD-E + 2 H^ +^ + 2e– à^ FADH^2 -E^ FeS –0. Big Drop!
Big Drop!
- NAD+^ , FMN, and FAD accept electrons. The flavin nucleotides can accept one or two electrons, and can also donate one electron at a time to acceptors that can only accept single electrons
- Ubiquinone, also called Coenzyme Q, is an isoprene lipid that readily accepts electrons. Upon accepting two electrons, it picks up two protons to give an alcohol, ubiquinol (CoQH 2 ). Its found IN the inner membrane.
- Iron-sulfur complexes (Fe-S) that can only carry one electron at a time (role is different than in aconitase).
Electron Transport
Cytochromes
- Small one-electron carrier proteins
- Iron-coordinating porphyrin-ring derivatives
- b / b 1 , c, or a/a 3 differ by ring additions
Electron Transport Cytochromes
- Mobile electron carrier; a peripheral membrane protein - Cytochromeintermembrane space (IMS). c moves through the
- A soluble heme-containing protein
- Heme iron can be either ferrous (Fe 2+^ , reduced) or ferric (Fe 3+^ , oxidized).
- Cytochrome c carries a single electron.
- The two redox forms have different spectra:
Electron Transport
Cytochrome c
- Intense Soret band near 400 nm absorbs blue light and gives cytochrome c an intense red color.
