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Oxidative Phosphorylation ( Respiratory Chain). FADH 2 2ADP. FAD 2ATP. NADH, H + + 1/2 O 2 + 3ADP, P i. NAD + + H 2 O + 3ATP. Electron transport. Where – mitochondria Why – make ATP When – supply (ADP) and demand (ATP). H +. III. I’. II. ATP syn. - PowerPoint PPT Presentation
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1. Outline the 4 w’s for the bridging reaction (pyruvate dehydrogenase multienzyme complex), and the Krebs Cycle. What feature of the bridging reaction allows amino acids and sugars to be made into fat, but does not allow fat to be made into amino acids or sugars. Explain.
2. Describe the structure of the mitochondria. 3. Describe the function of each of the following enzymes: the pyruvate
dehydrogenase multienzyme complex, NADH dehydrogenase, CoQ-cyctochrome c oxidoreductase, cytochrome c, and cytochrome oxidase.
4. Describe the 4 w’s for Oxidative Phosphorylation. Explain the difference between oxidative phosphorylation and electron transport. Explain how ATP synthase works and why this depends on the proton gradient. Explain how the connection between electron transport and ATP synthase is broken by the uncoupler protein (UCP), and by 2,4 dinitrophenol.
5. Describe the role of the glycerol phosphate shuttle in muscle Oxidative Phosphorylation. What is the difference between the mitochondrial and cytoplasm forms of glycerol phosphate dehydrogenase and how does this impact energy production.
6. Outline the 4 w’s for all the pathways of metabolic main street.
7. Outline the 4Ws for the pentose phosphate pathway. Describe the importance of the pentose phosphate pathway to fatty acid synthesis and neuron health. Explain the role of NADP+/NADPH to Fatty acid synthesis and in the Wernicke Korsakoff syndrome.
8. Indicate the reaction catalyzed by, the pathway involved, and describe the metabolic role of the following enzymes: Glucose-6-P dehydrogenase, transketolase/tranaldolase, superoxide dismutase, and glutathione reductase.
9. Molecular structures to draw/recognize: ribose-5-phosphate, ROS (superoxide, hydroxide radicals, and hydrogen peroxide).
Glucose
AcetylCoA
Pyruvate
NADH/FADH2
Citric Acid Cycle
C6
C4
C5
oxaloacetate
ATP
Glycolysis
Bridging Rx.
Oxidative Phosphorylation
ADP O2
NAD+/FAD
Metabolic Mainstreet
GluconeogenesisFat↑↓
fatty Acids
amino acids↑↓
Protein
no return
ketone bodies
Oxidative Phosphorylation(Respiratory Chain)
NADH, H+ + 1/2 O2 + 3ADP, Pi
NAD+ + H2O + 3ATP
Electron transport
FADH2 2ADP
FAD 2ATP
Where – mitochondria Why – make ATPWhen – supply (ADP) and demand (ATP)
ATP syn
Oxidative PhosphorylationElecton Transport creates a Proton Gradient
ATP synthase utilizes the gradient to fuel ATP production
IIII
IV
II
H+
H+H+
ADP + Pi → ATP
DG˚′ = -nFDE˚′The Oxidative phosphorylation pathway exchanges the free energy provided by redox reactions into a proton gradient. The electric potential of the gradient drives the spontaneous production of ATP from ADP,Pi.
I
III
IV
Electron Transport Complexes
CoQ-Cytochrome C oxidoreductase 250kCoQH2 + 2 CytC(Fe3+) → 2H+ + 2 CytC(Fe2+) + CoQ
Cytochrome C Oxidase 160k 6 CytC(Fe2+) + O2 → 2 H2O + 6 CytC(Fe3+)
II Succinate-CoQ reductase (FADH2) 140kFADH2 + CoQ → FAD + CoQH2
H+
H+
H+
NADH dehydrogenase
IVIQ
III
c
H+ H+ H+
H+H+ H+
NADH, H+ + CoQ → NAD+ + CoQH2
CoQH2 + 2 CytC(Fe3+) → 2H+ + 2 CytC(Fe2+) + CoQ
4 CytC(Fe2+) + O2 → 2 H2O + 4 CytC(Fe3+)
Coenzyme Q is … a) polar b) nonpolar c) ionic
I NADH dehydrogenase: NADH, H+ + CoQ → NAD+ + CoQH2
II Succinate dehydrogenase: FADH2 + CoQ → FAD + CoQH2
III CoQ:cytochrome C oxidoreductase : CoQH2 + 2 CytC(Fe3+) → 2H+ + 2 CytC(Fe2+) + CoQ
IV Cytochrome Oxidase 4 CytC(Fe2+) + O2 → 2 H2O + 4CytC(Fe3+)
CoQ and cytochrome C (Fe3+/Fe2+) are ‘mobile’ electron carriers in Oxidative Phosphorylation
H+
III
III
ATP syn
I’
H+DpH = -1.4
Oxidative PhosphorylationThe pH of the inner membrane space will be ….
a) > than b) < than c) = to The pH of the mitochondrial matrix?
Transport of ADP and Pi into the Matrix
Proton Gradient = Energy Graient
H+
ADP + Pi
ATPsynthase Fo
F1
ATP
H+
The proton gradient turns the transmembrane portion of ATP synthase (F0) creating a pinwheel effect that leads to ATP generation.
The turning of the transmembrane portion of ATP synthase leads to the release of H+ into the matrix and ATP production. At any time a b subunit can have ADP/Pi, ATP, or nothing bound (1 of each).
a
a
a
bb
b
ADP,Pi
ATP
g
F1-ATP Synthase
ATP
Asp- + H+out
Asp Conformational DAsp Asp- + H+
in
A key asparticacid residue
facilitates the H+ driven‘spinner’
ADP,Pi
b
a
a
a
bb
g
F1-ATP Synthase
ADP,PiATP
ATP
ATP
a
a
a
bb
b
ADP,PiATP
g
F1-ATP Synthase
ATP
Transport of ADP and Pi into the Matrix
Summary of the Electron Flow in the Respiratory Chain
Glucose + 2ADP + 2NAD+
AcetylCoA
2Pyruvate + + 2ATP + 2NADH in cytosol
NADH/FADH2
KrebsCycle
C6
C4
C5
C4
ATP
Glycolysis
Bridging Rx.
OP
ADP O2
NAD+/FAD
Metabolic Mainstreet
How?Glycerol Phosphate or
Malate/Aspartate Shuttles
Muscle ― 2 ATP per Glycolysis NADH
Liver ― 3 ATP per Glycolysis NADH
The Glycerol Phosphate shuttle allows NADH produced in the cytosol toProduce aerobic ATP in the matrix without actually entering the mitochondria.
DHAP Glycerol-3-P Dehydrogenase (cytosol)
Glycerol-3-P
E-FADH2 E-FAD
Glycerol-3-P Dehydrogenase (mt)
NADH,H+ NAD+
QQH2II
Glycerol – Phosphate Shuttle
Pathway Direct OP
Glycolysis
Bridging Rx
Krebs Cycle
2ATP
none
2GTP
2NADH out 2FADH2 in = 4
2NADH = 6
6NADH = 182FADH2 = 4
Gross muscle ATP output – Additional loss of ATP due to ‘overhead’
Glucose
AcetylCoA
Pyruvate
NADH/FADH2
KrebsCycle
C6
C4
C5
ATP
Glycolysis
Bridging Rx.
OP
ADP O2
NAD+/FAD
Metabolic Mainstreet
oxaloacetate
2 ATP ― anaerobic
34 ATP ― aerobic Bridging Rx + Krebs + OP
OP UncouplersWhat would happen if H+ entered mitochondria without going through ATP synthase?
a) ATP would be produced b) heat would be produced c) both of above d) neither of above
1. 2,4 – dinitrophenol a weak nonnpolar acid
2. UCP (uncoupler Protein)
a passive H+ transport
Transport H+ across membrane without generating ATP
ADP + Pi ATP
ATPsynthase Fo
F1
NO2
OHNO2
O-
NO2H+
NO2
pH ~ 5.5
pH ~ 7.0
NO2
O-
NO2
+ H+
H+
ATPsynthase Fo
F1
UCP
ADP + Pi > ATP
Hibernating animals use UCP to stay room in winter in lieu of ATP production for muscle activity.
Free RadicalsMolecules that contain unpaired electrons
Superoxide ion •O2
-Nitric oxide NO•
Hydroxide radical OH•
Reactive Oxygen Species (ROS) – Molecules that are free radicals or readily converted into free radicals. They are strong oxidizing agents.Metabolically generated ROS/RNOS include above and hydrogen peroxide (H2O2).
H2O2 + Fe2+ Fe3+ + OH- + OH•
O2- + H2O2 + H+ O2 + H2O + OH•
ROS generation by Metabolism
Oxidative Phosphorylation & cytochrome oxidase O2 + 4H+ + 4e- → 2H2O
About 3-5% of the O2 metabolized by OP gets released prematurely as an ROS.
1) O2 + e- O2-
2) O2- + e- + 2H+ H2O2
3) H2O2 + H+ + e- H2O + OH•4) OH• + H+ + e- H2O
ROS generation by Metabolism
Toxin + cytP450(Fe2+) + O2 reduced toxin + cytP450(Fe3+) + H2O
Toxins include alcohol, pharmaceutical and recreational drugs, non-nutritive food molecules …. , that induce cytochrome P450 production in Liver… etc.
Monoamine oxidase in neurons –Dopamine is neurotransmitter: ↓Parkinson’s ↑Schizophrenia dopamine degradation H2O2
Neurons are particularly sensitive to environmental insult.
ROS – harmful Reactions
DNA + ROS modified bases or single strand breaks. These can lead to ↑mutations or apoptosis.
Protein + ROS fragmented or cross-linked protein. These can lead to ↓[Pro] or plaque buildup.
Polyunsaturated Lipids + ROS damaged cell membrane or athersclerosis . These can lead to cell death or heart disease ….
Defenses against ROS
Superoxide Dismutase (SOD) 2H+ + O2
- H2O2
Glutathione Peroxidase Glutathione (GSH) is the tripeptide gGlu-Cys-Gly
2GSH + H2O2 2 H2O + GS-SGDegrades lipid peroxides as well as H2O2 to minimize lipid damage
Glutathione Reductase
GS-SG + 2NADPH 2 GSH + 2NADP+
Superoxide ion •O2
-Nitric oxide NO•
Hydroxide radical OH•
Hydrogen peroxide H2O2
AntioxidantsVitamin E and Vitamin CFlavinoids: green tea, red wine, chocolate ….Carotinoids: fruits and veggies …..
What do they do? 1) Directly scavenge free radicals 2) Inhibit enzymes that can generate ROS 3) Combination of above.
Caution: Antioxidants can produce FR themselves and excesses may have pro-oxidant rather than antioxidant activity. Some clinical studies show excessive supplements cause more harm than good.
Resveratrol
Found in skin of red grapes & red wine.May activate sirtuin which is implicated in the epigenetic control of gene expression.May up-regulate SOD expression.
Catechin
Found in cocoa and white/green tea.
Epigallocatechin 3-O-gallate EGCG
AntioxidantsThese molecules taken as are considered beneficial components of fruits and vegetables etc.They may function to supplement the bodies normal defense against ROS. This could happen by serving as targets for ROS oxidation but also may involve enzyme expression or inhibition.Studies using pure forms of these compounds show mixed results.
Pentose Phosphate Pathway
Glucose-6-P + 2 NADP+ + H2O
Ribose-5-P + CO2 + 2 NADPH, H+
Why? Production of NADPH as reducing agent fatty acid synthesis & glutathione recycling
Where? Liver and adipose – neurons (brain)
When? NADP+ stimulates – NADPH inhibits mass action signals need for production
particularly important
3 Enzymes- includes … Glucose-6-P dehydrogenase
Transketolase (TPP cofactor) & Transaldolase
TK 2C5 ↔ C7 + C3
Net 3C5 Û 2C6 + C3 or …. 6C5 Û 5C6
TA C7 + C3 ↔ C6 + C4
TK C5 + C4 ↔ C6 + C3
What? – Reversible exchange of ribose/glucose
Why? – Retain proper balance of ribose/glucose
Where? – Liver, adipose, neurons (brain)
When? – As needed – regulated by mass action (equilibrium) DG = DG°´ + RT ln Q
Glycolysis ---Gluconeogenesis
Glucose ↓↑Glucose-6-P ↓↑C3 Intermediate ↓↑Pyruvate
NADPH + R-5-P (C5) + CO2
PPP
Nucleic Acids
Fat Synthesis & Glutathione Reductase
NADP+
TK
TA
Pentose Phosphate Pathway
Wernicke Korsakoff SyndromeLesions in Wernicke’s area of brain - left posterior of temporal lobe – probably due to neuron death.Causes speech comprehension problems, amnesia, peripheral neuritis.
Genetics (‘nature’)TK binding to TPP 10x weaker more common in “Europeans”
Environment (‘nurture’)Exacerbated by thiamine deficiency – common in alcoholics.
TK mutationv
[TPP] Normal [TPP]Thiamine deficiency