Part 3: Electron Shuttles, ETC & Chemiosmosis
Cellular Respiration
Recall: Location
Glycolysis occurs in the cytoplasm
Electron transport chain (ETC) starts in the mitochondrial matrix
The NADH produced during glycolysis must make its way into the mitochondria
Electron Shuttle
Electron ShuttleNADH produced in glycolysis must be
transported from the cytoplasm into the mitochondria to enter the ETC.
Mitchondria is not permeable to NADH produced in the cytoplasm
Shuttling of NADH is indirect
Two shuttle mechanisms:glycerol phosphate shuttlemalate-aspartate shuttle
Glycerol Phosphate Shuttle In brain tissue and skeletal muscle tissue Results in FADH2 in the matrix 2e- from NADH get shuttled into the mitochondria
and become part of FAD to become FADH2
CYTOPLASM INTERMEMBRANE SPACE
MATRIX
NADH
NAD+
DHAP
Glycerol 3-phosphate
FADH2
FAD
ETC
Glycerol 3-phosphate
DHAP
Malate-Aspartate Shuttle In liver, kidney, heart Results in NADH in the matrix 2e- from NADH get shuttled into the mitochondria
and become part of NAD+ to become NADHINTERMEMBRANE
SPACECYTOPLASM MATRIX
ETC
Aspartate
NADH
NAD+
Oxaloacetate
Malate
NADH
NAD+
Oxaloacetate
Malate
Aspartate
Two Methods of ATP Synthesis
Two Methods of ATP SynthesisSubstrate-level phosphorylation direct ATP formation through phosphate
transfer from substrate to ADP Occurs in glycolysis & Kreb cycle
Oxidative phosphorylation indirect ATP formation through redox
reactions involving O2 as a final electron acceptor
Driven by the electron transport chain
Substrate-level Phosphorylationenzyme transfers a phosphate group
from a substrate molecule to ADP rather than adding an inorganic
phosphate to ADP as in oxidative phosphorylation
Figure 9.7
Enzyme Enzyme
ATP
ADP
Product
SubstrateP
+
Oxidative Phosphorylation Involves 2 processes that occur on the
inner mitochondrial membrane (IMM) Electron Transport Chain:
Energy in electrons of NADH and FADH2 used to drive H+ against its concentration gradient
Electrons fall to oxygen (final electron acceptor)
Chemiosmosis: Using facilitated diffusion of H+ to drive the
synthesis of ATP
Electron Transport Chain OverviewThe ETC removes energy stored in
the NADH and FADH2 molecules to: Move protons against its concentration
gradient creating a proton gradient across the inner mitochondrial membrane (IMM)
Final electron acceptor is oxygen which converts H2O
All reactions are redox reactions
Electron Transport Chain (ETC)
Made of electron carrier molecules embedded in the inner membrane of mitochondria
Most carriers are protein molecules except for ubiquinone (Q)
ETC Thermodynamics Each electron transfer
step is energetically favourable
Each carrier in the chain has a higher electronegativity than the carrier before it
Electrons from NADH and FADH2 lose energy (pulled downhill) by each electron carrier
ETC & Oxygen Final electron
acceptor is the very electronegative oxygen
Oxygen drives the redox reactions
Lack of oxygen prevents this whole process from occurring
H2O
O2
NADH
FADH2
FMN
Fe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
2 H + + 12
I
II
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Free
ene
rgy
(G) r
elat
ive
to O
2 (k
cl/m
ol)
ETC & Chemiosmosis Overview
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carners
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
ETC Components: Complex I
2 e- from NADH are transferred to Complex I
Protons are pumped across the inner mitochondrial membrane (IMM) by Complex I
ETC Components: Q
e- are transferred from Complex I to ubiquinone (Q)
Q is lipid soluble can move within
the phospholipid bilayer
mobile component within the IMM
ETC Components: Complex III
e- are transferred from Q to Complex III
Protons are pumped across the IMM by Complex III
ETC Components: Cyt C
e- are transferred from Complex III to cytochrome c (cyt c)
cyt c is a mobile component on the surface of IMM (peripheral), in the intermembrane space
ETC Components: Complex IV
e- are transferred from cyt c to Complex IV
Protons are pumped across the IMM by Complex IV
ETC Components: O2
O2 is the final electron acceptor of the ETC
enough e- pass through the ETC to produce full H2O molecules
FADH2 Pathway
Figure 9.15
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Cyt c
I
II
III
IV
FADH2
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
ATPsynthase
Q
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
X
ETC Components: Complex II
2e- are transferred from FADH2 to Complex II
no protons are pumped across the IMM
e- are transferred from Complex II to Q and proceed through the rest of ETC
Complex II
FADH2 FAD+
Q
ETC Components: Complex II
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carners
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
Electrochemical Proton Gradient
Low H+
High H+
ETC Summary
NADH e- transferred to O2; three proton pumps activated
FADH2 e- transferred to O2; two proton pumps activated
electrochemical proton gradient formed across IMM
H2O
O2
NADH
FADH2
FMN
Fe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
2 H + + 12
I
II
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Free
ene
rgy
(G) r
elat
ive
to O
2 (k
cl/m
ol)
Figure 9.13
Electron Transport Chain NADH is oxidized and FMN (complex I)
is reduced↓
FMN is oxidized as it passes electrons to an iron sulfur protein, FeS (complex I).
↓ FeS is oxidized as it pass electrons to
ubiquinone Q. FADH2 enters at complex II to Q, bypassing complex I.
↓ Q passes electrons on to a succession
of electron carriers (in complex III and IV), most of which are cytochromes.
↓ Cyt a3 , the last cytochrome passes
electrons to oxygen.
Oxidative Phosphorylation
Low H+
High H+
Proton Motive Force: Chemiosmosis The electrochemical gradient produced by the
ETC: High proton concentration in the intermembrane space
Chemiosmosis: facilitated diffusion of proton down the concentration gradient
Oxidative phosphorylation: Oxidation (ETC) coupled with phosphorylation (ATP
synthesis) Occurs by coupling passive movement of protons to
produce ATP through the enzyme complex ATP synthase
ATP is produced as protons flow through ATP synthase
ATP Synthase: Complex V
Fo = rotor Transmembrane Proton channel
F1 = knob, rod Peripheral catalytic sites
that phosphorylate ADP to ATP
Figure 9.14
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+ H+
H+
P i
+ADP
ATP
A rotor within the membrane spins clockwise whenH+ flows past it down the H+
gradient.
A stator anchoredin the membraneholds the knobstationary.
A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob.
Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. MITOCHONDRIAL MATRIX
ATP Synthase: Complex V
Rotational Catalysis Protons flowing through the F0
component cause the subunits in the rod to rotate. electrochemical gradient translates into
mechanical energy When an irregularly shaped
subunit rotates, it contacts a different subunit.
As a result, the subunits change conformation, which changes their affinity for ATP.
subunit
Catalytic subunit 3 conformation:
loosely binds ADP and P tightly binds ADP and Pi to form ATP releases ATP
When the interacts closely with the subunit, ATP is synthesized
Each of the 3 subunits in the F1 component take turn catalyzing the synthesis of ATP
Animation ETC
http://www.youtube.com/watch?v=lRlTBRPv6xM&feature=related
Proton Gradient & ATP synthasehttp://www.youtube.com/watch?v=3y1dO4nNaKY&feature=related
ATP synthasehttp://www.youtube.com/watch?v=PjdPTY1wHdQ&feature=related
Cellular Respiration Lecture:
http://www.youtube.com/watch?v=qviLDKDJNKM&feature=related
ATP Production
In general:1 NADH 3 ATP molecules1 FADH2 2 ATP moleculesThe ETC is coupled with ATP
synthesis. The latter is dependent on the former.
ATP Production Summary
Cellular Respiration Step
Energy Molecules Produced
ATP Totals
Glycolysis 2 ATP2 NADH
2 ATP4-6 ATP
Oxidative Decarboxylation
2 NADH 6 ATP
Krebs Cycle 6 NADH2 FADH2
2 ATP
18 ATP4 ATP2 ATP
TOTAL 36-38 ATP
ATP Production Summary
Cellular Respiration Step
Energy Molecules Produced
ATP Totals
Glycolysis 2 ATP2 NADH
2 ATP4-6 ATP
Oxidative Decarboxylation
2 NADH 6 ATP
Krebs Cycle 6 NADH2 FADH2
2 ATP
18 ATP4 ATP2 ATP
TOTAL 36-38 ATP
Electron shuttlesspan membrane
CYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose2
Pyruvate
2AcetylCoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
MITOCHONDRION
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol
Maximum per glucose:About
36 or 38 ATP
+ 2 ATP + 2 ATP + about 32 or 34 ATP
or
Figure 9.16
Cellular Respiration Summary
Amino acids
Sugars Glycerol Fattyacids
GlycolysisGlucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citricacidcycle
Oxidativephosphorylation
FatsProteins Carbohydrates
Figure 9.19
Catabolism of various molecules from food
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphateInhibits Inhibits
Pyruvate
ATPAcetyl CoA
Citricacidcycle
Citrate
Oxidativephosphorylation
Stimulates
AMP
+– –
Figure 9.20
Regulation of Cellular Respiration