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Electron Transport Chain
Mitochondrial Structure
Electron Transport Chain Overview
The ETC removes energy stored in the NADH and
FADH2 molecules to:
1. create a proton gradient across the inner
mitochondrial membrane
2. convert O2 to H2O.
All reactions are redox reactions.
Electron Transport Chain Animation
ETC Animation
ETC Components
ETC Components: Complex I
 Complex 1: NADH
Dehydrogenase
 2 e- from NADH are
transferred to Complex I
 Protons are pumped
across the inner
mitochondrial
membrane (IMM) by
Complex I (active
Transport)
ETC Components: Q
 e- are transferred from
Complex I to ubiquinone
(Q)
 Q is a mobile
component within the
IMM
ETC Components: Complex III
 Complex III:
Cytochrome b-c1
 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, in the
intermembrane space
ETC Components: Complex IV
 Complex IV:
Cytochrome Oxidase
 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
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
ATP
ATP
H+
H+
H+
Intermembrane
space
Cyt c
Protein complex
of electron
carners
Q
I
III
Inner
mitochondrial
membrane
II
FADH2
NADH+
Mitochondrial
matrix
IV
FAD+
2 H+ + 1/2 O2
NAD+
(Carrying electrons
from, food)
FADH2
Electron transport chain
FAD
Electron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
Figure 9.15
H2O
FADH2 Pathway
 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
ETC Thermodynamics
NADH
 FADH2 enters the chain
50
at a lower energy than
NADH
FADH2
Free energy (G) relative to O2 (kcl/mol)
40
I
FMN
Multiprotein
complexes
FAD
Fe•S
Fe•S
II
O
III
Cyt b
30
Fe•S
 2 electrons from NADH
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
20
produce a max of 3 ATP
 2 electrons from FADH2
10
produce a max of 2 ATP
0
2 H + + 1 2
O2
H2O
Electrochemical Proton Gradient
ETC Summary
1. NADH e- transferred to O2; three proton pumps
activated
2. FADH2 e- transferred to O2; two proton pumps
activated
3. electrochemical proton gradient formed across
IMM
Electron Transport Chain Animation
ETC Animation
Proton Motive Force: Chemiosmosis
The electrochemical gradient (chemiosmosis)
produced by the ETC can now be used to generate
ATP through the process of oxidative
phosphorylation (OXPHOS).
OXPHOS occurs through the enzyme complex ATP
synthase.
OXPHOS Animation
ATP Synthase Complex
Two components:
1. proton channel / rotor
embedded in IMM
2. catalytic sites that
phosphorylate ADP to
ATP
This is an example of
facilitated diffusion
(passive transport)
ATP Production
oxidative phosphorylation - ATP is produced as
protons flow through ATP synthase.
In general:
1. 1 NADH  2.5 – 3 ATP molecules
2. 1 FADH2  1.5 – 2 ATP molecules
The ETC is coupled with ATP synthesis. The latter is
dependent on the former.
ATP Production
Cellular
Respiration
Step
Glycolysis
Glycolysis
Oxidative
Oxidative
Decarboxylation
Decarboxylation
Krebs Cycle
Krebs Cycle
Energy
Molecules
Produced
2 ATP
2 NADH
2 NADH
2 ATP
special case
6 ATP
6 NADH
2 FADH2
2 ATP
18 ATP
4 ATP
2 ATP
ATP Totals
ATP Production– Aerobic Respiration
Cellular
Respiration
Step
Glycolysis
Oxidative
Decarboxylation
Krebs Cycle
TOTAL
Energy
Molecules
Produced
2 ATP
2 NADH
2 NADH
6 NADH
2 FADH2
2 ATP
ATP Totals
2 ATP
4-6 ATP
6 ATP
18 ATP
4 ATP
2 ATP
36-38 ATP
Why 36-38 ATP?
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
Figure 9.16
6 NADH
Citric
acid
cycle
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP