Download Ch 9: E.T.C./ Oxidative Phosphorylation

Ch 9 (Part 3):
9.4 - E.T.C./
Oxidative
Phosphorylation
● So far, in glycolysis & the Krebs cycle, 1
glucose molecule has resulted in:
 4 ATPs (2 from glycolysis, 2 from
Krebs)
 10 NADH (2 from gly., 2 from acetylCoA step, 6 from Krebs Cycle)
 2 FADH2 (from Krebs Cycle)
● Following glycolysis and the Krebs
cycle, NADH and FADH2 account for
most of the energy extracted from food
● These two electron carriers donate
electrons to the electron transport
chain, which powers ATP synthesis via
oxidative phosphorylation
ELECTRON TRANSPORT
CHAIN (E.T.C.)
● E.T.C. = a collection of
molecules (mostly protein
complexes) embedded in the
inner membrane of
mitochondrion (foldings of
inner membrane form
CRISTAE)
The Pathway of Electron
Transport
● the groups along the chain alternate between
reduced & oxidized states as they accept
and donate electrons
● each successive group is more
electronegative than the group before it, so
the electrons are “pulled downhill” towards
OXYGEN (the final electron carrier!)
NADH
50
Free energy (G) relative to O2 (kcal/mol)
FADH2
40
FMN
I
Multiprotein
complexes
FAD
Fe•S II
Fe•S
Q
III
Cyt b
30
Fe•S
Cyt c1
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
IV
Cyt c
Cyt a
Cyt a3
20
10
0
2 H+ + 1/2 O2
H2O
ATP
● as molecular oxygen (O2) is reduced, it
also picks up H+ from the environment
to form water (H2O)
ATP Production of the E.T.C.
Typically, the ATP produced is as follows:
1 NADH

3 ATP
“exchange
rate”
1 FADH2 
2 ATP
(FADH2 is “dropped off” at a lower point in
the E.T.C., so it generates fewer ATPs)
Chemiosmosis: The EnergyCoupling Mechanism
● Electron transfer in the electron transport
chain causes proteins to pump H+ from
the mitochondrial matrix to the
intermembrane space (active transport)
● H+ (protons) then move back across the
membrane, passing through channels in
ATP synthase
Chemiosmosis: The EnergyCoupling Mechanism
● ATP synthase uses the exergonic flow of
H+ to drive phosphorylation of ATP
● This is an example of CHEMIOSMOSIS,
the use of energy in a H+ gradient to drive
cellular work
● The energy stored in a H+ gradient
across a membrane couples the
redox reactions of the electron
transport chain to ATP synthesis
● The H+ gradient is referred to as a
PROTON-MOTIVE FORCE,
emphasizing its capacity to do work
(inner matrix)
● protons
then diffuse
back across the
membrane through
the ATP synthase
complex
which causes the
phosphorylation of
ADP to
form ATP!
(intermembrane space)
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
as shown when
H+ flows past
it down the H+
gradient.
H+
A stator anchored
in the membrane
holds the knob
stationary.
A rod (or “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
H+
ADP
+
P
ATP
i
MITOCHONDRAL MATRIX
Three catalytic
sites in the
stationary knob
join inorganic
phosphate to
ADP to make
ATP.
Inner
mitochondrial
membrane
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP
H+
H+
H+
H+
Intermembrane
space
Cyt c
Protein complex
of electron
carriers
Q
IV
III
I
ATP
synthase
II
Inner
mitochondrial
membrane
FADH2
NADH + H+
2H+ + 1/2 O2
H2O
FAD
NAD+
Mitochondrial
matrix
ATP
ADP + P i
(carrying electrons
from food)
H+
Electron transport chain
Electron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
Oxidative phosphorylation
Chemiosmosis
ATP synthesis powered by the flow
of H+ back across the membrane
ELECTRON
TRANSPORT CHAIN
ANIMATION!
SUMMARY:
● most energy flows in this sequence:
Glucose  NADH  E.T.C.  proton  ATP
motive
force
PROCESS
Glycolysis
ATP
produced
by subs.
phos.
2 ATP
oxid. of
pyruvate to
acetyl CoA
Krebs
cycle
2 ATP
Reduced
coenz.
2 NADH
(go to ETC)
ATP
produced by
oxid. phos.
(in the
E.T.C.)
TOTAL
ATPs
4-6 ATP
6-8
2 NADH
(go to ETC)
6 ATP
6
6 NADH
2 FADH2
18 ATP
4 ATP
24
TOTAL
ATPs
36-38!
(go to
ETC)
● approximately 40% of energy in glucose
is converted to ATP
● the remaining energy is lost as heat
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
2
Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2
Acetyl
CoA
6 NADH
Citric
acid
cycle
+ 2 ATP
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
About
36 or 38 ATP
**actual ATP total’s are slightly less – when we factor in “real”
exchange rates and the energetic cost of moving the ATP formed in the
mitochondrion out into the cytosol, where it will be used**