1. Ch 9 (Part 3): 9.4 - E.T.C./ Oxidative Phosphorylation

2. ● 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 acetyl-CoA step, 6 from Krebs Cycle)
 2 FADH2 (from Krebs Cycle) x2

3. ● 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

4. 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)

6. 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!)

7. Free energy (G) relative to O2 (kcal/mol)
NADH 50
FADH2
Multiprotein
complexes 40 I
FMN
FAD
Fe•S
Fe•S II Q
III
Cyt b
Oxidative
phosphorylation:
electron transport
and chemiosmosis
Glycolysis
Citric
acid
cycle
Fe•S 30
Cyt c1
Free energy (G) relative to O2 (kcal/mol) IV
Cyt c
Cyt a
ATP
ATP
ATP
Cyt a3 20 10
2 H+ + 1/2 O2
H2O

9. ● as molecular oxygen (O2) is reduced, it also picks up H+ from the environment to form water (H2O)

10. ATP Production of the E.T.C.
Typically, the ATP produced is as follows:
1 NADH  3 ATP
1 FADH2  2 ATP
(FADH2 is “dropped off” at a lower point in the E.T.C., so it generates fewer ATPs)
“exchange
rate”

12. Chemiosmosis: The Energy-Coupling 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

13. Chemiosmosis: The Energy-Coupling 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

14. ● 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

18. the ATP synthase complex which causes the phosphorylation of ADP to
(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)

20. A rotor within the membrane spins as shown when H+ flows past
INTERMEMBRANE SPACE H+
A rotor within the membrane spins as shown when H+ flows past
it down the H+ gradient. H+ H+ H+ H+ H+ 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+
Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.
ADP +
ATP P i
MITOCHONDRAL MATRIX

21. Electron transport chain
Inner
mitochondrial
membrane
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and chemiosmosis
Glycolysis
ATP
ATP
ATP H+ H+ H+ H+
Protein complex
of electron
carriers
Cyt c
Intermembrane
space Q IV I
III
ATP
synthase
Inner
mitochondrial
membrane II
2H+ + 1/2 O2
H2O
FADH2
FAD
NADH
+ H+
NAD+
ADP + P
ATP i
(carrying electrons
from food) H+
Mitochondrial
matrix
Electron transport chain
Electron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered by the flow
of H+ back across the membrane
Oxidative phosphorylation

22. SUMMARY: ● most energy flows in this sequence:
Glucose  NADH  E.T.C.  proton  ATP
motive
force

23. TOTAL ATPs PROCESS ATP produced by subs. phos. Reduced coenz.
ATP produced by oxid. phos. (in the E.T.C.)
TOTAL ATPs
Glycolysis
2 ATP
2 NADH
(go to ETC)
4-6 ATP
6-8
oxid. of pyruvate to acetyl CoA
2 NADH (go to ETC)
6 ATP 6
Krebs cycle
6 NADH
2 FADH2
18 ATP
4 ATP 24
36-38!

25. ● approximately 40% of energy in glucose is converted to ATP
● the remaining energy is lost as heat

26. CYTOSOL
Electron shuttles
span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Glycolysis
Oxidative
phosphorylation:
electron transport
and
chemiosmosis 2
Pyruvate 2
Acetyl
CoA
Citric
acid
cycle
Glucose
+ 2 ATP
+ 2 ATP
+ about 32 or 34 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
About
36 or 38 ATP
Maximum per glucose:
**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**