1. Biological oxidation is the cellular process by which organic substances like carbohydrates, fats, and proteins release energy through redox reactions, producing CO2, H2O, and ATP. 2. In the mitochondria, electrons are transferred through redox carriers in the electron transport chain from NADH or FADH2 to oxygen, driving the pumping of protons across the inner mitochondrial membrane and building an electrochemical gradient. 3. The potential energy of this proton gradient is harnessed by ATP synthase to phosphorylate ADP, coupling electron transport to oxidative phosphorylation and the production of ATP through chemiosmosis.

1. Chapter 7
Biological Oxidation

2. Biological oxidation is the
cellular process in which the
organic substances release energy
(ATP), produce CO2 and H2O
through oxidative-reductive
reactions.
organic substances:
carbohydrate, fat and protein

3. 7.1 Principal of Redox Reaction
The electron-donating molecule in a
oxidation-reduction reaction is called
the reducing agent or reductant;
the electron-accepting molecule is the
oxidizing agent or oxidant:
for example:
Fe2+ (ferrous) lose -e
Fe3+ (ferric) gain +e

4. Redox reaction = reduction-oxidation
reaction
Several forms of Biological Reduction
1. Gain of electrons
2. Hydrogenation
3. Deoxygenation
Several forms of Biological Oxidation
1. Loss of electrons
2. Dehydrogenation
3. Oxygenation

5. oxidation-reduction potential
( or redox potential), E : it is a
measure of the affinity of a
substance for electrons. It decide the
loss (or the gain) of electrons.
A positive E: the substance has a
higher affinity for electrons , accept
electrons easily.
A negative E: the substance has a
lower affinity for electrons , donate
electrons easily.

6. E0`, the standard redox
potential for a substance :is
measured under stander
condition(25℃, 1mmol/L reaction
substance),at pH7, and is expressed
in volts.

7. Section 7.2
Respiration Chain and
Oxidative Phosphorylation

8. 7.2.1 Respiratory Chain
Term:
A chain in the mitochondria consists of a number of
redox carriers for transferring electrons from the substrate
to molecular oxygen to form oxygen ion, which combines
with protons to form water.

9. Redox carriers including 4 protein
complexes
1.Complex I:
NADH:ubiquinone oxidoreductase
NADH:CoQ oxidoreductase
2.Complex II:
Succinate dehydrogenase
3.Complex III:
cytochrome bc1 (ubiquinone Cyt c oxidoreductase)
4.Complex IV:
cytochrome oxidase

10. Complex I ( NADH:ubiquinone
oxidoreductase)
Function: transfer electrons from NADH to CoQ
Components:
NADH dehydrogenase (FMN)
Iron-sulfur proteins (Fe-S)
complex Ⅰ
NADH→
→CoQ
FMN; Fe-SN-1a,b; Fe-SN-4; Fe-SN-3; Fe-SN-2

11. R=H: NAD+;
R=H2PO3:NADP+
1. NAD(P)+: Nicotinamide Adenine Dinucleotide Phosphate)

12. Oxidation of NADH is a 2-electron(2e),
2-proton(2H) reaction
NAD+ or NADP+
NADH or NADPH

13. 2. FMN can transfer 1 or 2 hydride ions
ach time
FMN: flavin mononucleotide
Accepts 1 H+ and 1 e- Accepts 2 H + and 2 e to form semiquinone
= stable free radical to give fully reduced form

14. 3. Iron-sulfur clusters (Fe-S) transfers 1electron at a time, without proton
involved
Fe3++e-
Fe2+

15. 4.Ubiquinone (CoQ) is lipid-soluble, not a
component of complex Ⅰ , can transfer 1 or 2
hydride ions each time.
Function:
transfer electrons and protons from
complex Ⅰ , Ⅱ to complex Ⅲ .

16. NADH+H+
NAD+
FMN
Reduced Fe-S
Q
FMNH2
Oxidized Fe-S
QH2
Matrix
Intermembrane space

17. Complex II : Succinate dehydrogenase
(Succinate: CoQ oxidoreductase )
Function: transfer electrons from succinate to CoQ
Components:
Succinate dehydrogenase (FAD, Fe-S)
Cytochrome b560
Complex Ⅱ
Succinate→ Fe-S1; b560; FAD; Fe-S2 ; Fe-S3
→CoQ

18. Cytochromes a, b, c are heme proteins,
their heme irons participate redox
reactions of e- transport.
Fe3++e-
Fe2+

19. Intermembrane space
Matrix
Succinate

20. Complex III:
cytochrome bc1 (ubiquinone Cyt c
oxidoreductase)
Function: transfer electrons from CoQ to cytochrome c
Components: iron-sulfur protein
cytochrome b(b562, b566)
cytochrome c1
complex Ⅲ
QH2→
b562; b566; Fe-S; c1
→Cyt c

21. Cytochrome c is soluble, which will transfer
electrons to complex Ⅳ
Intermembrane
space
Matrix

22. Complex IV: cytochrome oxidase
Function: transfer electrons from Cyt c to molecule oxygen, the
final electron acceptor.
Components: cytochrome aa3
copper ion (Cu2+)
Cu2+ + e-
Cu+
Complex IV
Cyt c →
CuA→a→a3→CuB
→ O2

24. Cytochrome c
Coenzyme Q
ubiquinone/ol

25. Sequence of respiratory chain
Principles:
e- tend to flow from a redox pair with a lower E°to one with a
higher E°
In the e--transport chain, e--carriers are arranged in order of
increasing redox potential, making possible the gradual release
of energy stored in NADH, FADH2

26. 呼吸链中各种氧化还原对的标准氧化还原电位
Redox potential
氧化还原对
redox pair
NAD+/NADH+H+
FMN/ FMNH2
FAD/ FADH2
Cyt b Fe3+/Fe2+
Q10/Q10H2
Cyt c1 Fe3+/ Fe2+
Cyt c Fe3+/Fe2+
Cyt a Fe3+ / Fe2+
Cyt a3 Fe3+ / Fe2+
1/2 O2/ H2O
Eº'0(V)
E
-0.32
-0.30
-0.06
0.04（或0.10）
0.07
0.22
0.25
0.29
0.55
0.82

28. There are two respiratory chains
NADH respiratory chain
NADH Complex Ⅰ CoQ Complex Ⅲ
cytochrome c Complex Ⅳ O2
Succinate (FADH2) respiratory chain
Succinate ComplexⅡ CoQ ComplexⅢ cytochrome c
ComplexⅣ O2

29. NADH
respiration
chain
FADH2
respiration
chain

30. 7.2.2 Oxidative Phosphorylation
The oxidation of organic nutritions produces the energy-rich
molecules, NADH and FADH2.
The oxidation of NADH or FADH2 in mitochondrial is the electron
transferring through respiration chain.
The free energy produced in electron transferring supports the
phosphorylation of ADP to form ATP.
The oxidation of NADH or FADH2 and the formation of ATP are
coupled process, called Oxidation Phosphorylation.

31. The Chemiosmotic Theory
The free energy of electron transport is conserved by pumping
protons from the mitochondrial matrix to the intermembrane
space so as to create an electrochemical H+ gradient across the
inner mitochondrial membrane. The electrochemical potential of
this gradient is harnessed to synthesize ATP.
Peter Mitchell

32. Electrochemical H+ gradient (Protonmotive force)
2 components involved
1. Chemical potential energy due to
difference in [H+]
in two regions separated by a
membrane
2. Electrical potential energy that results
from the separation of charge when a
proton moves across the membrane
without a electron.

33. Complex I:
4 H+ expelled
per e--pair
transferred to
Q
Complex III:
4 H+ expelled per
e--pair transferred
to Cyt c
Complex IV:
2e- + 2 H+ from
matrix convert ½ O2
to H2O; 2 further H+
expelled from

34. Proton pumping: Reductiondependent conformational switch of an
e--transport complex
Conformation 1
(high affinity for H+)
Conformation 2
(low affinity for H+).

35. ATP Synthase
Intermembrane space
Inner
(ab2c9-12)
Membrane
Matrix
C ring
(α3β3γδε
)

36. β-subunit take up ADP and Pi to form ATP
ADP + Pi
ATP
Each of 3 βsubunits
contains an active
site
F1: multisubunit
complex that catalyzes
ATP synthesis
F 0 = proton-conducting
transmembrane unit

37. When protons flow back through F0 channel, γ-subunit is
rotated by the rotation of c ring, then the conformations of
β-subunits are changed, this lead to the synthesis and
release of ATP. To form a ATP need 3 protons flow into
matrix.
H+ flow
β-subunit has three conformations:T (tight), L (loose), O (open)

38. Translocation of ATP , ADP and Pi.
ADP3- ATP4-
H+
H2PO4- H+
Intermembrane
胞液侧
space
F0
基质侧
Matrix
F1
ATP4ADP3H+
H2PO4- H+

39. When protons flow back through F0 channel, γ-subunit is
rotated by the rotation of c ring, then the conformations of
β-subunits are changed, this lead to the synthesis and
release of ATP. To form a ATP need 3 protons flow into
matrix.
H+ flow
β-subunit has three conformations:T (tight), L (loose), O (open)

41. P/O ratios
P/O ratio is the rate of phosphate incorporated into ATP to
atoms of O2 utilized. It measure the number of ATP
molecules formed per two electrons transfer through the
respiratory chain.
 NADH respiratory chain : 2.5,
 FADH2 respiratory chain: 1.5

42. During two electrons transfer through NADH respiratory chain,
ten protons are pumped out of the matrix.
To synthesis and translocation an ATP, four protons are needed.
So, two electrons transport can result in 2.5 ATP.
To succinate respiratory chain , two electrons transport can result
in 1.5 ATP.

43. Regulation of Oxidative Phosphorylation
1.PMF (proton motive force) regulate the electron transport.
higher PMF
lower rate of transport
2.ADP concentration
resting condition: energy demanded is low, ADP concentration is
low, the speed of Oxidative Phosphorytion is low.
active condition: the speed is high.

44. Inhibitor of Oxidative
Phosphorylation
1.Inhibitor of electron transport
Succinate
Antimycin A
Cyanide, Azide
Carbon Monoxide
×
×
×
Retonone
Amytal

45.  2.Uncoupling agents
uncoupling protein (in brown adipose tissue),
2,4-dinitrophenol, Pentachlorophenol
heat
H+
Intermenbran space
Ⅰ
Ⅱ
H
Cyt c
uncoupling
protein
F0
Q
Ⅲ
Ⅳ
F1
Matrix
+ H+
H+
ADP+Pi ATP
2,4-dinitrophnol

46. 3.Oligomycin bonds at the connection of F 0
and F1, inhibit the function of ATP synthase.
Intermembrane space
Matrix
Oligomycin
C ring

47. Succinate
Ⅱ
Retonone
Amytal
Antimycin A
×
Ⅰ
Ⅲ
×
×
Uncoupling
agent
Oligomycin
Ⅴ
×
Ⅳ
×

48. ATP and other Energy-rich compounts
ATP has two energy-rich phosphoric acid anhydride
bonds, the hydrolysis of each bond release more
energy than simple phosphate esters.
NH 2
N
N
OH
OH
OH
N
OH
OH
N
p O p OCH2 O
O= P O
～
～
OH
H
H
H
H
OH OH
AMP
ADP
ATP

49. Some Energy-rich compounds
Structure
Exemple
creatine phosphate
phosphoenolpyruvate
acetyl phosphate
Acetyl CoA
ΔGº’

50. The hydrolysis of energy-rich bond:
ΔGº’ = -5 ～ -15kcal/mol
The compounds with energy-rich bond are
high-energy
compounds.
The hydrolysis of low-energy bond:
ΔGº’ = -1 ～ -3kcal/mol
The compounds with low energy bond are
compounds.
low-energy

51. Transport of high-energy bond energies
1.Substrate level phosphorylation
Glycerate 1,3-biphosphate + ADP
Glycerate 3-phosphate +ATP
ΔGº’ = -4.5kcal/mol
Phosphoenolpyruvate +ADP
Pyruvate + ATP
ΔGº’ = -7.5kcal/mol

52. 2.ATP is the center of energy producing and
utilizing.
ATP
Oxidative
Phosphorylation
Energy
utilization
Substrate level
phosphorylation
~P
~P
ADP

53. 3.Other nucleoside triphosphates are
involved in energy transport.
GTP: gluconeogenesis
protein synthesis
UTP: glycogen
CTP: lipid synthesis

54. 4.Transport of the terminal phosphate
bond of ATP to the other nucleoside
Function of nucleoside diphosphate kinase
ATP + UDP
ATP + CDP
ATP + GDP
ADP + UTP
ADP + CTP
ADP + GTP
Function of adenylate kinase
ADP + ADP
ATP + AMP

55. 7.3 Energy from cytosolic NADH
A mitochondrial NADH produce 2.5 ATP
A cytosolic NADH must be transported into mitochondrial
for oxidation by two methods.
Glycerol phosphate shuttle
1.5 ATP
Malate aspartate shuttle
2.5 ATP

56. Glycerol phosphate shuttle
CH2OH
CH2OH
Electron chain
Glycerol
phosphate
dehydrogenase
NAD+
C=O
C=O
CH2O- Pi
NADH+H
+
CH2O- Pi
dihydroxyacetone
phosphate
dihydroxyacetone
phosphate
CH2OH
CH2OH
CHOH
CHOH
CH2O- Pi
CH2O- Pi
Glycerol
phosphate
FADH2
FAD
Glycerol
phosphate
Intermembran
space
Glycerol
phosphate
dehydrogenase
Inner menbran

57. Malate aspartate shuttle
O
Aspartate
-OOC-CH2-C-COO-
H 3N
Malate
α-ketoglutarate
carrier
+
-
-
OOC-CH2-C-COO
Aspartate
H
oxaloacetate
oxaloacetate
Glutamate
NADH
+H+
Glutamate
Electron chain
NADH
+H+
NAD+
α-ketoglutarate
α-ketoglutarate
OH
NAD+
-OOC-CH2-C-COOH
Malate
cytosol
Glutamate-aspartate
carrier
inner mitochondrial
membran
Malate
matrix

58. 7.4 Other Biological Oxidations
Monoxygenases
dioxygenase --add 2 atoms of O2
oxygenase to organic compounds.
monoxygenase (mixed-function oxidase, hydroxylase)
--adds 1 oxygen atom to organic compounds as a hydroxyl group.
RH + NADPH + H+ + O2
ROH + NADP+ + H2O

59. The chief compounds of monoxygenase:
Cyt b5, Cyt P450, Cyt P450 reductase(FAD,FMN)

60. Free Radical Scavenging Enzymes
Free Radical: the groups with an unpaired electron.
(such as O2﹣ 、 H2O2 、• OH)
1.Superoxide dismutases(SODs)
2O2﹣ + 2H+
SOD
H2O2 + O2
peroxidase
H2O + O2

61. 2.Glutathione peroxidase
H2O2
(ROOH)
2G –SH
NADP+
Glutathione
Glutathione
reductase
peroxidase
H2O
(ROH+H2O)
G –S – S – G
NADPH+H+

62. 3.Catalase (in peroxisomes)
2H2O2
catalase
2H2O + O2

63. summary