Biological oxidation is the process by which organic substances like carbohydrates, fats, and proteins release energy through redox reactions in cells. This energy is captured in the form of ATP, which is used to power various cellular processes. The electron transport chain located in the inner mitochondrial membrane facilitates the transfer of electrons from electron carriers like NADH and FADH2 to oxygen. This releases energy to synthesize ATP through oxidative phosphorylation and substrate-level phosphorylation. Key components of the electron transport chain include complexes I-IV which contain enzymes, cofactors, and cytochromes that sequentially pass electrons from one to the next until they reach oxygen, the final electron acceptor.

1. Biological oxidation

2. • Biological oxidation is the cellular process in
which the organic substances release energy
(ATP) produce CO₂ & H₂O through oxidative-
reductive reactions.
• Organic substances carbohydrate, fat &
proteins.
• Biological oxidations are catalyzed by
intracellular enzymes. The purpose of
oxidation is to obtain energy.

4. • Cells obtain free energy in a chemical form
from the degradation & use it for :-
- Synthesis of biomolecules.
- Muscle contraction
- Nerve impulse conduction
- During catabolism some of the free energy is
trapped to make ATP.

5. High energy compound
• Energy rich compounds.
• Compounds contains high energy bonds,
indicated as (῀).
• On hydrolysis , will release large amount of
energy. It librates free energy at least 7
cal/mol at pH -7.0.
• Liberate less than 7 cal/mol is called low
energy compounds.

6. • All high energy compounds on hydrolyzed
liberate more energy than that of ATP.
Eg:- phosphoenol pyruvate , 1,3-bisphospho-
glycreate , phosphocreatine .
• Most of the high energy compounds contain
phosphate group is known as high energy
phosphate compounds.

7. ATP is the universal currency
for biological energy
• Consists of an adenine, ribose & triphosphate.
• Hydrolysis of ATP to ADP release -7.3 Kcal/mol.
• Energy utilized for biosynthesis of
macromolecules , muscle contraction, active
transport , etc.
• ATP act as donor of high-energy phosphate to
low energy compounds , makes them energy
rich.

10. • Act as an energy link between the catabolism &
anabolism .
• Three major sources of high energy phosphates:-
-Glycolysis
-TCA cycle
-Oxidative phosphorylation
• Synthesis of ATP:- two types:-
- Oxidative phosphorylation
- Substrate level phosphorylation .

11. ATP-ADP CYCLE

13. • High energy phosphates :- ∆G
- Phosphoenolpyruvate - 14.8
- Carbaomyl phosphate - 12.3
- 1,3-BPG - 11.8
- Phosphocreatine - 10.3
- S-adenosylmethionine - 10.0
- Acetyl CoA -7.7
- ATP ADP + Pi - 7.3
Important high energy compounds

14. compounds ∆G
• ADP AMP+ Pi -6.6
- glucose-1-P -5.0
- Fructose-6-P - 3.8
- Glucose-6-P - 3.3
- Glycerol-3-P -2.2
Low energy phosphates

15. • Storage forms of high energy phosphates :-
• Phosphocreatine :- seen in skeletal muscle ,
heart & brain .
• Lohmann reaction:- catalyzed by creatine
kinase
• Creatine phosphocreatine +
+ ATP ADP +43.1 KJ/mol

16. Oxidation & reduction
• Oxidation:- removal of electrons
• Reduction :- gain of electron
• Reducing agent = e- donating molecule
• Oxidizing agent = e- accepting molecule
• for example:-
Fe ₂ + (ferrous) lose –e (reducing)
Fe 3+ (ferric) gain +e (oxidizing)
• They together make a conjugate redox pair/
redox couple.

17. • In oxidation & reduction reactions electrons
are transferred from one molecule to another
molecule through different ways :-
- Transferred directly as electrons :-
Fe 2⁺ + Cu2⁺ Fe 3⁺ + Cu⁺
- Transferred in the form of hydrogen atom
H= H⁺ + e-
- In the form of hydride ion (H-).

18. Redox reaction
• Redox reaction = reduction-oxidation reaction
• Several forms of Biological Reduction
1. loss of electrons
2. Hydrogenation
3. Deoxygenation
• Several forms of Biological Oxidation
1. gain of electrons
2. Dehydrogenation
3. Oxygenation

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

20. • Electrons tend to flow from one redox couple
to another in the direction of the more
positive system.
• standard redox potential :-is measured under
standard condition , at pH-7, and is expressed
in volts.

26. Electron transport chain
carbohydrate, Fatty acids, a.a
( metabolized)
NAD,FAD
mitochondria
NADH⁺, H⁺, FADH₂
(ETC)
transfer e-,liberate energy(ATP)
½ O₂

27. Mitochondria
• outer membrane :-relatively permeable.
• inner membrane :- permeable only to those
things which have specific transporters .
- ETC & ATP synthesizing system located in it.
- Phosphorlyting subunits ( centers for ATP
production).
• Matrix :- enzymes for TCA, beta- oxidation &
oxidation of amino acid.

29. Electron transport chain
• Final common pathway in the aerobic
cells by which electrons derived from
various substrates are transferred to
oxygen .
• series of oxidation reduction enzymes,
coenzymes & electron carrier
cytochrome.
• Location :- inner mitochondrial
membrane.

30. Components
• NAD ⁺
• NAD, FAD dehydrogenase
• FAD, FMN
• Coenzyme Q
• Iron containing proteins
- Iron sulfur protein associated with :-
- FMN & Cytochrome b
• Cytochrome b, c,c₁ & aa₃

31. Entry of electrons in respiratory chain

32. Nicotinamide nucelotide
• Found as two coenzymes :- NAD, NADP
• Derived from vitamin niacin .
• Involved in ETC .
• NAD⁺ is reduced to NADH + H ⁺ by dehydrognase
with removal 2 H atom.
• Substrate:- glyceraldehyde-3-P
- Pyruvate
- Isocitrate
- malate
-alpha keto-glutarate .

33. Flavoproteins
• NADH dehydrogenase is complex
enzyme.
- Consist of non-heme iron , Fe S,
- Flavoprotein with FMN as prosthetic gp.
- FMN accept two e⁻& H⁺ to form FMNH ₂
• Succinate dehydrogenase also
flavoprotein with FAD as coenzyme

34. • Iron sulphur protein : - ( Fe S)
- Present in two form – oxidized & reduced
- One Fe S transfer e- from FMN to
coenzyme Q
- Other transfer e- from Cyt b to Cyt C.
• Coenzyme Q :- also called ubiquinone
- Lipid soluble.
- Transfer e- & protons from complex I ,II to
III.

35. Cytochromes
• Colored component
• Conjugated proteins, containing iron gp. as ferric
state.
• It accept e- & are reduced to ferrous .
• As the e- pass to next component it reoxidized to
ferrous
• Three types :- cyt a, cyt b, cyt c
- Cyt a :- a & aa₃
- Cyt c :- c & c₁
cyt b FeS cyt c cyt c ₁ cyt aa₃ O₂

36. Cytochrome c :-
- mw:- 13,000
- Small protein of 104 a.a. & heme gp.
- Central member of ETC.
- Loosely bound to inner mitochondrial
membrane.

37. • Cytochrome a & a3 :-
- Terminal component of ETC.
- React directly with molecular oxygen.
- Also contains copper.

38. How the electrons Transfer in ETC
Role of components
• NAD⁺ :- accept & transfers one H⁻(one H ⁺,2e⁻ )
• FMN or FAD or coenzyme Q:-
- accept & donates two hydrogen( H ₂ i.e. 2H ⁺ ,
2e-) at a time.
• Each cytochrome or iron sulfur protein :-
-accept & transfers one e- but no hydrogen ion.

43. Complex II:
• Succinate dehydrogenase
(Succinate: CoQ oxidoreductase)
• Function:- transfer electrons from succinate to
CoQ
Components:-
Succinate dehydrogenase (FAD, Fe-S)
Cytochrome b

44. Complex III
• Co Q -Cyt c oxidoreductase
• Function: -transfer electrons from Co Q to
cytochrome c
• Components:- iron-sulfur protein
cytochrome b (b562, b566)
cytochrome c1

45. Complex IV
• Cytochrome oxidase
• Function: - transfer electrons from Cyt c to
molecule oxygen, the final electron acceptor.
• Components: - cytochrome aa₃
copper ion (Cu+)