The document discusses biological oxidation and electron transport chain. It covers several topics: 1. Stages of oxidation of foodstuffs and the enzymes/co-enzymes involved in biological oxidation. 2. High energy compounds like ATP that are produced. ATP hydrolysis releases energy that drives cellular reactions. 3. The electron transport chain, which involves a series of redox reactions and protein complexes to establish an electrochemical gradient used for ATP synthesis.

1. BIOLOGICAL OXIDATION AND ELECTRON
TRANSPORT CHAIN
DIPAK KUMAR SINGHA
ASST. PROFESSOR
CALCUTTA INSTITUTE OF
PHARMACEUTICAL TECHNOLOGY &
AHS
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2. BIOLOGICAL OXIDATION AND ELECTRON
TRANSPORT CHAIN
The students must be able to answer questions on the
following topics:
➢ Stages of Oxidation of Foodstuffs
➢ Redox potentials
➢ Biological oxidation
➢ Enzymes and co-enzymes involved biological oxidation
➢ High energy compounds
➢ Organization of electron transport chain
➢ Oxidative Phosphorylation
➢ Chemiosmotic theory
➢ Proton pump
➢ ATP synthesis
➢ Inhibitors of ATP synthesis

3. Biological
Oxidation and Electron
Transport Chain
Bioenergetics or biochemical thermodynamics deals with the study of
energy changes (transfer and utilization)in biochemical reactions. The
reactions are broadly classified as exergonic (energy releasing) and
endergonic (energy consuming)
Free energy
The energy actually available to do work ( utilizable)is kkown as free
energy. Changes in the free energy (G) are valuable in predicting
the feasibility of chemical reactions

4. Negative and positive G
lf free energy change (G) is represented by a negative sign, there is a
loss of free energy. The reaction is said to be exergonic, and
proceeds spontaneously. On the other hand, a positive + G indicates
that energy must be supplied to the reactants. The reaction cannot
proceed spontaneously and is endergonic/endothermic in character.
The hydrolysis of ATP is a classical example of exergonic reaction
ATP + H2O--+ ADP + Pi (AG' =-7.3 Cal/mol)
➢ The reversal of the reaction (ADP + Pi -+ ATP) is endergonic and
occurs only when there is a supply of energy of at least 7.3 Cal/mol
(AG' is positive).
➢ The free energy change becomes zero (delta G = 0) when a
reaction is at equilibrium.

5. • At a constant temperature and pressure, AC is dependent on the
actual concentration of reactants and products. For the conversion of
reactant A to product B (A -+ B), the following mathematical relation
can be derived

6. Biological Oxidation
• Oxidation is defined as the loss of electrons and reduction as the gain
of electrons. This may be illustrated by the interconversion o f ferrous
ion (Fe2+)to ferric ion (Fe3+)

7. All the enzymes involved in this process of biological oxidation
belong to the major class of oxidoreductases. They can be
classified into the following 5 headings:
1. Oxidases
These enzymes catalyze the removal of hydrogen from
substrates, but only oxygen can act as acceptor of hydrogen,
so that water is formed.
AH2 + ½ O2 A + H2O
This group includes Cytochrome oxidase (terminal
component of ETC), tyrosinase,
polyphenol oxidase,
catechol oxidase and monoamine oxidase.
Enzymes and co-enzymes involved biological oxidation

8. 2. Aerobic Dehydrogenases
These enzymes catalyze the removal of hydrogen from a substrate, but
oxygen can act as the acceptor. These enzymes are flavoproteins and the
product is usually hydrogen peroxide.
AH2 + O2 A + H2O2
These flavoproteins contain either FMN or FAD as prosthetic group.
3. Anaerobic Dehydrogenases
• These enzymes catalyze the removal of hydrogen from a substrate but
oxygen cannot act as the hydrogen acceptor. They therefore require co-
enzymes as acceptors of the hydrogen atoms. When the substrate is
oxidized, the coenzyme is reduced.
• NAD+ linked Dehydrogenases: NAD+ is derived from nicotinic acid, a
member of the vitamin B complex (see Chapter 37). When the NAD+
accepts the two hydrogen atoms, one of the hydrogen atoms is removed
from the substrate as such.
• H2 H + H+ + e–
• AH2 + NAD+ → A + NADH + H+

9. i. Glyceraldehyde-3-phosphate dehydrogenase
ii. Isocitrate dehydrogenase
iii. Malate dehydrogenase
iv. Glutamate dehydrogenase
v. Beta hydroxyacyl CoA dehydrogenase
vi. Pyruvate dehydrogenase
vii. Alpha ketoglutarate dehydrogenase.

10. b. NADP+ linked dehydrogenases: NADPH cannot be oxidized with
concomitant production of energy. NADPH is used in reductive
biosynthetic reactions like fatty acid synthesis and cholesterol synthesis.
An example of NADPH linked dehydrogenase is the glucose-6-phosphate
dehydrogenase.
c. FAD-linked dehydrogenases: When FAD is the coenzyme,
(unlike NAD+), both the hydrogen atoms are attached to the flavin ring.
Examples:
i. Succinate dehydrogenase
ii. Fatty acyl CoA dehydrogenase
iii. Glycerolphosphate dehydrogenase
d. Cytochromes: All the cytochromes, except cytochrome oxidase, are
anaerobic dehydrogenases. (Cytochrome oxidase is an oxidase, see
above).
All cytochromes are hemoproteins having iron atom. Cytochrome b,
cytochrome c1, and cytochrome c are in mitochondria while cytochrome
P-450 and cytochrome b5 are in endoplasmic reticulum.

11. 4.Hydroperoxidases
a. Peroxidase: Examples of peroxidases are glutathione peroxidase
in RBCs (a selenium containing enzyme), leukocyte peroxidase and horse
radish peroxidase. Peroxidases remove free radicals like hydrogen
peroxide. H2O2 + AH2 (peroxidase) 2 H2O + A
b. Catalase: Catalases are hemoproteins. Peroxisomes are subcellular
organelles having both aerobic dehydrogenases and catalase.
2 H2O2 (catalase) 2 H2O + O2
5. Oxygenases
a. Mono-oxygenases: These are otherwise called mixed function oxidases.
Here, one oxygen atom is incorporated into the substrate and the other
oxygen atom is reduced to water. These enzymes are also called
hydroxylases because OH group is incorporated into the substrate.
A-H+ O2+ BH2--(hydroxylase)→ A-OH+ H2O+ B
i. Phenylalanine hydroxylase
ii. Tyrosine hydroxylase
iii. Tryptophan hydroxylase

12. iv. Microsomal cytochrome P-450 mono-oxygenase is oncerned
with drug metabolism.
v. Mitochondrial cytochrome P-450 mono-oxygenase. The figure
“450” denotes that it absorbs light at 450 nm, when the
heme combines with carbon monoxide. It is required for steroid
hydroxylation in adrenal cortex, testis and ovary.
v. Nitric oxide synthase
• b. Di-oxygenases: They are enzymes which incorporate both
atoms of a molecule of oxygen into the substrate, e.g.
tryptophan pyrrolase and homogentisic acid oxidase
A + O2 AO2

13. High energy compounds
These compounds when hydrolyzed will release a large quantity of energy,
that is, they have a large ΔG0’’. The high energy bond in compounds is
usually indicated by a single bond (~). The free energy of hydrolysis ΔG0’ of
an ordinary bond varies from –1 to –6 kcal/mol. For example, glucose-6-
phosphate has a free energy of only 13.8 kJ/mol (–3.3 kcal/mol). On the
other hand, the free energy of high energy bonds varies from >25 kJ/mol (–7
to –15 kcal/mol). High energy compounds are listed below.

14. Adenosine Triphosphate (ATP)
i. ATP is the universal currency of energy within the living cells.
Structure of ATP.
ii. The hydrolysis of ATP to ADP (under standard conditions)
releases –30.5 kJ/mol or –7.3 kcal/mol (ΔG0’ = – 7.3). The energy
in the ATP is used to drive all endergonic (biosynthetic)
reactions. The energy efficiency of the cell is comparable to any
machine so far invented. ATP captures the chemical energy
released by the combustion of nutrients and transfers it to
synthetic reactions that require energy.
iii. At rest, Na+-K+ -ATPase uses up one-third of all ATP formed. Other
energy requiring processes are, biosynthesis of macromolecules,
muscle contractions, cellular motion using kinesin, dyenin etc.
iv. ATP is continually being hydrolyzed and regenerated. An average
person at rest consumes and regenerates ATP at a rate of
approximately 3 molecules per second, i.e. about 1.5 kg/day!

15. At this juncture, it is interesting to review different
types of reactions undergone by ATP.
1. Glucose + ATP → Glucose-6-phosphate + ADP Here ATP is hydrolyzed to ADP level
and phosphate is incorporated in the product.
2. Pyruvate + CO2 +ATP → Oxaloacetate + ADP + Pi Here ATP is hydrolyzed to ADP
level, but phosphate is released.
3. Fatty acid + CoA + ATP → Fatty acyl CoA + AMP + Ppi The ATP is hydrolyzed to AMP
level, but pyrophosphate is released.
4. Ribose-5-P + ATP → Phosphoribosyl pyrophosphate + AMP Although ATP is
hydrolyzed to AMP level, the pyrophosphate is added to the substrate.
5. Amino acid + ATP → Aminoacyl adenylate + Ppi Here AMP group is incorporated
into the product.
6. Methionine + ATP → S-adenosyl methionine + PPi + Pi Here adenosyl group is
incorporated into the product.
Cyrus Fiske and Yellapragada Subbarao discovered ATP in 1929; Karl Lohmann
showed its importance in muscle contraction in 1929. In
1941, Fritz Lipmann (Nobel prize, 1953) showed that ATP is the universal
carrier of chemical energy in the cell and coined the expression “energy
rich phosphate bonds”. Alexander Todd (Nobel Prize 1957) elucidated its
structure.

16. ATP ADP Cycle
• The hydrolysis of ATP is associated with the release of large amount of
energy.
• ATP + H2C ------+A DP + Pi + 7.3 Cal.

17. ANY
QUESTION?