The document discusses biological oxidation and the electron transport chain. It covers topics like the stages of foodstuff oxidation, redox potentials, enzymes and co-enzymes in biological oxidation, high energy compounds, the organization of the electron transport chain, oxidative phosphorylation, and ATP synthesis. It notes that food is broken down and oxidized to generate reducing equivalents like NADH and FADH2, which then enter the electron transport chain to release energy that is used to synthesize ATP through oxidative phosphorylation.

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. Stages of Oxidation of Foodstuffs
First Stage
Digestion in the gastrointestinal tract converts the
macromolecules into small units. For example, proteins are
digested to amino acids. This is called primary metabolism
(Fig. 2.1).
Second Stage
The products of digestion are absorbed, catabolized to smaller
components, and ultimately oxidized to CO2. The reducing
equivalents are mainly generated in the mitochondria by the
final common oxidative pathway, citric acid cycle. In this
process, NADH and FADH2 are generated. This is called
secondary or intermediary metabolism (Fig. 2.1).

4. Third Stage
These reduced equivalents (NADH and FADH2) enter into the
electron transport chain (ETC), or Respiratory chain, where
energy is released. This is the tertiary metabolism or Internal
respiration or cellular respiration (Fig. 2.1).
The energy production by complete oxidation of one molecule
of glucose is 2850 kJ/mol and that of palmitate is 9781 kJ/mol.
This energy is then used for synthetic purpose in the body
(Fig. 2.2).
Phototrophs harvest the energy of light (plants).
Chemotrophs harvest energy from oxidation of fuel
molecules. Principles of bioenergetics and thermodynamics

5. Fig. 2.1: Oxidation of foodstuffs in three stages
FADH2

6. Fig. 2.2: ATP generation. Food is catabolized; energy from
food is trapped as ATP; it is then used for anabolic reactions

7. Box 2.1: Summary of bioenergetics
• 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. C hangesi n the free energy (G) are valuable in
predicting the feasibility of chemical reactions
1. Free energy is a measure of the energy available to perform useful
work
2. ΔG can predict the direction of a chemical reaction
3. Chemical reactions can be coupled, which allows an energetically
unfavorable reaction to conclusion
4. ΔG measured under physiological conditions may be different from
that at a standard state

8. REDOX POTENTIALS
Redox potential of a system is the electron transfer potential E0
‫׳‬. Oxidation is defined as the loss of electrons and reduction as
the gain in electrons.
When a substance exists both in the reduced state and in the
oxidized state, the pair is called a redox couple.
The redox potential of this couple is estimated by measuring
the electromotive force (EMF) of a sample half cell
connected to a standard half cell.
The sample half cell contains one molar solution each of the
reductant and oxidant.
The reference standard half cell has 1 M H+ solution in
equilibrium with hydrogen gas at one atmosphere pressure.
The reference half cell has a reduction potential of zero mV.

9. Negative and Positive Redox Potential
• The oxidation-reduction potential or, simply, redox potential,
is a quantitative measure of the tendency of a redox pair to
lose or gain electrons. The redox pairs are assigned specific
standard redox potential (Eo volts) at pH 7.0 and 25"C.
When a substance has lower affinity for electrons than
hydrogen, it has a negative redox potential. If the substance
has a positive redox potential, it has a higher affinity for
electrons than hydrogen. Thus NADH, a strong reducing agent,
has a negative redox potential (–0.32 V ), whereas a strong
oxidant like oxygen has a positive redox potential (+0.82 V).
Table 20.1 gives the redox potentials of some of the important
redox couples of the biological system. A summary is shown in
Box 20.1.

10. TABLE 2.1: Redox potentials
Oxidant Reductant Eo' (in V)
NAD+ NADH + H+ –0.32
Cytochrome b+++ Cytochrome b++ +0.07
Co-enzyme Q Coenzyme QH2 +0.10
Cytochrome c+++ Cytochrome c++ +0.22
Cytochrome a+++ Cytochrome a++ +0.29
O2 + 2H H2O +0.82

11. ANY
QUESTION?