Bioenergetics and oxidative
phosphorylation

What is meant by bioenergetics
• Bioenergetics describes the transfer and utilization
of energy in biologic
• systems. It makes use of a few basic ideas from the
field of thermodynamics, particularly the concept
of free energy

Free energy
• The direction and extent to which a chemical
reaction proceeds is
• determined by the degree to which two factors
change during the reaction.
• Enthalpy
• Entropy

Free energy change
• Negative ∆G
• net loss of energy, and
• the reaction goes spontaneously
• Positive ∆G
• net gain of energy, and
• the reaction does not go spontaneously
• ∆G is zero
• the reactants are in equilibrium

Standard free energy change
• ∆G = ∆Go

Electron transport chain
• Glucose metabolism upto glycolysis and TCA cycle
yields reduced coenzymes.
• reduced coenzymes can, in turn, each donate a pair
• of electrons to a specialized set of electron carriers,
collectively called
• the electron transport chain (ETC)

• As electrons are passed down the ETC, they lose
much of their free energy.
• This energy is used to move protons across the
inner mitochondrial
• membrane , creating a proton gradient that drives
the production of
• ATP from ADP and inorganic phosphate (Pi)

• The ETC (except for cytochrome c) is located in the
inner
• mitochondrial membrane and is the final common
pathway by which
• electrons derived from different fuels of the body
flow to oxygen (O2)

Outer mitochondrial membrane
• outer membrane contains s pecial channels
(formed by the protein porin), making it freely
permeable to
• most ions and small molecules

Inner mitochondrial membrane
• inner membrane is a specialized structure that is
impermeable to most small ions, including
• protons and small molecules such as ATP, ADP,
pyruvate, and
• other metabolites important to mitochondrial
function.
• So specialized transporters are present to move
molecules and ions across that membrane.

Mitochondrial matrix
• rich in protein
• include the enzymes responsible for the oxidation of
pyruvate, amino acids,
• and fatty acids (by β-oxidation) as well as those of the
tricarboxylic acid (TCA) cycle.
• The synthesis of glucose, urea, and heme occurs
partially in the matrix of mitochondria.
• matrix contains NAD and FAD (the oxidized forms of the
two coenzymes that are required as hydrogen
acceptors), and ADP and Pi which are used to produce
ATP.

Organization of ETC
• The inner mitochondrial membrane contains five
separate protein complexes, called Complexes I, II,
III, IV, and V

• These complexes accept or donate electrons to the
relatively mobile electron carriers, coenzyme Q a
nd cytochrome c.
• With the exception of coenzyme Q, which is a lipid-
soluble quinone, all members of this chain are
proteins.
• All the complexes may contain iron as part of Fe-S
center, may contain iron as prosthetic group of
heme as in cytochrome s, may contain copper as
Complex 4.

Site specific INHIBITORS of ETC

Complex 5 or ATP synthase
• synthesizes ATP using the energy of the
• proton gradient. It contains a domain (Fo) that
spans the inner mitochondrial membrane, and an
extramembranous domain (F1)
• that appears as a sphere that protrudes into the
mitochondrial matrix.

• after protons have been pumped to the
intermembranous space, they reenter the matrix by
passing through a proton channel in the Fo domain,
driving rotation
• of the c ring of Fo domain.

ATP synthesis is coupled to
electron transport through
the proton gradient

Oligomycin tells about tight
coupling of ETC with ATP formation.

Thank you 💕