1. The document discusses electrochemical processes in biology, which involve the transfer of electrons between sites of oxidation and reduction separated by membranes. Energy from electron transfer is stored as electrochemical proton gradients across membranes and used to synthesize ATP. 2. Key components of biological electron transfer systems include quinones, flavins, iron-sulfur proteins, and the electron transfer chains in mitochondria and chloroplasts. These systems facilitate the transduction of chemical energy into work through redox reactions. 3. The concept of redox potential can be applied to small, non-statistical biological systems by considering their equilibrium with larger macrosystems. This explains why electron transfer chains contain many components overlapping a wide range of potential levels

1. Oleh :
Endang Nurtriningsih (0906555235)
Priska Andini Putri (0906

2. Introduction
the coordinated processing of
 The life of plants is driven by
a vast number of chemical reactions.
 All chemical reactions are accompanied by a redistribution
of electrical charge in the reacting molecules.
 In the electrochemical process the overall reaction is divided
into two conjugated reactions. An electron is released from a
molecule in one location, where as in another site it is added
to another molecule. The site of the system where the
oxidative process occurs is usually called the anodic site
(anodic), and the site where reduction proceeds is called
cathodic site (cathode).

3.  The scheme of electrochemical oxiation of hydrogen by
oxygen may be written as the following pair of conjugated
reactions :

H2 – 2e → 2H+ released of electrons at anodic site
½ O2 + 2H- + 2e → H2O addition of electrons at cathodic site
 Inasmuch as the anodic and cathodic
sites are separated spatially and
processes at these sites are
conjugated, electrochemical
systems must include at least
two phase with different types
of conductivity.

4.  Electrochemical processes depend on electrical fields.
The electrochemical potential, total work required to
bring particle i from a vacuum into a phase :
+ z FΦ
µ =µ
i i i
where,
ziFΦ : electrostatic work required to bring a charge zie
from infinity in a vacuum to inside phase
F : Faraday number, the quantity of electricity associated
with 1 mol of elementary charge, 96500 C

5. 
 Electrochemical processes enable the direct
transformation of chemical energy into work. In
chemical reactions the total change in energy of a
reacting system is transformed into heat and, thus, into
chaotic movement of molecules.

6. Electrochemistry in Engineering and
Biology

 Scheme of an electrochemical systems in engineering (A) and in
biology (B). In the former case the electromotive force arises across the
gap in an electron conductor, in the latter it arises across a phase with
ionic conductivity.

7.  Panel A represent the scheme of an electrochemical engineering
device such as, for example, a battery. Metals are used as phases
with electronic conductivity, and ionic conductors are usually
electrolyte solution. Electromotive force, ΔE, is a difference in

electrical potentials arises between two electrodes and can be used
to perform work.
 Panel B represent the scheme of an bioelectrochemical device. The
electron conductor is continous, whereas the phase with ionic
conductivity is split.
 Nature designed biochemical mechanisms with the conductive
medium, insulator for the separation of aqueous phases and the
electronic conductor to provide the transfer electrons between the
points where they are released and accepted.
 Phospolipid membranes, which surround cells and subcellular
structures such as chloroplast and mitochondria, play the role of
insulators. The function of an electron conductor in biological
systems is performed by electron transfer chain.

8. Thermodynamics of Electrochemical
Systems



9.  The expression for the equilibrium electrode potential in the
case of a redox reaction proceeding with the participation of m
protons and n electrons is

 The redox potential of a system measure its capability to display
electron donor or acceptor properties, or to function as a
reducing or an oxidizing agent. A system with high positive
redox potentials may act as an oxidant toward a system with
less positive potential and vice versa.
 As the values of redox potentials are specified against the SHE,
they characterize the reducing “power” of redox system
compared to that of molecular hydrogen at 1 atm and 25oC in
acid solution.

10. Biological Redox Systems

 Redox systems, involved in biochemical processes,
present example of several types of substances.
Among them are a variety of quinoid compounds,
derivatives of isalloxazine, derivatives of nocotinoic
acid, metalloporphyrins, and iron-sulfur protein.

11. The Quinones
 in plants primarily as
 These substances are present
p-benzo and p-naphtho-quinones with various side
chains. The molecules of these compounds do not
change their overall configuration during redox
reactions.

12. Isoalloxazines (Flavins)

 Present a somewhat different
type of quinoid structure. Their
ability to undergo redox
conversion is due to the ease in
reorganizing their system of
conjugated bonds.
 The representatives of the
flavins are riboflavin (vitamin
B2), flavin mononucleotide
(FMN) and flavin adenine
dinucleotide (FAD).

13. Derivatives of Nicotinic Acid

 This significant group of substances capable of undergoing
redox conversions is represented mainly by NAD+
(nicotinamide adenine dinucleotide) and NADP+ (nicotinamide
adenine dinucleotide phosphate).
 A molecule of NADP+ differs from that of NAD+ by the
presence of an additional phosphate group linked to one of the
two five-member ribose cycles.

14. The Iron-Sulfur Proteins
(Ferredoxins)

 It contain in their active center several
iron atoms (usually between one and
four) linked to the protein body via
sulfur bridges.
 They play a definite role in
photosynthetic electron transfer,
nitrogen fixation, the reduction of
nitrates and nitrites, and other
processes. The function due to changes
in the valences of their iron atoms.

15. Arrangement of the Electrochemical
Processes

 Sequence of redox component along transfer electron
due to flow of electrons from a high energy level to a
lower is called electron transfer chain (ETC).
 The mitochondrial ETC is often referred to as the
respiratory chain because the step of biological
oxidation of organic matter and reduction of oxygen
occurs here.

16. The Respiratory Chain

 Electrons are delivered to the ETC from the reduced
components of the Krebs cycle.
 The first link of the ETC consists of enzymes known as the
pyridene-dependent dehydrogenases.
 The next link of the chain, to which NADH releases the
transfer electrons, is the flavoprotein NADH
dehydrogenase.
 The ubiquinones are found farther down the chain.
 The subquent path of electrons along the chain begins at
the potentials of ubiquinone and continues down to the
equilibrium potential oxygen.

17. Electron Transfer at Photosynthesis

 The process of photosynthesis involves the oxidation
of water followed by the released of oxygen and the
generation of highly substances, whch are then used
to carbon dioxide.
 Simultaneously, ATP is produced by the energy of
electron flow down the ETC.
 The electron transfer chain is arranged more
intricately than that in mitocondria, but the basic
principle is quite similar.

18. Coupling of Electron Flow with The Synthesis
of ATP

 The coupling of electron flow to the synthesis of ATP is
provided by the arrangement of thylakoid bags as closed
containers whose internal volume is separated from the
outer medium by a membrane.
 The components of the electron transfer chain are
localized across the membrane asymetrically in quite a
definite fashion.
 The ETC embedded the membrane plays the role of an
electronic conductor.
 Electron s enter the ETC and leave it as the result of
anodic or cathodic electrochemical reactions at the
membrane-water interface.

19. 
 The path of electron flow along the ETC embedded in the
membran begins at the level of NADH and terminates in
the reduction oxygen.
 As a result an electrochemical potential gradient of
protons arises across the membrane.
 The gradient is the form in which energy is stored across
the membranes of chloropasts and then used to produce
ATP.
 Electronchemical proton gradients comprise two
components, one due to the difference in hydrogen ion
concentration and the other due to the difference electrical
potential.

20. 
 In biological electrochemical systems such as
chloroplasts and mitocondria, energy is stored in the
membrane structure as a transmembrane gradient of
proton electrochemical potential.
 The energy stored as the transmembrane gradient of
electrochemical potential drives the processes of ATP
synthesis.
 Synthesis of ATP in mitochondria is driven by the
inward flow of protons through ATPase, whereas in
chloroplasts the ATPase is oriented oppositely and is
driven by outward proton flow.

21. Is The Notion of Redox Potential Applicable to
Small Systems?

 The redox potential of a system depends upon the
ratio between the number of molecules in an
oxidized state and those in a reduce state.
 In large systems this ratio, i.e., the degree of
oxidation, varies in a continous manner.
 The situation changes, however, for a small system
consisting only a few particles.
 In considering biological objects, we have dealt with
small, nonstatistical systems.

22. 
 The energy-transducing complexes embedded in the
membranes of mitochondria or chloroplasts contain
only a few molecules that develop redox properties
and provide the translocation of electrons through
the membrane.
 In analyzing, the usual approach based on a
statistical background can hardly be regarded as
justified.
 Hypothesis by Ludwig Boltzmann, the time average
state of a sufficiently large number of molecules.

23. 
 The redox potential of a small system is imposed by
the redox potential of the macrosystem with which a
small system is in equilibrium.
 The relationship between the redox potential and the
probability that the molecule will be found in one of
two conjugated redox states, i.e., to be either a donor
or an acceptor of electrons, gives a key to
understanding why electron transfer chains are
designed from a large set of components that overlap
a wide range of potential levels in small steps.