The document discusses how oxidation-reduction reactions are central to metabolism as they allow for the transfer of electrons between molecules, with some molecules becoming reduced by gaining electrons and others becoming oxidized by losing electrons. Key electron carriers in metabolic redox reactions include coenzymes like NADH and FADH2, which can transfer electrons between different reactions. Energy released from redox reactions is then harnessed to drive the phosphorylation of ADP to form ATP, the main energy currency molecule in cells.

1. The
potential
energy of
the water at
the top of a
waterfall is
transformed
into kinetic
energy in
spectacular
fashion.
The Importance of
Energy Changes and
Electron Transfer in
Metabolism

2. The synthesis of glucose and other sugars in plants, the production of ATP from ADP, and the elaboration of
proteins and other biological molecules are all processes in which the Gibbs free energy of the system must
increase. They occur only through coupling to other processes in which the Gibbs free energy decreases by an
even larger amount. There is a local decrease in entropy at the expense of higher entropy of the universe.
p.416

3. Ilya Prigogine (1977)
won Nobel Prize

4. How are oxidation and reduction involved in
metabolism?
 Oxidation-reduction reactions: redox reactions; electrons
are transferred from donor to acceptor.
 Oxidation : loss of electrons; reduction: the gain of
electrons
 Substance that losses e- : the one that is oxidized (reducing
agent/reductant)
 Substance that gains e- : the one that is reduced (oxidizing
agent/oxidant)
eg. Oxidation alcohol aldehyde Carboxylic acid CO2
process
alkane

5. The half reaction of oxidation of
ethanol to acetaldehyde
Many biologically
important redox
reactions involve
coenzymes, such as
NADH and FADH2.
These coenzymes
appear in many
reactions as one of
the half-reactions that
can be written for a
redox reaction.
p.420

6. Another important electron acceptor is the oxidized form of FADH2.
Other several coenzymes contain flavin
group; derived from the vitamin riboflavin
(vit B2)
p.421

7.  ATP can be hydrolized
easily and the reaction
releases energy
 The coupling of energy-
producing reactions
and energy-requiring
reactions is a central
feature in metabolism
of all organisms
 The phosphorylation of
ADP to produce ATP
requires energy (can be
supplied by oxidation
of nutrients)
 The hydrolysis from
ATP to ADP releases
energy
FIGURE 15.5 The phosphoric anhydride bonds in ATP are
“highenergy” bonds, referring to the fact that they require or release
convenient amounts of energy, depending on the direction of the
reaction.

8. “High energy bond”
 High energy bond: term
for a reaction in which
hydrolysis for a specific
bond releases a useful
amount of energy.
 Another way to indicate
such a bond is ~P.
 The energy of hydrolysis
of ATP is not stored
energy, just an electric
current – ATP and electric
current must be produced
when they are needed.
FIGURE 15.7 Hydrolysis of ATP to ADP (and/or hydrolysis of ADP to AMP)

9. Table 15-1, p.425

10. Fig. 15-8, p.425

11. The oxidation processes takes
place when the organism needs
the energy that can be generated
by the hydrolysis of ATP
Example:
Let’s examine biological reaction that
release energy.
Glucose 2 Lactate ions
∆G°’= -184.5 kJmol-1= -44.1 kcal mol-1
2 ADP + 2 Pi 2 ATP
∆G°’= 61.0 kJ m mol-1= 14.6 kcal mol-1
The overall reaction:
Glucose + 2 ADP + 2 Pi 2 Lactate
ions + 2 ATP
The hydrolysis of ATP produced by
breakdown of glucose can be
coupled by endergonic processes.
eg. muscle contraction in exercise
(jogger/long distance-swimmer)
Fig. 15-9, p.426

12. Activation process is where a step
frequently encountered in
metabolism. A component of
metabolic pathway (metabolite) is
bonded to other molecule,
coenzyme, and the free enrgy
change for breaking this new bond is
negative.
eg. A – metabolite, B – substance
A + coenzyme A-coenzyme
A-coenzyme + B AB + coenzyme
Example of coenzyme: coenzyme A
(CoA)
Fig. 15-10, p.428

13. Fig. 15-11, p.429

14. Fig. 15-12, p.430

15.  In carbohydrate metabolism, glucose-6-phosphate reacts
NADP+ to give 6-phosphoglucono-δ-lactone. In this reaction, which
substance is oxidized and which is reduced? Which substance is
oxidizing agent and which is reducing agent?

16.  there is a reaction in which succinate reacts with FAD to give
fumarate and FADH2. In this reaction, which substance is oxidized
and which is reduced? Which substance is oxidizing agent and
which is reducing agent?

17. Electron transport and
oxidative phosphorylation

18.  Oxidative phosphorylation: the synthesis of ATP from
ADP using energy from mitochondrial electron transfer
from NADH + H+ and FADH2 to O2. (ADP + Pi ATP)
 Give rise to most of the ATP production associated with
the complete oxidation of glucose.
 Substrate-level phosphorylation: the synthesis of ATP
from ADP using energy from the direct metabolism of a
high energy reactant.
(A-P + ADP B + ATP).
This reaction occur in glycolysis and Kreb cycle
(carbohydrate metabolism).

19. Fig. 20-1, p.541

20. C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP
Note: on average, 2.5 moles of
ATP are generated for each
mole of NADH and 1.5 moles of
ATP are produced for each mole
of FADH2.
Fig. 20-2, p.541

21. Essential information
 The e- transport chain consists of four multi-subunit
membrane-bound complexes and two mobile e- carriers
(CoQ and cytochrome c)
 The reaction that take place in three of these complexes
generate enough energy to drive the phosphorylation of
ADP to ATP.
• Complex I
 known as NAD-CoQ oxidoreductase – catalyzes the
first steps of e- transport chain. (NADH to CoQ)
 this complex includes several proteins that contain an
iron-sulfur cluster and the flavoprotein that oxidizes
NADH.
 proven to be a challenging task because of its
complexity (iron-sulfur clusters).
• CoQ is mobile - it is free to move in the membrane and pass the e -
to complex III for further transport to O2

22. NADH + H+ + CoQ → NAD+ + CoQH2
Fig. 20-5, p.546

23. Complex II
 catalyzes the transfer of e- to CoQ, known as succinate-
CoQ oxidoreductase.
 its source of e- is differs from oxidizable substrate
(NADH) – the substrate is succinate (from TCA/Kreb
cycle), which is oxidized to fumarate by a flavin enzyme.
Succinate + E-FAD → Fumarate + E-FADH2
E-FADH2 + Fe-Soxidized → E-FAD + Fe-Sreduced
Fe-Sreduced + CoQ + 2H+ → Fe-Soxidized + CoQH2
 the overall reaction is exergonic, but there’s not enough
energy to drive ATP production + no hydrogen ions
pumped out of the matrix during this step.

24. Complex III
 CoQH2-cytochrome c oxidoreductase (cyt reductase)
catalyzes the oxidation of reduced coenzyme Q (CoQH2) –
the e- are passed along to cyt c.
CoQH2 + 2 Cyt c [Fe (III)] → CoQ + 2 Cyt c [Fe (II)] + 2 H+
note: the oxidation of CoQ involves two e-, whereas the reduction of Fe (III)
to Fe (II) requires only one e- → two molecules of cyt c are required for
every molecule of CoQ

25. Complex IV
 The 4th complex, cytochrome c oxidase, catalyzes the final
steps of e- transport → transfer the e- from cyt c to oxygen.
 cytochrome c oxidase is an integral part of the inner
mitochondrial membrane and contains cyt a and a3 and
two Cu2+ (is an intermediate e- acceptors that lie between
two a-type cyt).
 The overall reaction:
2 Cyt c [Fe(II)] + 2 H+ + ½ O2 → 2 Cyt c [Fe(III)] + H2O
Cyt c → Cyt a → Cu2+ → Cyt a3 → O2
 Both cyt a form the complex known as cytochrome
oxidase. The reduced cytochrome oxidase is then
oxidized by O2, which reduced to water.

26. So, from all four complexes, there are 3 places where e-
transport is coupled to ATP production by proton pumping:
 NADH dehydrogenase reaction
Oxidation of cyt b
Reaction of cytochrome oxidase with O2

27. Cytochromes and other Iron-Containing Proteins
of Electron Transport
Fig. 20-9, p.551
NADH, FMN and CoQ, the cytochromes are macromolecules and found in all types
of organisms and located in membrane.

28. p.551

29. Fig. 20-13, p.555

30. In glycolysis (carbohydrate metabolism), the NADH
produced in cytosol, but NADH in the cytosol cannot
cross the inner mitochondrial membrane to enter the
e- transport chain.
The e- can be transferred to a carrier that can cross the
membrane.
The number of ATP generated depends on the nature
of the carrier.

31. Glycerol-phosphate shuttle
- This mechanism observed in
mammalian muscles and brain.
Fig. 20-21, p.561

32. Malate-aspartate shuttle
- Has been found in
Fig. 20-22, p.562 mammalian kidney, liver
and heart.

33. Table 20-3, p.563

34. 4 different sources of energy
available for working muscles
after rest:
• Creatine phosphate- reacts
directly in substrate-level
phosphorylation to produce
ATP
• Glucose from glycogen
muscles stores; initially
consumed by anaerobic
metabolism
• Glucose from the liver
(glycogen stores and
gluconeogenesis) – consumed
by anaerobic metabolism
• Aerobic metabolism in the
muscles mitochondria.