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
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)
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
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?
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).
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
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.
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.
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.
Hinweis der Redaktion
The potential energy of the water at the top of a waterfall is transformed into kinetic energy in spectacular fashion.
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.
The characteristics of isolated, closed, and open systems. Isolated systems exchange neither matter nor energy with their surroundings. Closed systems may exchange energy, but not matter, with their surroundings. Open systems may exchange either matter or energy with the surroundings.
FIGURE 15.2 Comparison of the state of reduction of carbon atoms in biomolecules: -CH2O- (fats) >-CHOH- (carbohydrates) >- C=O (carbonyls) >-COOH (carboxyls) > CO2 (carbon dioxide, the final product of catabolism).
FIGURE 15.8 When phosphoenolpyruvate is hydrolyzed to pyruvate and phosphate, it results in an increase in entropy. Both the formation of the keto form of pyruvate and the resonance structures of phosphate lead to the increase in entropy.
FIGURE 15.9 The role of ATP as energy currency in processes that release energy and processes that use energy.
FIGURE 15.10 (a) The structure of coenzyme A. (b) Space-filling model of coenzyme A.
FIGURE 15.11 The hydrolysis of acetyl-CoA. The products are stabilized by resonance and by dissociation.
FIGURE 15.12 The role of electron transfer and ATP production in metabolism. NAD+, FAD, and ATP are constantly recycled.
FIGURE 20.1 A proton gradient is established across the inner mitochondrial membrane as a result of electron transport. Transfer of electrons through the electron transport chain leads to the pumping of protons from the matrix to the intermembrane space. The proton gradient (also called the pH gradient), together with the membrane potential (a voltage across the membrane), provides the basis of the coupling mechanism that drives ATP synthesis.
FIGURE 20.2 Schematic representation of the electron transport chain, showing sites of proton pumping coupled to oxidative phosphorylation. FMN is the flavin coenzyme f lavin m ono n ucleotide, which differs from FAD in not having an adenine nucleotide. CoQ is coenzyme Q (see Figure 20.4). Cyt b , cyt c 1, cyt c , and cyt aa 3 are the hemecontaining proteins cytochrome b , cytochrome c 1, cytochrome c , and cytochrome aa 3, respectively.
FIGURE 20.4 The oxidized and reduced forms of coenzyme Q. Coenzyme Q is also called ubiquinone.
FIGURE 20.5 The electron transport chain, showing the respiratory complexes. In the reduced cytochromes, the iron is in the Fe(II) oxidation state; in the oxidized cytochromes, the oxygen is in the Fe(III) oxidation state.
FIGURE 20.7 The compositions and locations of respiratory complexes in the inner mitochondrial membrane, showing the flow of electrons from NADH to O2. Complex II is not involved and not shown. NADH has accepted electrons from substrates such as pyruvate, isocitrate, -ketoglutarate, and malate. Note that the binding site for NADH is on the matrix side of the membrane. Coenzyme Q is soluble in the lipid bilayer. Complex III contains two b -type cytochromes, which are involved in the Q cycle. Cytochrome c is loosely bound to the membrane, facing the intermembrane space. In Complex IV, the binding site for oxygen lies on the side toward the matrix.
FIGURE 20.9 The heme group of cytochromes. (a) Structures of the heme of all b cytochromes and of hemoglobin and myoglobin. The wedge bonds show the fifth and sixth coordination sites of the iron atom. (b) A comparison of the side chains of a and c cytochromes to those of b cytochromes.
FIGURE 20.13 The creation of a proton gradient in chemiosmotic coupling. The overall effect of the electron transport reaction series is to move protons (H+) out of the matrix into the intermembrane space, creating a difference in pH across the membrane.
FIGURE 20.21 The glycerol–phosphate shuttle.
FIGURE 20.22 The malate–aspartate shuttle.
Cancer survivor and champion cyclist Lance Armstrong on his way to a third Tour de France victory.