oxidative phosphorylation - ✔✔ oxidation-reduction reactions that allow the flow of electrons from
NADH and FADH2 to reduce
molecular oxygen to
... [Show More] water. The electron flow, which is very exergonic,
takes place in four large protein complexes that are embedded in the inner mitochondrial membrane, together called the respiratory chain or the electron-transport chain.
The mitochondrial matrix is the site of the - ✔✔ reactions of the citric acid cycle and fatty acid oxidation.
Inner mitochondria - ✔✔ oxidative phosphorylation takes place in the inner mitochondrial membrane.
the inner membrane is intrinsically impermeable - ✔✔ A large family of transporters shuttle metabolites such as ATP, pyruvate,
and citrate across the inner mitochondrial membrane.
electron-transfer potential - ✔✔ In oxidative phosphorylation, the electron-transfer potential of NADH or FADH2 is converted into the phosphoryl-transfer potential of ATP.
measure of phosphoryl-transfer potential - ✔✔ The measure of phosphoryl-transfer potential is already familiar to us: it is given by ΔG°′ for the hydrolysis of the phosphoryl compound. The corresponding expression for the electron-transfer potential is E′0, the reduction potential (also
called the redox potential or oxidation-reduction potential).
redox potential - ✔✔ couple can be determined by measuring the electromotive force generated by a
sample half-cell connected to a standard reference half-cell. A negative reduction
potential means that the oxidized form of a substance has lower affinity for electrons than does H2. A positive reduction potential means that the oxidized form of a substance has higher affinity for electrons than does H2.
strong reducing agent - ✔✔ a strong reducing agent (such as NADH)is poised to donate electrons and has a negative reduction potential,
strong oxidizing agent - ✔✔ (such as O2) is ready to accept electrons and has a positive reduction potential.
Electron Flow Through the Electron-Transport Chain
Creates a Proton Gradient - ✔✔ The driving force of oxidative phosphorylation is the electron-transfer potential of
NADH or FADH2 relative to that of O2
Energy released - ✔✔ The energy released by the reduction of each electron carrier generates a proton gradient that is then used for the synthesis of ATP and the transport of metabolites across the mitochondrial membrane.
Indeed, each proton transported out of the matrix to the cytoplasmic side correspondsto 21.8 kJ mol-1 (5.2 kcal mol-1) of free energy.
The Electron-Transport Chain Is a Series of Coupled
Oxidation-Reduction Reactions - ✔✔ Electron flow from NADH to O2 is accomplished by a series of intermediate electron carriers—a bucket brigade of electron carriers—that are coupled as members of sequential redox reactions.
Electron flow - ✔✔ The members of the electron-transport chain are arranged so that the electrons always flow to components with more positive reduction
potentials (a higher electron affinity).
Complexes - ✔✔ Electrons are transferred from NADH to O2 through a chain of three large protein
complexes called NADH-Q oxidoreductase, Q-cytochrome c oxidoreductase,and cytochrome c oxidase
respirasome. - ✔✔ These complexes appear to be associated
in a supramolecular complex termed the respirasome.
ETC - ✔✔ A fourth large protein complex, called
succinate-Q reductase, contains the succinate dehydrogenase that generates FADH2 in the citric acid cycle (p. 349). Electrons from this FADH2 enter the electron-transport chain at Q-cytochrome c oxidoreductase.
FADH2 flow - ✔✔ First of all, electrons from FADH2 feed into the chain "downstream" of those from NADH because the electrons of FADH2 have a lower reduction potential (Table 20.1). As a result, FADH2-derived electrons pump fewer protons and thus yield fewer molecules of ATP. Second, note that iron is a prominent electron carrier, appearing in several places. Iron in the electron transportchain appears in two fundamental forms: associated with sulfur as iron-sulfur clusters located in iron-sulfur proteins (also called nonheme-iron proteins, and as components of a heme-prosthetic group
Coenzyme Q, - ✔✔ Another key feature of the electron-transport chain is the prominence of
coenzyme Q (Q) as an electron carrier. Coenzyme Q, also known as ubiquinone
because it is a ubiquitous quinone in biological systems, is a quinone derivative
with a long isoprenoid tail, which renders the molecule hydrophobic and allows
it to diffuse rapidly within the inner mitochondrial membrane, where it shuttles protons and electrons about
quinones - ✔✔ for quinones, electron-transfer reactions are coupled to proton binding
and release, a property that is key to transmembrane proton transport.
Proton gradient - ✔✔ Electron flow within these transmembrane complexes leads to the transport of protons across the inner
mitochondrial membrane.
Flow of protons - ✔✔ the flow of two electrons from NADH to coenzyme Q through NADH-Q
oxidoreductase leads to the pumping of four hydrogen ions out of the
matrix of the mitochondrion.
proton - ✔✔ cytochrome c oxidase uses this energy to pump four additional protons from the
matrix to the cytoplasmic side of the membrane in the course of each reaction
cycle for a total of eight protons removed from the matrix
outer mitochondrial membrane - ✔✔ outer mitochondrial membrane is freely permeable to small molecules. This is because it contains proteins called porins,
inner membrane - ✔✔ The inner membrane is folded into a series of internal ridges called cristae.
innner mitochondrial membrane - ✔✔ The _________ membrane is the site of electron transport and ATP synthesis.
chapter 21 - ✔✔ During the electron flow, protons are pumped from the mitochondrial matrix to
the outside of the inner mitochondrial membrane, creating a proton gradient.
Energy is thus transformed as electron transfer potential is converted into a proton gradient, an energy-rich circumstance because the entropy of the protons is reduced. [Show Less]