- Electron transport chain and oxidative phosphorylation
- Overview of the electron transport chain(ETC)
- NADH and FADH2 are produced by glycolysis, b-oxidation of fatty acids, the TCA cycle, and other oxidative reactions.(MCQ)
- NADH and FADH2 pass electrons to the components of the ETC, which are located in the inner mitochondrial membrane.(MCQ)
- NADH freely diffuses from the matrix to the membrane
- whereasFADH2 is tightly bound to enzymes that produce it within the inner mitochondrial membrane.(MCQ)
- Mitochondria are separated from the cytoplasm by two membranes.
- The soluble interior of a mitochondrion is called the matrix.
- The matrix is surrounded by the inner membrane, which contains vast infoldings to increase surface area, known as cristae.
- The transfer of electrons from NADH to oxygen (O2) occurs in three stages, each of which involves a large protein complex in the inner mitochondrial membrane.
- Some of the genes for the large protein complexes are encoded by nuclear DNA, while others are coded for by mitochondrial DNA (mtDNA).(MCQ)
- Each complex uses the energy from electron transfer to pump protonsto the cytosolic side of the inner mitochondrial membrane.
- An electrochemical potential or proton-motive force is generated
- ATP is produced as the protons enter back into the matrix through the ATP synthase complex.
- During the transfer of electrons through the ETC,some of the energy is lost as heat.
- The electron transport chain has a large negative G0’, thus electrons flow from NADH (or FADH2) toward O2.(MCQ)
- Components of the electron transport chain
- The reduced cofactors, NADH and FADH2 ,transfer electrons to the ETC.
- Flavin mononucleotide (FMN)receives electrons from NADH and transfers them through iron- sulfur (Fe-S) centers to coenzyme Q(MCQ)
- FMN is derived from riboflavin.
- Coenzyme Q (CoQ)
- receiveselectrons from FMN and also through Fe-S centers from FADH2(MCQ)
- FADH2 is not free in solution like NAD+ and NADH; it is tightly bound to enzymes.
- CoQ can be synthesized in the body.
- It is not derived from a vitamin.
- Cytochromes receive electrons from the reduced form of CoQ.
- Each cytochrome consists of a heme group associated with a protein.
- The iron of the heme group I reduced when the cytochrome accepts an electron.
- Fe3+ becomes Fe2+(MCQ)
- Heme is synthesized from glycine and succinyl coenzyme A (CoA) in humans(MCQ)
- O2 ultimately receives the electrons at the end of the electron transport chain and is reduced to water (H2O).
- The three major stages of electron transport
- Transfer of electrons from NADH to coenzyme Q(ComplexI)
- NADH passes electrons via the NADH dehydrogenase complex to FMN.
- NADH is produced by the alpha-ketoglutarate dehydrogenase, isocitrate dehydrogenase, and malate dehydrogenase reactions of the TCA cycle, by the PDH reaction that converts pyruvate to acetyl CoA, by beta-oxidation of fatty acids, and by other oxidationreactions.(MCQ)
- NADH produced in the mitochondrial matrix diffuses to the inner mitochondrial membrane where it passes electrons to FMN, which is tightly bound to a protein..(MCQ)
- FMN passes the electrons through a series of Fe-S protein complexes to CoQ, whichaccepts electrons one at a time, forming first the semiquinone and then ubiquinol.
- The energy produced by these electron transfers is used to pump protons to the cytosolic side of the inner mitochondrial membrane.
- Transfer of electrons from CoQtocyto chrome C
- CoQ passes electrons through Fe-S centers to cyto chromes b and c1 (complex III), which transfer the electrons to cytochrome c(MCQ)
- The protein complex involved in these transfers is called cytochrome c reductase.
- These cytochromes each contain heme as a prosthetic group but have different apoproteins.
- In the ferric (Fe3+) state, the heme iron can accept one electron and be reduced to the ferrous (Fe2+) state.
- Because the cytochromes can only carry one electron at a time, CoQ acts as an adapter between the two electron transfers in complex I, and the one electron transfer in com-plex III.(MCQ)
- The energy produced by the transfer of electrons from CoQ to cytochrome c is used to pump protons across the inner mitochondrial membrane
- Proton flow back into the mitochondrial matrix, via the ATP synthase, will drive ATP synthesis.(MCQ)
- Electrons from FADH2 (complex II), produced by reactions such as the oxidation of succinate to fumarate by succinate dehydrogenase, enter the electron transport chain at the CoQ level(MCQ)
- Transfer of electrons from cyto chromec to oxygen
- Cytochrome c transfers electrons to the cytochrome aa3 complex(complex IV), whichtransfers the electrons to molecular O2, reducing it to H2O.
- Cytochrome c oxidase catalyzes this transfer of electrons(MCQ)
- Cytochromes a and a3 each contain a heme and two different proteins that each contain copper.(MCQ)
- Two electrons are required to reduce 1 atom of O2; therefore, for each mole of NADH that is oxidized, 1/2 mole of O2 is converted to H2O.(MCQ)
- The energy produced by the transfer of electrons from cytochrome c to O2 is used to pump protons across the inner mitochondrial membrane.
- ATP production
- As elements of the ETC pass electrons from complex I to IV, an electrochemical potential or proton-motive force is generated.
- The electrochemical potential consists of both a membrane potentialand a pHgradient.
- The cytosolic side of the membrane is more acidic (i.e., has a higher [H+]) than thematrix.
- The protons can reenter the matrix only through the ATP synthase complex(complex V, theF0–F1/ATPase), causing ATP to be generated.
- The (F0) component forms a channelin the inner mitochondrial membrane, throughwhich protons can flow.
- The (F1) is the ATP-synthesizing head, projecting into the mitochondrial matrix that is connected to the F0 portion via a stalk.
- Total ATP production
- For every mole of NADH that is oxidized, 1/2 mole of O2 is reduced to H2O, and about 2.5 moles of ATP are produced. (MCQ)
- Each mole of NADH oxidized leads to 10 moles of protons being extruded from the matrix.
- Because it requires four moles of protons entering the ATP synthase to generate one mole of ATP, 2.5 moles of ATP can be generated per 10 moles of protons extruded.
- For every mole of FADH2 that is oxidized, about 1.5 moles of ATP are generated because the electrons from FADH2 enter the chain via CoQ, bypassing the NADH dehydrogenase step(MCQ)
- For each mole of FADH2 oxidized, six moles of protons are extruded across the inner mitochondrial membrane.
- The ATP-ADP antiport.
- ATP produced within mitochondria is transferred to the cytosol in exchange for ADP by a transport protein in the inner mitochondrial membrane known as the ATP-ADP antiporter (adenine nucleotide translocase [ANT])
Inhibitors of the electron transport chain (A Very High yield MCQ Topic )
- Applied aspects
- Leber’shereditary optic neuropathy (LHON)(MCQ)
- mitochondrial DNA (mtDNA) disorder
- have point mutations in the gene for cytochrome reductase
- Patients are typically males in their20s to 30s who develop loss of central vision.
- Kearns-Sayre syndrome(MCQ)
- mtDNA defect known
- havemutations in complex II of the ETC.
- These patients manifest with short stature, complete external ophthalmoplegia, pigmentary retinopathy, ataxia, and cardiac conduction defects
- Leigh disease(MCQ)
- An mt DNA disorder
- mutations in cytochrome oxidase.
- present with lactic acidemia,developmental delay, seizure, extraocular palsies, and hypotonia.
- The disorder is usually fatal by the age of 2 years
Electron Transport Chain
PART I – Oxidative Phosphorylation, Electron Transport Chain
Cellular Respiration (Electron Transport Chain)
NDSU Virtual Cell Animations Project animation ‘Cellular Respiration (Electron Transport Chain
Electron Transport Chain
Cellular Respiration 5 – Oxidative Phosphorylation
This tutorial is the fifth in the Cellular Respiration series. This tutorial provides an overview of Oxidative Phosphorylation, in particular the Electron Transport Chain
Electron Transport System
Dr. Cohen’s notes used to refer to reducING potential (the potential to reduce other things). That’s what I based the video off of, but it’s not actually a term. The real term, to which the notes now refer, is reducTION potential (the potential to be reduced). Both are right, because the terms mean exactly the opposite thing. Electrons move spontaneously from a low reducTION potential (low potential to be reduced/gain electrons) to a high reducTION potential (high potential to be reduced/gain electrons). They also move spontaneously from a high reducING potential (high potential to give off electrons) to a low reducING potential (low potential to give off electrons).
Electron Transport Chain Animation