ETC
INTRODUCTION:
- The final common pathway in aerobic cells by which electrons derived from various substrates are transferred to oxygen.
- Enzymes of ETC are present in inner mitochondrial membrane.
- 4 complexes:
- Complex I : NADH- CoQ oxidoreductase
- Complex II: Succinate- CoQ reductase
- Complex III: CO-Cytochrome Coxido reductase (Q-Cycle)
- Complex IV: Cytochrome-COxidase
SEQUENCE OF ELECTRON CARRIER:
- Sequence of electron carriers in the mitochondria in electron transport chain: Substrate → NAD*→ FAD àCO enz. Q → 2cyt b → 2 cyt C1 → 2 cyt C → 2cyt (a+a3) → O2
- The redox potential in the ETC is in increasing order except in the case of ubiquinone (Co enzyme Q).
- Sequence:
- Q accepts electrons via complex I and complex II
- The Q cycle couples electron transfer to proton transport in complex III
- Molecular oxygen is reduced to water via complex IV
- Complexes I, III and IV act as proton pumps.
- Flavoproteins are important components of Complexes I and II.
- H2S inhibits complex IV
- Action of physiological uncoupler is Inhibition of ATP synthesis only not ETC
- The oxidized flavin nucleotide (FMN or FAD) involves the transfer of two electrons (to form FMNH2 or FADH2) or they accept one electron to form the semiquinone.
- Iron-sulfur proteins (non heme iron proteins, Fe-S) are found in Complexes I, II, and III.
- Inhibitor of FOF1 ATPase in Electron transport chain is Oligomycin
COMPOUND AFFECTING ELECTRON TRANSPORT:
Compounds which affect electron transport chain and oxidative phosphorylation
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Complex I to Co-Q specific inhibitors |
Complex II to Co-Q |
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Complex III to cytochrome c inhibitors |
Complex IV inhibitors |
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Site between succinate dehydrogenase & Co-Q |
Inhibitors of oxidative phosphorylation |
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Uncouplers |
Physiological uncouplers |
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- The classic poisons H2S, carbon monoxide and cyanide inhibit Complex IV and can therefore totally arrest respiration.
- Cyanide inhibits electron flow, proton pumping, and ATP synthesis.
- Role of molecular oxygen in ETC To act as last electron acceptor
- Action of physiological uncoupler is Inhibition of ATP synthesis only not ETC
- Malonate is a competitive inhibitor of Complex II.
- Fatal infantile mitochondrial myopathy and renal dysfunction: severe diminution or absence of most oxidoreductases of the respiratory chain.
- In ETC, Oxidative phosphylartion (ATP formation) is regulated by NADH Co-Q reductase, Cytochrome C oxidase, Co-Q-Cytochrome C reductase
- MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke) is an inherited condition due to NADH-Q oxidoreductase (Complex I) or cytochrome oxidase (Complex IV) deficiency
Exam Question
- In ETC, Oxidative phosphylartion (ATP formation) is regulated by NADH Co-Q reductase, Cytochrome C oxidase, Co-Q-Cytochrome C reductase
- Role of molecular oxygen in ETC To act as last electron acceptor
- Complex II is not associated with liberation of energy
- ETC occurs in mitochondria generates ATP & transport reducing equivalent
- Action of physiological uncoupler is Inhibition of ATP synthesis only not ETC
- H2S inhibits complex IV
- Inhibitor of FOF1 ATPase in Electron transport chain is Oligomycin
- In ETC, complex-4 is inhibited by CO, CN?,H2S, azide
Don’t Forget to Solve all the previous Year Question asked on ETC
