BIOCHEM 2EE3 Lecture Notes - Lecture 11: Cytochrome C Oxidase, Coenzyme Q10, Reduction Potential

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2EE3- Module 11: Electron Transport and ATP Synthesis
ETC
Electron transport chain, ETC, has 5 embedded protein complexes and 2 electron carriers in the inner mitochondrial
membrane
oComplex I, II, III, IV, V; Coenzyme Q and C
-Complex I-IV: accept electrons and shuttle them along the ETC, and serve as a pump to pump protons out of the
mitochondrial matrix into the intermembrane space
-Electron carriers are lipid soluble and help transport the electrons because they do not diffuse well through the
membrane (they’re charged and lack a hydrophobic interior)
oShuttling of electrons is driven by the reduction potential of the coenzymes and each of the individual redox
centres until the final electron acceptor, oxygen
Reduction potential: affinity something has for electrons
oNADH has the lowest reduction potential at the beginning of ETC; Oxygen has the highest at the end
Shuttling Electrons through ETC
-Each protein has a redox centre that is reversible reduced and reoxidized through the movement of electrons through
them
-Each protein complex can have 2+ types of redox centroxygen have an increasing reduction potential as electron
passes from I to III to IV and finally to O2
-All redox centres in between NADH and O
Redox centres can be categorized as:
1. Coenzymes
2. Fe-S clusters
3. Cytochromes
4. Cu
Mechanism of Electrons
1) NADH donates electrons to Complex I
2) I passes electrons to III*
3) FADH2 donates its electrons to II which passes them to III*
a. FADH2 (coenzyme in TCA cycle) is covalently bound to II: succinate dehydrogenase
*Coenzyme Q shuttles electrons through to membrane to III
4) III passes electrons to IV**
**Coenzyme C shuttles electrons through membrane to IV
5) Electrons lastly reach O2 where it it makes water
a. Catalyzed by cytochrome oxidase, part of IV
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