BIOC 311 Lecture Notes - Lecture 16: Brown Adipose Tissue, Intermembrane Space, Cytochrome C Oxidase

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18 Jun 2016

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Recall: how many atp you can get per oxygen molecule consumed. Each complex of etc is very large (mw in hundreds of thousands, e. g. complex i. 850 kda, 26 subunits) and embedded in imm with segments exposed on both sides of the membrane. Among the redox active groups there are fe-s clusters (electrons carriers). The oxidized and reduced states of all fe-s clusters differ by one formal charge regardless of the number of fe atoms they contain. Note that fe-s cluster handle/process only one electron at a time. The redox active centres in cytochromes are heme moieties. Each heme contains a porphyrin ring with different substituent groups. The porphyrin is coordinated with the redox active iron atom which reversibly alternates between fe2 and fe3 oxidation states. (iron in middle can alternate between different states fe2 or fe3 state). Similarly to iron- sulfur clusters, heme can handle one electron at a time.

Related Questions

Can you answer the following questions:

1. Carbon monoxide is considered toxic because it acts on Complex IV. How would the addition of carbon monoxide to actively respiring mitochondria affect the relative oxidation-reduction states of all components of the electron-transport chain?

A) All four complexes would remain oxidized because they function as a multisystem complex.

B) Complexes I and III would be reduced, but complexes II and IV would be oxidized because the

electrons come from FADH2 oxidation, not NADH.

C) Complexes I, II, and III would be oxidized but Complex IV would remain reduced.

D) Complexes I, II, and III would be reduced and Complex IV would be oxidized.

E) All four complexes would remain reduced because they function as a multisystem complex.

2. Electrons are not very soluble in hydrophobic environments such as a bilipid membrane. What evidence is there that electrons move from complex to complex through the lipid membrane?

A) Cytochrome C is the electron carrier in the membrane and undergoes a head-over-heel flip to set up the proton gradient.

B) Cytochrome C is the electron carrier in the membrane and contains a cydrophoric porphyrin center.

C) CoQ is the electron carrier within the membrane and seems to be confined to the respirasome.

D) CoQ is the electron carrier within the membrane and it contains a hydrophobic porphyrin center.

E) FeS clusters are the carriers within the membrane and the electrons move from one cluster to the

next in a chain-like fashion.

3. What is the rationale for saying that âelectrons flow down the electron-transport chainâ?

A) Electrons flow from oxidized carriers to reduced carriers in discrete steps like a staircase.

B) Electrons flow from half-reactions with more positive redox potentials to more negative.

C) Electrons flow from reactions that continuously generate negative free energy values.

D) Electrons flow from the outer surface to the inner surface, a top down perception.

E) Because we think of electrons flowing like a liquid, the only direction electrons can flow is down.

BIOC 311 Lecture Notes - Lecture 16: Brown Adipose Tissue, Intermembrane Space, Cytochrome C Oxidase

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