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BIOC13H3 Lecture Notes - Lecture 17: Rieske Protein, Oxidoreductase, Heme

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School
UTSC
Department
Biological Sciences
Course
BIOC13H3
Professor
Jason Brown

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BIOC13:(Lecture(19( ( Final(
March(22,(2018(
63#
ETN$III!
!"#$%&'()))(*+,-./!01"234"#&(!(5'67"4&78219:&;(
<1482184&(
• Made#of#3#core#proteins#and#8#accessory#ones#
• Two#complex#III#actually#fuse#together#(they#are#a#dimer)#
• There#is#a#cytochrome#b#(2#heme#groups)#and#cytochrome#c#(1#heme#group)#
• There#is#also#a#rieske(protein#that#contained#the#ISC#
• Its#job#is#to#oxidize#Q#and#pass#the#electrons#to#cytochrome#c#
=/!02%&(
• There#are#2#binding#sites#for#Q:#
o Outer#binding#site#(Qo)#
o Inner#binding#site#(Qi)#
• The#Q#from#complex#I#and#II#(currently#reduced)#binds#to#Qo#site#
• 1st#electron#is#sent#to#the#ISC#in#the#rieske#protein#
o Then#goes#to#cytochrome#c1#and#then#to#the#mobile#carrier#cytochrome#c#
• 2nd#electron#goes#to#cytochrome#bL#then#cytochrome#bH#and#then#to#Q#in#the#Qi#
o Q#at#this#site#is#oxidized#
• You#are#left#with#a#fully#reduced#
cytochrome#c#carrier#and#a#partially#
reduced#Qi#
o The#partially#reduced#Qi#is#
radical#and#therefore#ROS#can#
be#produced#
• The#cycle#repeats#and#you#get:#
o 2#reduced#cytochrome#c#
carriers#
o 1#fully#reduced#Qi#
o This#Qi#then#moves#to#the#Qo#
site#and#is#oxidized#again#à#
cycle#
• This#Q-cycle#is#important#to#proton#
pumping#
o When#Qi#is#reduced,#protons#
are#picked#up#and#oxidizing#it#
transfers#the#protons#to#the#
other#side#
o 2#protons#are#moved#across#for#each#electron#
• 4#H+#are#pumped#for#2e-#or#per#NADH#
• Passing#electron#from#Q#to#rieske#=#huge#energy#release#
o This#is#where#protons#can#be#transferred#and#physically#linked#
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BIOC13:(Lecture(19( ( Final(
March(22,(2018(
64#
• Cytochrome#b#and#c#have#similar#potentials#and#thus#energy#isn’t#released#
there#
• No#energy#released#from#moving#electron#to#cytochrome#c#
>%&214"?(@916?A(
• Need#to#ensure#that#the#electrons#don’t#take#the#same#pathway#
• This#is#kinetically#gated#
• When#Q#binds#to#the#Qo#site,#electron#pass#to#ISC#
o This#has#high#electron#affinity#
• Rieske#confirmation#changes#to#that#the#ISC#is#moved#too#far#for#the#second#
electron#to#pass#there#
o Electron#must#be#passed#to#cytochrome#bL#as#a#result#
)?36B61"4:(
• There#are#2#groups#of#inhibitors:#some#act#on#Qo#and#others#act#on#Qi#
• Stops#the#reduction#of#Complex#III#so#electron#can’t#pass#through#
• This#makes#the#Q-cycle#non-functional#
!"#$%&'()C(*!01"234"#&(2(5'679:&;(
• Since#complex#IV#is#where#O2#accepts#the#final#electrons,#it#is#assumed#a#lot#of#
ROS#would#be#produced#
• In#actuality,#very#little#ROS#is#produced#here#and#to#understand#why,#first#need#
to#understand#the#chemistry#of#oxygen#
!3&#6:140("D(5'0A&?(
• Require#4e-#to#reduce#O2#
to#H2O#with#3#
intermediates#
(superoxide,#hydrogen#
peroxide#and#hydroxyl#
radical)#
• Of#the#intermediates,#
superoxide#and#
hydroxyl(radical(are#the#
ones#most#likely#to#
produce#ROS#as#they#are#the#most#unstable#
• In#order#to#avoid#ROS,#Complex#IV#avoids#forming#those#intermediates#all#
together#but#it#isn’t#as#simple#as#just#giving#up#2e-#at#a#time#
• Oxygen#is#biradical#à#its#ground#state#has#two#radicals#and#a#single#bond#
o If#it#were#a#singlet#with#a#double#bond,#it’d#actually#be#excited#and#form#
ROS#
o These#radicals#spin#in#same#direction#
• Due#to#spin,#the#electrons#MUST#come#from#different#atom#
o The#electrons#from#the#same#NADH#would#have#different#spin#
o We#need#electrons#with#the#same#spin#and#thus#need#electrons#from#
different#NADH#
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Document Summary

Its job is to oxidize q and pass the electrons to cytochrome c. Final: cytochrome b and c have similar potentials and thus energy isn"t released there, no energy released from moving electron to cytochrome c. Inhibitors: there are 2 groups of inhibitors: some act on qo and others act on qi, stops the reduction of complex iii so electron can"t pass through, this makes the q-cycle non-functional. Complex iv (cytochrome c oxidase: since complex iv is where o2 accepts the final electrons, it is assumed a lot of. In actuality, very little ros is produced here and to understand why, first need to understand the chemistry of oxygen. Inhibitors: cyanide inhibits complex iv by binding to heme a3. It makes the heme"s reduction potential more negative and thus passing electrons to it is too unfavourable: as a result, etn is shut down.

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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 “electrons flow down the electron-transport chain”?

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.

1. During the TCA cycle, four reactions occur in which a pair of electrons are transferred from a substrate to an electron accepting coenzyme. These reactions are catalyzed by?

2.During the TCA cycle, four reactions occur in which a pair of electrons are transferred from a substrate to an electron accepting coenzyme. These reactions are catalyzed by?

3.Potent respiratory poison, including carbon monoxide, azide and cyanide have their toxic effect by binding to the heme a3 site of _____.

4.The first step in the TCA cycle is the condensation of the two-carbon acetyl group with a four-carbon _____ to form a six-carbon citrate molecule?

5.The inner mitochondrial membrane is virtually devoid of ____, and and rich in ____, which are characteristics of bacterial plasma membranes.

6.Iron sulfur centers are joined to the protein by linkage to a sulfur atom of a/n ___.

7.Decarboxylation of pyruvate and transfer of the acetyl group to CoA , along with the reduction of NAD+ is catalyzed by ___.

8.When FADH2 is the electron donor, electrons are passed directly to ____ in the respiratory chain

9.With the exception of ____, all of the redox centers within the respiratory chain that accept and donate electrons are prosthetic groups.

10.It iis evident fromt eh net equation fo the TCA cycle that the primary products of the pathway are the reduced coenzymes _____.

11. Complex III catalyzes the transfer of electrons from ___ to ___.

12. The passage of a pair of electrons from NADH to ubiquinone in the respiratory chain is accompanied by movement of roughly four protons from (the) ___ to (the) ___.

13. When NADH is the electron donor, electrons pass the respiratory chain by means of ____.

14. The matrix of the mitochondrion has a gel-like consistency owing to the presence of a high conentration of _____.

These are questions I missed on a quiz the instructor does not post what the answers should be and has not responded to my emails please help.

Thanks,

Amber