Electron Transport Chain Flashcards
Where is the electron transport chain located
mitochondrial inner membrane (MIM)
What is the electron transport chain
The ETC is a stepwise series of catalytic redox carriers that are also integral membrane proteins (pass e- from one molecule to another).
Do standard reduction potential values increase or decrease in the electron transport chain
Standard reduction potential values, E°, of the electron carriers of the ETC increase in a sequence that correspond to their position in the chain.
**The substrate keeps getting better and better as it goes down the chain so the reduced potential increases
What is the standard reduction potential (E^o)
the tendency of a molecule to be reduced. The more positive the potential is, the more likely it will be reduced.
IMAGE NOTE: The reaction in blue is more favourable because it gives a greater standard potential (iron has a stronger standard potential so copper gives an electron to iron)
Describe this image of standard reduction potentials of redox carriers
DONT REMEMBER SEQUENCE OR NUMBERS, BASICALLY IT MEANS THAT AS IT LOWERS THE ELECTRONS WANTS TO MOVE THEIR BECAUSE THERE IS A BETTER REDUCED POTENTIAL (-0.4 ->0.8)
What is the electron transport chain made of:
1) 4 complexes (I, II, III and IV):
-Proteins embedded in the mitochondrial internal membranes. (integral proteins = part/embedded of the membrane)
-Bound to redox groups : FAD+, flavin mononucleotide (FMN), proteins with an Fe-S center and cytochrome
2 mobile electron transporters (only thing that moves or travels in the ETC):
-Coenzyme Q (CoQ or ubiquinone)
-Cytochrome c
What happens in complex 1
NADH converted to coenzyme Q
Another name for complex 1
NADH-dehydrogenase
What does coenzyme flavin mononucleotide and iron sulfur clusters do in complex 1
Make used of the coenzyme flavin mononucleotide (FMN) and 8 iron-sulfur clusters (Fe-S) which transfer e- to coenzyme Q (mobile element0
What are the 3 roles of complex 1
- Receives reducing equivalents (2e-) from NADH
- Transfer 2e- to coenzyme Q via the FMN and the Fe-S proteins.
- Pump 4H+ from the mitochondrial matrix to the intermembrane space, by using energy generated by e- transfers from NADH to ubiquinone
Describe the pathway of complex 1
NADH donates 2e- to FMN and then travels up 1e- at a time up the iron-sulfer clusters, where coenzyme Q (ubiquinone) becomes QH2 with the donation of 2 e-
How many electrons can flavin monoculeotides of complex 1 accept
1 to 2 electrons
Describe the iron-sulfur clusters structure (4 things)
- Iron is associated with sulfur atoms (cysteines from the protein)
-But also to inorganic sulfur (bottom image)
-Reduction of Fe3+ into Fe2+
-Fe-S cluster can only accommodate one electron at a time.
Describe 2 stage process of the reduction of coenzyme Q
Complete reduction requires 2 electrons and two protons (from the matrix)
Two-stage process:
1. Semiquinone intermediate (only 1 e- present)
2. QH2 (ubiquinol) is soluble and can diffuse to Complex III. (now 2 e- present)
T or F: Does QH2 bypass complex II
True
Why would complex II be skipped by QH2
We skip complex II because it is from the TCA cycle and is only used for FAD to produce Fe-S (coenzyme II is only for the TCA cycle)
Why would complex II be skipped by QH2
We skip complex II because it is from the TCA cycle and is only used for FAD to produce Fe-S (coenzyme II is only for the TCA cycle)
What does complex II do
Convewrts FADH2 to ubiquinone
What is complex II also called
succinate dehydrogenase (The very same enzyme which catalyses the 6th reaction of the TCA cycle)
Complex II is composed of
Composed of multiple proteins with iron-sulfur clusters (Fe-S) which transfer e- to coenzyme Q
What are the 3 roles of Complex II (FADH2 to ubiquinone)
- Establishes a direct link between the TCA cycle and the electron transfer chain.
- Receives reducing equivalents (e-) from FADH2
- Transfer e- to coenzyme Q via the Fe-S proteins.
Does complex II pump any protons?
Complex II DOES NOT PUMP ANY PROTONS (so it produces less ATP because it uses FADH2 instead of NADH (produces 4 protons in complex I)
What is complex III composed of
-2 cytochromes b (b562 (b low) and b566(b high))
-2 proteins with Fe-S clusters
-1 cytochrome c
-1cytochrome c1
What are the 3 roles of complex III (QH2 to cytochrome c)
- Receives reducing equivalents (2e-) from coenzyme QH2
- Transfer e- to cytochrome c via the cytochrome c1 and Fe-S proteins.
- Pump protons (4H+, 2H+ for each e-) from the mitochondrial matrix to the intermembrane space, by using energy generated from reducing cytochrome c
Describe the structure of cytochrome c
Cytochrome c contains a heme group that contains an iron group that can only accommodate 1 iron at the time, so needs 2 cytochrome c
How many cytochrome c are generated from QH2 in the Q cycle
- QH2 is carrying 2 reducing equivalents (2e-)
- Cytochrome c can only accommodate 1e-
- Therefore, 2 reduced cytochrome c will be produced for each QH2 molecule
Q cycle:
2 QH2 will generate 4 reduced cytochrome c
Describe the first stage of the q cycle
QH2 coming in and inside it will give 1 e- to the iron sulfur cluster, the e- then goes to cytochrom c1 then to cytochrome c which will then go to complex IV
QH2 stores the second e- onto complex II and will instead go to heme bL then hem bH and will then go to another cytrochrome c (e- is stored on Q-)
Describe the 2nd stage of the Q cycle
-Second QH2 comes in gives to iron to C1 then cytrocohrom
-Second e- goes to BL then BH and the the electron is added to Q- to produce QH2 (2H+ bind to Q2- = QH2)
Describe the net equation and entire Q cycle
In mechanism we use only 1 QH2 because we technically use 2 for the 2 stages, but we produced 1 QH2 so therefroe 2QH2 went in and 1 QH2 came out so overall spent 1 QH2
What happens in complex IV
cytochrome c is converted to O2
T or F: complex IV is not the final stage of the electron transport chain
False it is
What is complex IV made of
Homodimer composed of 3 subunits:
1) Subunit I contains 2 heme groups (a and a3) and 1 copper ion (CuB)
2) Subunit II contains 2 copper ions (CuA)
3) Subunit III
What are the 3 roles of complex IV
- Receives reducing equivalents from cytochrome c (mobile element)
- Transfers e- to molecular oxygen = reduces oxygen in the mitochondrial matrix, which makes water
- Pumps protons (2H+, 1H+ for each e-) into the intermembrane space via a proton channel.
**Just remember that complex IV will take e- from cytochrome c and use tons of copper and iron to transfer e- to molecular oxygen which gets reduced and produces a lot of water
If we start with FADH2 we skip [blank]
complex I
How many protons (H+) are pumped into the intermembrane space when NADH is oxidized by the electron transport chain (2 electrons)
10 protons
How many protons are transfer to the intermembrane space when FADH2 is oxidized by the ETC?
6 protons (H+)
