Electron Transport: Complex I Flashcards
What does Complex I of the electron transport chain do?
Catalyzes the oxidation of NADH by Coenzyme Q
Which molecule is reduced by complex I? Which is oxidized?
CoQ is reduced; NADH is oxidized to NAD+
Is the reaction catalyzed by Complex I exergonic or endergonic?
Very exergonic
What is the structure of Complex I?
Very large, L-shaped with one arm embedded in the inner membrane and one extending into the matrix. Contains a flavin mononucleotide (FMN) redox prosthetic group.
How does FMN (flavin mononucleotide) differ from FAD?
Absence of AMP and presence of 6-7 [Fe-S] clusters.
What are the Fe-S complexes in FMN attached to?
4 Cys sulfhydryl groups
How is Fe coordinated in each Fe-S cluster in complex I?
By 4 S atoms in a tetrahedral arrangement.
True or false: Coenzyme Q is lipid soluble. Why or why not?
True; it has a long, hydrophobic tail that is soluble in the mitochondria’s lipid membrane
What is the oxidized state Fe in the Fe-S cluster? What is the reduced state? How many oxidations/reductions does each undergo?
Fe3+ is the oxidized state; Fe2+ is the reduced state; under go one oxidation/reduction (only differ by one formal charge, regardless of the number of Fe atoms).
How many oxidation states do FMN and CoQ each have? How many electrons can each donate and accept?
3 states; can donate and accept 1 or 2 electrons
True or false: FMN is tightly bound to proteins.
True
What is CoQ’s tail comprised of?
Isoprenoid units (10 units in mammals–hence it is called Q10)
How do electrons get from NADH to CoQ?
We don’t know.
True or false: Redox centers must touch for electron transfer to take place.
False; electrons can jump up to 14 angstroms
What do electron transfers over 14 angstroms (between molecules) require?
A redox chain (because transfer rate decreases exponentially with distance; it is too slow)
What two types of prosthetic groups are contained by Complex I?
1) FMN
2) Fe-S
Where do the electrons of NADH enter the electron transport chain?
Complex I
What is the path of electron transfer through Complex I
NADH to FMN, then through a series of 7 Fe-S clusters, then to Q.
How many electron transfers can NADH participate in?
2
How many electrons can cytochromes of Complex III (to which CoQ passes its electrons) transfer?
1
The flow of 2 electrons from NADH to Coenzyme Q through Complex I causes how many H+ to be pumped out of the mitochondrial matrix into the cytosolic side of the inner mitochondrial membrane?
4 H+ pumped to cytosolic side (fate of these protons unknown)
How are protons transported across a membrane?
Hopping along a chain of H-bonded groups (as in hydrogen bonding) on a proton called a “proton wire”
How many protons move to the intermembrane space for each 2 electrons that pass from NADH to CoQ?
4 protons
What are the inhibitors of Complex I?
Rotenone or amytal
