Electron Transport: Complex I

Question 1

What does Complex I of the electron transport chain do?

Answer 1

Catalyzes the oxidation of NADH by Coenzyme Q

Question 2

Which molecule is reduced by complex I? Which is oxidized?

Answer 2

CoQ is reduced; NADH is oxidized to NAD+

Question 3

Is the reaction catalyzed by Complex I exergonic or endergonic?

Answer 3

Very exergonic

Question 4

What is the structure of Complex I?

Answer 4

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.

Question 5

How does FMN (flavin mononucleotide) differ from FAD?

Answer 5

Absence of AMP and presence of 6-7 [Fe-S] clusters.

Question 6

What are the Fe-S complexes in FMN attached to?

Answer 6

4 Cys sulfhydryl groups

Question 7

How is Fe coordinated in each Fe-S cluster in complex I?

Answer 7

By 4 S atoms in a tetrahedral arrangement.

Question 8

True or false: Coenzyme Q is lipid soluble. Why or why not?

Answer 8

True; it has a long, hydrophobic tail that is soluble in the mitochondria’s lipid membrane

Question 9

What is the oxidized state Fe in the Fe-S cluster? What is the reduced state? How many oxidations/reductions does each undergo?

Answer 9

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).

Question 10

How many oxidation states do FMN and CoQ each have? How many electrons can each donate and accept?

Answer 10

3 states; can donate and accept 1 or 2 electrons

Question 11

True or false: FMN is tightly bound to proteins.

Answer 11

True

Question 12

What is CoQ’s tail comprised of?

Answer 12

Isoprenoid units (10 units in mammals–hence it is called Q10)

Question 13

How do electrons get from NADH to CoQ?

Answer 13

We don’t know.

Question 14

True or false: Redox centers must touch for electron transfer to take place.

Answer 14

False; electrons can jump up to 14 angstroms

Question 15

What do electron transfers over 14 angstroms (between molecules) require?

Answer 15

A redox chain (because transfer rate decreases exponentially with distance; it is too slow)

Question 16

What two types of prosthetic groups are contained by Complex I?

Answer 16

1) FMN

2) Fe-S

Question 17

Where do the electrons of NADH enter the electron transport chain?

Answer 17

Complex I

Question 18

What is the path of electron transfer through Complex I

Answer 18

NADH to FMN, then through a series of 7 Fe-S clusters, then to Q.

Question 19

How many electron transfers can NADH participate in?

Answer 19

2

Question 20

How many electrons can cytochromes of Complex III (to which CoQ passes its electrons) transfer?

Answer 20

1

Question 21

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?

Answer 21

4 H+ pumped to cytosolic side (fate of these protons unknown)

Question 22

How are protons transported across a membrane?

Answer 22

Hopping along a chain of H-bonded groups (as in hydrogen bonding) on a proton called a “proton wire”

Question 23

How many protons move to the intermembrane space for each 2 electrons that pass from NADH to CoQ?

Answer 23

4 protons

Question 24

What are the inhibitors of Complex I?

Answer 24

Rotenone or amytal