Electron Transport and ATP Synthesis

Question 1

How electron transport chain works

Answer 1

Reduced coenzymes (NADH, QH2) pass electrons down a reduction potential gradient, ultimately to molecular O2
O2 gains electrons and becomes water

Question 2

Oxidative phosphorylation

Answer 2

Proton gradient drives ATP synthesis

Question 3

Mitochondrial inner membrane

Answer 3

Highly folded (cristae) and impermeable to polar/ionic substances
Critical membrane for electron transport

Question 4

Mitochondrial matrix

Answer 4

Contains enzymes for citric acid cycle

Question 5

Cytosol

Answer 5

Site of glycolysis

Question 6

Overview of electron transport

Answer 6

1. NADH/QH2 (from TCA cycle and fatty acid oxidation) in the matrix pass electrons through many carriers, last to O2
2. H+ are pumped to the intermembrane space, creating a charge gradient
3. H+ flow is used to drive ATP synthesis by ATP synthase

Question 7

Chemiosmotic theory

Answer 7

H+ concentration gradient serves as the energy reservoir for ATP synthesis

Question 8

Uncouplers

Answer 8

Synthetic compounds which disrupt the relationship between oxidation and phosphorylation
Allow O2 to be reduced, but destroy H+ gradient as soon as it’s formed

Question 9

Complex I of electron transport chain

Answer 9

Transfers 2 electrons from NADH to coenzyme Q

Question 10

Mechanism of complex I

Answer 10

1. 2 electrons are transferred from NADH to FMN (flavin mononucleotide)
2. Single electron transfers from FMNH2 to Fe-S cluster
3. Single electron transfers from Fe-S cluster to Q, forming QH2

Question 11

For every 2 electrons that pass through complex I, how many H+ are pumped to intermembrane space?

Answer 11

4 H+ are pumped into intermembrane space

Question 12

Complex II of electron transport chain

Answer 12

Also called succinate dehydrogenase (complex from step 6 of TCA cycle)
Releases very little free energy and doesn’t directly contribute to H+ gradient

Question 13

Mechanism of complex II

Answer 13

1. 2 electron transfer from succinate to FAD
2. Single electron transfers from FADH2 to Fe-S
3. Single electron transfers from Fe-S cluster to Q, forming QH2

Question 14

Complex III of electron transport chain

Answer 14

Also called ubiquinol (QH2): cytochrome c oxidoreductase

Catalyzes transfer of electrons from QH2 to cytochrome c

Question 15

Mechanism #1 of complex III

Answer 15

1. 1 electron transfer from QH2 to cytochrome bL
2. Single electron transfers from cytochrome bL to Fe-S cluster
3. Single electron transfers from Fe-S cluster to cytochrome c

Question 16

Mechanism #2 of complex III

Answer 16

1. 1 electron transfer from QH to cytochrome bL to cytochrome bH
2. Single electron transfers from cytochrome bH to Q (forming 1 QH2)

Question 17

Each QH2 that passes through complex III results in translocation of how many H+?

Answer 17

4 H+/QH2

Question 18

Complex IV of electron transport chain

Answer 18

Also called cytochrome c oxidase

Catalyzes transfer of electrons from cytochrome c to O2

Question 19

Mechanism of complex IV

Answer 19

Single electron transfers until the final transfer to O2

Cytochrome c -> Cu A -> heme a -> heme a3 -> Cu B -> O2

Question 20

2 components of ATP synthase

Answer 20

F0 component

F1 component

Question 21

F0 component of ATP synthase

Answer 21

Pore/channel
Embedded in inner mitochondrial membrane
Consists of a and c subunits (protons pass through channel at a/c subunit interface)

Question 22

F1 component of ATP synthase

Answer 22

Catalytic portion
Anchored to inner membrane (matrix side) by F0
Contains 3 catalytic sites for ATP synthesis

Question 23

Mechanism of ATP synthase

Answer 23

1. A proton travels through F0, causing the c-subunit “rotor” to turn one subunit
2. When enough torque has been applied (~3 H+), the gamma subunit “jumps” 120 degrees, causing simultaneous conformational shifts in the active sites (ADP and Pi are joined together to make ATP)

Question 24

Gamma subunit of F1 component

Answer 24

Portion of F1 component that F1 rotates around (similar to spindle)

Question 25

Adenine nucleotide translocase

Answer 25

Transport protein that exchanges matrix ATP for cytosolic ADP (inner membrane is impermeable to ATP)

Question 26

Cost for transportation of ATP

Answer 26

1 H+/ ATP transported

Question 27

of ATP/NADH2

Answer 27

2.5 ATP

Question 28

of ATP/FADH2

Answer 28

1.5 ATP

Question 29

Glycerol phosphate shuttle mechanism

Answer 29

NADH reduces dihydroxyacetone phosphate to glycerol 3-phosphate, which then transfers electrons to membrane-bound FAD

Question 30

Malate-aspartate shuttle mechanism

Answer 30

Complicated process which uses malate (toward matrix), aspartate (toward cytosol), and redundant enzymes to shuttle 2 electron packets from NADH to the matrix