Lecture 25 - Oxidative Phosphorylation

Question 1

What complexes of the electron transport chain form the respirasome?

L25 S9

Answer 1

Complex I, III, and IV

Question 2

What is complex I and what reaction does it catalyze?
What unique features does it have?
What does it pass electrons to?

L25 S14

Answer 2

NADH dehydrogenase/NADH-Q oxidoreductase

Reaction:
-NADH + Q + 5H+ (matrix) -> NAD+ + QH2 + 4H+ (intermembrane space)

Pumps protons

Contains Fe-S clusters that pass electronS

Electrons transferred to ubiquinone (Q)

Question 3

What is complex II and what reaction does it catalyze?
What unique features does it have?
What does it pass electrons to?

L25 S15

Answer 3

Succinate-Q reductase

Connects to succinate dehydrogenase in TCA

Does not release FADH2

Does not pump protons

Contains Fe-S clusters that pass electrons

Electrons transferred to ubiquinone (Q)

Question 4

What is Coenzyme Q?

L25 S10

Answer 4

Ubiquinone

Mobile electron carrier that is contained in the membrane (hydrophobic tails)

Carriers electrons from complex I and II to complex III

Question 5

What is complex III and what reaction does it catalyze?
What does it pass electrons to?

L25 S17

Answer 5

Q-cytochrome c oxidoreductase

QH2 + 2Cyt C(ox) + 2H+ (matrix) -> Q +2Cyt C(red) + 4H+(intermemrbane space)

Pumps protons

Takes electrons from QH2 and passes them to cytochrome C

Question 6

What is complex IV and what reaction does it catalyze?
What unique features does it have?
What does it pass electrons to?

L25 S18

Answer 6

Cytochrome c oxidase

4Cyt c(red) + 8H+ (matrix) + O2 -> 4 Cyt c(ox) + 2H2O + 4 H+ (intermembrane space)

Pumps protons

Contains 2 heme groups and 3 Cu atoms that pass electrons

Reduces O2 to water using 4 electrons

Question 7

What reactive oxygen species are produced and what are the consequences of these?

L25 S22

Answer 7

• superoxide
• peroxide (hydrogen peroxide)

H2O2 can be used for signaling at normal levels however is toxic at high levels

Superoxide anion is toxic at all levels

Question 8

What enzymes remove ROS?

L25 S24

Answer 8

Superoxide dismutase (SOD):
-superoxide + 2H+ -> O2 + H2O2

Catalase:
-2H2O2 -> O2 + 2H2O

Question 9

What are examples of antioxidants?

L25 S24

Answer 9

• glutathione peroxidase
• vit-E
• vit-C
• superoxide dismutase (SOD)
• catalase

Question 10

What are the different types of superoxide dismutase?

L25 S25

Answer 10

• Cu/Zn SOD1 (cytosolic)

- Mn/Zn SOD2 (mitochondrial)