1.7 Respiratory chain, oxidative phosphorylation

Question 1

Which protein complexes take part in the electron transport chain?

Answer 1

Respiratory complex:

• I
• II
• III
• IV

Question 2

Respiratory complex I

Answer 2

• NADH dehydrogenase
• NADH + H⁺ used as the initial H⁺/electron donor
• Pumps 4 protons from the matrix → IM space

Question 3

Respiratory complex II

Answer 3

• Succinate dehydrogenase
• Succinate → Fumarate

Question 4

Respiratory complex III

Answer 4

• Produces reduced cytochrome c
• Translocation of 4 protons

Question 5

Respiratory complex IV

Answer 5

• Cytochrome-c oxidase
• Produces water
• Translocation of 2 protons

Question 6

Draw the respiratory chain

Answer 6

Question 7

Answer 7

H⁺

Question 8

• Enzyme
• Reaction

Answer 8

NADH dehydrogenase

• NADH → NAD⁺ + H⁺

Question 9

• Enzyme
• Reaction

Answer 9

Succinate dehydrogenase

• Succinate → Fumarate

Question 10

• Enzyme
• Reaction

Answer 10

Cytochrome-C oxidase

• 2H⁺ + ¹/₂O₂ → H₂O

Question 11

Answer 11

ATP synthase

Question 12

Q

Answer 12

Coenzyme Q (Ubiquinone)

Question 13

C

Answer 13

Cytochrome-C

Question 14

Cytochromes

Answer 14

Small proteins containing a haem group

Question 15

Importance of the respiratory chain

Answer 15

• Major source of energy
• Main driver of proton gradient across inner membrane
• Production of water from hydrogens

Question 16

Location of the respiratory chain

Answer 16

Inner membrane of mitochondria

Question 17

How is ATP formed in oxidative phosphorylation?

Answer 17

Via proton motive force (Chemiosmotic theory)

• Protons move nanometer of ATP synthase
• This condenses ADP + Pi → ATP
• ATP enters matrix

Question 18

List the inhibitors of chemiosmosis and which complexes they inhibit

Answer 18

• Rotenone (Complex I)
• Malonate (Complex II)
• Antimycin-A (III)
• Cyanide & Carbon monoxide (IV)
• Oligomycin (V)

Question 19

Uncoupling factors

Answer 19

• Lipid soluble weak acids
• Dissolve in the membrane → Act as H⁺ carriers
• Block oxidative phosphorylation

Question 20

How do uncoupling factors block oxidative phosphorylation?

Answer 20

• By dissipating the H⁺ electrochemical gradient
• H⁺ pumped out are carried back in
• No pH or electrical gradient

Question 21

Give examples of uncoupling factors

Answer 21

• Thermogenin
• Dinitrophenol

Question 22

Thermogenin

Answer 22

• Produced in brown adipose tissue of newborn + hibernating animals
• Blocks H⁺ gradient → Stimulates respiration
• Free energy of the respiratory chain is dissipated as heat

Question 23

Dinitrophenol

Answer 23

• In cattle
• Yellow mucous membranes + Toxicosis

Question 24

Define P/O proportion

Answer 24

Refers to the amount of ATP produced from the movement of 2 electrons through the electron transport chain, by reducing 1 oxygen atom.

Question 25

Give the P/O proportion of the respiratory chain

Answer 25