8. oxidative phosphorylation and ETC

Question 1

where does the ETC occur

Answer 1

inner membrane of mitochondria

Question 2

what are the protein complexes and small components involved in ETC?

Answer 2

•4 protein complexes (Complex 1 - IV)

3 proton pumps (Complex I, III, IV)

1 link to TCA cycle (Complex II succinate dehydrogenase)

•2 small components (CoQ, cytochrome c)

Question 3

Complex I

Answer 3

NADH dehydrogenase

• At least 34 polypeptides (880kDa)
• NADH binds to complex I
• Accepts electrons from NADH.
• Transfers electrons to CoQ (via FMN and Fe-S protein).
• 4 H+ pumped out

Question 4

complex II

Answer 4

succinate dehydrogenase

• Enzyme of TCA cycle (succinate to fumarate)
• Accept electrons from FADH2
• Transfers electrons to CoQ via Fe-S proteins (part of succinate dehydrogenase)

Question 5

coenzyme Q

Answer 5

Ubiquinone / ubiquinol

• Small lipid soluble compound – hydrophobic quinone
• Diffuses rapidly with IMM – mobile carrier
• Accept electrons from Fe-S proteins from Complex I and complex II
• Transfers electrons to complex III /cytochrome c (Q cycle)

Question 6

complex III

Answer 6

cytochrome c reductase

• Heme prosthetic group
• Accepts electrons from CoQ
• Transfers them to cytochrome c.
• Two protons pumped across IMM

Question 7

cytochrome c

Answer 7

• Peripheral membrane protein loosely bound to IMM.
• Bind to Complex III and transfers electrons to Complex IV
• Highly conserved

Question 8

complex IV

Answer 8

cytochrome c oxidase

• 13 protein subunits containing 2 heme groups and 3 copper ions.
• Accepts electrons from cytochrome c
• Transfers them to 1/2O2 which is reduced to form H2O
• 8 protons pumped across IMM

Question 9

why are electrons transferred?

Answer 9

accepting electron carrier has high affinity for electrons than the donating carrier (redox potential)

Question 10

Answer 10

Question 11

ATP synthase

Answer 11

complex V

• IMM
• Composed of two subunits

–F1 ATPase - generates ATP.

–F0 Coupling factor - proton channel spanning IMM

Question 12

how does ATP synthase produce ATP?

Answer 12

Protons pass through channel in F0 back into matrix

This drives rotation of C ring of F0 causing conformational change in F1 (beta subunit) causing ATP to be synthesised from ADP +Pi

Question 13

ATP yield from NADH and FADH

number of molecules formed from one molecule of O

P/O ratio

Answer 13

3 atp (2.5)

2 atp (1.5)

Question 14

How many ATP molecules are formed from TCA cycle?

Answer 14

–3NADH + 1FADH2 + 1GTP = 9ATP + 2ATP + 1ATP = 12 ATP (10).

–Overall for 1 molecule of glucose - 38 (30) ATP generated.

Question 15

Agents affecting oxidative phosphorylation

Answer 15

• ATPase inhibitors - oligomycin
• Site specific inhibitors of electron transport chain
• Uncouplers - neutralise the proton gradient and prevent ATP synthesis

Question 16

Answer 16

Question 17

how do uncouplers act?

Answer 17

Make IMM permeable to protons so they can diffuse through IMM so no proton gradient

But ETC still going and TCA cycle but gradient wont be maintained, naturally or chemically

Question 18

uncoupling agents

Answer 18

• Chemicals – dinitrophenol (DNP slimming pill)
• Energy formed from ETC dissipated as heat, internal temp high, used as a slimming pill because all the metabolic pathways going on (so energy is used increases metabolic rate), but not producing ATP
• Natural - uncoupling proteins

Question 19

UCP1

Answer 19

• Thermogenin
• Mitochondria of brown adipose tissue (surrounds organs eg. Kidney)
• Energy from electron transport used to generate heat - nonshivering thermogenesis.
• NB in new borns and hibernating animals