Biochemistry - The Electron Transport System

Question 1

Overview

Answer 1

Reducing power stored in NADH and FADH2 is converted into ATP via oxidative phosphorylation

• Protons are pumped or transferred from matrix to inter-membrane space which leaves the matrix negatively charged and with a higher pH
• Electrochemical potential powers ATP Synthesis

Question 2

Coenzyme Q

Answer 2

Lipid soluble molecule

• Ubiquinone
• Can be reduced to Semiquinone (dangerous) or fully to Ubiquinol

Question 3

Complex 1

Answer 3

NADH Dehydrogenase

• FMN accepts e- from NADH in the matrix
• NAD+ is used in CAC
• e- passed down a chain of Fe-S complexes
• Ubiquinone accepts the e- (Ubiquinol which goes to Complex 3) changing the shape of complex 1 in IMS allowing protons to be pumped through
• Pumps 4 Protons for 1 NADH

Question 4

Quantum Tunneling

Answer 4

e- can jump from Fe2+ to Fe3+ if atoms are close together (acts as a wire)
- If these electrons fail to move through this they will remain in the matrix forming super oxides and creating damage to Complex 1

Question 5

Complex 2

Answer 5

• Succinate Dehydrogenase is embedded in inner membrane and FADH2 is bound within it (stop dangerous free radical production)
• Succinate is oxidised to Fumarate and FAD is reduced to FADH+
• e- are passes to rezeki Fe (similar to Fe-S) and then passed to Cytochrome C
• Cytochrome C passes e- to Ubiquinone reducing it to Ubiquinol
• Ubiquinol moves to complex 3

Question 6

Complex 3

Answer 6

Cytochrome b-c1 Complex

• Ubiquinol donates 2H to Complex 3 which are then moved into the matrix
• 2 more protons are moved into the matrix by Complex 3 via Q cycle
• 2 Cytochrome C accepts 1 e- each from 2 Semiquinone and moves to complex 4
• Transfers 4 H+ into the IMS

Question 7

Complex 4

Answer 7

Cytochrome C Oxidase

• Cytochrome C and Oxygen are coming in
• Cytochrome C passes its e- to a series of Cytochromes with Iron and Copper in them
• These e- are used to split O2 into its molecular atoms and reform with 2H from the matrix producing water
• Complex 4 is reduced and changes shape pumping 2H+ into the matrix for 2e- from 2CC
• CCO is re-oxidised when it releases protons and moves back to original shape

Question 8

Respirasome/Supercomplex

Answer 8

• Complex 1, 3, 4 form a super complex and together they shift 10 protons into the IMS
• Supercomplex can also be formed with Complex 3, 4 and one of Complex 2/ETF/G3PD which shifts 6 protons

Question 9

ETF

Answer 9

Electron Transfer Flavoprotein

- Works like complex 2 and uses FADH2 to feed ubiquinol into Complex 3

Question 10

Mitochondrial G3PD

Answer 10

Glycerol-3-phosphate dehydrogenase

• irreversible oxidation of glycerol-3-phosphate to dihydroxyacetone phosphate producing FADH2
• Then transfers 2e- from FADH2 to ubiquinone to make ubiquinol for complex 3

Question 11

Rotenone

Answer 11

Is an anaesthetic which binds to complex 1 and blocks e- flow to Q

Question 12

Antimycin A

Answer 12

Blocks the Q cycle in Complex 3

Question 13

Cyanide

Answer 13

NO, H2S, CO all inhibit complex 4

Question 14

Malonate

Answer 14

Inhibits complex 2

Question 15

Uncoupling Proteins

Answer 15

Damaged inner mitochondria membranes (via oxidative stress) activates uncoupling proteins which increases the leakiness of mitochondria

• so less ATP is produced as protons are lost
• In hibernators this can be good as leakiness produces heat allowing them to wake up
• GDP regulates respiration by stopping the leakiness