M2b L13

Question 1

Explain what is meant by oxidation-reduction potential

Answer 1

electrons are being extracted from food and put into NAD+ making NAD+ + H+
electrons are carried over from one carrier to the next, electrons hop over, next one has a slightly stronger affinity, electrons hop over until it reaches the oxygen
measure of the ability of a biochemical system to oxidize or reduce

Question 2

Outline the connection between oxidation-reduction potential and free energy

Answer 2

little bits of free energy are released during each step of the ETC, results in conservation of energy, used to make ATP

Question 3

Explain why electrons from NADH/H+ or FADH2 can be accepted by oxygen

Answer 3

because they deliver them down the transport chain

Question 4

Describe the four membrane-bound complexes of the mitochondrial electron transport chain

Answer 4

complex I: entry point for NADH/H+, pumps 4 protons, energy released is used to pump protons to other side of membrane
complex II: succinate dehydrogenase (FADH2) shuffles electrons, gets protons to UQ. UQ takes 2 protons and electrons for succinate
complex III: accepts e- from mobile carrier UQ (1 to 3 or 2 to 3) several electrons carriers, releases energy, pumps 4 protons
complex IV: accepts e- from cytochrome c pumps 2 protons, electrons end up on O2

Question 5

Describe the mobile electron carriers

Answer 5

Ubiquinone (UQ): moves freely in the membrane in a hydrophobic environment (moves electrons 1 to 3 or 1 to 2)
Cytochrome c, moves electrons 3 to 4, moves along the surface of the membrane on the side where the protons accumulate

Question 6

Describe the pathway of electron transfer through the mitochondrial electron transport chain and where this is linked to H+ translocation

Answer 6

TCA cycle can only work if there is NADH/H+ and FAD available so it can take up the electrons, NADH/H+ and FADH2 are re-oxidized during ETC, electrons are removed, recycle them as NAD+ and FAD they go back to the TCA and it can continue

Question 7

Explain why complex II does not contribute to the electrochemical gradient

Answer 7

There is insufficient free energy available as the electrons are transferred from FADH2 to ubiquinone because of Coenzyme Q

Question 8

Describe the electrochemical gradient and explain how it is formed across the membrane as a result of electron transport

Answer 8

gradient is formed from energy released during e- transfer the protons make the intermembrane space more acidic, external face +ly charged, more protons, matrix face -ly charged

Question 9

Describe the effect of specific inhibitors of the electron transport chain

Answer 9

Inhibitors block oxidation and reduce both ATP generation and oxygen consumption
Specific inhibitors can block electron flow at each complex
Rotenone at complex I prevents transfer of e- UQ (does not fully affect the ETC, get electrons from CIII)
Halothanes at complex I prevents transfer of e- UQ
Antimycin A (antibiotic) inhibits complex III
Cyanide, CO bind to Complex IV