Oxidative Phosphorylation / ETC

Question 1

What physical characteristic allows the H+ gradient to be created

Answer 1

The IMM in immpermeable to charged ions

Question 2

The 3 main electron carriers in the ETC

Answer 2

1. Cytochromes
2. Iron sulfur proteins
3. Coenzyme Q (aka ubiquinone)

Question 3

Cytocromes

Answer 3

Heme backbone

3 cytochrome structures

• A
• B (heme cytochrome)
• C

The iron on the heme cycles between reduced and oxidized state

Question 4

Iron sulfur proteins

Answer 4

Iron = accepting/releasing e-

Iron is caged between the sulfurs (either free or from cysteine)

Question 5

Coenzyme Q (ubiquinone)

Answer 5

Can accept 2e- from NADH

Go through a semiuinone radical

CoQ = greasy hydrophobic tail…therefore it is embedded in the IMM

—> makes it a mobile carrier…transfers electrons from one carrier to another

Question 6

NADH dehydrogenase complex

Answer 6

‘Complex I’

Removes e- from NADH

Entry point for NADH

Main carrier = iron/sulfur protein

Pumps out 4H+

Question 7

Succinate dehydrogenase complex

Answer 7

‘Complex II’

FADH2 —> FAD

Entry point for FADH2

Main carrier = iron/sulfur protein

NO H+ pumped out

Question 8

Ubiquinone cytochrome C oxidoreductase complex

Answer 8

‘Complex III’

Receives electrons from complex 1 or 2…becomes reduced

Main carrier = heme and iron/sulfur proteins

4H+ pumped out

Question 9

Cytochrome C complex

Answer 9

In between complex 3 and 4

Carrier electrons from 3 —> 4 one electron at a time until complex 4 has 4 electrons

NO H+ pumped out

Question 10

Cytochrome oxidase complex

Answer 10

‘Complex IV’

Transfers electrons from cytochrome C —> O2

Main carriers = heme and 2 copper groups

Pumps 2H+ out

Question 11

Electron entry points

Answer 11

Electrons enter and are transferred to CoQ…

A. NADH = complex I

B. FADH2 = complex II

C. Glycerol-3P dehydrogenase in the IMM

D. Fatty acid oxidation

Question 12

ATP Synthase complex

Answer 12

Converts chemical gradient of H+ —> ATP ultimately

2 parts:

• Head (F1) = where ATP synthesis takes place
• round base (F0)

Bottom = 10 subunits that twist
Shaft = epsilon and gamma connect rotor to head groups...

Question 13

ATP synthase mechanism

Answer 13

As protons move down the gradient created by the ETC…

The circular base in the membrane turns…

As the head groups turn and contact the shaft…conformational changes that allows ADP —> ATP

Takes 4H+ to completely turn the subunit enough to make 1 ATP

***not substrate-level phosphorylation

Turns 100X per second

Question 14

If the H+ gradient gets too steep…

Answer 14

ATP synthesis stops

Not enough energy to push more protons against that gradient in the ETC

= respiratory control

= consequence of ETC being linked to oxidative phosphorylation

Question 15

Oligomycin

Answer 15

ETC inhibitor

Binds to F0 —>

Closes H+ channel —>

Stops ATP synthesis —>

H+ gradient becomes steeper

RESULT: O2 consumption stops

Question 16

Rotenone

Answer 16

ETC inhibitor

Common in pesticide

Inhibits e-transfer from complex 1 to oxidized ubiquinone

RESULT: everything upstream remains reduced…everything downstream = oxidized

Question 17

Antimycin A

Answer 17

ETC inhibitor

Blocks CytoC —>

Oxidation of reduced ubiquinol and transfer of e- to complex 3 is stopped

RESULT = NADH, Q, and cytochrome B are reduced …the rest (downstream) stay oxidized

Question 18

Cyanide and carbon monoxide

Answer 18

ETC inhibitor

Inhibits cytochrome oxidase in complex 4

Preventing final reduction of O2

RESULT: entire chain is reduced except for O2 at the end

Question 19

Atractyloside

Answer 19

Inhibits ATP/ADP antiporter

Inhibiting oxidative phosphorylation

Question 20

2, 4 - dinitrophenol (DNP) and FCCP

Answer 20

ETC uncoupler

In acidic cytosol…binds to H+ makes it neutal…so it can re-enter through the IMM

RESULT: disrupts the gradient

Question 21

Thermogenin

Answer 21

Natural ETC uncoupler

In shoulders and back brown fat

Produces heat for the body

RESULT: dirsupts the H+ gradient

Question 22

Niclosamide (NEN)

Answer 22

Salt of a drug usually used to treat tapeworms,

Now under investigation for a potential Type II diabetes medication

Question 23

Effect of pyruvic or lactic acid in cytosol

Answer 23

Lowers cytosolic pH

—> F1 subunit dimerizes —> inhibits ATP synthase reaction

Question 24

What else uses the gradient as means of transport across the MM?

Answer 24

1. Phosphate = symport with H+ ions into matrix
2. Pyruvate = symport with H+ into matrix
3. ADP/ATP antiporter

Question 25

Total yield per glucose after ETC…

Answer 25

30-32 ATP

Depending on which shuttle used