Leyland 8 oxidative phosphorylation

Question 1

Oxidative Phosphorylation

Answer 1

• Mitochondria
• Electron transport &ATP synthesis
• NADH & FAD2H re-oxidised
• O2 required (reduced to H2O)
• Lots of energy (ATP) produced

Question 2

Complete oxidation of glucose :

Answer 2

C6H12O6 + 6 O2 à 6 CO2 + 6 H2O DGO = -2870 kJ/mole

Question 3

At the end of stage 3 catabolism (citric acid cycle) :

Answer 3

• all C-C bonds have been broken and oxidised à CO2

* all C-H bonds have been broken & H-atoms (H+ + e-) transferred to NAD+ and FAD.

Question 4

ENERGY

Answer 4

ATP (2 from glycolysis)
GTP (2 from citric acid cycle) = 124 kJ/mole
(ADP + Pi à ATP + H2O DGo = 31 kJ/mole)

Question 5

High energy electrons in NADH & FAD2H transferred to O2 with

Answer 5

the release of large amounts of energy.

energy is used to drive to ATP synthesis

Question 6

1 • Electrons transferred through

Answer 6

series of carrier molecules to O2, with release of energy

Question 7

2 • Release of energy results in the

Answer 7

transfer of proton H+ from the matrix to the intermembrane space
=> proton gradient across the inner mitochondrial membrane

Question 8

3 • proton motive force (pmf)

Answer 8

• Protons (H+) can only return across membrane via the ATP synthase => drives ATP synthesis.

Question 9

Components of the electron transport chain (ETC)

Answer 9

• transporter molecules in the mitochondrial membrane allow NADH into the matrix

Question 10

chemiosmotic hypothesis

Answer 10

• the proton motive force generated by the ETC can be used to drive ATP synthesis
• catalysed by the ATP synthase

Question 11

1. Glycerol 3-phosphate shuttle

Answer 11

cytoplasmic Mitochondrial
NADH + H+ -> E-FAD

to

NAD + + E-FADH2

glycerol 3-phosphate shuttle

mitochondrial glycerol 3-phsophate dehydrogenase

Question 12

2. Malate-aspartate shuttle

Answer 12

cytoplasmic mitochondrial
NADH + NAD +

to

NAD+ + NADH

cytoplasmic Mitchondrial

Question 13

How much ATP is produced?

Answer 13

• each NADH produces 2.5 molecules of ATP

* each FADH2 produces 1.5 molecules of ATP

Question 14

Regulation of oxidative phosphorylation

Answer 14

• availability of ADP controls the rate of oxidative phosphorylation
• high ATP : ADP ratio inhibits OXPHOS
• high ATP : ADP ration inhibits citric acid cycle

Question 15

Inhibitors of oxidative phosphorylation:

Answer 15

1. Inhibition of the electron transfer chain
2. Inhibition of ATP synthase
3. Inhibition of ATP export
4. Uncoupling electron transport from ATP synthesis

Question 16

1. Inhibition of the electron transfer chain

Answer 16

Rotenone = insecticide
Amytal
Antimycin A = antibiotic

Question 17

2. Inhibition of ATP synthase

Answer 17

e.g. oligomycin, dicyclohexylcarbodiimide (DCC

Question 18

3. Inhibition of ATP export

Answer 18

e.g. bongkrekic acid

Question 19

4. Uncoupling electron transport from ATP synthesis

Answer 19

e.g. 2, 4-dinitrophenol
Causes increased permeability of the inner mitochondrial membrane to H+

-therefore the proton motive force is dissipated to produce heat

Question 20

Thermogenin (UCP-1)

Answer 20

Natural uncoupler proteins play an important physiological role
Thermogenin or uncoupling protein 1 (UCP-1)
• Present in brown adipose tissue
• Transmembrane protein of inner mitochondrial membrane
• Allows transport of H+ back into matrix without passage through ATP synthase

Heat generated by the dissipation of the proton gradient

Question 21

In response to cold, noradrenaline (norepinephrine) activates :

Answer 21

• Lipases (releases fatty acids from triacylglycerols)
• FA oxidation generates NADH/FAD2H
• Electron transport chain stimulated
• Thermogenin transports H+ back into mitochondria
• Generation of heat
• Newborn infants - to maintain heat, particularly around vital organs
• Hibernating animals – generation of heat to maintain body temperature

Question 22

Oxidative phosphorylation summary

Answer 22

requires membrane associated complexes( Inner mitochondrial membrane)

energy coupling indirectly thru generation & subsequent utilisation of proton gradient

not possible w/o O2

major process for ATP syth in cells that need lots of energy

Question 23

substrate level phosphorylation

summary

Answer 23

requires soluble enzymes (cytoplasmic & mitochondrial matrix)

energy coupling directly thru formation of high energy of hydrolysis bond (phosphoric-grp transfer)

to limited extent in absence of O2

minor process for ATP synth in cells