Chapter 13 ( Citric Acid Cycle And Oxidative Phosphorylation )

Question 1

Krebs cycle general formula ?

Answer 1

Acetyl-CoA ( 3NAD + FAD + GDP + Pi ) ———-> 2 CO2 ( 3NADH + FADH2 + GTP )

Question 2

Location of the enzymes in citric acid cycle ?

Answer 2

All of them are in the matrix of mitochondria except succinate dehydrogenase which is in the inner membrane

Question 3

Oxidation of what fuels that yield Acetyl-CoA ?

Answer 3

Glucose 
Fatty acids 
Keton bodies 
Ketogenic amino acids 
Alcohol

Question 4

What is the major control enzyme of citric acid cycle ? Its activators and inhibitors ?

Answer 4

Isocitrate dehydrogenase
Activated by NADH and ATP
Inhibited by ADP

Question 5

Intermediates of Krebs cycle that serve other functions ?

Answer 5

Citrate : may leave the mitochondria to deliver acetyl-CoA into the cytoplasm for fatty acid synthesis
Succinyl-CoA : high energy intermediate that can be used for heme synthesis and to activate Kenton bodies in extra hepatic tissue
Malate : can leave the mitochondria for gluconeogenesis

Question 6

Enzyme that function both in Krebs cycle and electron transport chain ?

Answer 6

Succinate dehydrogenase ( present in the inner membrane of mitochondria )

Question 7

Inhibitors of NADH dehydrogenase ( complex l ) in ETC ?

Answer 7

Barbiturates 
Rotenone ( an insecticide )

Question 8

Components of the wire in electron transport chain ?

Answer 8

NADH dehydrogenase ( complex l )
Coenzyme Q
Cytochrome b/c1 ( complex lll )
Cytochrome C
Cytochrome a/a3 ( complex lV )

Question 9

Proton translocators in ETC ?

Answer 9

Complex l , lll , lV

Question 10

Describe oxidative phosphorylation ?

Answer 10

As protons flow into the mitochondria through the F0 component of ATP synthase as a result of ETC , their energy is used by the F1 component of ATP synthase to phosphorylate ADP into ATP using Pi

Question 11

Cyanide : Sources ? Mechanism ? Antidotes ?

Answer 11

Sources :
Burning polyurethane ( foam stuffing in furniture and mattress )
Byproduct of nitroprusside
Mechanism : binds irreversibly to Cytochrome a/a3 ( complex lV ) in ETC preventing electron transfer to oxygen and producing changes like tissue hypoxia
Antidotes:
Nitrites ( convert Hb to met-Hb which binds cyanide in the blood before reaching the tissues )
Na thiosulphate ( converts cyanide to thiocyanate which is less toxic )
Vitamin B12 ( binds to cyanide

Question 12

Carbon monoxide : sources ? Mechanism ? Antidote ?

Answer 12

Sources : propane heaters , gas grills , vehicle exhaust , house fire , smoking , methylene chloride based paint strippers
Mechanism : binds to cytochrome a/a3 also binds to Hb displacing oxygen
Antidote : Hyperbaric oxygen

Question 13

Inhibitor of cytochrome b/c1 ?

Answer 13

Antimycin

Question 14

Inhibitor of Coenzyme Q ?

Answer 14

Doxorubicin

Question 15

Inhibitor of the F0 component of ATP synthase ?

Answer 15

Oligomycin

Question 16

Examples for synthetic and natural Uncouplers of ETC ?

Answer 16

Synthetic : 
2,4-dinitrophenol
Aspirin 
Natural : 
UCP ( thermogenin )

Question 17

The enzyme responsible for substrate level phosphorylation in Krebs cycle ?

Answer 17

Succinyl-CoA synthetase

Question 18

Dehydrogenases of Krebs cycle ?

Answer 18

1- Isocitrate dehydrogenase (NAD)
2- Alpha-ketoglutarate dehydrogenase (NAD)
3-Succinate dehydrogenase (FAD)
4-Malate dehydrogenase (NAD)