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Biochemistry > Krebs and ETC > Flashcards

Krebs and ETC Flashcards

1
Q

what is the link between glycolysis and the citric acid cycle?

A

the transport of pyruvate into the mitochondrial matrix

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2
Q

what enzymes are in pyruvate dehydrogenase?

A

E1, E2 and E3

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3
Q

what enzyme is E1?

A

pyruvate dehydrogenase

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4
Q

what is enzyme E2?

A

dishydrolipoyl transacetylase

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5
Q

what is enzyme E3?

A

dihydrolipoyl dehydrogenase

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6
Q

what are the 5 cofactors of pyruvate dehydrogenase?

A

thiamine, riboflavin, pantothenate, niacin and lipoate

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7
Q

how is pyruvate dehydrogenase regulated?

A

regulated allosterically and using covalent phosphorylation

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8
Q

what is PDH inhibited by?

A

by E2 and E3

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9
Q

how is PDH activated?

A

by dephosphorylation

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10
Q

what two types of coenzymes are needed to convert pyruvate to acetyl CoA?

A

catalytic converters and stoichiometric cofactors

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11
Q

what are the catalytic converters?

A

thiamine pyrophosphate (TTP), lipoid acid and flavin adenine dinucleotide (FAD)

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12
Q

what are the stoichiometric cofactors?

A

CoA and nicotinamide adenine dinucleotide (NAD)

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13
Q

what are the products of the link reaction?

A

CO2 and 2 NADH

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14
Q

how is acetyl joined into the citric acid cycle?

A

the acetyl group of the acetyl CoA binds to oxaloacetate

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15
Q

what is the enzyme of the first step?

A

citrate synthase

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16
Q

what occurs in the first step?

A

citrate synthase catalyses the binding of acetyl and oxaloacetate to form citrate

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17
Q

what conformational change occurs in the first step?

A

the enzyme binding to oxaloacetate causes a confirmational change which facilitates the binding of the substrate

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18
Q

what is the enzyme of the second step?

A

aconitase

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19
Q

what kind of reaction does aconitase catalyse?

A

isomerization reaction

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20
Q

what occurs in the isomerization reaction of step 2?

A

the enzyme removes and adds back water to cis-aconitate at different positions

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21
Q

what substrate is produced in step 2?

A

citrate to Isocitrate

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22
Q

what causes step 2 to be driven in one direction?

A

rapid use of Isocitrate

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23
Q

what is the enzyme of the 3rd step?

A

Isocitrate dehydrogenase

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24
Q

what enzyme has 2 different isoforms?

A

Isocitrate dehydrogenase

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25
Q

what are the 2 different isoforms of this enzyme?

A

one uses NAD+ and one uses NADP+ as an electron acceptor

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26
Q

what is the substrate and product of the 3rd step?

A

Isocitrate is converted to alpha ketoglutarate

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27
Q

what type of reaction occurs in the 3rd step?

A

oxidative due to losing a hydrogen and carboxylation due to giving off a CO2

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28
Q

what is the enzyme used in the 4th step?

A

alpha-ketoglutarate dehydrogenase

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29
Q

what is different about 4th step compared to the other step?

A

it uses a complex of different enzymes

30
Q

what product is formed from alpha-ketoglutarate?

A

succinyl-CoA and CO2

31
Q

what is the enzyme of the 5th step?

A

succinyl-CoA synthetase

32
Q

what reaction does succinyl-CoA synthetase catalyse?

A

succinyl-CoA to succinate

33
Q

how is GTP formed in step 5?

A

hydrolysis of thioester bond to form phosphodiester bond with an inorganic phosphate, which is then transferred to histidine residue and then to GTP from GDP

34
Q

what is the enzyme of the 6th step?

A

succinate dehydrogenase

35
Q

what reaction does succinate dehydrogenase catalyse?

A

oxidation of succinate to fumarate

36
Q

what is different about the succinate dehydrogenase enzyme?

A

it is the only enzyme tightly bound to the inner mitochondrial membrane

37
Q

what does succinate dehydrogenase depend on?

A

FAD as it uses FAD to become oxidised

38
Q

what enzyme is used in the 7th step?

A

fumarate

39
Q

what is specific about the fumarase enzyme?

A

it is a stereospecific enzyme

40
Q

what reaction does fumarase catalyse?

A

hydration of fumarate to malate

41
Q

what is not recognised by fumarase?

A

cis-malate, which is a cis form of fumarate

42
Q

what enzyme is involved in the 8th step?

A

malate dehydrogenase

43
Q

what reaction does malate dehydrogenase catalyse?

A

malate to oxaloacetate

44
Q

what does malate dehydrogenase depend on?

A

NAD

45
Q

what pulls the reaction of the 8th step forward?

A

oxaloacetate being depleted at a fast rate

46
Q

what is the citric acid cycle regulated by?

A

ATP/GTP and NADH concentrations

47
Q

what are the 3 control points of the citric acid cycle?

A

PDH, Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase

48
Q

what 3 steps of the cycle are irreversible?

A

citrate synthase, Isocitrate dehydrogenase and alpha ketoglutarate dehydrogenase

49
Q

how many molecules of NADH are produced in the cycle?

A

3 for each molecule of pyruvate

50
Q

how many molecules of FAD are produced in the cycle?

A

1 molecule for each molecule of pyruvate

51
Q

what are decarboxylases?

A

enzymes that control the removal of carbon

52
Q

what are dehydrogenases?

A

enzymes that control the removal of H molecules

53
Q

what is chemisomosis?

A

the coupling of the ETC with ATP synthesis

54
Q

what are the electron carriers that carry electrons to the ETC?

A

NADH and FADH

55
Q

how do the electron carriers form H2O?

A

donate the electrons to the final electron acceptor of O2

56
Q

where does the ETC take place?

A

in the inner mitochondrial membrane

57
Q

what does complex I do?

A

catalyses the oxidation of NADH

58
Q

what does complex II do?

A

catalyses the oxidation of FADH by ubiquinone

59
Q

what does CoQ do?

A

shuttles electrons from complex I and II to III

60
Q

what does Complex III do?

A

catalyses oxidation of CoQ by cytochrome c, it is a proton pumping site

61
Q

what does cytochrome c do?

A

shuttles electrons between III and IV

62
Q

what does complex IV do?

A

catalyses the 4 electron reduction of H2O

63
Q

how is ATP synthesised from the chain?

A

the chain moves H ions into the inter membrane space, and they then move back across the membrane via ATP synthase

64
Q

how much ATP comes from NADH and FADH?

A

2.5 ATP from NADH and 1.5 from FADH

65
Q

how is a total 30 ATP generated?

A

5 from glycolysis, 5 from link reaction and 18 from citric acid cycle

66
Q

what are uncouplers?

A

they inhibit oxidative phosphorylation by uncoupling the ETC from oxidative phosphorylation

67
Q

how do uncouplers prevent the electrical gradient from being formed?

A

because the uncouplers transport protons across the membrane

68
Q

how is energy released in the presence of an uncoupler?

A

dissipated as heat

69
Q

what are the natural uncouplers?

A

thermogenic, uncoupling protein

70
Q

what are the synthetic uncouplers?

A

2,4,-dinitrophenol

71
Q

how is heat generated in brown fat?

A

thermogenin present in brown fat which allows H+ transport across the mitochondrial membrane

Biochemistry (9 decks)

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