Krebs and ETC

Question 1

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

Answer 1

the transport of pyruvate into the mitochondrial matrix

Question 2

what enzymes are in pyruvate dehydrogenase?

Answer 2

E1, E2 and E3

Question 3

what enzyme is E1?

Answer 3

pyruvate dehydrogenase

Question 4

what is enzyme E2?

Answer 4

dishydrolipoyl transacetylase

Question 5

what is enzyme E3?

Answer 5

dihydrolipoyl dehydrogenase

Question 6

what are the 5 cofactors of pyruvate dehydrogenase?

Answer 6

thiamine, riboflavin, pantothenate, niacin and lipoate

Question 7

how is pyruvate dehydrogenase regulated?

Answer 7

regulated allosterically and using covalent phosphorylation

Question 8

what is PDH inhibited by?

Answer 8

by E2 and E3

Question 9

how is PDH activated?

Answer 9

by dephosphorylation

Question 10

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

Answer 10

catalytic converters and stoichiometric cofactors

Question 11

what are the catalytic converters?

Answer 11

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

Question 12

what are the stoichiometric cofactors?

Answer 12

CoA and nicotinamide adenine dinucleotide (NAD)

Question 13

what are the products of the link reaction?

Answer 13

CO2 and 2 NADH

Question 14

how is acetyl joined into the citric acid cycle?

Answer 14

the acetyl group of the acetyl CoA binds to oxaloacetate

Question 15

what is the enzyme of the first step?

Answer 15

citrate synthase

Question 16

what occurs in the first step?

Answer 16

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

Question 17

what conformational change occurs in the first step?

Answer 17

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

Question 18

what is the enzyme of the second step?

Answer 18

aconitase

Question 19

what kind of reaction does aconitase catalyse?

Answer 19

isomerization reaction

Question 20

what occurs in the isomerization reaction of step 2?

Answer 20

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

Question 21

what substrate is produced in step 2?

Answer 21

citrate to Isocitrate

Question 22

what causes step 2 to be driven in one direction?

Answer 22

rapid use of Isocitrate

Question 23

what is the enzyme of the 3rd step?

Answer 23

Isocitrate dehydrogenase

Question 24

what enzyme has 2 different isoforms?

Answer 24

Isocitrate dehydrogenase

Question 25

what are the 2 different isoforms of this enzyme?

Answer 25

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

Question 26

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

Answer 26

Isocitrate is converted to alpha ketoglutarate

Question 27

what type of reaction occurs in the 3rd step?

Answer 27

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

Question 28

what is the enzyme used in the 4th step?

Answer 28

alpha-ketoglutarate dehydrogenase

Question 29

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

Answer 29

it uses a complex of different enzymes

Question 30

what product is formed from alpha-ketoglutarate?

Answer 30

succinyl-CoA and CO2

Question 31

what is the enzyme of the 5th step?

Answer 31

succinyl-CoA synthetase

Question 32

what reaction does succinyl-CoA synthetase catalyse?

Answer 32

succinyl-CoA to succinate

Question 33

how is GTP formed in step 5?

Answer 33

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

Question 34

what is the enzyme of the 6th step?

Answer 34

succinate dehydrogenase

Question 35

what reaction does succinate dehydrogenase catalyse?

Answer 35

oxidation of succinate to fumarate

Question 36

what is different about the succinate dehydrogenase enzyme?

Answer 36

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

Question 37

what does succinate dehydrogenase depend on?

Answer 37

FAD as it uses FAD to become oxidised

Question 38

what enzyme is used in the 7th step?

Answer 38

fumarate

Question 39

what is specific about the fumarase enzyme?

Answer 39

it is a stereospecific enzyme

Question 40

what reaction does fumarase catalyse?

Answer 40

hydration of fumarate to malate

Question 41

what is not recognised by fumarase?

Answer 41

cis-malate, which is a cis form of fumarate

Question 42

what enzyme is involved in the 8th step?

Answer 42

malate dehydrogenase

Question 43

what reaction does malate dehydrogenase catalyse?

Answer 43

malate to oxaloacetate

Question 44

what does malate dehydrogenase depend on?

Answer 44

NAD

Question 45

what pulls the reaction of the 8th step forward?

Answer 45

oxaloacetate being depleted at a fast rate

Question 46

what is the citric acid cycle regulated by?

Answer 46

ATP/GTP and NADH concentrations

Question 47

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

Answer 47

PDH, Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase

Question 48

what 3 steps of the cycle are irreversible?

Answer 48

citrate synthase, Isocitrate dehydrogenase and alpha ketoglutarate dehydrogenase

Question 49

how many molecules of NADH are produced in the cycle?

Answer 49

3 for each molecule of pyruvate

Question 50

how many molecules of FAD are produced in the cycle?

Answer 50

1 molecule for each molecule of pyruvate

Question 51

what are decarboxylases?

Answer 51

enzymes that control the removal of carbon

Question 52

what are dehydrogenases?

Answer 52

enzymes that control the removal of H molecules

Question 53

what is chemisomosis?

Answer 53

the coupling of the ETC with ATP synthesis

Question 54

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

Answer 54

NADH and FADH

Question 55

how do the electron carriers form H2O?

Answer 55

donate the electrons to the final electron acceptor of O2

Question 56

where does the ETC take place?

Answer 56

in the inner mitochondrial membrane

Question 57

what does complex I do?

Answer 57

catalyses the oxidation of NADH

Question 58

what does complex II do?

Answer 58

catalyses the oxidation of FADH by ubiquinone

Question 59

what does CoQ do?

Answer 59

shuttles electrons from complex I and II to III

Question 60

what does Complex III do?

Answer 60

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

Question 61

what does cytochrome c do?

Answer 61

shuttles electrons between III and IV

Question 62

what does complex IV do?

Answer 62

catalyses the 4 electron reduction of H2O

Question 63

how is ATP synthesised from the chain?

Answer 63

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

Question 64

how much ATP comes from NADH and FADH?

Answer 64

2.5 ATP from NADH and 1.5 from FADH

Question 65

how is a total 30 ATP generated?

Answer 65

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

Question 66

what are uncouplers?

Answer 66

they inhibit oxidative phosphorylation by uncoupling the ETC from oxidative phosphorylation

Question 67

how do uncouplers prevent the electrical gradient from being formed?

Answer 67

because the uncouplers transport protons across the membrane

Question 68

how is energy released in the presence of an uncoupler?

Answer 68

dissipated as heat

Question 69

what are the natural uncouplers?

Answer 69

thermogenic, uncoupling protein

Question 70

what are the synthetic uncouplers?

Answer 70

2,4,-dinitrophenol

Question 71

how is heat generated in brown fat?

Answer 71

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