citric acid cycle

Question 1

what occurs to Acetyl-CoA in the citric acid cycle?

Answer 1

it is oxidized to produce 2CO2 molecules

Question 2

what are the sources of Acetyl-CoA?

Answer 2

carbs, FA and amino acid catabolism

Question 3

how many C is Acetyl-CoA?

Answer 3

2C

Question 4

what does Acetyl-CoA condense with? what does it form?

Answer 4

condenses with oxaloacetate to form citrate

Question 5

how many carbons are oxidized in the CAC?

Answer 5

2 C are oxidized to form 2 CO2 molecules per Acetyl-CoA molecule

Question 6

how many high energy products are made per Acetyl-CoA?

Answer 6

3 NADH
1 FADH 2 / QH2
1 GTP

Question 7

where does the CAC occur?

Answer 7

in the mitochondrial matrix

Question 8

how many reactions are in the CAC?

Answer 8

8

Question 9

what is the first step in the CAC? what enzyme is used? what is produced?

Answer 9

An irreversible reaction with oxaloacetate and Acetyl CoA to produce citrate
-catalyzed by citrate synthase
-generates co-enzyme A

Question 10

what is the second step in the CAC? what is produced?

Answer 10

a reversible isomerization to produce isocitrate

Question 11

what is the 3rd step in the CAC? what enzyme is used? what is produced?

Answer 11

an irreversible oxidative decarboxylation rxn
-catalyzed by isocitrate dehydrogenase (regulated)
-energy capture (produces NADH)

Question 11

what is the 4th step in the CAC? what enzyme is used? what is produced?

Answer 11

an irreversible oxidative decarboxylation to generate Succinyl CoA
-catalyzed by alpha-ketoglutarate dehydrogenase (regulated)
-energy capture step (produces NADH)

Question 12

what kind of molecule is succinyl CoA?

Answer 12

it contains a thioester which makes it a high energy molecule

Question 13

what is significant of the 4th step in the CAC (synthesis of succinyl CoA)?

Answer 13

it is similar to the PDH reaction

Question 14

what is an example of anabolic processes during the CAC?

Answer 14

the conversion of intermediates into amino acids

ex) alpha-ketoglutarate into glutamate

Question 15

what is the 5th step in the CAC? what is produced?

Answer 15

a reversible substrate-level phosphorylation to yield succinate
-energy capture (GTP/ATP)

Question 16

what occurs when [ADP] decreases in the matrix?

Answer 16

Question 17

what is the 7th step in the CAC? what is produced?

Answer 17

a reversible hydration rxn
-conversion of fumerate to malate

Question 18

what is the 8th step in the CAC? what is produced?

Answer 18

a reversible oxidation rxn to regenerate oxaloacetate
-energy capture (NADH produced)

Question 19

how is the CAC regulated?

Answer 19

regulated by enzymes:
-isocitrate dehydrogenase
-alpha-ketoglutarate dehydrogenase

AND [intermediates]
-NAD+/NADH ratio

Question 20

what are inhibitors of the CAC? What are activators?

Answer 20

inhibitors: NADH, ATP, citrate, succinyl CoA
activators: ADP, Ca++

-they reflect energy needs / usage

Question 21

what does high [citrate] affect?

Answer 21

it inhibits the CAC
-this is not physiologically relevant

Question 22

what does ATP affect in the CAC?

Answer 22

it is a direct allosteric inhibitor for isocitrate dehydrogenase
-conversion of isocitrate into alpha-ketoglutarate

Question 23

what does NADH affect in the CAC?

Answer 23

it is a direct allosteric inhibitor for isocitrate dehydrogenase and alpha ketoglutarate complex
-conversion of isocitrate into alpha-ketoglutarate and converion to succinyl CoA

Question 24

what does ADP affect in the CAC?

Answer 24

it is a direct activator for isocitrate dehydrogenase -conversion of isocitrate into alpha-ketoglutarate

Question 25

what does Ca++ affect in the CAC?

Answer 25

direct activator for alpha ketoglutarate complex -converion to succinyl CoA

Question 26

what does succinyl CoA affect in the CAC?

Answer 26

inhibits the alpha ketoglutarate complex

Question 28

what occurs when [ADP] increases in the matrix?

Answer 28

Question 29

what can CAC intermediates be used to synthesize?

Answer 29

AA, carbs, fats, nucleotides and other compounds -therefore, [intermediate] must be maintained or the effectiveness of the CAC will decrease

Question 30

what are anaplerotic reactions?

Answer 30

rxns that are needed in order to replenish intermediates of the CAC

Question 31

what reactions are anaplerotic?

Answer 31

Pyruvate Carboxylase- converts pyruvate to oxaloacetate by adding a carboxyl group AA breakdown

Question 32

what catalyzes the conversion of pyruvate to oxaloacetate? what kind of reaction is this?

Answer 32

catalyzed by pyruvate carboxylase -anaplerotic rxn

Question 33

what catalyzes the conversion of pyruvate to acetyl-CoA? what kind of reaction is this?

Answer 33

pyruvate dehydrogenase complex -oxidative decarboxilation

Question 34

what molecules activate and inhibit pyruvate carboxylase?

Answer 34

activated by acteyl-CoA inhibited by ADP

Question 35

what affect does acetyl-CoA have on pyruvate dehydrogenase complex?

Answer 35

it acts as an inhibitor

Question 36

how many ATP are generated from each Acetyl-CoA?

Answer 36

~10 ATP per acetyl-CoA -20 ATP are made per glucose

Question 37

how many NADH are made per glucose molecule in the CAC?

Answer 37

6 NADH -3 NADH per acetyl-CoA

Question 38

how many FADH2 are made per glucose in the CAC?

Answer 38

2 FADH2 -1 per acetyl-CoA

Question 39

how many GTP are made per glucose in the CAC?

Answer 39

2 GTP -1 GTP per acetyl-CoA

Question 40

how many ATP molecules are made from the complete aerobic oxidation of glucose?

Answer 40

32 ATP

Question 41

how many ATP are generated from the anaerobic glycolysis of glucose?

Answer 41

2 ATP

Question 42

how is lactate used in the CAC?

Answer 42

it is used as a metabolic fuel in anaerobic metabolism -reoxidizes NADH to be used in ETC

Question 43

why do yeast cells consume less glucose in the prescence of oxygen?

Answer 43

because aerobic respiration provides a higher energy yield, allowing them to generate more ATP with less glucose.