citric acid cycle Flashcards
what occurs to Acetyl-CoA in the citric acid cycle?
it is oxidized to produce 2CO2 molecules
what are the sources of Acetyl-CoA?
carbs, FA and amino acid catabolism
how many C is Acetyl-CoA?
2C
what does Acetyl-CoA condense with? what does it form?
condenses with oxaloacetate to form citrate
how many carbons are oxidized in the CAC?
2 C are oxidized to form 2 CO2 molecules per Acetyl-CoA molecule
how many high energy products are made per Acetyl-CoA?
3 NADH
1 FADH 2 / QH2
1 GTP
where does the CAC occur?
in the mitochondrial matrix
how many reactions are in the CAC?
8
what is the first step in the CAC? what enzyme is used? what is produced?
An irreversible reaction with oxaloacetate and Acetyl CoA to produce citrate
-catalyzed by citrate synthase
-generates co-enzyme A
what is the second step in the CAC? what is produced?
a reversible isomerization to produce isocitrate
what is the 3rd step in the CAC? what enzyme is used? what is produced?
an irreversible oxidative decarboxylation rxn
-catalyzed by isocitrate dehydrogenase (regulated)
-energy capture (produces NADH)
what is the 4th step in the CAC? what enzyme is used? what is produced?
an irreversible oxidative decarboxylation to generate Succinyl CoA
-catalyzed by alpha-ketoglutarate dehydrogenase (regulated)
-energy capture step (produces NADH)
what kind of molecule is succinyl CoA?
it contains a thioester which makes it a high energy molecule
what is significant of the 4th step in the CAC (synthesis of succinyl CoA)?
it is similar to the PDH reaction
what is an example of anabolic processes during the CAC?
the conversion of intermediates into amino acids
ex) alpha-ketoglutarate into glutamate
what is the 5th step in the CAC? what is produced?
a reversible substrate-level phosphorylation to yield succinate
-energy capture (GTP/ATP)
what occurs when [ADP] decreases in the matrix?
what is the 7th step in the CAC? what is produced?
a reversible hydration rxn
-conversion of fumerate to malate
what is the 8th step in the CAC? what is produced?
a reversible oxidation rxn to regenerate oxaloacetate
-energy capture (NADH produced)
how is the CAC regulated?
regulated by enzymes:
-isocitrate dehydrogenase
-alpha-ketoglutarate dehydrogenase
AND [intermediates]
-NAD+/NADH ratio
what are inhibitors of the CAC? What are activators?
inhibitors: NADH, ATP, citrate, succinyl CoA
activators: ADP, Ca++
-they reflect energy needs / usage
what does high [citrate] affect?
it inhibits the CAC
-this is not physiologically relevant
what does ATP affect in the CAC?
it is a direct allosteric inhibitor for isocitrate dehydrogenase
-conversion of isocitrate into alpha-ketoglutarate
what does NADH affect in the CAC?
it is a direct allosteric inhibitor for isocitrate dehydrogenase and alpha ketoglutarate complex
-conversion of isocitrate into alpha-ketoglutarate and converion to succinyl CoA
what does ADP affect in the CAC?
it is a direct activator for isocitrate dehydrogenase
-conversion of isocitrate into alpha-ketoglutarate
what does Ca++ affect in the CAC?
direct activator for alpha ketoglutarate complex
-converion to succinyl CoA
what does succinyl CoA affect in the CAC?
inhibits the alpha ketoglutarate complex
what occurs when [ADP] increases in the matrix?
what can CAC intermediates be used to synthesize?
AA, carbs, fats, nucleotides and other compounds
-therefore, [intermediate] must be maintained or the effectiveness of the CAC will decrease
what are anaplerotic reactions?
rxns that are needed in order to replenish intermediates of the CAC
what reactions are anaplerotic?
Pyruvate Carboxylase- converts pyruvate to oxaloacetate by adding a carboxyl group
AA breakdown
what catalyzes the conversion of pyruvate to oxaloacetate? what kind of reaction is this?
catalyzed by pyruvate carboxylase
-anaplerotic rxn
what catalyzes the conversion of pyruvate to acetyl-CoA? what kind of reaction is this?
pyruvate dehydrogenase complex
-oxidative decarboxilation
what molecules activate and inhibit pyruvate carboxylase?
activated by acteyl-CoA
inhibited by ADP
what affect does acetyl-CoA have on pyruvate dehydrogenase complex?
it acts as an inhibitor
how many ATP are generated from each Acetyl-CoA?
~10 ATP per acetyl-CoA
-20 ATP are made per glucose
how many NADH are made per glucose molecule in the CAC?
6 NADH
-3 NADH per acetyl-CoA
how many FADH2 are made per glucose in the CAC?
2 FADH2
-1 per acetyl-CoA
how many GTP are made per glucose in the CAC?
2 GTP
-1 GTP per acetyl-CoA
how many ATP molecules are made from the complete aerobic oxidation of glucose?
32 ATP
how many ATP are generated from the anaerobic glycolysis of glucose?
2 ATP
how is lactate used in the CAC?
it is used as a metabolic fuel in anaerobic metabolism
-reoxidizes NADH to be used in ETC
why do yeast cells consume less glucose in the prescence of oxygen?
because aerobic respiration provides a higher energy yield, allowing them to generate more ATP with less glucose.
