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10 Cards in this Set

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Why do ketone body synthesis?
Water soluble derivative of lipids called ketone bodies

From excess acetyl CoA when fat breakdown predominates.

Major fuel source of brain, if necessary
Where does Ketone body synthesis occur?
Liver mitochondiria
Conditions in which ketone bodies are produced
-Entry of Acetyl CoA into TCA depends on OAA
-OAA kept in low concentrations because it is immediately used by GNG
-When this happenes, OAA will not go to the TCA cycle
What happens when B-oxidation of FA occurs to form acetyl CoA, but OAA is not available (doing GNG)?
acetyl CoA diverted to form 3 ketone bodies: acetoacetate, 3-hydroxybutyrate, and acetone
1. 2 acetyl CoA's attach end-to-end-->acetoacetyl CoA
B-ketothiolase
CO2 removed
Unfavorable
2. A third acetyl CoA hooks onto acetoacetyl CoA-->3-hydroxy-3-methylglutaryl CoA (HMG-CoA)
HMG-CoA Synthase
Cleavage of this thioester linkage drives the unfavorable rxn forward
3. Acetyl CoA is clipped off
HMG-CoA-->acetoacetate
HMG-CoA Lyase
4. Acetoacetate spontaneously forms --> acetone or B-hydroxybutyrate
Spontaneous decarboxylation to form acetone

Produce NAD upon conversion to B-hydroxybutyrate
What happens under normal conditions, when we break down fats?
Acetyl CoA combines with OAA--citrate--TCA
What happenes under diabetic/starving conditions?
Pyruvate --> OAA by pyruvate carboxylase

OAA-->malate and transported out of the mitochondria

Malate --> OAA and goes to GNG

Acetyl CoA cannot combine with OAA because OAA is so quickly converted to malate