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2nd half of FA metabolism- Biochem


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Describe 1st step of B-oxidation of very long chain FA in Peroxisomes?
1st step of of B-oxidation is catalized by an FAD containing oxidase. e- are transfered from FADH2 to O2 which is then reduced to H2O2

Takes place in peroxisome because H2O2 is produced
What are similarities & differences of mitochondrial vs peroxisomal B-oxidation?
Both generate FADH2 & NADH but
Peroxisomal is less efficient because FADH can’t get through peroxisomal membrane (must be oxidized by O2)
Why do peroxysomal B-oxidation?
very long chain FA cannot cross mit membrane, must be broken up by peroxysomes
Describe oxydation of phytanic acid?
a peroxysomal alpha hydroxylase oxidizes the alpha carbon so that B oxidation can occur.
Refsum's disease
alpha oxidase enzyme is defective so we cannot break down phytanic acid
w-oxidation of FA
converts FA to dicarboxylic acids. Results in DC urea. Which is diagnostic for problem w/ B oxidation
4 steps of B-oxidation
1)Oxidation (ACoA dehyd)
2)Hydration (enol CoA hyd)
3)Oxidation(B hydroxy CoA hyd)
4)Cleavage (B keto thiolase)
Metabolism of Monosaturated Fats
2-3 enol-CoA isomerase - converts cis bond to trans
Metabolism of Polyunsaturated Fats
2-3 enol-CoA isomerase - converts cis bond to trans
2-4 dienol Co A reductase – reduces one of the double bonds
Propynyl Co A pathway
Propionyl CoA to Succinyl CoA. 1st step involves Propionyl CoA carboxylase (ABC enzyme) conversionof Propionyl CoA to methmylmalonyl CoA. Last step involves methyl-Malonyl CoA mutase conversion of Methylmalonyl CoA to Succinyl CoA. This last enzyme requires B12 therefore build up of Methylmalonyl CoA is diagnostic for B12 deficiency.
ABC enzymes
Pyruvate carboxylase -
Acetyl CoA carboxylase -
Propionyl CoA carboxylase -
MCAD deficiency
B oxidation in liver tissue in order for gluconeogenesis – if can’t do B-oxidation – hypoglycemic shock;
Feed child, replenished glycogen stores, in night using glycogen stores, next morning feed – child never in hard glucagon world. Never know about deficiency. Using liver glycogen always. When glycogen stores don’t get built up child needs to do gluconeogenis need to do B oxidation – usually dies in middle of night.
3 ketone bodies:
1)Acetoacetate can covert to:
2)Acetone (volitile)
3)D-B Hydroxybutyrate (more stable)
Why are ketone bodies made in liver cells only?
HMG Co A synthase –makes ketone bodies and found only in liver mitochondria
Why are ketone bodies broken down in tissues other than the liver
B-ketoacyl- CoA transferase is found in mitochondria outside liver -allows extrahepatic tissues to break ketone bodies down
Fuel for Brain
1) 24 hours
2)day 2-7
3) After 1 week
2) protein (mostly glucose from gluconeogenesis but some ketone bodies)
3)Fat & small amount of protein-mostly ketone bodies but some glucose from gluconeogenesis

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