Beta Oxidation Flashcards
how much energy comes from dietary triacylglycerols and fatty acids?
one third of energy needs come from dietary triacylglycerols
80% of energy needs of the mammalian heart and liver are met by oxidation of fatty acids
many hibernating animals rely almost exclusively on fats as energy source
why are fats an efficient fuel storage?
they carry more energy per carbon than saccharides because they are more reduced. they carry less water along because they are non polar
basically, glucose/glycogen are good for short term energy needs and quick delivery. fats are good for long-term energy needs because they store well and deliver slowly
how are lipids transported in the blood?
as chylomicrons, small bundles of tightly backed lipids (due to hydrophobic effect) bound by a phospholipid monolayer membrane. They transport form the small intestine to the rest of the body
what does hydrolysis of fats yield? what catalyzes and regulates this hydrolysis?
hydrolysis of fats yields fatty acids and glycerol (think of the structure of triacylglycerols and where they break). reaction is catalyzed by lipases and regulated by glucagon (says we are out of glucose) and epinephrine (says we need energy now)
where do the hydrolyzed products of fats go?
glycerol enters glycolysis after modification by glycerol kinase (uses ATP) and glycerol 3-phosphate dehydrogenase. this creates dihydroxyacetone phosphate which is made into glyceraldehyde 3-phosphate by triose phosphate isomerase. slide 8
fatty acids are transported to other tissues for fuel (go through B-oxidation in mitochondria)
how do fatty acids enter the mitochondria? which ones can freely diffuse?
small (<12 C) fatty acids diffuse freely across mitochondrial membrane
Larger fatty acids are transported via acyl-carnitine/carnitine transporter
what conversion is required in order for fatty acids to be transported or attached to phospholipids? know mech
fatty acids must be converted to acyl-CoA. uses enzyme fatty acyl-CoA synthetase, ATP and CoA-SH. slide 10 mech
describe the acyl-carnitine/carnitine transport process
acyl-CoA is converted to acyl-carnitine by carnitine acyltransferase I and allowed to pass through outer mitochondria membrane and then is transported through the inner mitochondrial membrane. Carnitine acytransferase II then coverts acyl-carnitine back into acyl-CoA.
slide 11
what is the point of the acyl-carnitine/carnitine transport?
allows more control and regulation of transport so FA are only oxidized when needed
stages of FA oxidation
- oxidative conversion of two carbon units into acetyl-CoA via B-oxidation with generation of NADH and FADH2
- oxidation of acetyl-CoA into CO2 via CAC with generation of NADH and FADH2
- generates ATP from NADH and FADH2 via respiratory chain
describe the B-oxidation pathway for saturated FA
- dehydrogenation: acyl-CoA dehydrogenase creates FADH2 and trans FA
- Hydration: enoyl-CoA hydratase creates B hydroxyacyl
- Dehydrogenation: B-hydroxyacyl-CoA dehydrogenase creates B-ketoacyl and NADH
- Thiolysis: acyl-CoA acetyltransferase (thiolase) creates a free acetyl-CoA and a shortened FA
slide 13
what is the end result of B-oxidation? list products and where they go. how much of each product is made (eg in a 16 C FA)
each round creates 1 acetyl-coA, 1 FADH2, and one NADH. acetyl CoA goes to CAC for further oxidation. NADH and FADH2 go to ETC for ATP production.
the last round of oxidation frees 2 acetyl-CoAs with the same process, so the end result is one less FADH2 and NADH than acetyl-CoA. a 16 C chain would produce 8 acetyl CoA and 7 NADH and 7 FAHD2
how does B-oxidation of saturated fats differ?
the cis double bonds in FA are not a substrate for enoyl-CoA hydratase, two additional enzymes are required.
enoyl-CoA isomerase: converts cis double bonds at C3 to trans double bonds
2,4-dienoyl-CoA reductase: reduces cis double bonds not at C3
monounsaturated fats use only isomerase, polyunsaturated use both
slide 16-17 draw mech
what happens when odd numbered FA are oxidized?
the final oxidation leaves a three carbon propionyl-CoA which is oxidized to succinyl-CoA which can enter CAC. mech slide 19
how is fatty acid synthesis and breakdown regulated? two key signal molecules
Insulin: triggers increase in FA synthesis and decrease in FA CoA transport into mitochondria and decreases B-oxidation
Glucagon: triggers decrease in FA synthesis and increases FA transport into mitochondria and increases B-oxidation
Both signals act through the enzyme acetyl-CoA carboxylase ACC which is the first step in FA synthesis. Insulin activates phosphatase which makes ACC active while glucagon activates PKA which makes ACC inactive
