Beta oxidation Flashcards
On a weight basis, how many times larger is the caloric yield from fatty acids compared to carbohydrates?
Double.
Roughly how much of our energy comes from fatty acid oxidation?
More than half of the body’s energy needs come from fatty acid oxidation (but not for the brain).
When may we derive more energy from fatty acid oxidation?
During fasting
What is beta oxidation?
The process of fatty acid oxidation to form acetyl CoA
What must happen before beta-oxidation and what enzyme is responsible?
What happens after this?
The first step of beta-oxidation is catalyzed by one of a family of Acyl CoA dehydrogenases which binds the fatty acids (different dehydrogenases for different sized fatty acids
Formation of an acyl CoA species catalyzed by acyl CoA synthetase.
Fatty acid + ATP + HS-CoA -> Acyl CoA + AMP (two high energy bonds are used) + Pi
Where does the generation of the acyl CoA species occur?
On the outer mitochondrial membrane
How do we get the Acyl CoA species into the mitochondrial matrix?
By using the carnitine shuttle.
Acyl CoA couples with the molecule carnitine to form acyl carnitine. Carnitine and acyl carnitine are moved in and out of the matrix by a translocase.
Carnitine acyltransferase I creates acyl carnitine, kicking off the CoA and replacing it with carnitine.
Carnitine acyltransferase II restores acyl coa, kicking off the carnitine and replacing it with the CoA.
Primary carnitine deficiency is what sort of disorder?
Autosomal recessive disorder.
What are some symptoms of primary carnitine deficiency?
Encephalopathies such as cardiomyopathies, muscle weakness and hypoglycaemia.
What causes primary carnitine disorder?
Mutations in the SLC22A5 gene which encodes a carnitine transporter result in a reduced ability of cells to take up carnitine.
Describe the reactions of beta oxidation and the products formed.
Acyl CoA undergoes a sequence of oxidation, hydration and oxidation and thiolysis reactions.
This results in the production of acetyl CoA and an Acyl CoA species two carbons shorter than before. On the final cycle (4 fatty Acyl CoA intermediate), two acetyl CoA molecules are formed.
Also forms FADH2 and NADH.
What is the general formula for an acyl CoA species which undergoes x beta oxidations?
For x beta-oxidation reactions:
Acyl CoA species (2(x+1) Carbon Fatty Acid) + xFAD + xNAD+ + xH2O + xCoA
forms
(x+1)acetyl CoA + xFADH2 + xNADH
When and why do ketone bodies form?
When: During periods of fasting or whenever oxaloacetate cannot be produced.
Why: Acetyl CoA requires oxaloacetate to enter the TCA cycle. When fat breakdown predominates, e.g during fasting, glycolysis doesn’t occur (as much) and so oxaloacetate isn’t produced (as much). This leads to acetyl CoA forming acetoacetate,
which forms D-3-hydroxybutyrate and acetone known collectively as ketone bodies.
Palmitate undergoes 7 beta oxidation reactions. What is the net gain of ATP?
7 beta oxidation reactions means 7 NADH and 7 FADH2.
1 NADH = 3 ATP
1 FADH2 = 2 ATP
Therefore 35 ATP is made from beta oxidation.
It will produce 8 acetyl CoA (2(7+1)), which each form 12 ATP from the oxidative phosphorylation of coenzymes NADH, FADH2.
Therefore 96 ATP are made from the oxidative phosphorylation process.
Therefore 131 ATP are generated.
However, 2 ATP were used to form the acyl CoA species, so a net gain of 129 ATP.
Mole for mole, fatty acid metabolism is significantly better/worse than glucose metabolism for ATP production?
Fatty acid metabolism is significantly better!
