Sean - B-oxidation Flashcards
What is B-oxidation?
The conversion of a fatty acyl-coenzyme A into acetyl-CoA with the release of energy
What 3 pathways are required for the complete catabolism of fatty acids to generate ATP?
B oxidation ->
Krebs cycle/TCA cycle ->
Electron transport chain
How many reactions are there in B-oxidation?
Four
In general, what happens in each round of the four reactions of B ocidation?
In each round, 2 x C atoms are removed from the fatty acid chain
What happens to the two carbons released from the fatty acid chain during B oxidation?
They produce a 2 carbon molecule called acetyl-coA
How many molecules of acetyl-CoA will a 16 carbon fatty acid produce?
8 molecules of acetyl Co A
What happens to Acetyl CoA?
It enters the Krebs Cycle
What is the simplest form of B-oxidation?
The metabolism of saturated fatty acids with an even number of carbons
What conditions complicate B-oxidation?
An uneven number of carbons to the chain
The presence of double bonds
How many molecules of acetyl CoA are produced from a round of B-oxidation?
1 molecule of acetyl CoA
Name the energy carriers involved in B oxidation
NAD+
FAD
What happens in the first B-oxidation reaction?
(3)
Acyl-CoA dehydrogenase catalyses the formation of a double bond at B carbon by removal of 2 H
The 2H are donated to FAD to form FADH2
Electrons are then transferred from FADH2 to the electron transport chain
What enzyme catalyses reaction one?
Acyl-coA dehydrogenase
What does Acyl-coA dehydrogenase do?
(2)
Enzyme in reaction one
Forms a double bond by removing 2 H
What happens to the two hydrogens removed at reaction 1?
They are given to energy carrier FAD to form FADH2
What does FADH2 do?
Carries electrons to the electron transport chain
What type of reaction is reaction one?
Dehydrogenation/Oxidation reaction (removal of hydrogens)
What happens in reaction 2?
(3)
H2O is added across the double bond between the alpha and beta carbons
Catalysed by enoyl-CoA hydratase
The hydroxyl group is always added to the B group (B-oxidation)
What enzyme catalyses reaction 2?
Enoyl-CoA hydratase
What does enoyl-CoA hydratase do?
Its add H2O across the double bond between the alpha and beta carbons -> putting the hydroxyl group on the B carbon (hence B-oxidation)
What type of reaction is reaction 2?
Hydration reaction
What happens in reaction 3?
(4)
Two hydrogens are removed from the B carbon to form a carboxyl group
Catalysed by B-hydroxyacyl-CoA dehydrogenase
NAD+ is reduced to NADH (accepts electrons)
NADH then donates it’s electrons to the electron transport chain to generate ATP
What enzyme catalyses reaction 3?
B-hydroxyacyl-CoA dehydrogenase
What does B-hydroxyl-CoA-dehydrogenase do?
It removes two H from the B carbon to form a carboxyl group
What is the energy carrier in reaction 3?
NAD+
What happens to NAD+ in reaction 3?
(2)
NAD+ accepts two hydrogens to form NADH (reduction)
NADH then transports it’s two electrons to the energy transport chain
What type of reaction is reaction 3?
Dehydrogenation/Oxidation reaction i.e. the loss of hydrogens
What happens in reaction 4?
(6)
The sulphur of a CoA-SH molecule attacks the chain (between a and B)
This causes the chain to split, with a 2 carbon acetyl group and a fatty acyl-CoA group being formed
The 2 carbon acetyl group covalently attaches to the CoA to form Acetyl Co-A
The fatty acyl-CoA will undergo B-oxidation again to produce more acetyl-CoA
The acetyl-CoA produced is fed into the citric acid cycle
Catalysed by thiolase (acyl-CoA acetyltransferase)
What does thiolase (acyl-CoA acetyltransferase) do?
(2)
Causes the splitting of a 2 carbon acetyl group from a fatty acid chain
Catalyses the formation of acetyl CoA and fatty acyl Co A
What are isoenzymes?
Different molecular forms of the same enzymes produced by different genes
What does the type of isoenzyme used depend on?
The length of the fatty acid chain
In general, fatty acyl-CoA chains smaller than 12 carbons are degraded by a set of isoenzymes produced where?
The mitochondrial membrane
In general, fatty acyl-CoA chains bigger than 12 carbons are degraded by a set of isoenzymes produced where?
The mitochondrial matrix
What is a thiolation reaction?
The addition of a group containing a sulphur molecule (SH-CoA)
