Lecture 29: FATTY ACIDS AS FUEL MOLECULES - FATTY ACID OXIDATION Flashcards
What is the preferred fuel for most tissues?
Fatty acids (example is red muscle)
What is the primary energy reserve in mammals?
Fat as TAG’s
What portion of body weight is fat?
5% to 25%
What happens with excess energy consumed as glucose?
It is stored as fat (Acetyl-CoA»_space; Free fatty acids»_space; Triacylglycerol)
Why do we store fuel as fatty acids?
Because fatty acids are more reduced than carbohydrates which means more energy is released when they are oxidised in pathways
What amount water is stored carbohydrate (glycogen)?
2/3 - because carbohydrates are polar
What happens to TAG in adipose tissue (storage)?
It is broken down into free fatty acids and glycerol by a lipase
What happens as the FFA’s and glycerol increase in concentration in the cell?
It creates a concentration gradient for them to passively move into the blood
What does glycerol do once it is in the blood?
Moves to the liver
How are FFA’s found in the blood?
In hydrophobic pockets of albumin proteins because FFA’s are hydrophobic and blood is mainly water. They can then passively move into cells which have a low concentration of FFA’s
How do FFA’s get into the cell?
Usually with the help of transporters across the membrane
How are FFA’s found in the cell?
They are held in FABP (fatty acid binding protein) which has a barrel structure because the cytoplasm of the cell is a hydrophilic environment
What must happen before fatty acids are oxidised?
They must be activated
When does activation occur?
Before the fatty acid enters the mitochondria
How are FFA’s activated?
By attachment to CoA to make a fatty acyl-CoA
What is the equation for fatty acid activation?
FFA + ATP + CoA-SH»_space; Fatty acyl-CoA + AMP + 2Pi
What is the energy required to activate FFA’s?
The energy equivalent of 2ATP because ATP is converted to AMP but only one ATP is required
What is the enzyme for FFA activation?
Acyl-CoA Synthetase
What is fatty acyl-CoA?
Carbon chain of any length
What is acetyl-CoA?
Two carbon chain
Where does oxidation of fatty acids occur?
In the mitochondrial matrix
What must the fatty acyl-CoA pass through?
Two membranes (inner and outer mitochondrial)
How does fatty acyl-CoA pass through the outer membrane?
A fatty acyl CoA carrier from the cytosol to the inter membrane space
How does fatty acyl-CoA pass through the inner membrane?
It requires the conversion to fatty acyl-carnitine as there is no fatty acyl-CoA carrier
What happens in the carnitine acyltransferase reaction?
CoA and carnitine are exchanged on the fatty acid which is a reversible reaction
What is the carnitine acyltransferase reaction?
Fatty acyl-CoA + carnitine»_space; fatty acyl-carnitine + CoA
What does beta oxidation use?
Fatty acids with an even number of carbons that are saturated (have no double bonds)
Is ATP made in beta oxidation?
No
What happens with the energy released in beta oxidation?
It is transferred to coenzymes NAD and FAD
What happens to the carbon chain in beta oxidation?
It is cut into 2C pieces
What is the product of beta oxidation?
Acetyl CoA which is further oxidised in the citric acid cycle
What type of reaction is reaction 1 in beta oxidation?
Oxidation
What happens in reaction 1 of beta oxidation?
A double bond is formed between the alpha and beta carbons. The 2 hydrogens removed are transferred to FAD to make FADH2
What type of reaction is reaction 2 in beta oxidation?
Hydration
What happens in reaction 2 of beta oxidation?
The water molecule splits over the double bond to form a single bond. Hydroxyl group on the beta carbon and hydrogen on the alpha carbon
What type of reaction is reaction 3 in beta oxidation?
Oxidation
What happens in reaction 3 of beta oxidation?
Two hydrogens are lost (from the OH and a H) to from a carbonyl bond. One of the hydrogens is accepted by NAD+
What do reactions 1 to 3 involve?
A rearrangement, energy captured in 2 redox reactions (by NAD and FADH), the chemistry around the bond is altered so it can be cleaved in reaction 4
What happens in reaction 4?
Acetyl - CoA is released, CoASH is added to the carbon chain and the 2C shorter fatty acyl-CoA enters the next round of beta oxidation
What is the products of each round of beta oxidation?
1 NADH, 1 FADH2 and 1 acetyl - CoA
What is the formula for the number of rounds of beta oxidation?
n(C)/2-1
How many rounds of beta oxidation for palmitate (16C)?
7
What is the equation for beta oxidation of palmitate (16C)?
palmitate-CoA + 7NAD+ + 7FAD + 7CoA + 7H2O»_space;> 8 acetyl - CoA + 7NADH + 7FADH2 + 7H+
