Energy production (lipids) - MEH 3 Flashcards
Describe the various classes of lipids.
- Fatty acids - fuel molecules.
- Triacylglycerols - fuel storage and insulation.
- Ketone bodies (C4) - water soluble fuel molecules.
Vitamins (A, D, E and K) - fat soluble.
What are lipids?
- Insoluble in water.
- Most only contain C, H and O. Phospholipids contain P, N).
- More reduced than carbohydrates. They release more energy when oxidised and complete oxidation requires more O2.
What are dietary triacylglycerols
How lipids are stored as fuel molecules and for insulation.
What is step 1 in the metabolism of triacylglycerols?
They are hydrolysed by pancreatic lipase in the small intestine to release glycerol and fatty acids. This requires bile salts and colipase.
Describe the catabolism of fatty acids. Also known as lipolysis.
Under stressful conditions, adipose tissue triacylglycerols are hydrolysed by the enzyme HORMONE-SENSITIVE LIPASE to release fatty acids and glycerol.
What is lipolysis activated and inhibited by?
Activated by adrenaline, glucagon, growth hormone, cortisol and thryoxine.
Inhibited by insulin.
Fatty acids are activated outside of the mitochondria, how do they cross the inner mitochondrial membrane for oxidation?
Carnitine CoA is used to shuttle the fatty acid across the inner mitochondrial membrane.
The acyl is attached to the carnatine (CAT1 enzyme), which is shuffled across the membrane into the matrix. Then the acyl bonds with the CoA the other side (CAT2 enzyme) and the carnatine is shuffled back.
CAT1 is inhibited by malonyl-CoA.
This process is regulated by AMP and insulin.
What happens after fatty acids and glycerols are produced in lypolysis?
Fatty acids are carried to tissues via the blood stream, bound non-covalently to albumin. These are called free fatty acids or non-esterified fatty acids.
Glycerol is transported in the blood to the liver where it is oxidised, converted to glucose, or used in synthesis of triacylglycerols.
How, when and why are ketone bodies formed?
The livery constantly generates ketone bodies from acetyl-CoA.
Synthesised in the liver from acetyl-CoA.
Acetone arises from the spontaneous decarboxylation of acetoacetate.
In the liver mitochondria by the actions of lysase and reductase enzymes. These are controlled by the insulin/glucagon ratio. When ratio falls lysase is activated and reductase is inhibited. When ratio rises, lysase is inhibited and reductase is activated and cholesterol synthesis occurs.
What are ketone bodies?
An alternative fuel that is used in preference to glucose by peripheral muscle tissues.
They are produced when acetyl CoA is in excess.
Soluble.
Acidic - pKa of 4. Can cause ketone acidosis (acidification of the blood) if ketone levels are high. Can be caused by untreated type 1 diabetes.
What is beta-oxidation?
The process by which fatty acids are oxidised to released energy. It occurs in mitochondria. Therefore, RBC and other cells without mitochondria cannot oxidise fatty acids.
A series of reactions that oxidises the fatty acid and removes a C2 unit each turn of the cycle until only 2 C atoms remain.
Requires: NAD+ and FAD.
Can’t occur in absence of oxygen which is needed in step 4 to re-oxidise NADH and FAD2H formed.
All C acid intermediates are converted to acetyl-COA.
Also can’t occur in CNS as fatty acids can’t cross blood brain barrier.
What are the intermediates created in beta-oxidation used for in stages 3 and 4 of catabolism?
To generate ATP.
What is an alpha-linolenic acid?
An 18-C chain with 3 double bonds. Often referred to as omega-3.
What is the function of kinases?
To phosphorylate their substrate.
They are enzymes.
