Lipid metabolism Flashcards
Lipid definition
Chemically diverse group of compounds which aren’t soluble in water
What is a fatty acid?
A long hydrocarbon chain with a terminal carboxyl group
Triacylglycerol (TAG)
Esters of 3 fatty acids with glycerol
What are phospholipids?
Esters of 2 fatty acids with glycerol attached to phosphate group and another alcohol
How are polyunsaturated fats made?
Further desaturation of monounsaturated fats
Animal vs Plant bonds
Animal: double bond between bond and carboxyl group
Plant: double bond between bond and methyl group
Prokaryote vs Eukaryote synthesis of fatty acids
Prokaryote: separate enzymes
Eukaryote: multifunctional enzyme complex
Acyl carrier protein (ACP)
- In bacteria, it is a 77 amino acid protein joined to a phosphopanthenine (PP)
- In animals, it is part of the fatty acid complex
When do chains become terminated?
At 16 carbons (palmitic acid)
What can phospholipids be synthesised into?
- Diacylglycerol
- Phosphatidylcholine
- Phosphatidylethanolamine
- Phosphatidylserine
- CDP-Diacylglycerol
- Phosphatidylinositol
- TAG
Intestine lipid transport
Transported as lipoproteins
Liver lipid transport
Transported as lipoproteins
Adipose tissue lipid transport
Releases fatty acids into bloodstream
What are apolipoproteins (apo)?
Diverse group of lipoproteins with a wide range of sizes
Functions of apolipoproteins (apo)
- Holds particle together
- Activation or inhibition of lipoprotein lipase (LPL)
- Recognition by receptors
Exogenous pathway
- Lipids are absorbed into small intestine
- Phospholipid, cholesterol, cholesterol ester, TAG are incorporated with apoB48 to form chylomicrons
- Chylomicrons are secreted into bloodstream and anchored to LPL
- LPL hydrolyses TAG and releases fatty acids
- When TAG has been broken down particle is released back into the circulation as a remnant
- The remnant is removed from the circulation after binding to receptors in the liver
Endogenous pathway
- In the liver phospholipid, cholesterol, cholesterol ester and TAG combine with apoB100 to form very low-density lipoprotein (VLDL)
- VLDL are secreted into the blood stream and interact with the LPL
- When TAG has been hydrolysed the particle is released as intermediate density lipoprotein (IDL) which is further converted into low density lipoprotein (LDL)
- This is removed from the circulation after interaction with specific cell surface receptors
What is discoidal HDL?
Products of liver and intestine rich in protein, phospholipid and free cholesterol
LDL vs HDL
LDL: deposits cholesterol in the arteries causing heart attacks
HDL: removes cholesterol from arteries
Where can fatty acid be metabolised?
Adipose tissue, liver, muscle
Name the 3 ways fatty acids are used for energy
- Released by LPL from chylomicrons
- Released by LDL from VLDL
- Released as NEFA from adipose tissue
