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What are the main families of phospholipid?
Phosphoglycerides, sphingolipids, Sterols
What is the general structure of phosphoglycerides?
Two fatty acyl chains esterified to glycerol-3-phosphate
What structure do the fatty acyl chains usually have in phosphoglycerides?
Chain 1 is usually saturated, chain 2 is usually unsaturated
What phosphoglyceride has a H R-group?
Phosphatidic acid (PA)
What phosphoglyceride has a choline R-group?
Phosphatidylcholine (PC)
What phosphoglyceride has a ethanolamine R-group?
Phosphatidylethanolamine (PE)
What phosphoglyceride has a serine R-group?
Phosphatidylserine
What phosphoglyceride has a inositol R-group?
Phosphatidylinositol
What intermediate is required for the synthesis of phosphoglycerides?
Phosphatidate
How can Phosphatidate be synthesised?
Synthesised in ER of cells from glycerol-3-phosphate
What must happen to Phosphatidate or the group to be added for phospholipid synthesis to occur?
One must be activated
How is glycerol-3-phosphate converted to Phosphatidate?
Acyl CoA adds fatty acyl chains to glycerol-3-phosphate, catalysed by acyl transferase
How is Phosphatidate acivated?
Cytidine triphosphate reacts with the Phosphatidate molecule, forming CDP-diacylglycerol.
This molecule can then react with the head group, forming the phospholipid
How can the head group of a phosphoglyceride be activated?
Head group reacts with ATP, forming phosphoryl-head group.
Then reacts with CTP, forming CDP-head group.
The CDP-head group can then react with the diacylglycerol molecule
What is the major route of phosphatidylcholine (PC) synthesis?
Via dietary choline activation
What is the minor route of phosphatidylcholine (PC) synthesis?
Synthesised in the liver by the methylation of phosphatidylethanolamine (PE) head group.
Occurs when dietary choline is insufficient
How can phosphatidylcholine be produced from dietary choline?
Choline converted to choline-phosphate then to CDP-choline.
Added to DAG to form PC.
Catalysed by CK, CCT, and CPT
What is the limiting step in the synthesis of phosphatidylcholine from choline?
Formation of CDP-choline, action of CCT is controlled by the membrane itself
How can phosphatidylserine (PS) be synthesised?
Synthesised by base-exchange reactions from phosphatidylcholine (PC) or phosphatidylethanolamine (PE)
Where is phosphatidylcholine found in the membrane?
~50% of membrane mass.
80-90% of the membrane outer leaflet is PC
What is the importance of phosphatidylcholine in the membrane?
Important for membrane structure and integrity.
Precursor of DAG signalling
Where is phosphatidylethanolamine found in the membrane?
15-25% of total phospholipids in mammals, mostly found on the inner leaflet
How is phosphatidylethanolamine synthesised?
Ethanolamine converted to phosphoethanolamine, then to CDP-ethanolamine and added to DAG.
Catalysed by EK, ECT, EPT
What are the functions of phosphatidylethanolamine?
Precursor for PC synthesis.
Substrate for PTMs.
Influences membrane topology.
Promotes cell and organelle membrane fusion
Where is phosphatidylserine found in the membrane?
5-15% of phospholipids in mammals, higher distribution in the inner leaflet of the membrane
What are the roles of phosphatidylserine?
Activator of PKC, exposure to surface contributes to platelet aggregation and elimination of apoptotic cells
What can be formed by the phosphorylation of phosphatidylinositol?
phosphatidylinositol phosphates (PIPs)
What is the function of phosphatidylinositol?
Roles in lipid signalling, cell signalling, and membrane trafficking
What is the most common fatty acid composition of phosphatidylinositols?
Chain 1 is usually stearic acid;
Chain 2 is usually arachidonic acid
What are alkyl-acyl-glycerophospholipids?
Phosphoglycerides containing an alkyl chain ether-lined to carbon 1 of glycerol
What can alkyl-acyl-glycerophospholipids be oxidised to form?
Vinyl ethers=70% of myelin.
What is is glycerol replaced by in sphingolipids?
Sphingosine
What is the structure of sphingosine?
Amino alcohol with a long hydrocarbon chain
Where are sphingolipids found?
Highest concentration in CNS, on outer leaflet
Where are phospholipids synthesised?
ER membranes
How are phosphatidylcholines moved to the outer leaflet of the membrane?
Flipped by flippase enzymes
