LECTURE 17 - PHOSPHOLIPIDS Flashcards
what are the different types of phospholipids?
phosphatidylcholine
phosphatidylethanolamine
phosphatidylserine
phosphatidylthreonine
phosphatidylinositol
phosphatidylglycerol
what is the structure of sphingomyelin (a sphingolipid)?
sphingolipids contain an amide bond between the sphingosine and the phosphate
what is the structure of glycolipids?
cerebrosides and gangliosides
what is the structure of sterols?
cholesterol and derivatives
what are the different fatty acids?
palmitate, oleate, sphingosine and stearate?
what are the roles of membrane lipids?
maintain in/out asymmetry of the membrane
create microdomains
signaling
how is in/out asymmetry of the membrane maintained?
flippase flips phospholipids inward
floppase flips phospholipids outwards
scramblase does both
what are the microdomains of the membrane?
RAFTS:
gangliosides
sphingomyelin
cholesterol
thick and stiff
NON RAFTS:
glycerophospholipids (PC, PS, PE)
thin and fluid
made of shorter and unsaturated chains
where does phospholipid synthesis happen?
in the ER
what are the steps of synthesis of glycerophospholipids:PI, PG, cardiolipin
step 1.
activation of phosphatidic acid by CTP
this releases CDP-diacylglycerol and PPi
the PPi reaction with pyrophosphatase is what drives this reaction forward
step 2.
adding inositol to make phosphatidylinositol or glycerol3P to make cardiolipin
the take home message is that you need a high energy intermediate before you can add the necessary stuffq
what is the kennedy pathway to make PE and PC
happens in all cell types
1. prime the head group with ATP
2. activate the head group
3. add the diacylglycerol
this pathway is special because you activate the head group instead of the phospholipid, but the concept of a high energy intermediate is still there
what is the one carbon pathway to have the PE to PC conversion?
happens in the liver ONLY
the enzyme is PEMT: phosphatidylethanolamine methyltransferase
this pathway represents 30% of the PC production in the liver
step 1:
add the methyl group
step 2:
repeat
step 3:
repeat
PC has three more methyl groups than PE
where does the added methyl come from in the one methyl pathway?
methionine is activated with ATP
this creates S-Adenosyl-L-methionine
this is a methyl donor molecule, a high energy intermediate
which function of the liver depends on PC production?
to make bile, you need a perfect ratio between cholesterol, bile salts and PC
if there is too much of one, the bile crystallizes and you get gallstones
how do the PE->PS and the PS->PE conversions happen?
PE->PS
phosphatidylethanolamine serine transferase
PS-> PE
phosphatidylserine decarboxylase
not a reversible enzyme but two separate ones
the CO2 is the difference between the two molecules
how are sphingolipids made?
- add an activated acyl to the serine backbone (palmitoyl CoA is the high energy intermediate)
2a. transfer a phosphocholine head group from PC to make sphingomyelin
2b. add a glucose head group from UDP glucose (high energy intermediate) to make cerebroside
where are phospholipases located?
they are present in the plasma membrane
what are the functions of phospholipases?
cleave phospholipids to:
generate signaling molecules
convert phospholipids
modulate the shape of the plasma membrane
what do the different phospholipases create from a phospholipid?
phospholipase A1: lysophospholipid
phospholipase C: diacylglycerol
phospholipase D: phosphatidic acid
what diseases are associated with phospholipase defficiency?
for example deficiency in sphingomyelinase causes Nieman-Pick Type A/B disease
what is the Land’s cycle?
phospholipid is cut into lysophospholipid by phospholipase A, this also releases a free fatty acid
lysophospholipid is converted back by lysophospholipid acyltransferase which takes a fatty acid from Acyl-CoA
how do lysophospholipids change the shape of the membrane?
create some curvature
this can be used for invagination and exvagination
