L18 Phospholipids Flashcards
TF: lipid droplets are in the plasma while lipoproteins are in the cells
False, it is the opposite
lipid droplets are found in the cell while lipoproteins are found in the plasma
Under which metabolic circumstances would TG synthesis be favoured?
A. When cells are dividing
B. To maintain membrane rafts balance
C. After a fatty meal
D. When fasting for > 12h
E. In case of stress, to provide signaling molecules
C
What are the 3 kinds of membrane lipids
phospholipids, glycolipids, sterols (cholesterol)
How are the structures of glycerophospholipids (phospholipids) and sphingolipids different
main difference is the backbone; sphingolipids have a sphingosine backbone while glycerophospholipids have a glycerol backbone
sphingolipids: sphingosine (long chain amino alcohol) backbone + 1 FA chain + polar head group
glycerophospholipids: glycerol backbone + 2 FA chains + phosphate group + polar head group
TF: all glycerophospholipids have the same polar head and FA chains
False, they can have different kinds of polar heads and different kinds of FA chains
What are the roles of membrane lipids? (3)
- in/out asymmetry (leaflet asymmetry essential for function)
- microdomains (RAFTs vs NON-RAFTs)
- Signaling (PI, PIP3, PIP2, IP3)
What is the difference between a RAFT and NON-RAFT domain?
RAFT: thick and stiff (sphingomyelin, cholesterol, other)
NON-RAFT: thin and fluid (glycerophospholipids)
What is sphingomyelin and how is it different from sphingolipids
sphingomyelin is a sphingolipid that is more similar to phospholipids as it has a phosphate and choline group (polar)
Under which metabolic circumstances should PL synthesis be favoured? (choose all that apply)
A. In case of stress, to provide signaling molecules
B. After a fatty meal
C. When fasting for > 12h
D. To maintain membrane rafts balance
E. When cells are dividing
A, D, E
Where can phospholipids be found INSIDE the cell
endoplasmic reticulum (ER)
phospholipid and neutral lipid biosynthesis
Why are there so many kinds of glycerophospholipids
to aid in membrane fluidity (under conditions of temperature change for example), signaling, other housekeeping roles
TF: RAFT domains have more double bonds in their FA chains than NON-RAFT domains
False, non-raft domains have more double bonds and thus are more fluid
TF: Longer FA chains in the plasma membrane increases fluidity
false, short FA chains result in increased fluidity of the plasma membrane
How are PI, PG, and Cardiolipin synthesized?
- Activate Phosphatidic acid using CTP to generate high energy intermediate, 2Pi released drive the reaction forward and make it irreversible
- PI = add inositol to intermediate
PG = add glycerol-3-phosphate
Cardiolipin = 2PG + Cardiolipin synthase (release 1 glycerol)
TF: Kennedy pathway occurs in all cell types
True
Explain the Kennedy pathway and what it produces
Kennedy pathway produces PE and PC (phospholipids)
We start with ethanolamine or choline and invest 1 ATP to prime the head group
Then, 1 CTP is invested to make a high energy intermediate by activating the head group
Polar head group is then added to diacylglycerol to make PE (if starting with ethanolamine) or PC (if starting with choline)
What is the difference between [PI, PG, Cardiolipin] synthesis and [PE, PC] synthesis? What do they have in common?
PI, PG, Cardiolipin pathway activates the phosphatidic acid while PE, PC pathway (Kennedy pathway) activates the head group
They both generate a high energy intermediate
How does PE->PC and what is the significance of this?
It transforms PE -> PC by adding 3 methyl groups to PE: this is done by PEMT
*the methyl comes from 5-adenosyl-L-methionine
This pathway produces 30% of PC in liver and is only present in the liver
What is the one carbon pathway? What happens
Methionine interacts with ATP to generate 5-adenosyl-L-methionine. Within the structure of 5-adenosyl-L-methionine, there is a highly unstable soulful group (sulfonium) thereby making it a very good 1 carbon donor
Why are 2 pathways needed to synthesize PC? (Kennedy pathway and PE->PC PEMT conversion pathway)
Why is this regulation necessary
Abundant PC production is needed in the liver mainly for bile production (mainly composed of bile salts, cholesterol, PC)
Bile composition follows a tight ratio or else gallstones can be produced
What symptom is observed if you have PEMT deficiency?
Gallstones
What is the high energy intermediate in the PEMT pathway?
5-adenosyl-L-methionine
List the kinds of glycerophospholipids (6)
PI, PG, Cardiolipin, PE, PC, PS
How is PE transformed into PS? What about the other way around?
PE->PS = transferase (ethanolamine group is replaced by serine group)
PS->PE = decarboxylase (lose 1 CO2)
How are sphingosines synthesized?
An activated acyl - Fatty-acyl-CoA (from FA - serine - and CoA - palmitoyl-CoA - reaction) is added to a serine backbone thus making ceramide
Ceramide can interact with either PC resulting in sphingomyelin or UDP-glucose resulting in cerebroside (glycosphingolipid)
What are phospholipases, what do they do, and where are they located
They are enzymes that will remodel lipids by acting on the existing phospholipids at specific sites
Cleave phospholipids to: generate signalling molecules, convert phospholipids (Lands’ Cycle), modulate plasma membrane shape
Mostly located on plasma membrane
What is an example of a phospholipase for signalling?
PLC where the g-alpha-q activates PLC which will act on PIP2 to generate IP3 (and DAG) for secondary messenger effects
What is CDP
It acts as an active carrier and plays a role in glycerophospholipids synthesis (activation of high energy intermediates)
