Lipids and the Lipid Bilayer
What are the top 4 mamallian phospholipids? What is the net charge on each?
Phosphatidyl-ethanolamine: neutral Phosphatidyl-serine: negative Phosphatidyl-choline: neutral Sphingomyelin: neutral (sphingosine backbone, not glycerol)
Where are newly synthesized lipids inserted into?
The cytosolic side of a bilayer.
What is a triglyceride molecule? What is its polarity?
A non-polar molecule containing 3 fatty acids ester bonded to a glycerol backbone. It is used for energy storage.
What is a micelle?
A phospholipid monolayer formed naturally when phopholipids are exposed to water so as to reduce the interaction between water and the non-polar tail of the phospholipid.
What is a sphingolipid?
A phospholipid with a longer and more saturated fatty acid chain, that causes tight packing of the hydrocarbon tails.
What is a lipid raft?
A region of a phospholipid membrane that contains a high concentration of sphingolipids and cholesterol, creating a microdomain in the membrane that is thicker and less fluid.
What is a phospholipid and what are its components?
An amphipathic lipid that is highly utilized in membranes. Contains a polar head (choline, phosphate, glycerol) and 2 fatty acid tails.
What is a liposome?
An artificially generated lipid bilayer.
What is the function of cholesterol in a plasma membrane?
Cholesterol reduces membrane permeability as it packs against phospholipid tails directly beneath the polar heads, restricting movement.
How are assymetrical membranes related to apoptosis?
During apoptosis, phosphatidyl-serines are translocated from the inner layer to the outer layer of the bilayer, which signals macrophages (detect the unusual negative charge) to digest the dying cell.
Where are protein complexes involved in signalling generally located in the lipid bilayer?
In lipid rafts.
What is the function of a glycosyltransferase? Where are they found?
It adds sugar groups to precursor glycolipids in the lumen of the golgi complex.
What is the function of a charged glycolipid?
It changes the electrical field across the membrane, leading to a concentration of calcium ions to the membrane surface.
What is an inositol phospholipid?
It is a type of phospholipid (lower abundance) that plays a role in important signalling pathways such as PIP2 cleavage into DAG and IP3. It can also serve as a dock or a substrate for signalling enzymes like kinases and lipases.
What is the function of a phospholipid translocator?
It transports newly synthesized phospholipids to the cytosolic end of a phospholipid bilayer. It can also flip lipids to the non-cytosolic monolayer.
How does cholesterol decrease permeability?
Its presence in the outer monolayer restricts the movement of phospholipids in that monolayer, reducing the ability for water soluble molecules to pass through.
What is the difference between saturated and unsaturated fatty acid tails?
Saturated: no double bonds -> saturated with Hydrogens Unsaturated: double bonds present -> kinky structure, less H bonds
What kind of backbone is found on a glycolipid?
Sphingosine backbone
Describe a red blood cell membrane (phosholipid composition and localization.
The red blood cell membrne is assymmetrical, given that Phosphatidyl-cholines, Sphingomyelins and glycolipids concentrate on the outer monolayer, whereas Phosphatidyl-serines concentrate on the inner membrane monolayer. This results in a charge difference between the two layers.
Where are phospholipids synthesized in a cell?
The smooth ER.
What is the function of a glycolipid?
They are found exclusively on the outer monolayer of the plasma membrane, where they interact with some exterior molecules (eg. lectins -> CHO binding proteins).
How do plasma membranes accommodate different membrane proteins?
They have bilayers that contain a mixture of different phospholipid types that can aggregate into certain regions to accommodate the requirements of some membrane proteins.