L31 Structure and Function of Plasma Membrane Flashcards
Plasma membranes have been described as having ‘a trilaminar staining pattern’. Explain this.
When stained with osmium there appears to be 2 dark lines separated by a lightly stained central zone.
Resembles train tracks.
Hydrophilic heads form dark layers and the middle is the hydrophobic tails (which do not stain).
How much of a cell membrane is made of lipid molecules?
30-80%
What lipids are found in cell membranes?
Phospholipids, glycolipids, sterols
How long are phospholipid fatty acid ‘tails’?
14-24 carbon atoms long
When surrounded by water, cone-shaped (single chain) lipid molecules aggregate to form a __?__
micelle
When surrounded by water, cylindrical-shaped (double tailed) lipid molecules aggregate to form a __?__
bilayer
What is a glycerol based phospholipid known as?
Phosphoglyceride
What are the main phosphoglycerides in the plasma membrane?
Phosphatidylcholine
Phosphatidylethanolamine
Phosphatidylserine (-)
Phosphatidylinositol
Which of these molecules has an overall negative charge?
a) Phosphatidylcholine
b) Phosphatidylethanolamine
c) Phosphatidylserine
d) Phosphatidylinositol
c) Phosphatidylserine
What is the main sphingolipid in the plasma membrane?
Sphingomyelin
What type of molecule forms the head of a phospholipid?
A polar molecule
e.g. choline, ethanolamine, serine, inisitol
In a phospholipid, the fatty acid chains need to attach to __?__
glycerol or sphingosine
How are glycolipids formed?
Addition of CHO group(s) to lipids.
Glycerol-based: glycolipid
Sphingosine-based: sphingolipid
Combo of glycerol and sphingosine: glycosphingolipid
What are the most common glycosphingolipids?
- Cerebrosides
- Gangliosides
In what cells are glycosphingolipids prominent?
Nerve cells.
Think of the names of the most common glycosphingolipids:
- Cerebroside
- Ganglioside
Phosphatidylserine is a negatively charged phosphoglyceride in the plasma membrane. The other common phosphoglycerides are uncharged. What purpose does phosphatidylserine serve?
Phosphatidylserine is located on the inside of the membrane. During apoptosis the plasma membrane modifies a lot and internal proteins become exposed at the surface. This will now be on the outside and allow macrophages to recognise the apoptosis bodies.
Eukaryotic plasma membranes contain large amounts of cholesterol. What is the role of cholesterol in the PM?
- Maintains stability and integrity of PM
- Decreases permeability of PM
- Decreases fluidity
How does the plasma membrane’s composition affect fluidity?
- shorter chain length on phospholipid reduces the tendency of the tails to interact with one another
- Cis-double bonds produce kinks in the hydrocarbon chains that make them difficult to pack together
How does temperature affect the fluidity of the plasma membrane?
Movement of phospholipids decreases as the temperature drops and increases as it rises.
In what ways can a phospholipid move within the membrane?
They can rotate, diffuse laterally (within their monolayer), and - rarely - they can flip into the other side of the bilayer.
What are integral membrane proteins?
- Embedded within bilayer
- Hydrophobic segments have affinity for interior of bilayer
- Hydrophilic regions extend into aqueous phase
What are peripheral membrane proteins?
- Lack hydrophobic segment, therefore sit on the periphery, linked to polar heads of the phospholipids.
- Glycosylphosphatidylinositol (GPI) anchors
What are lipid-anchored membrane proteins?
- Hydrophilic, sit on surface of membrane attached to a lipid molecule in the bilayer.
