02_Membranes of the Cell Flashcards
What was the classical experiment that first deduced the lipid composition of membranes?
1890s, Overton: placed plant root hairs in different solutions with different solutes; lipophilic substances moved into root hair more readily than lipid-insoluble ones => boundary of cells must be lipid.
What is the most studied cell membrane, and why? (4 points)
the membrane of the RBC, because:
- low cost and high abundance in blood
- already present as single cells and don’t need to be separated from complex tissue
- simple compared to other cells (no contaminating internal cell membranes)
- can obtain intact membranes (called ghosts) through osmotic shock and hemolysis
What is a solution with a higher solute concentration than the cell cell called? What is the effect of placing a cell in this solution?
Hypertonic solution; net water loss => cell shrivels
A cell is placed in solution and it swells; what kind of solution was this? (hyper/hypo/isotonic)
Hypotonic solution
What kind of solution must RBCs be placed in to obtain ghosts?
Hypotonic solution
How did Gorter & Grendel (1925) reach the conclusion that cells must have a double layer membrane?
They extracted lipids from RBC membranes, measures their surface area on water and compared this to surface area of an RBC. They found that the area covered ~twice the SA of an RBC => the membrane must be a bilayer.
Who initially proposed the fluid mosaic model of cell membranes? Briefly describe the model.
Singer & Nicholson (1972)
lipid bilayer is fluid and able to move; proteins penetrate the bilayer, forming a mosaic.
What can be found in the hydrophobic core of the lipid bilayer?
Hydrophobic proteins + acyl chains
What is the approximate width of the lipid bilayer?
~30Å
What are the three major classes of lipids making up eukaryotic membranes?
Glycerolipids, Sphingolipids, Sterols
What is defined as carbon 3 on the glycerol backbone?
Where phosphate group attaches
When the R group in a glycerolipid is choline, it is called __________
phosphatidylcholine (aka lecithin)
What is the backbone in sphingolipids?
Sphingosine
What is the R group in sphingomyelin?
Choline
What are plant, fungi and animal sterols called?
Phytosterols, ergosterols, cholesterols
Sphingolipids accept acyl chains through a(n) _______ bond.
amide
What is the parent compound for ALL phospholipids?
Phosphatidic acid (a phosphomonoester)
What is (usually) the net charge of the phosphate head group at physiological pH?
-
Which phospholipid does PE stand for?
Phosphatidylethanolamine
Which two phospholipids are abundant in mitochondrial membranes?
Phosphatidylglycerol
Diphosphatidylglycerol (aka cardiolipin – CL)
Which phospholipids are neutral?
phosphatidylcholine & phosphatidylethanolamine
Which phospholipids are more abundant in the cytosolic leaflet?
PS, PE, PI
Which glycerolipids are NOT found in bacteria?
PI, PC
What glycerol are glycerolipids in archaea based on?
glycerol-1-phosphote
