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What is the definition of Amphiphillic.
A molecule with both Hydrophillic and Hydrophobic properties.
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What is a Phosphoglyceride?
- A similar molecule to a triglyceride, whereby on of the hydroxyl groups is attached to a phosphate-based group.
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What is a "Leaflet"?
A leaflet is one side of a monolayer.
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Breifly describe "spin labeling" in terms of membranes.
- Spin labeling is the process by which an atom in a species (often nitroxyl) can be traced by interacting with unpaired electrons in a similar way to NMR.
- Spin labeling is often used to trace the motion of phospholipids within a membrane.
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Can phospholipids migrate between leaflets? If so, how often does this occur?
Phospholipids can migrate in a process known as "flip-flop", however they only do so rarely.
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What is another Term for Cytosolic?
Intracellular.
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How might a newly created Phosphoglyceride get to the extracellular leaflet?
It could "flip-flop" randomly (very rare), or it could do so with the aid of phospholipid translocators.
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What is the phase transition of a membrane?
The temperature at which it's phospholipids make up a crystalline structure.
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What might affect Phase Transition?
- Chain length (More, stronger interactions).
- Saturation (Unsaturated chains pack less efficiently, therefore interact less).
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With respect to membrane fluidity, what might a Yeast cell do in response to a temperature drop?
A yeast cell will make it's phospholipid tails shorter in response a drop in temperature in an attempt to moderate fluidity.
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How does Cholesterol affect membranes?
Cholesterol's rings immobilize the upper end of fatty chains of local phospholipids. Therefore the membrane becomes more rigid and less permeable to water soluble particles.
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Does Cholesterol affect Permeability, Solubility, or Both.
Cholesterol mostly affects permeability. However is also affects the fluidity of the membrane in high concentrations such that it prevents crystallization.
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Could this picture be an accurate example of a membrane? Explain.
Yes. It could be an example of a Lipid Raft. Often, Lipids with longer tails will come together to accommodate specific proteins.
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What is the Indicator "A" referring to in the following picture? Why is it between two monolayers?
- A Lipid Droplet.
- It is between two monolayers because it is hydrophobic and therefore will interact with the hydrophobic ends of the phospholipid tails.
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What are Lipid Droplets?
Reservoirs in the membrane containing neutral, hydrophobic, lipids.
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Are the Intracellular and Extracellular sides of a membrane the same? If not, how so?
- No, the cell membrane is asymmetric.
- The membrane can differ in concentrations of phospholipids, charge, proteinds, carbohydrates and more.
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Phosphatidylcholine and Sphingomyelin are found on the ____ membrane, whereas Phosphatidylethanolamine and Phosphatidylserine are found on the ____ membrane.
A) Inner (Intracellular), Outer (Extracellular).
B) Outer (Extracellular), Inner (Intracellular).
B) Outer (Extracellular), Inner (Intracellular).
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When might cell asymmetry be important?
- Cell asymmetry is especially important in cell signalling.
- Two examples of this are the action of Phosphokinase C and Phospholipase.
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What is the role of Phosphokinase C?
Phosphokinase adds phosphates to phosphodatylinositol in order to promote other protein activity.
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What is the role of phospholipases?
Phospholipases may also respond to extracellular stimulus. Phospholipases will cleave phospholipids bound with phosphates leaving a membrane bound fragment and another fragment to go and cause other effects.
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How is membrane asymmetry important to apoptosis?
When a cell undergoes apoptosis, the phosphodatylserine molecules usually found on the cytosolic membrane translocate rapidly to the extracellular membrane. These can then be recognized by other cells.
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What are glycolipids?
Glycolipids are Sugar Containing Molecules usually found in animal cells.
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What is the difference between Glycolipids and Gangliosides?
Gangliosides contain Oligosaccharides with sialic acid residues giving them a negative charge.
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The following picture is could be an example of which type of membrane protein?
A Transmembrane protein.
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Why do Transmembrane Proteins have to be amphiphilic?
So they can interact with both the polar phosphate heads, and the hydrophobic hydrocarbon tails.
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Not all membrane proteins span the entire bilayer. Of those that don't, how might they be anchored in the membrane?
- An Alpha Helix anchor could be embedded into one leaflet.
- A covalently attached lipid chain could serve to anchor the protein to the membrane.
- Similar to the above, some proteins will attach to phosphodatylinositol covalently.
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