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Phospholipids are amphipathic, what is meant by this

The contain both hydrophilic and hydrophobic parts. A hydrophilic (polar) phosphate group and the non-polar hydrophobic fatty acid tails


Both lipids and proteins are often tagged by complex sugars in the membrane, T or F



What is the proposed role of lipid rafts

Lipid rafts are thought to play a role in signalling and some forms of endocytosis


Other than lipid rafts, what other ways are there of segregating proteins in the cell membrane

Caged behaviours, fenced domains and tight junctions all act to segregate proteins in the membrane


What is the general role of proteins in the cell membrane

Mediate interactions with the surrounding environment as well as playing a role in motility and the uptake of nutrients


Which organisms produce omega 3 fatty acids

Sea plants, fish and nuts


Describe the nomenclature of omega fatty acids

Furthest carbon away from the carboxyl group in a fatty acid is called the omega (?) carbon. The position of the first double bond determines the name of the ?-fatty acid


What percentage of the intracellular membrane is made up of phosphatidylserine molecules and how does this account for its charge

4% - however this accounts for most of the intracellular negative charge


What makes fatty acid tails unsaturated

The presence of double bonds within the hydrocarbon tails


Why is it that unsaturated fats allow the membrane to be flexible

Unsaturated fatty acid tails pack loosely together allowing the bilayer to remain fluid


Give an example of where glycosylation is important

Sphingomyelin is often glycosylated forming gangliosides which are very important in neurons. They exhibit progressive structural complexity. Neural stem cells carry simple sugars whereas mature neurons carry highly branched sugars. The presence of gangliosides acts as a signal that the neuron has matured. Myelination of neurons by Schwann cells is determined by the sugar maturation. Defects in ganglioside synthesis can lead to a variety of neurological disorders


What is the general role of lipids in the cell membrane

Provide flexibility and continuity


What configuration are the double bonds that make up unsaturated fatty acids usually in

This cis conformation which introduces sharp kinks


What causes phospholipids to form sealed compartments when placed in water

The repulsion by water of the hydrophobic regions makes the lipid bilayer hide its edges and form a sealed compartment which is energetically favourable


What is meant by the term lipid rafts

Cholesterol and sphingolipids can form microdomains called lipid rafts. These lipid rafts are thicker regions of the membrane that form under the influence of membrane proteins that drive this domain formation


Explain the significance of phosphatidylserine in apoptosis and cell death

Phosphatidylserine flips to the outer surface only upon apoptosis which takes place during cell death. This acts as a marker of cell death with lipid asymmetry of the plasma membrane breaking down. This in turn causes the cell membrane to become permeable to small molecules.


What methods are there for sugars to be attached to the cell membrane

Sugars can either be attached to the membrane via proteins or via lipids


Land plants do not contain the enzyme to insert the double bond in the carbon 3 position – to make ?-3, T or F



List the four major phospholipids present in cell membranes

Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and sphingomyelin


Why do disulphide bonds only form in the extracellular environment

Cysteines present on the intracellular side of membrane proteins will be in their reduced form and will not form disulphide bonds. Cysteine exposure to the extracellular environment results in oxidisation and the formation of disulphide bridges


Describe the dynamic behaviour of phospholipids in the membrane

The behaviour of phospholipid molecules in a lipid bilayer is extremely dynamic. Phospholipids can rotate or exchange and diffuse in the lateral plane of the membrane. Phospholipids can also flip-flop (transfer between leaflets), but this occurs slowly and is very rare


One-legged (two tailed) lipid molecules form vesicles encapsulating water, T or F

F – two-legged phospholipids do


What is the role of phosphatidylserine exposure to the extracellular environment in an intact organism

Exposure of phosphatidylserine on the cell surface labels the dead cell and its remnants so that they are rapidly consumed by macrophages


What is the role of phosphatidylinositol in the cell membrane

Plays an important role in cell signalling (cancer, vesicle traffic etc.). Phosphatidylinositol can be phosphorylated thereby increasing its negative charge


What is the role of the negative charge present on the intracellular side of the cell membrane

The negative charge repels intracellular molecules and vesicles


Which side of the membrane are sugars found attached to

The outside of the membrane


Myristoyl anchors are used to link peripheral proteins with the cell membrane. What kind of linkage is present in these anchors

Amide linkage between the terminal amino group of a protein and myristic acid


Explain what is meant by the hydration layer and its tole in the cell membrane

The hydrophilic head group of the phospholipids usually have several water molecules surrounding it creating the hydration layer. The hydration layer presents a physical obstacle for random vesicle fusion with the plasma membrane and each other


Which side of the membrane are sugars usually attached

The extracellular surface


What is the role of sphingolipids in the formation of lipid rafts

Fatty acid chains of sphingolipids are longer and straighter than other phospholipids these rafts are thicker than rest of plasma. Sphingolipids carry long saturated fatty acids and thus segregate with cholesterol into distinct lipid rafts