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cell membranes, their components & factors effecting membrane…
cell membranes, their components & factors effecting membrane structure & permeability
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phospholipids
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phosphate group has a negative charge, making it polar (attracted to water)
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at an air-water interface phospholipids arrange themselves so that the hydrophilic heads are in contact with water & the hydrophobic tails point away from the water
when shaken in water phospholipids form stable spherical structures called micelles - the polar hydrophilic heads on the outside in contact with the water & the hydrophobic tails facing inwards to from a hydrophobic interior
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phospholipid bilayer
the extracellular & the cytoplasm are both water-based (polar) environments - the phospholipids arrange in a bilayer thus enabling the existence of separate aqueous compartments
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hydrophilic polar heads - point towards the aqueous medium - externally & internally. The polar heads form hydrogen bonds with water in the cytoplasm & the surrounding fluid
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the fluid-mosaic model
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Fluid
individual phospholipid molecules are constantly moving within their layer. proteins within the membrane move about within the phospholipid bilayer. Membrane flexibility allows cellular shape change.
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Model
its only a theoretical idea of what it would look like its not accepted science. Its the best representation of the concept we have based on the scientific evidence we've collected
the membrane is fluid - phospholipids are free to move (only some proteins are free to move - like icebergs & islands)
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cholesterol
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cholesterol molecules are positioned between phospholipids in a membrane bilayer, with the hydrophobic end interacting with the heads & the hydrophobic end interacting interacting with the tails, pulling them together & reducing the lateral movement of phospholipids
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cells of organisms living at high temps have a higher cholesterol content - helps to stabilise membrane & reduce fluidity
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receptors
chemicals (e.g. drugs, hormones, neurotransmitters, antibodies) bind to complementary receptor proteins
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e.g. insulin receptor - hormones such as insulin & glycogen bind to receptors & trigger a response in the cell, Insulin triggers internal responses in the liver & muscle cells leading into an increase in glucose channels
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recognition proteins
glycoproteins
proteins in the cell membrane containing short, branching carbohydrate chains that project into the extracellular fluid
glycolipids
phospholipids that contain short, branching carbohydrate chains
act of signalling molecules for cell recognition, cell interactions & cell signalling
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glycocalyx layer
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it helps stabilise the membrane structure so they are particularly numerous in cells exposed in hostile conditions
e.g. the small intestine where changes in pH & friction threaten the structural stability of the cell surface membrane
the carbohydrate chains are very hydrophilic & attract water with dissolved solutes, helping the cell interact with its watery environment & obtain dissolved substances.
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