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plasma membranes (strand 2) - Coggle Diagram
plasma membranes (strand 2)
external cell membranes are known as plasma membranes they control the movement of substances into and out of the cell
phospholipids (polar phosphate head) attracted to other polar molecules (hydrophilic), fatty acid tail (non polar) hydrophobic
because of their hydrophobic and hydrophilic parts, phospholipids arrange themselves micelles or bilayers in water or aqueous solutions
structure of the membrane
phospholipids form a bilayer
hydrophilic heads point to the outside
hydrophobic tails point to the inside
functions
allow lipid soluble substances to enter and leave the cell
prevent water solubles entering and leaving the cell
make the cell flexible and sealed
proteins in the bilayer
on the surface
give mechanical support or act as receptors on the outside of cells
spanning the bilayer
channel proteins which are water filled and allow water soluble ions to diffuse across the membrane and carrier proteins that bind to ions or molecules that aren't water soluble
function of proteins in the membrane
provide support
act as channels for transport of water soluble substances
allow active transport across the membrane through carrier proteins
form receptors on the surface of the cell for identifying them
help hold cells together where required
act as receptors for hormones
cholesterol
molecules of cholesterol occur in the phospholipid bilayer
add strength
cholesterol molecules are very hydrophobic so prevent loss of water and dissolved ions from the cell
prevent too much movement in the membrane
glycolipids
carbohydrates bonded to lipids
carbohydrate element extends out of the surface of the cell
act as receptors for chemicals
glycolipids help cells attach on to one another to form tissues
glycoproteins
proteins in the membrane with carbohydrate chains attached
act as receptors for chemicals
allow cells to recognise each other (allow lymphocytes to recognise an organisms own cells)