cell membrane Flashcards
membranes control what passes through them
cell-surface membrane surround cells - barrier between the cell and its environment controlling which substances enter and leave the cell
the membranes around organelles divide the cell into different compartments - they act as a barrier between the organelle and the cytoplasm
why are membranes called partially permeable
they’re partially permeable as they let some molecules through but no others - substances can move across the membrane by diffusion, osmosis or active transport
why are cell membranes ‘fluid mosaic’
describe the arrangement of molecules in the membrane
phospholipid molecules form a continuous bilayer
this bilayer is fluid because the phospholipids are constantly moving
proteins are scattered through the bilayer, like tiles in a mosaic eg channel and carrier proteins
what do phospholipids do
they form a barrier to dissolved substances
the head is hydrophilic so it attracts water
the tails are hydrophobic so it repels water
the molecules automatically arrange themselves into a bilayer - the heads face out towards the water on either side of the membrane
the centre of the bilayer is hydrophobic so the membrane doesn’t allow water-soluble substances through it - it acts as a barrier to these dissolved substances
what does cholesterol do
gives the membrane stability
cholesterol is a type of lipid
present in all cell membranes excluding bacterial
fit between the phospholipids - bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together - restricting movement of the phospholipid
this makes the membrane less fluid and more rigid
maintain shape of animal cells (no cell wall) important for cells that aren’t supported by other cells eg red blood cells
