2.5.1 structure/function of membranes Flashcards
what’s the role of plasma membranes?
controls what enters/leaves the cell (partially permeable)
communication i.e. cell signalling
cell recognition (so immune system doesn’t destroy its own cells)
site of some chemical reactions
role of membranes within the cell?
provide compartmentalisation to membrane bound organelles (lysosomes, mitochondria, chloroplasts) to protect cell components and contain incompatible reactions in separate areas to allow specific conditions to be maintained
used for vesicles (endocytosis and exocytosis)
provides surface area for a reaction e.g. mitochondria
why do the phosphate heads and lipid tails arrange in a bi-layer?
membranes arrange in this way because cells normally exist in aqueous environments so the polar hydrophylic heads face outwards to interact with water on either side of the membrane and the center becomes a hydrophobic core that acts as a barrier to water soluble substances
what sort of substances can pass straight through the membrane?
fat soluble or very small molecules e.g. steroids, CO2, O2, cholesterol, vitamins A E K and D
what is a membrane composed of?
a hydrophylic phosphorus head and a hydrophobic lipid tail
what is cholesterol?
a lipid with a hydrophobic and hydrophylic end that’s positioned between phospholipids
what’s the role of cholesterol?
it stabilises the membrane by each end interacting with the membrane and it reduces permeability to charged particles
too much and it crystallises and becomes too rigid
too little and it’s too fluid
role of a carrier protein?
will change shape and “flip around” when attached to a molecule to move substances from one side to the other; has an important role in both passive and active transport
role of a channel protein?
forms pores that provide a hydrophilic channel to allow the passive movement of polar molecules/ions down a concentration gradient; they’re gated and shaped for specific molecules e.g. one will have a complementary shape to glucose
what’s a glycoprotein?
a glycolax receptor made of carbohydrates that’s attached to a protein to act as a recognition site for chemicals to bond to in cell signalling (acts as stabilisers because they form hydrogen bonds with water)
what’s a glycolipid?
a receptor site for cell signalling that’s attached to a lipid - called cell markers/antigens and can be recognised by the cells of the immune system as self or non-self
