(05) Transport Across Cell Membranes Flashcards
define non-mediated transport
does not directly use a transport protein
define mediated transport
moves materials across membrane with the help of a transport protein
define passive transport
moves substances down conc / electrochem gradients only using kinetic energy
define active transport
uses energy to drive substances AGAINST conc / electrochem gradients
define vesicular transport
NOT ASSESSED
molecules engulfed in vesicles to be moved across membrane, either by exocytosis (out of cell) or endocytosis (encapsulate and bring into cell)
non-mediated transport can only occur via…
passive diffusion across the lipid bilayer
non-polar, hydrophobic molecules
direction depends on conc
what is non-mediated transport important for? also give some examples of molecules that are transported in this manner
absorption of nutrients / excretion of wastes
O2, CO2, N2, fatty acids, steroids, small alcohols, ammonia, fat-soluble vitamins
what is an ion channel? describe its structure
pathway which shields ions through hydrophobic bilayer
hydrophobic amino acids on outside
water filled pore lined by hydrophilic amino acids
note that ions do not bind to pore, hence rapid
what is ionic selectivity and how do ion channels structurally perform this?
only allows certain ions to pass
excludes based on CHARGE and SIZE
determined by the specific amino acids lining the pore
eg. ring of negative charge = ion selectivity filter, does not allow other negatively charged ions like Cl- through
SIZE of filter determines which positive ions can pass
what are examples of stimuli for gating of ion channels?
voltage, ligand binding, cell volume (stretch), pH (linked to metabolism), phosphorylation (linked to cell signalling pathways)
what is the patch clamp technique?
suck an electrical seal into tip of pipette with a clump of membrane
measure the current of ions that flow through –> ion channel function
what do detected current fluctuations in current flowing through a channel represent?
conformational changes in channel structure associated with gating
what is the main difference between carrier mediated transport and ion channel transport?
carrier mediated requires the molecule to be transported to be BOUND to the carrier, which undergoes a conformational change to release the molecule on the other side of the membrane
hence it’s a LOT SLOWER