Membrane transport Flashcards
function of biological membranes
semi permeable barrier, controls what substances enter and exit the cell
protection
accept signals
scaffolding for biochemical processes
intercellular interaction
compartmentalisation of cells
how to increase diffusion
lipid soluble, small molecular weight, large concentration gradient (also uncharged)
define flux
number of molecules passing through a unit area over a given time (mol/cm2/s)
A larger flux means a larger concentration gradient hence higher membrane permeability
osmolarity vs tonicity
concentration of all the solutes dissolved in the aqueous solution (OsmolL) is osmolarity
tonicity is whether a cell shrinks or swells due to osmosis
hypo hyper iso
iso-osmolar: both cells have the same osmolarity
isotonic: cell does not shrink or swell
hypotonic: cell swells
hypertonic: cell shrinks
channels and pores structure
pores: always open eg aquaporins
channels: open or closed
(voltage gated, ligand gated intracellular or extracellular and mechanically gated)
channels and pores function
highly specific
increase concentration gradient, increase rate of diffiusion
energy from concentration gradient
carrier proteins structure and types
never open to both inside and outside of cell at the same time
uniport - moves 1 solute across membrane at a time cotransporters - transport of 1 solute across membrane depends on SIMULTANEOUS transport of other solute
symport/antiport - second solute trasported in the same/opposite dirrection as the first solute
carrier proteins function
conformational change occurs when solute binds to protein
highly specific binding site
energy is from conc gradient, whichever solutes is stronger
good scavengers for solutes at low concentrations, transport rate saturates at high concentrations affected by speed and number of carriers
how to change rate of carrier transport
temperature dependent
transport rate can be reduced through competition for binding sites
pharmacologically blocked by drugs or toxins
pump types
- P type pump for ions (conformational change, phosphorylates itself)
- ATP Binding Casette pumps for larger molecules
- V type proton pump
- F type ATP synthase pump
NaK pump
- specific binding site, directional transport, energy from ATP
- for every 1 ATP, 3 Na+ out, 2 K+ in, electrogenic, inside of cell more negative than outside, resting membrane potential of -70mV
secondary active transport
when symporter or antiporter uses an ion moving down its concentration gradient to move another molecule against its concentration gradient
Na glucose carrier Na out of cell
1) Na removed from cell with NaK pump, primary active transport, energy from ATP
Na glucose carrier Na and glucose into cell
Na and 2 glucose molecules in ECF bind to binding sites of symport protein, conformational change occurs, protein opens to inside of the cell, Na and glucose are transported into cell
Na+ concentration gradient is much larger than glucose, provides energy
- secondary active transport of glucose
- transport of Na+ down concentration gradient, but energy provided from conc. gradient set up from Na K pump
Na glucose carrier glucose into bloodstream
facilitated diffusion of glucose out of cell into bloodstream through channel proteins
types of endocytosis
phagocytosis
pinocytosis
receptor mediated endocytosis (involves clathrin)
coat proteins
COPI - golgi
COPII - ER
clathrin - plasma membrane and golgi
exocytosis proteins involved
rab proteins - guide vescicle to target membrane, bind to rab effectors that thether them to membrane
SNARE proteins - mediate fusion with membrane, v and t SNAREs
