Membrane Transport Flashcards
features of membrane
thin film of lipid and protein held by covalent attractions
lipid bilayer
5nm
impermeable barrier
fatty acids and lipids structure
long hydrocarbon with carboxyl one end and methyl other
free or covalent bonds to glycerol
phospholipid structure
typical bilayer
2 fatty acids covalently bonded to glycerol (1 unsaturated)
3rd hydroxyl group on glycerol bonded to phosphate
what is phosphate bonded to in a phospholipid
choline
ethanol amine
serine
amphipathic
hydrophobic head and hydrophilic tail
(fatty acid non polar uncharged, phosphate polar and charged)
thermodynamics and bilayers
polar dissolve = energetically favourable = more disordered / increased entropy
non polar opposite
formation on bilayer due to amphipathic nature
avoids water exposing the head causing a cage and energetically favourable (all spontaneously form sealed compartments)
why are bilayers dynamic
phospholipids can move laterally, flex and rotate
what regulates fluidity
low temp = phase transition = rigid and packed closer together
how is ridgity prevented
by cis double bonds and cholesterol
cis double bonds
causes a kink as double bind on same side so cant be rigid and is thinner
cholesterol
steroid ring region of cholesterol stiffens upper region of fatty acid chain = immobilised, less able to move laterally, less fluid
issue of too much cholesterol
prevent phospholipid compacting together and too rigid
what are lipid rafts
randomly distributed
van der Waals not string enough to hold molecules together
sphingolipids are long saturated getting closer together and attract forces strong enough to hold adjacent molecules
purpose of lipid rafts
independent monolayers can interact with each other in lipid rafts
proteins congregate here to prepare for transport
glycoproteins
proteins glycosylated in RER and golgi
glycolipids
lipids from SER glycosylated in golgi
where are glycoproteins and lipids found
non cytoplasmic side of membrane = cho coating = protective
what % of nuclear genome encodes membrane proteins
20
examples of membrane proteins
alpha helix
single pass
multi pass
transmembrane proteins
beta sheet
covalently bonded to lipid
embedded into membrane
peripheral membrane proteins
what is it called when membranes are coated in carbohydrate
glycocalyx
how do non polar molecules get transported across membranes
diffuse across
how do small uncharged polar molecules get transported across membranes
slowly diffuse
how do large uncharged polar molecules get transported across membranes
probably with transporter
how do ions molecules get transported across membranes
need mechanism
membrane transport proteins
transmembrane multi pass proteins (no contact with hydrophobic core) allowing ions through
carrier proteins
bind solute and undergo conformational change to transfer
channel proteins
interact only weakly with solute from aqueous pore they pass through
what causes an electrochemical gradient
ions (have a concentration and charge)
active transport - coupled carriers
symporters (same direction) and antiporters (opposite direction)
coupled carriers - symporters
electrochemical gradient = stored energy
transports ion = releases free energy
used to pump molecules eg glucose in same direction against conc gradient by a conformational change in shape
coupled carriers - antiporters
eg malate moves in against while kept out with gradient causing malate to move in
active transport - ATP driven pumps
Na K pump.
uses free energy from atp hydrolysis to actively pump out 3 k and 2 Na in by a phosphate group attaching causing a conformational change in shape
2 types of active transport
coupled carriers
atp driven pumps
channel proteins
form pores
can cause poor regulation
can be gated
transport ions by facilitated diffusion
how is acidity of lysosomes maintained
pumping of H ions across membrane by ATPase pump
what types of gated channels are there
voltage
ligand extra or intracellular
mechanically
