Lecture 8 - Membranes as Permeability Barriers Flashcards
what is the relative permeability of a lipid bi layer for the normal range of solutes in the body ?
use knowledge , dont try memorise
Small uncharged polar molecules - H20, Urea, Glycerol can pass through membrane
Hydrophobic molecules can pass through the membrane
large uncharged polar molecules cannot pass through the membrane
Ions are charged - cannot pass through the molecules
how and why does passive transport occur ?
it will occur down a concentration gradient
depends on the permeability (permeability coefficient) of that specific molecule
and the specific cell - it erythrocytes have different permabilities as they are specified to carry out there role
within the cell we have transport processes, why do we need these ?
maintain Ion gradients maintain PH regulate volume of the cell expell waste and toxic products release enzymes / hormones generate ion gradients for action potential
give the common forms of Ion transport proteins
ligand gated ion channels -binding of a signal can open/close channel - facilitated diffusion - no energy used
voltage gated ion channels - membrane depolarisation causes the channel to open - ions can enter down an electrochemical gradient
explain the difference between active and passive transport
active transport requires energy (ATP)
involves the movement of molecules from low to high concs
passive transport (eg - facilitated diffusion) - from a high to low conc - does not use ATP
passive and active potential is also dependent on the membrane potential for ions !
a high conc ratio - high conc outside vs inside or a high membrane potential will greatly increase the rate of ions/molecules moving into the membrane
what is the electrochemical gradient ?
the cocentration of ions on either side of the membrane will create a conc gradient AND and electrical (charge) gradient aswell
if an open transport channel allows for it - ions will move down this electrochemical gradient
Give the Values for the free ion distribution across the membrane
you need to learn these !!
Na+ - 145mM OUTSIDE of cell - 12mm INSIDE cell - electrochemical gradient is moving inwards
K+ - 4mM OUTSIDE of cell - 155mM INSIDE cell - gradient moves K+ outwards
Ca2+ - 1.5mM OUTSIDE of cell - 10^-7 INSIDE of cell - chemical gradient is moving inwards
Cl- - 123mM OUTSIDE of cell - 4.2mM INSIDE of Cell - gradient is movign Inwards
Ca2+ and Cl- and NA+ move IN
K+ moves OUT
give an example of a primary active transporter - and explain how it functions
Ca2+ ATPase in the plasma membrane
Known as PMCA
Uses ATP hydrolysis to transport a Ca2+ out of the membrane
explain the process of co transport
an ion/molecules that is transported alongside the target molecule
symport - co transport ion moves in the same direction as the target
antiport - co transport ion moves in the opposite direction as the target
give an example of a co-transport protein
Na+ - K+ - ATPase - the Sodium (Na+) Pump
Na+ has an inward electochemical gradient and K+ has an outward chemical gradient
using ATP hydrolysis it transports 3 Na+ OUT and moves 2 K+ IN
this is active transport
ANTIPORT
the process give a net result of the inner membrane becoming more negative by a net of -1
it is called a P type ATPase - phosphorylates on Aspartate
it is very important for generating the ion gradients that are used to allow secondary active transport and action potentials
only a small contribution to the resting membrane potential
how does the sodium pump affect membrane potential ?
the movement of 2 K+ into the membrane generates a high inner membrane K+ concentration
K+ then diffuese out of the cell VIA channels
this is mainly responsible for generating the resting membrane potential of -70mV
how is Ca2+ transported within the cell ?
Ca2+-Mg2+-ATPase - uses ATP to transport Ca2+ OUT of the cell - high affinty - low capacity (happens at low concs, but not very quick/efficient at moving calcium)
Na+ - Ca2+ - exchanger
ANTIPORT
3Na+ IN for 1 Ca2+ out - net gain of a positive charge inside the cell -
the inward flow of sodium down its conc gradient drives the flow of calcium out of the cell against its conc gradient
Low afiinty , high capacity - only good at high concs - but it can move alot of Ca2+
what is the Na+-H+ exchanger ?
a Sodium pump, puts 3Na+ outside the membrane
this can then facilitated the transport of H+
it is an ANTIPORT that transports 1 Na+ into the membrane for 1 H+ outside the memebrane - maintain PH by alkinasiation of cell
how does sodium glucose co transport work ?
sodium pump spits out 3 Na+
this Na+ gradient allows for the Na+/glucose SYMPORT to transport glucose inside the cell
the energy of Na+ provides the energy for transport of Glucose in. NOT ATP
how are transportes affected in cystic fibrosis?
CTFR channel does not function - Cl- cannot be transported outside the cell as effectively in gut
membrane potentials all messed up
how are transporters affected in diarrhoea
CTFR channel is activated - moves too much Cl- out of the cell in gut
membrane potential all messed up
