Membranes 3 Flashcards
Ion channels
selective and gated
2 classes of membrane transport protein
carrier and channel
Carrier proteins
small organic molecules eg AAs and sugars
Alternative axis mechanism- don’t have continuous channel through membrane
Substrate binding site one side- when subs binds conformational change and subs released other side
Subs on side with low conc less likely to bind- ensures movement only high to low conc
Energy independent
3 types of transport
uniport symport and antiport
coupled transport
carried out by symporters and antiporters
transport of 2 different types of molecules interdependent on one another for transport
Use energy released from movement of one ion (Na+/H+ usually) down electrochemical gradient to power import/export of small molecule/different ion
Symport
same direction
Move substrates against conc gradient
Have co-transported ion
Antiport
opposite direction
Have co-transported ion, also against conc gradient
Lactose permease
bacterial membrane protein
Transports lactose and protons same direction
Don’t require direct energy via ATP hydrolysis but do require energy for transport of H+- secondary active transport
uniport
transport of single type of molecule down its conc gradient
secondary active transport
Use energy stored in electrochemical gradient to transport substances
Channel proteins
open/closed
continuous channel through which ions can travel
passive vs active
passive doesnt require expenditure of energy but active does
Active for driving solute against conc gradient or for charged molecule, electrochemical gradient
Active Na+/K+ antiporter
3 Na+ out, 2 K+ in per hydrolysis of ATP, creates a gradient
Pumping of Na+ out creates Na+ gradient across membrane
Active Na+/glucose symporter
Requires sodium gradient across the membrane to co-transport glucose against its conc gradient
Secondary active transport as Na+ gradient generated by active transport
What makes electrochemical gradient
conc gradient and membrane potential
Ion channels
selective and gated
Gating controlled by conditions inside and outside cell
Patch clamp recording
Method for measuring ion channels
small area of membrane removed and seals end of glass capillary
Random- may not contain ion channels
Set up electrical circuit and measure current throughout circuit- see if channels are open/closed, because current only flows when channels open
An electrical device ‘clamps’ electric potential across the membrane at pre-determined value. Inward or outward movement of ions quantified by amount of electrical current needed to maintain mem potential at ‘clamped value’
Gating
voltage gated channels respond to change in voltage across membranes
Ligand gated, the ach receptor
Mechanically gated channels in auditory cells eg touch receptors
Ion channels in nerve cells
open, closed or inactivated
After short time open during dep., become inactivated and don’t go back to closed state till mem becomes repolarised. Hence can’t open again till back to resting potential
Propagation of AP
AP influences neighbouring regions of plasma membrane and is therefore a wave of dep.
AP moves in 1 direction as channels behind it are inactivated
At nerve terminals
When AP reaches terminal VGC channels open, Ca enters cell causing fusion of vesicles and release of nt
NTs bind to ligand gated ion channels on post syn membrane
Other functions of membrae proteins
Enzyme receptors: have enzymatic activity altered(often activated) by binding of ligand Linkers: cell-cell contact cell- ECM adhesion (integrins)
Simple diffusion
O2, CO2 drugs
Facilitated
Glucose, AAs (uniporters)
Active transport
Ions, small hydrophilic molecules, lipids
Cotransport
Glucose and AAs (symporters), various ions and sucrose (anti)
