Ion Channels and Transporters Flashcards
(42 cards)
two general types of transport proteins
carrier and channel proteins
channel proteins
discrimination based on size and charge
open channels and allow ions and water to slip through
movement is fast and direction is dependent on the solute concentration gradient
carrier proteins
enzyme-like binding site for solute molecule
transmembrane transport involves conformational change
movemen of ions is slow and reversible
two types of channels
ion-specific channels for ion permeability, found in most if not all cell types, used for inter-and intracellular signaling
non-specific channels - allow many kinds of molecules to pass through
gap junction
comprised of six subunits in a hexagonal array and allows passage of water soluble molecules between cells
degree of opening of the junction is controlled by the concentration of intracellular ions
alpha toxin
water soluble protein from staphylococcus aureus
forms a pore in the membrane of many cell types and allows passage of water-soluble, uncharged molecuels less than 2 kDa, ATP, and Ca2+
two general types of carriers
transporters (or exchangers) - proteins that selectively ransport large water-soluble molecules and ions across membranes down their concentration gradient, facilitated diffusion
ATPases - transporters that couple transport with hydrolysis of ATP, energy expenditure allows movement up concentration gradient
glucose transporters
a family of transporters that bind glucose on the EC surface and leads to release on the cytoplasmic side
driven by high EC glucose concentrations
glucose-Na transporter
in some cells such as kidney tubules and intestinal cells, glucose concentration is too high, and this transporter binds NA+ and glucose simultaneously
transport is facilitaed by coupling it to the movemen of Na+ down its concentration gradient
basic amino acid transporter
a Na+ independent transport of basic and neutral amino acids into cells
neutotrasnmitter transporter
reseponsible for the reuptake of neurotransmitters at nerve terminals
Na-H exchanger
couples the movement of Na+ into cells twith H+ out
since metabolic activity generates H ions, this exchanger helps regulate intracellular pH
Na/K-ATPase
moves Na+ out and K+ into cells, responsible for creating Na+ and K+ concentration differences across the membrane
maintains cellular membrane potential and cell volume
uses about 25% of total energy consuption in humans at rest
Ca-ATPase
transports Ca2+ out of cells or into organelles
maintains low intracellular Ca2+ level which is important in cell signalling
H-ATPase
moves H+ out of the cell or into organelles
inmitochondria, this protein works in revers and generates ATP
ABC transproters
a family of proteins with both transporter and ATPase activity
are used to move a wide variety of molecules into cells and organelles faster than would occur by simple diffusion
How many subunits are ion-specific channels made up of?
six transmembrane domains
How many subunits form the central pore region of a ion-specific channel?
four - allows ions to mvoe in and out of the cell
How fast is the transition form an open to closed state in an ion-specific channel?
instantaneous
mechanisms that affect ion-specific channel opening and closing
changes in membrane potential
binding of a ligand to the channel
mechanical stretching of the membrane
two substates of close ion-specific channels
closed but activateable
close and inactivated
two ways of reactivating inactivated ion-specific channels
changing of membrane potential or unbinding of ligand
factors that affect the magnitude of the current through an open ion-specific channel
driving force (Vm - Eion) for the conducting ion and the duration that the channel stays open
current through an open channel obeys Oh’s Law (Iion = dV/Rm)
probability that an ion-specific channel will open at a specified voltage or ligand concentration
follows a Poisson distribution (bell-shaped curve)
