Powerpoint 3 Chapter 13 Flashcards
active transport
pumps use energy to drive unfavorable transport
passive transport
channels allow rapid thermodynamically favorable transport without use of energy
membrane potential formula
dG=RTln(C2/C1) + ZFdV
p-type
forms phospho-enzyme intermediate
Na,K,ATPase transport per ATP
3 Na+ out, 2K+ in
Na+ concentration in and out of cell
14 mM in, 143 mM out
K+ concentration in and out of cell
10 mM out, 100mM in
dG of ATP hydrolysis
-50 kJ /mol
Ca++ ATPase
responisble for maintaining low Ca++ in muscle for relaxation. Located in sarcoplasmic reticulum. High conc in SR, low in cytoplasm.
Ca++ ATPase structure
T domain binds two Ca++. N domain binds ATP. P domain contains Asp that is phosphorylated. A domain links them.
high affinity Ca++binding state of Ca++ ATPase
without ATP bound
inhibitor of Na+,K+,ATPase
foxglove (contains digitoxigenin, a caridotonic steroid)
affect of Na+,K+,ATPase inhibition
increased Na+ in cell. slows down Na+,Ca++ anitporter. Increases Ca++ in heart muscle.
flippases
facilitate membrane lipid asymmetry
type 1 ABS transporters
in prokaryotes. import nutrients
type 2 ABC transporters
in prokaryotes and eukaryotes. function as efflux pumps.
MsbA
an ABC transporter that functions as a lipid exporter
ABS transporter mechanism
open form, no ATP bound. substrate binds, induces conformational change allowing ATP to bind. ATP binds, conformational change allows substrate to other side of membrane. hydrolysis of ATP to reopen
three types of secondary transport
symport, antiport, uniport
uniporter
allows same molecule in or out of cell
lactose permease
symporter that uses a pH gradient to drive uptake of lactose into cell
mechanism of lactose permease
H+ binds from outside. lactose binds from outside. lactose deposited inside. H+deposited inside.
membrane channels
use facilitated diffusion. are gated. have ion specificity
membrane channels gates are turned on or off by (3)
ligands, membrane potential, mechanical means
patch-clamp technique
used to measure ion flow through membrane using a glass pipette to form a seal on a patch of membrane. can observe single channels.
sodium and calcium channel structure
four fold symmetry. Four repeating DNA sequences. Pore consisting of four identical subunits of two membrane spanning alpha-helices.
structure of K+ channel
a K+ ion can travel 22A into the membrane until the path becomes too narrow (3A) and it must shed solvated water to pass. Carbonyl groups at the 3A pore specifically stabilize K+ through electrostatic interaction. K+ is pushed by incoming K+ through 4 binding sites of similar affinities within the 3A pore
ion channels are similar to enzymes in that?
they lower the activation energy required for movement across the membrane
why does the K+ channel reject passing of Na+ even though Na+ is smaller?
the carbonyl groups within the channel that aid in desolving ions out of water are positioned specifically for the stability of K+. The free energy of resolvation of Na+ in the channel is lower than the free energy of desolvation from water
segments of K+ channel that form pore
S5 and S6
voltage sensor segment of K+ channel
S4 positively charged helix
action potential of Na and K channels
neurotransmitter causes flow of Na in and K out. Voltage sensing paddles of Na and K are pulled into membrane and rapid amount of Na flows in and K out until approaching Na equilibrium. Reversing polarity of membrane causes Na channel to close causing membrane potential to drop to K equilibrium at which point the K channel closes.
ball-and-chain model for channel inactivation
tethered “ball” is floating in cytoplasm. Depolarization opens channel and creates binding site for ball. Binding of ball inactivates channel. Inactivated state returns to closed state spontaneously.
Shaker K+ channel inactivation due to ?
N-terminal peptide
? is the archetype of the ligand-gated ion channels
acetylcholine receptors
nerve impulses are communicated across synapses by ?
neurotransmitters
presynaptic and postsynaptic membrane separated by ?
synaptic cleft
neurotransmitters contained in ?
synaptic vesicles
acetylcholine receptor is a ? channel
ligand-gated
purification of acetylcholine receptor occured in ?
torpedo memorota
how acetylcholine receptor is purified
homogenize tissue with nonionic detergent. run extract over resin with covalently attached cobratoxin. elute bound protein.
acetylcholine receptor structure
5 subunits. 2 alpha, 1 beta, gamma and delta subunits. Each subunit has 4 membrane spanning alpha-helices, extracellular beta strand region, and one alpha helix inside the cell.
acetylcholine binding to acetylcholine receptor
binds to N-termini of alpha subunits at the a-d and a-g interface
acetylcholine receptor response to binding
15 degree rotation in membrane spanning helix M2
