BIOL2200 Lecture Notes - Lecture 4: Symporter, Active Transport, Nicotinic Acetylcholine Receptor
MEMBRANES BIOL2200 LECTRURE 4
Aquaporins
Transport water across plasma membrane
oChanges in osmotic pressure cause cells to shrink (hypertonic)/swell (hypotonic)
K=10^9 s^-1 (fastest enzyme catalyse k = 4 x 10^7 s^-1
Do not allow H3O+ transport (Arg^195 repels cations)
Chain of waters is prevented: no proton hopping determined by the way that the biding
sites are situated
Aquaporin expression in frog oocyte
Ion channels hole in membrane regulated by a gate
Differ from transporters
oFlux ~ unrestrictive diffusion > transporters
oLigand - or voltage gated
Open only for ms
oCannot be monitored biochemically
oInstead monitored electrically - patch-clamp (monitoring one-few channels)
Bacterial K+ channel diffusion based
K+ [asses 10,000x more readily than Na+
4 subunits, 2 TM helices each
Carbonyls coordinate K+ - replace waters
Voltage-gated K+ channel
TM helix with 4 Arg moves according to electric field
Voltage - and ligand-gated channels in neurons
Muscle contraction
oAction potential in the motor neuron opens voltage-gated Ca2+ channel and
released acetylcholine
oAcetylcholine opens nicotinic acetylcholine receptor (ligand-gated channel)
Acetylcholine transient ligand
Na+/K+ antiporter
Associated with learning and memory and disorders (schizophrenia,
epilepsy, drug (eg. Nicotine) addiction, Alzheimer's)
oDepolarisation of membrane lead to opening of voltage-gated Na+ channel and
generation of action potential
oCa2+ channels release Ca2+ from sarcoplasmic reticulum
oSame family as GAB and Gly receptors (Cl- and HCO3- channels) and serotonin
receptor (cation channels)
Consequences of defective ion channels
Voltage gated Na+ channel: muscle paralysis/stiffness
Cystic fibrosis
Toxins target ion channels
oFugu tetrodotoxin: voltage-gated Na+ channel
oBlack mamba dendrotoxin: voltage-gated K+ channel
oTubocurarine, conbrotoxin, bungarotoxin: acetylcholine receptor
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Document Summary
Changes in osmotic pressure cause cells to shrink (hypertonic)/swell (hypotonic) K=10^9 s^-1 (fastest enzyme catalyse k = 4 x 10^7 s^-1. Do not allow h3o+ transport (arg^195 repels cations) Chain of waters is prevented: no proton hopping determined by the way that the biding sites are situated. Ion channels hole in membrane regulated by a gate. Instead monitored electrically - patch-clamp (monitoring one-few channels) K+ [asses 10,000x more readily than na+ Tm helix with 4 arg moves according to electric field. Muscle contraction: action potential in the motor neuron opens voltage-gated ca2+ channel and released acetylcholine, acetylcholine opens nicotinic acetylcholine receptor (ligand-gated channel) Associated with learning and memory and disorders (schizophrenia, epilepsy, drug (eg. nicotine) addiction, alzheimer"s: depolarisation of membrane lead to opening of voltage-gated na+ channel and generation of action potential o o. Same family as gab and gly receptors (cl- and hco3- channels) and serotonin receptor (cation channels) Toxins target ion channels o o o.
