Post on 21-Dec-2015
Two main classes of membrane transport proteins
Both:SpecificityMulti-TM
Hydrophilicsolutes crossmembrane via hydrophilic proteinpathway
(aka carriers, permases, or transporters)
Conformationchange
AqueousPores (faster)
Ionophores are tools to increase permeability of membranes to specfic ions
Made by microorganisms
Mobile ion carriersChannel formers
A23187
Active transport can be driven by ion gradients
Primary active transport: ATP-drivenSecondary active transport: ion-driven
Na is the usual co-transported ion
ABC transporters:
1. Amino acids, sugars, ion, polysaccharides,peptides, proteins, flipping of lipids
1. MDR gene: hydrophobic drugs, chemotherapy2. Malaria: chloroquine3. Yeast mating pheromone4. Peptides from degration into ER5. Cystic fibrosis:regulator of Cl- channel
We will not talk about gap junctions herePorins stay in outer membrane of bacteria, mitochondria andChloroplastsChannels in the plasma membrane are narrow and selective And can open and close--ion channels, only “downhill”
Channels form hydrophilic pores, selective
The “ball-and-chain” model of voltage-gated K+ channel inactivation
20 aa
Driven by state of lowest energy
Patch-clamprecording ofcurrent flowthrough Individualchannels
All or nothing
Conductance
Duration
Rate
Neuromuscular junctionis one of the best studied synapse
Acetylcholine receptoris the first ion channelto be purified, cloned, Reconstituted, recorded single channel,3-D structure
Five sets of channels are involved in neuromuscular transmission
(from a nerve impulse to muscle contraction)
Summary
1. Ions and larger polar molecules cannot cross the lipid bilayer;
2. Two types of transport proteins: carriers and channels;3. Passive and active transport;4. Three types of active transport;5. Mechanisms of cotransport;6. Na-K pump and ABC transporters;7. Channels: voltage-gated and ligand gated;8. Selectivity of K channels;9. Action potential, voltage-gated Na channel, voltage-gated
K channel, myelination;10. Single-channel recording;11. Neuromuscular junction as an example of synapse,
functions of ion channels.