Ion Channels Flashcards
Ion Channels
Integral proteins that span the cell membrane and form conduits for ions to pass through the lipid bilayer
Ion Channel Properties
Selective
Open and close in response to signals
Conduct ions at rapid rates
Voltage gated ion channels
Respond to changes in membrane potential
Ligand gated ion channels
Respond to chemical transmitters
Mechanically gated ion channels
Respond to pressure or stretch
Cation
Positive ion
Anion
Negative ion
Exchanger
Can use the energy stored in conc. gradient of one ion to transport another ion against its conc. gradient
Hetero-oligomers
5 different subunits
Homooligomers
6 subunits are the same
Single polypeptide chain
Organized into 4 repeating motifs
Smaller ions have a hydrated diameter that is..
Larger than that of larger ions
Selectivity Filter
High negative site that allows na+ to pass through but not K+
Localized conformational change
Ion channel only changes in one spot
Generalized structural change
Ion Channel changes all along the channel
Blocking Particle change
Blocking particle swings into and out of the channel mouth
Laws of electrodiffusion
Laws of binding of ions to specific amino acids along the pore of an ion channel
IV Curve
Rate of flow of current
Dissociation constant
The ligand concentration at which current reaches 1/2 of its max value
Simple resistors
Linear
Conducts ions in a constant manner at all voltages
Rectifying Channel
Non-linear
Conducts ions more readily in one direction than the other
Superfamilies
Ligand Gated Channel
Gap-Junction Channel
Voltage-Gated Channel
Ligand Gated Channel Superfamily
5 subunits
4 transmembrane helixes each
Gap-Junction Channel Superfamily
One pair of hemichannels
Each hemichannel has 6 identical subunits
Each subunit contains 4 alpha helixes
Voltage Gated Channel Superfamily
Single Polypeptide chain
4 homologous motifs
Each motif has 6 alpha helixes
S5-S6 strand is P loop (Selectivity Filter)
Ion Channel Families with P regions
Voltage gated K+ channel
Inward-Rectifying K+ channel
K+ channel with 2 P regions
Glutamate receptor channels
Voltage Gated K+ Family
Four subunits
Each subunit has 6 transmembrane segments
Each subunit has a pore forming P-region
Inward Rectifying K+ channels Family
Four subunits
Each subunit has 2 transmembrane segments
Transmembrane segments connected by a P region
K+ channel with 2 P regions Family
2-4 subunits
4 transmembrane segments
2 pore forming P regions
Glutamate receptor channel family
P region enters and exits on the cytoplasmic side of the membrane
4 subunits
2 transmembrane segments
High energetic cost of K+ ions to enter bilayer is minimized by…
- Inner chamber filled with polar water
2. 4 helixes provide dipole whose negative charge points toward inner chamber
Ions in outer configuration
Positions 1 and 3
Ions in inner configuration
Positions 2 and 4
Chloride Channels
2 identical subunits each forming a selective Cl- pore
18 alpha helixes
Move Cl- against concentration gradient using H+ gradient
Myotonia
Abnormal prolonged muscle contraction
K+ channel selectivity filter
Parallel (Barrel Stave)
Cl- channel selectivity filter
Anti-parallel
