Chapter 5 Flashcards
What are the 5 approaches to studying ion channels?
Molecular tools, artificial expression of channels in Xenopus Oocytes, Site-directed mutagenesis, electron microscope and x-ray crystallography.
What is affinity chromatography?
It is a method for separating molecules based on highly specific chemical interactions, such as via antibodies & ligands.
The significance of cDNA
created from mRNA
can be inserted in Xenopus oocyte, to do site directed mutagenesis.
Site directed mutagenesis
Replacing a single amino acid in protein to understand the effects
M2 in acetylcholine receptor
can bend, and determined if anything can go through the channel. Also undergoes conformation change when ligant (Ach) binds.
Is Ach very selective?
Nah. So it is only good to study for gating mechanism
nACHRs
Represents “cys-loop” channel super family
5 sub units needed
All subunits have at least 50% homology
One subunit is ALPHA subunit that is the ligand binding site
Each subunit contains 4 membrane spanning domains (M1-M4)
One single giant protein. Contains no subunit.
Sodium & Calcium channels
Myasthenia gravis or Sever muscle weakness.
Options for treatment?
Autoimmune disease
Body makes antibodies against its own nAChRs
Blocks binding of Ach at these receptors in neuromuscular junction.
Reduces number of receptors present at synapses
Treatment: Drugs that enhance synaptic transmission & immunosuppressive therapy
How is potassium different from calcium channel?
It is composed of individually transcribed units. Similar to acetylcholine.
P loop
selectivity filter
S4
ONLY STUDIED IN POTASSIUM CHANNELS
voltage sensitive filter
twists like a towel instead of moving up and down
untwisting leads to the opening of the pore
What determines, which ions can pass through a channel?
Size & Charge
Where does the variability in function come from?
It comes from the variability in sub-units
What are the two main synapses in the brain?
GABA & Gultamate
