NPB 100 Lecture 4

NPB 100 Lecture 4 - Lecture 4 -Shaker gene in Drosophila...

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Lecture 4 -Shaker gene in Drosophila -if mutated, animal will shake for a little bit, every now and then -suspect that it has to do with the generation of AP -the gene codes for a membrane protein -Shaker channel (voltage-gated K channel) -6 transmembrane regions (S1-S6) -middle of the complex is channel across membrane -consists of 4 subunits -on the S4, a chain of charged amino acids orientade vertically -acts as voltage sensor, control of gating -selectivity filter (for K), the partial loop -does inactivate unlike the K channels in squid axons -inactivation due to group of 20 amino acids at the end -they are free to swing around and get in the way of the channel and block it -same as for Na channels -on slide 2 atomic structure of K channel -yellow and red are lipid bilayer -structure on the outside forms a cup -part of overall selectivity filter (reject chloride ions) -little green dot in center is K ion
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-strings of amino acids coming out close to the K ion -selectivity filter and also mechanisms by which K ion can leave behind its water -the amino acids are charged and come just close enough together to balance the charges of the cloud of water molecules around K ion -a K ion in solution can move into that area y Brownian motion -when it encounters this region, it can slip through with no energetic cost because the charges of the amino acids can balance the energy that would be lost -in a similar Na, the strings are at a different distance apart, appropriate for Na but not K -Slide 3 Voltage-gated Na channel -4 Shaker motifs repeating along -4 transmembrane region -similar to Ca channels -a gene family -Slide 4 -depolarization caused by stretch-activated channels -voltage-gate K and Na channels in axons, allows influx of Na, giving rise to depolarization and AP -once AP arises, act as local depolarization, amplification -AP can then spread all the way to the end
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NPB 100 Lecture 4 - Lecture 4 -Shaker gene in Drosophila...

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