Announcements Midterm paper comments back today Finally Homework

Announcements Mid-term paper comments back today (Finally). Homework #8 assigned today 4/19/10): FRET, Nerves Due next Monday, 4/26/10 (Last one). Wednesday, 4/21/10: Quiz on reading from ECB, Nerves. This Friday, 4/23/10: email your final topic verbal and oral presentation. Include both a write-up and PDF of the research paper. It must be on a totally different topic (technique and biology) than mid-term presentation. I will get back to you by Monday 4/26/10. Final Paper: due evening May 5 th. Final presentation—need two days (3 meetings): Monday May 3 rd, Wednesday May 5 th, night of Wednesday May 5 th. , 5 pm (okay? ) (Pizza included. ) Final Lectures: W, April 21 st; M April 26 th; W April 28 th

how many different ion channels? Ans: 25 -30, 000 genes: 5000 -6, 000 genes. One or more polypeptide/ion channel– could get less, or more, ion channels.

Ion Channels 0 m. V (Outside) 0 m. V (Inside) open (depolarized) -60 to -100 m. V (Inside) closed (polarized)

Valium binds to serotonin (ligand) receptor called GABA receptor– relaxes nerves.

Action Potential– Nerves Firing http: //www. biologymad. com/Nervous. System/nerveimpulses. htm

To close ion channels, to stop wave: 4. Na+ spontaneously close 5. K+ open brings membrane potential back down negative.

Gradient set-up by Na/K Transporters [will go over]

Membrane permeant to only one ion What is voltage (electrical potential) in each case Membrane permeant to Na+ Membrane permeant to K+ V>0 or <0? Just a tiny amount of charge causes potential, much less than 15 m. M or 150 m. M. What causes charge to stop flowing? A sufficiently large force (electrical potential) preventing more ions from going. Given that V ~ -60 m. V and Na/K are two major ions, which is your membranes permeant to? K+

What is Boltzmann’s Factor? : Zexp(-Ei/k. T) Probability of being inside/outside? exp(Eout-Ein/k. T) e Let f = voltage Energy outside? = q fout = 0 Energy inside? = q fin e -

q = ? For Na+? +59 m. V if permeable only to Na+ If permeant to only K+, resting potential = -59 m. V

http: //www. biologymad. com/Nervous. System/nerveimpulses. htm

Is the Ion Channel Digital or Analog?

Charged amino acids (largely in the voltage sensor) move.

K+ S 3 S 5 S 6 S 2 S 4 S 1

Suggests model where 2 states that differ in energy by q. V Where q is about 13 e, or 13 e/4 per S 1 -S 4 sub-unit; V= -80 m. V. q is part of channel—gating current, not ionic current!

How does gate spontaneously shut-off? How fast?

Nerve Impulse propagate, not spread, because Na+ spontaneously shut-off.

Point mutation in Potassium Gene that affects Potassium Channel

Class evaluation 1. What was the most interesting thing you learned in class today? 2. What are you confused about? 3. Related to today’s subject, what would you like to know more about? 4. Any helpful comments. Answer, and turn in at the end of class.