1. Announcements Homework #8 assigned today 4/19/10, due next Wednesday. 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, 5pm (Pizza included.) Final Lectures: W, April 21 st ; M April 26 th ; W April 28 th

2. Quiz (Chpt 12, ECB) 6. Different types of stimuli influence the opening and closing of ion channels. List three classes of gated ion channels that are controlled by different stimuli: _________ ____________, ______________ and ________________. 1. Membrane transport proteins can be divided into two main classes: ___________ and ___________. The basic difference between these two classes of membrane transport proteins is the way they___________________ _______. 2. In passive transport, an uncharged solute or an ion is transported ___________its electrochemical gradient. In active transport, an uncharged solute or an ion is transported __________it concentration or electrochemical gradient in a process that requires _______________. 3. Solute transfer carried out by transporters can be ______________; transport by channels is _________________. 4. The Na + -K + pump in the plasma membrane of animal cells is _____________ that actively transports Na + _______of the cell and K + ______. 5. Neurons propagate signals in the form of ______ _____________, which are usually mediated by voltage- gated ________________ that open in response to ______________of the plasma membrane transporters channels discriminate between solutes down against energy active or passive always passive an ATPase out in action potentials Na + channels depolarization voltage- gated ligand-gated stress-activated (Mechanosensitive)

3. 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.

4. Ion Channels 0 mV -60 to -100 mV (closed, polarized) 0 mV (open, depolarized)

6. Shaker Potassium Ion Channels

7. Start of Action Potential --pressure, vibration receptors, located in skin, and various internal organs (joints, tendons and tissues that lines the organs and blood vessels), connected to a sensory neuron. They are the largest of the skin's receptors and are believed to provide instant information about how and where we move. I said Ca 2+ released, e.g. by muscle. But nerve propulsion also starts by sodium inflow, largely with mechanosensitive receptors. In skin cells, mechanically-gated sodium channels. The Pacinian Corpuscle http://www.biologymad.com/NervousSystem/nerveimpulses.htm Proprioception is our "body sense".

8. Bezanilla, 2008, Nature Reviews Potassium & Sodium Channel Similar K + Channel: homotetramer S1-S6 Na + Channel heterotetramer S1-S6: with each sub-unit havingslight variations) K+ S5 S6 S4 S3 S2 S1

9. X-ray Crystal Structure K+ S5 S6 S4 S3 S2 S1

10. Structure of Pore-Domain (S5-S6) is known (KvAP, Kv1.2… all yield the same structure) But how S4 (and S1-S3) move, remain controversial. Explains ion selectivity (K + > Na + ) and rapid ion flux. Excellent agreement between LRET/FRET and Crystallography Rod MacKinnon won Nobel Prize

11. Notice Selectivity Filter (GYG)

12. If 10,000 fold selectivity, what is E Na vs. E K ? Ans: 9.2kT Hydration Energy Sodium channel been crystallized. C=O just right for Na +.

13. Inside Outside

15. Point mutation in Potassium Gene that affects Potassium Channel

16. How does gate turn on/shut off? K+K+ K+K+ Open K+K+ -0.1 V Outside Closed High K+ (Low Na+) Low K+ (High Na+) 0 V 0 mV + + + K+ S5 S6 S4 S3 S2 S1

17. How does gate (S4) move? General Models Piston? Paddle? Jiang et al. Nature, 2003 Roderick MacKinnon Blaustein and Miller, Nature 427, 499-500. (2004). Resting S4 S4S4 Rotation? Cork- screw? Crevice Reshaping?

18. LRET using stationary toxins Only 2Å change! Not much change MacKinnon Model Not translation model. We believe rotation model.

19. 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.