Biology Week 7, Notes
Biology Week 7, Notes BIO203
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This 11 page Class Notes was uploaded by Pratiti Ghosh-Dastidar on Sunday October 16, 2016. The Class Notes belongs to BIO203 at Miami University taught by Dr. James in Fall 2016. Since its upload, it has received 4 views. For similar materials see Cell Biology in Biology at Miami University.
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Date Created: 10/16/16
Pg – 61 Dealing w/ water and osmosis a) Animal b) Plant c) Protozoan Gellike cytoplasm resist Rigid all walls resist swelling Use H2O contractile swelling. Use H2O press to inc. vacuoles. - Transports ions in and our to rigidity by stiffening reg H2O structure allows it to stand. Channels can only dissipate the [ ] gradient. It can never generate [ ] gradients. o Direction ( passive trans.) : hi low [ ] Passive transport o Nonselective: large diameter Porins Gap junctions: junction b/w cells that allow them to function in a Found on outer membrane. coordinated manners. Can move into membrane Relatively large pores from cytosol membrane extra cell matrix and then decide if it can connected to same protein in adjacent cell. Allows transfer b/w move in or out of all cells without interacting with outside environment. Pg -62 Selective (specific) [passive trans] Majority super specific o Aquaporins: only allow H2O (not even other ions) to pass through o Ion channels Na+, K+, Cl-, Ca2+ Often gated (normally closed, but can be simulated to open) open channels spend most time open “gate” Found in plasma membrane First found in red blood cells. Water channel that can regulate and increase the rate that H2O passes through. Tetramer is formed as func. Unit. H2O moves toward higher solute [ ] because there’s a lower H2O [ ] there Ion Channel Ex) K+ ion channel Overall structure: multiple Alpha helices. Not uniformly shaped hole o hole of pore aides in . It does not need to go through a conform change during of ions. Ions interact w/ H2O well ions have shell C+ H2O molecule o K+ interacts Pg – 63 H2O gets stripped off H2O ions via O in carbonyl group via the filler (side chains) Why don’t Na+ ions (smaller than K+) pass through the channel? o It’s can’t coordinate with carbonyl group to strip H2O This is a constitutively open channel b/w force to allow to . o Interior cell slightly Pg – 64 a) Exact balance of charges on each side of the membrane means the membrane potential is zero. b) Few +ve ions cross the membrane (right to left), setting up a nonzero membrane potential. Major Players? o K+/Na+ ATPase o K+ leaky channels 1) a. Pumps 3 Na+ out and 2 K+ into cell 9using ATP) b. This establishes concentration gradients i. High Na+ [ ] outside ii. High K+ [ ] inside 2) Leaky K+ Channels a. When channel opens allows K+ to flow down its concentration gradient. i. Inside to outside b. This dampens the [ ] gradient, however with this +ve ion leaving the cell, it increases the charge separation b/w the cytosol and the extracellular space. i. +ve on the outside ii. –ve on the inside Pg -65 Resting membrane potential sep of charges across membrane inside slightly outside. Estab K+ ion and leaky K+ ion channel to move K+ across and its [ ] gradient. o It stabilizes when voltage gradient stops net movement of K+ even though K+ [ ] grad exists. As [ ] grad dampens, the dif. Of charges increasing. Eventually movement of [K+} leaving charge dif exactly equal stopping the net movement estab. Resting membrane potential 1) Na+/K+ ATPase estab [ ] gradient of K+ 2) Leaky K+ channel lets K+ leave 3) [ ] grad. Dampen; sep of charges inc. 4) Reaches equilibrium of movement of [K+] ions leaving and the difference of charges. Pg – 66 Neurons form central nervous system o Job: transmit elect. Signal across body o Unique structure all one cell Dendrites usually shorter and more numerous than axon Signal received by dendrites towards cell body Axon: usually one much longer o Can be < 1mm to more that 1m in length. o Bound by plasma membrane o Into flows away from cell body o Axon branches axon terminal signal transmitted to another cell. Evolved to generate action potential Cell body sums up the signal and it make a “decision” whether to send signal down axon or not Nerve is a cluster of neurons. Fun fact: Grant squids have super fast reflexes. They have the largest axons known in . Action Potential: localized, brief, rapid reversal of potential across the plasma membrane Happen is a small section of axon, then its moved across the axon. Pg -67 Depolarizing stimulaus dampens the resting membrane potential o If it can dampen enough to reach threshold potential then action potential occurs. All or nothing either it occurs or it doesn’t It happens rapid depolarization and the repolarization occurs. Time: milliseconds How measured One electrode inside cell and one outside, measure voltage difference Axon from animal. What’s involved Na+/K+ ATPase and leaky K+ channel needed to establish resting MP. OTHER CHANNELS: voltage gated Na+ Na+ and K+ channel o At membrane poten its closed o When depolarizes opens allowing Na+ and K+ to diffuse down [ ] grad. o In activated state: blocks movement of Na+ ions short time later reconverts to closed but is capable of being opening Pg – 68 After depolarization, Na+ channel must open first b/c based on Na+ [ ] gradient it will flow inside cell making more positive after Na+ inactivates , K+ so it flows out making cell more negative. After repolarization Na+/K+ ATPase is used to return everything to normal (resting membrane potential) Depolarization Stimulas slowly open Na+ channel to establish if potential How does action potential move down axon? Propagation: each started by depolarization event. o Certain Na+ channels more inside cell depolarizing regions b/w adjacent region. o b/c Na+ moves inside cell depolarizing regions b/w adjacent region. o b/c Na+ moves in all direction causing depolarizing stimulus. o Cannot move in opposite direction b/c Na+ voltage channel will be activated and by the time it reactivates, the action potential is too far away, so it will be activated by the next action p. from the cell body. Pg - 69 In order to pass through the (space b/w terminal and dendrite) signal must be converted to pass through this pass space and the reconverted to electrical signal. o This allows the making of complex networks on connected neurons o Myelin increases the rate of propagation. Chemical synapse composed: terminal of cell + synptic cleff mem of cell Cleft: is a fluid filled gap (extracellular fluid) Entire sys. Is in aqueous soln. Note: There are electrical which don’t require conversion of the signal. resides (filled w/ chemicals called neuro transmitters) o Chemical signal which allows transport through chemical It is a membrane bound . On post synaptic membrane there is nero transmitter receptor it’s a gated channel. o When binded channel opens and allows ions to flow through and chemical signal can be reconverted to electrical signal On pre terminal there is a Ca2+ ion voltage gated channel when action potential ready to fire, Ca2+ diffuses in ([ ] grad). Pg – 70 Inc. in Ca2+ ions stimulate exo cytosis of nero transmitter receptor neuro transmitter bind to ion channel conform change ion flows stimulated de polarization. NOTE: plasma membrane Ca2+ ion ATPase reestab. The [ ] gradient of ca2+ Electrical Chemical Electrical sig. ( on next page). - points o Excitory synapse wants to send signal o does not want signal Depopolarizes cell closer to threshold w/ pos. ions into cell Not all or none can vary in strength Many causes Cl- ion moves neg. charged ion into cell moving cell further from threshold less likely to send signal through. Summary - Nuro transmitters can be or inhibitory. Pg – 71 Picture of movement Signal `