国外大学细胞生物学课件英文4bioy

1、国外大学细胞生物学课件英文4bioy国外大学细胞生物学课件英文4bioyW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved2transportrateIon channels have a high transport rateW2011 D103 Cell Biology - lect3Selective for a specific ion (size and charge) selectivity filter that arranges molecules to pass

2、in a single file (rate limiting) No actual ion binding site as found in carriersIon channels are selectiveW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved5Selective for a specific ion 4Ion channels can be opened by voltage, ligands or mechanically.Exception: K+-leak

3、 channelsIon channels are gatedW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved6Ion channels can be opened byW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved5Membrane potential - resting potentialResting potential (no more flow of i

4、ons)G concentration = G potentialmembrane potential: voltage difference across a membrane due to a slight ion misbalancegenerated by electrogenic pumping by Na+/K+ pump with a net flow of positive charge out of the cell)Membrane potential=0 but: concentration gradient!W2011 D103 Cell Biology - lectW

5、2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved6How to calculate the resting potential?G potential =zFVG concentration=RTln co/ciThe Nernst equation is used to calculate the contribution of one ion to the membrane potential (assuming that the membrane is only permea

6、ble to that particular ion).for monovalent ion at 37CGoldman equation takes the permeability for each ion into considerationW2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved7K+ = 140mMNa+= 5mMK+ = 5mMNa+=140mMVK = 62 log10 (5mM/140 mM)=

7、-89 mVVNa= 62 log10 (140mM/5mM= 89 mV Is the overall membrane potential 0?Calculating electrochemical potentialsNo, as the membrane is not permeable to all ions at all times.W2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved8Plasmamembran

8、eMicroelectrodeinside cellAxonNeuronMicroelectrodeoutside cellVoltmeter70 mVK+ leak channels allow K+ ions to cross the membrane in an unregulated manner. Overall membrane potential is close to resting potential for K+ only K+-leak channels are open at all times the opening of other ion channels is

9、strictly regulatedThe resting potential of an animal cell is -70 mVW2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved9-70 mVStimulus that surpasses threshold+40 mVNa+ influx into the cell is regulated by voltage-gated Na+-channelsW2011 D1

10、03 Cell Biology - lectThe behavior of Na+ channels in response to a stimulusW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved10The behavior of Na+ channels iW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved11 stimulus Ligand-gated Na+

11、 ch. open - slight depolarization (less negative) Voltage-gated Na+ ch. open - Na+ rush into the neuron: depolarization Voltage-gated Na+ ch. become inactivated Voltage-gated K+ ch. open slowly - K+ rushes out of the cell: repolarization Voltage-gated Na+ ch. close Voltage-gated K+ ch. close slowly

12、- membrane hyperpolarization ion concentrations return to resting levels: approx -70 mVThe formation of an action potentialW2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved12Why do APs move unidirectional? Action Potential Occurs if thre

13、shold is reached Temporary change in membrane potential from -70 mV to +40mVall or nothingno weakening over long distance Fast propagation Up to 1m/0.01 s= 100 m/s = 360 km/hr = 220 miles/hr How are action potentials propagated? W2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lecture 4 Suett

14、erlin and MacGregor - all rights reserved13Voltage-gated Na+-channels cannot be activated when in inactive state. Only closed voltage-gated Na+-channels can be opened W2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved14Schwann cellSaltato

15、ry (jumping) conduction: APs are only generated at the nodes of ranvier Most Na+-channels are concentrated at the nodes of ranvierTwo main advantages: faster and conserves metabolic energy.Myelination increases the speed of AP propagationW2011 D103 Cell Biology - lectW2011 D103 Cell Biology - lectur

16、e 4 Suetterlin and MacGregor - all rights reserved15Exoplasmic domaincytoplasmic domainTransmembrane domainP0 homo-oligomerization is required for wrapping the Schwann cell membrane around the axon.What is the molecular mechanism of myelination?W2011 D103 Cell Biology - lectW2011 D103 Cell Biology -

17、 lecture 4 Suetterlin and MacGregor - all rights reserved16 Inflammatory demyelination condition: lesions leading to scaring (sclerosis) onset: 29-33 nerve transmission is disrupted leading to a wide range of symptoms (fatigue, visual disturbances, loss of balance and coordination, altered sensation

18、, abnormal speech, bladder and bowel problems, loss of memory, impotence) Life span is not affected There is no cure! cause not clear: auto-immune response possibly instigated by virus infection/Multiple sclerosis (MS)W2011 D103 Cell Biology - lectConversion between electrical and chemical signals a

19、t the synapseW2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved17Presynaptic terminal:Electrical to chemical signalPostsynaptic terminal:Chemical to electrical signalConversion between electrical W2011 D103 Cell Biology - lecture 4 Suetterlin and MacGregor - all rights reserved18Ion channels ion specific (due to selectivity filter) (mostly) gated high transport rate transport is saturableMembrane potential (= voltag