Properties of the living organism. Interaction between living organism and the enviroment. Processing informations. Definitions

Transcription

1 thermodynamcs energy materal Interacton between lvng organsm and the envroment Propertes of the lvng organsm Separaton from the envroment: Strctly controlled energy and materal transport. Changng n the envroment: accomodaton Open system: free materal and energy exchange Condton: nformaton from the envronment, rght and fast processng and adequate response. Processng nformatons Defntons nformaton processng answer stmulus: any effects on the organsm (sgnal and nose) outer stmulus from the envroment (e.g. lght, sound etc.) nner stmulus: from the organsm (glucose concentraton, ph of the blood etc.) 1

2 Smple responses n plants Fast moton n plants phototropsm geotropsm Senstve plant Smple responses n anmals Anmals and the human bengs nsuln producton Moton (requres fast processes) Chemcal system : hormones melann producton More complex and faster system: nerves and muscles 2

3 Membranes n the cell Structure of the s cell Role of the cell : separaton and controlled nteracton to the envroment Base matrx: phospholpd blayer. Protens, polysachards, etc. Inner s: formaton of ntracellular spaces (compartments). Several base processes take place on the. hydrophllc regon hydrophobc regon locaton: at the extracellular space at the ntracellular space trans molecules Phospholpds Phospholpd structures n water Polar head (hydrophyllc regon) apolar chans (hydrophobc regon) polar watermolecules phospholpds n water phospholpd mcelle Smls sml gaudet (smlar lkes smlar) From energetc vewpont these arrangments are more favorte. Lyotrop lqud crystals. (structure depends on the concentraton) Ansotropc, partally orederd structure, but lqud materals. 3

4 Restng potental Typcal on dstrbutons observaton In restng state about -30 és -90 mv voltage may be measured between the extraand ntracellular space. observaton The on concentraton s dfferent on the two sdes of the. Intracellular space (mm/l) Extracellular space(mm/l) electrodes extracellular space Squd gant axon Na + K + Cl Squd gant axon Na + K + Cl Intracellular space Frog muscle Rat muscle Frog muscle Rat muscle Dffuson of the ons Dffuson through the Dffuson of neutral partcles. In the case of charged partcles the electrc work must be taken nto the consderaton! Intensve quantty: chemcal potental Intensve quantty: electrochemcal potental Use the permeablty constant as characterstc quantty! p = D/d ntal state z: no. of charges F: Faraday constant. : electrc potental e zf D dffuson constant d thckness of the moble ons (permeable ), fnal state equlbrum. equlbrum: e e 1 2 Nernst-equaton RT zf ln c c 1 2 equlbrum: c(1) = c(2) = 0!!! 4

5 Donnan-equlbrum Intal condtons: There are non permeable ons. Electrc neutralty both sdes (the sum of the charges s zero) c(1) c(2) Rato of concentratons (extracell./ntracell.) Ion Na + K + Cl - squd frog Rght soluton? electrc blayer rat Calculated potetals on the base of Nernst-equaton for dfferent ons and the measured potental (mv) -potental (meas.) Na + K + Cl - Squd gant axon Frog muscle Rat muscle Sgnfcant dfferences between the measured and calculated values! Man dfference n the case of Na +. on Typcal values for the heart Extracell. space (mm) Intracell. space (mm) rato (extra/ntra) Na K Cl Ca

6 Calculated potental on Na + K + Cl - Ca 2+ Donnan-equlbrum In the case of the phenomenon descrbed by Donnan constant potental dfference may be observed between two sdes of the. Membrane potental (mv) (37-85) There are moble and mmoble ons. In the case of equlbrum the electrochemcal potental s same. Concluson On the base of the measured values there s no Donnan-equlbrum between two sdes of the. (The concentraton dfference of the Na + s too hgh for example!) The bologcal system s not n equlbrum! Passve process (dffuson) may change the state to the equlbrum. Actve (energy consumpton) processes are necessary to keep steady state. The role of actve transport Charge and materal transport exst, the concentraton were not constant, e.g. slow nflow of Na + nto the cell. Dfferent, energy consumer mechansms, socolled pumps ensure the steady state. (e.g. Na + -K + pump, Na + -Ca ++ etc.) 6

7 Na-K pump Ion flow n the 3 Na + on and 2 K + exchange extracellular space neutral partcles (sngle) charged partcles requres ATP! ctoplasm extracellular space J pc J pc c F RT ctoplasm J flux p permeablty constant c- concentraton gradent J flux p permeablty constant c- concentraton gradent F Faraday constant T temperature potental dfference R - gas constant The base of the transport-model Goldman-Hodgkn-Katz (GHK) potental equaton The s n rest but there s no equlbrum between two sdes. The potental s constant the net on flow through the s zero. The potental gradent n the s constant d/dx = const. condton of steady state: (the net flux s zero) RT F p ln p Na Na c c e Na Na p p K K c c e K K p p J k k Cl Cl c c Cl e Cl 0 p permeablty constant of an on e extracellular space ntracellular space 7

8 Smplfed GHK equaton Electrc model of the RT pc ln F pc e Na Na c c e K K (p = relatve permeablty constant, compared to the K + ) ntracellular space extracellular space The model descrbng the restng potental and the on current: p (calc.) (mv) (meas.) (mv) Squd gant axon 0, Frog muscle 0, Accordng to the man ons model for restng potental Changng of the potental The defnton of the stmulus: changng of the potental transmts the nformaton. C represents the capacty, R - characterzes the resstance aganst the flow of the gven on, E voltage source representng the potental Changng of the restng potental s due to the specfc on flow though the. 8

9 Changng the potental Depolarzaton, hyperpolarzaton experment stmulus stmulus detecton response hyperpolarzaton depolarzaton exponental ncreasng and decreasng. Depolarzaton (example) rod n dark Hyperpolarzaton rods n the eye: photochemcal effect results the hyperpolarzaton of the. rod n lght har cells n the ear: Mechancal effect - depolarzaton. dark current actvated transducn closed on channel 9

10 n relatve unt Synaps (example) synaptc space postsynaptc Propagaton of the changng along the vescules place of the local changng exponental decreasng presynaptc nerve cell A possble mechansm: the released acetyl cholne bondng to the receptor opens an on-channel. Extenson of the electrc model: cable model Electrc propertes: tme constant extracellular space on the base of the exponental answer of the : (responses accordng to the dstance of the place of the stmulus) ntracellular space m R C m m R e - longtudnal resstance of the extracellular space. R - longtudnal resstance of the ntracellular space. These elements connect to each other the dfferent parts of the. the tme, whle the changng decreases or ncreases by factor e. 10

11 n relatve unt Electrc propertes: space constant on the base of the propagaton of the changng along the : Propagaton of the depolarzaton r m (W cm 2 ) r (W cm 2 ) (ms) dameter (m) (cm) Squd nerve , ,5 (responses accordng to the tme) T = 0 Crawfsh nerve ,25 Rm R R e R R the dstance, where the changng decreases by factor e. m R R e Frog muscle ,2 Both the tme constant and the space constant depend on the dameter. The value of the space constant shows that these are local phenomena they are not able to propagate too far. Processes n nerves and muscles Acton potental depolarzaton threshold a depolarzaton below the threshold (local response) b depolarzaton below the threshold (local response) c depolarzaton above the threshold - acton potental 1 voltage senstve Na + - channels 2 - voltage senstve K + -channels

12 Ion flow durng acton potental K + channel the nflow of the Na + s fast at the begnnng accordng to the non-equlbrum state. g = (1/r) conductvty Propertes of the acton potental Why s t fast? depolarzaton repolarzaton depolarza ton threshold The frst step s fast! (slow, long process s not sutable for fast response.) rato of on concentraton (extra/ntracellular space) on Na + K + U (mv) Squd restng potental Frog 6.0 0, negatve pot. postve rat

13 Smple calculaton Debye-length and dffuson Let the radus of a cell 20 m! The volume s: ~ l. amount of the K + : ~ mol. surface of the cell: ~ cm 2. capacty of the : ~ F. (specfc capacty: ~1 F/cm 2 ) on the base of restng potental: ~ C ~ mol on. The changng affects only the small envronment of the and transports a small amount of ons. the on concentraton close to the Speed of the dffuson d 3Dt example: D ~ 10-9 m 2 /s, t = 0,1 ms d ~ nm (Compare d, the average dstance, to the Debye length!) The dffuson transports the ons far from the. Electrochemcal potental (rat muscle) Comparson e c2 RT ln zf c 1 Na + e Na ln K + K + e K ln ~ kj/mol ~ kj/mol In rest there s a large thermodynamc force for Na +! e K ln ~ kj/mol After reversng the polarty ths force s hgh for K +! Large force acts on Naons. Fast passve nflow. No energy consumpton. Changng of the potental result the outflow of the K +. If were equlbrum. (Donnan-equlbrum) Changng of the potental: requres energy and were slower! 13

14 Modfed electrc model extracellular space Propagaton of the acton potental (ap) t tme dfference exponental decreasng at x the local changng s enough large to produce a new ap. depolarzaton threshold ntracellular space speed ~ x/t The trans rsestance s represented by varable resstors, that makes possblechangng the speed of the on flow. Advantage Shape s ndependent from the stmulus: not senstve to the external effects, noses. propagates far wthout any attenuaton. Fast makes possble fast responses. Speed of the propagaton space constant depends on: dameter, R m, R r m (W cm 2 ) (ms) dameter (m) (cm) Squd Crawfsh frog

15 Saltatorc propagaton Role of the myeln sheath t tme dfference depolarzaton threshold x larger! Larger speed. (due to the myeln R m s large) R m very large, space constant s large too At the nodes of Ranver: R m ~ 50 W cm 2 about 10 4 Na + -channel/m myeln sheath nodes of Ranver cat n. saphaneus the tme that s necessary to cover 6 cm Speed large space constant: about m/s fber Speed of the propagaton dameter (m) Speed (m/s) a b g d < No sheath < Rm R R e R R m ncreasng dameter ncreasng R m and decreasng R. 15

16 Refracter state Role of the refracter state absolute relatve absolute: Na-channels are open, no new ap. relatve: only larger stmulus s able to produce new ap. refracter state drecton of propagaton the refracter state prevents the back propagaton of the ap. When s t not true Rectfcaton: synaps ntated at the end ntated at the center propagaton synaptc space vesclues presynaptc nerve postsynaptc neuro-transmtters emtted by the vescules depolarze the postsynaptc and result acton potental after the synapse. The structure makes mpossble the back propagaton. Undrectonal step! propagaton 16

17 Not a whtdrawal? Electrc synaps remember: speed of the dffuson d 3Dt the sze of the synaptc space s about a few 10 nm! protens konnexonfehérjék 2-3 nm bdrectonal, no rectfcaton. the dffuson s very fast f the dstance s small! the delay s not more than a few hundred s! More characterstcs for the nvertebrates. man: e.g. heart muscle. Concluson Developed a fast system based on electrc phenomena of the. The charges are ons, so ths system s slower than equpment s used by us. The stmulus (sgnal) s able to propagate far wthout any attenuaton. 17