4 Membrane_ Ionic Gradient and Memb Potential Jan 2013

7/28/2019 4 Membrane_ Ionic Gradient and Memb Potential Jan 2013

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Topics

1. Introduction

2.Energy and thermodynamics

3.Feeding and digestion

4. Ionic gradient, electrical potential

5.Electrical signals and neurons

6.Cytoskeletons, motor proteins and muscle

7.Heat production and body temperature


2/110

Learning

Doing (experience)

Thinking

(reflection)

Information

Changes in

knowledge, skills,

attitude, value,

belief, etc.


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Transport

Diffusion

http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.html

http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion

_works.html

Facilitated diffusionhttp://highered.mcgraw-

hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitate

d_diffusion_works.html

Transport across cell membrane (active transport)

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.html

Active transport animation

http://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swf
http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.htmlhttp://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swfhttp://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swfhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.html


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_works.html


hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis

_works.html


hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodi

um_potassium_pump_works.html

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html


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http://www.youtube.com/watch?v=ULR79TiUj80


8/110

Chemical composition of some purified membranes

(in percentages)

Membrane Protein Lipid Carbohydrate

Myelin 18 79 3

Plasma membrane

Human erythrocyte 49 43 8

Mouse liver 44 52 4Amoeba 54 42 4

Halobacterium

purple membrane 75 25 0

Mitochondrial

inner membrane 76 24 0

Chloroplast

Spinach lamellae 70 30 0


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Why was phospholipids chosen as the basic

component of biomembranes during

evolution?

A) Water has very high surface tension (70

dynes/cm).Therefore it is impossible to use pure water to

form closed structures.

Phospholipid can lower the surface tension ofwater to 1-2 dynes/cm so that it can be spread

out naturally.


13/110

http://www2.hawaii.edu/~yzuo/research1-surfactant.html
http://www2.hawaii.edu/~yzuo/research1-surfactant.htmlhttp://www2.hawaii.edu/~yzuo/research1-surfactant.htmlhttp://www2.hawaii.edu/~yzuo/research1-surfactant.htmlhttp://www2.hawaii.edu/~yzuo/research1-surfactant.html


14/110

B) A lipid bilayer sheet would be an unstable

structure if it had a free edge at which the

hydrophobic region of the bilayer were in

contact with water.

Hence, phospholipid membranes

spontaneously seal to form closed structures.


15/110

Learning

Doing (experience)

Thinking

(reflection)

Information

Changes in

knowledge, skills,

attitude, value,

belief, etc.


16/110

Learning = new information + new

skills + new experience

Learning =making new connections

between information, skills andexperience

Learning = un-learn + re-learn


17/110

Topics

1. Introduction


3.Feeding and digestion

4. Ionic gradient, electrical potential





18/110

K+ K+

Na+ Na+

Cl-Cl-P-

1.Selective permeable to various ions and solutes

2.Thin and can separate charge (behaves as a

capacitor)

Mg++

+

++

++

+

+

_

_

_

_

_

_

_

_ +


19/110


20/110

Diffusion is the movement of

molecules from a region of

higher concentration to a

region oflower

concentration.

Prior knowledge:


21/110

Diffusion is the movement ofmolecules from a region of

higher concentration to a

region oflower

concentration = No diffusion

when there isnoconcentration gradient


22/110


23/110

Rate of movement of

individual molecules(distance/time)

Slow


24/110

Rate of movement of


The same

Slow


25/110

Rate of movement of


Not so slow


26/110

What is the meaning of Diffusion?

Diffusion is a kinetic property of molecules

related to temperature

i.e., a type ofthermal motion.

Diffusion velocity of individual moleculesdistance

timedisregarding the direction

is m (Grahams law)

Temp (oK)

XXX not concentration


27/110

Rate of movement of


Effects of

concentration

gradient

(no change)

But, how about #molecules/time through

the imaginary barrier? (Low flux )


28/110

Rate of movement of


Effects of

concentration

gradient

(no change)

But, how about #molecules/time through

the imaginary barrier? (Higher flux)


29/110

1)Why is there the movement of individual

molecules at a certain temperature?

Because of heat - kinetic theory

2)Why is there the net movement of moleculesin bulk across an imaginary or physical barrier?

Because of the presence of a chemical

potential gradient.

(Flux = moleArea Time)


30/110

Rate of movement of


In equilibrium

with the

surroundings

(Will moleculesstop moving?)

NO!!! But, net flux =0 Net flux would stop


31/110

Will there be movement ofsolute molecule from a

region of high concentrationto low concentration in

waterat -80oC, at -200oC?


32/110

Diffusion is themovement of

molecules from aregion of higherconcentration to aregion of lower

concentration.

This definition of diffusion conveys a wrongmeaning of diffusion!!!


33/110

So, what do you think aboutthe definition below?

Molecules move from a regionofhigher concentration to a

region oflower concentration

by diffusion.


34/110

Learning

Doing (experience)

Thinking

(reflection)

Information

Changes in

knowledge, skills,

attitude, value,

belief, etc.


35/110

Todays task:

Can you define diffusion

using your own words?

A Question for thought:

Is it a good idea to useperfume to explain

diffusion?


36/110

Can living systems survive by depending

on only diffusion of substances across

their biomembranes?

NO !!

But why?

1) Not all substances can dissolve in lipids.

2) Diffusion cannot maintain the gradients

required for the living system to function


37/110

Solution??

Facilitated diffusion

Active Transport


38/110

Transport

Diffusion




_works.html

Facilitated diffusion


hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitate

d_diffusion_works.html

Transport across cell membrane (active transport)

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.html

Active transport animation

http://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swf
http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.htmlhttp://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swfhttp://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swfhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/Diffusion.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.html


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Active Transport :

a process in which the system gains free

energy (cellular energy is involved)

C1C2G RT In C2

C1

0.01M1mole

0.1M

G = RT In0.1

0.01

= 1.98 x 293 x 2.303 x log 10

= 1340 cal


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downhill

uphill


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Active Transport process :

Final stateHigh electrochemical

potential

Initial state

Low electrochemical

potential

G = +

The mechanism involved does not define the process!!!

Heres where the confusion comes in !!!


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Solar energy/light

Chemical potential energy e.g. Na+ or K+ gradient

Chemical energy, ATP

Chemical energy, e.g. carbohydrate

Electrical energy, e.g. membrane potential

Heat

Heat

Heat

Heat


44/110

Solar energy/light




Heat

Heat

Heat


45/110

Is it true that only

processes which involve

the movement of a

substance against its

chemical and/or electrical

potential gradient(s) are

regarded as active

transport processes?

Yes.


46/110

K+ K+

Na+ Na+

Cl-Cl-P-

An important function of the plasma membrane is to

maintain an ionic composition in the cytosol very different

from that of the surrounding fluid.


47/110

small subunit(55,000)

2 sites for K+ and one for ouabain

3 sites for Na+

ADP + PiATP

Catalytic site of ATP

large subunit

(120,000)

oligosaccharideK+ Na

+

K+ Na+


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49/110

NKA in action

http://www.youtube.com/watch?v=bGJIvEb6x6w&NR=1
http://www.youtube.com/watch?v=bGJIvEb6x6w&NR=1http://www.youtube.com/watch?v=bGJIvEb6x6w&NR=1


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Intracellular Extracellular

Na+ 15 mM

K+ 150 mM

Na+ 140 mM

K+ 4 mM

ATP

ADP + Pi

3 Na+

2 K+

The primary active transport of sodium and potassium ions

in opposite directions by the Na,K-ATPase in plasmamembranes is responsible for the low sodium and high

potassium intracellular concentrations. For each ATP

hydrolysed, 3 sodium ions are moved out of a cell and 2

potassium ions are moved in.


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Active Transport

1) Active Transport process

2) Active Transport mechanisms

e.g. i) 10 active pump

(Na+, K+- ATPase, Ca2+ - ATPase)ii) 20 active pump

(Glucose, Na+ - Cotransport Mechanism)

Here four thermodynamic processes are involved.

a) K+ transport

b) Na+ transport

c) ATP hydrolysis

d) Overall coupled transport


52/110

Other ATPase pumps

e.g.1)Ca2+- ATPase pumps calcium ions out of the

cytoplasm, maintaining a low intracellular

concentration.2) A proton pump causes acidification of the

stomach contents.


53/110

Solar energy/light





Heat

Heat

Heat

Heat

pure artificial phospholipid bilayer


54/110

pure artificial phospholipid bilayerWater H2O

Gases

CO2

N2

O2

Small uncharged

polar molecules

Large uncharged

polar molecules

Urea

Ethanol

Glucose

Ions

K+, Na+

Mg++, Ca++

CI-, HCO3-, HPO4

2-

Charged

polar

molecules

Amino

acids

ATP4-

G6-P2-

X

X

X

I f ilit t d diff i f


55/110

Is facilitated diffusion of

charged ions or molecules

(e.g. K+, Na+ etc.) through the

biomembrane the same asfacilitated diffusion of

uncharged molecules (e.g.

glucose) or simple diffusion

of lipid soluble molecules

through the lipid bilayer?


56/110

A measure ofhydrophobicity is the partition coefficient,

the equilibrium constant for partition of the moleculebetween oil and water.

In relation to this, biomembrane can be described asdifferentially or selectively permeable.

Partition coefficient

amount dissolving in oil

amount dissolving in water


57/110

Certain membrane proteins speed up the

movement ofspecific ions or molecules

across the membrane - facilitateddiffusion - without using cellular energy


58/110

1. The flux is far greater than would beexpected from a simple diffusion model

based on hydrophobicity and Ficks law.

2. The process is substrate specific;

each protein transport only a single species

of ion or molecule, of a single group of closelyrelate molecules.


59/110

3. There exists a maximal rate of transport.

4. There exists the pH and temperature optima.


60/110

Solar energy/light





Heat

Heat

Heat

Heat


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62/110


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Aquaporin



64/110


charged ions or molecules

(e.g. K+, Na+ etc.) through the

biomembrane the same asfacilitated diffusion of

uncharged molecules (e.g.

glucose) or simple diffusion

of lipid soluble molecules

through the lipid bilayer?

No,

they are not quite

the same.


65/110

1. Foruncharged molecules or lipid

soluble molecules, the only 2 types of

energy involved are heat and chemical

potential.

Forcharged molecules, electrical

potential is also involved.


66/110

Na+

Cl-

What is the speed of ions in motion?

Can you call it diffusion? No!!

A

Na+

Cl-+ -

Current


67/110

2. Foruncharged molecules, C1 = C2 at

equilibrium,i.e. C = 0.However, forcharged molecules,

C = 0 at equilibrium.Also, V1 = 0.

Now equilibrium is achieved between

Chemical potential difference = Electricalpotential difference.

X X


68/110

3 F h d l l th t


69/110

3. Foruncharged molecules, the movement

of individual molecules is due to thermal

motion, or heat.

Such diffusion velocity (distance / time) is

relatively slow.

Forcharged molecules, the movement of

individual molecules can be affected by

an electrical potential and the velocity canbe very fast.

Such a movement = diffusion.X


70/110

Na+

Cl-



A

Na+

Cl-+ -

Current


71/110

Topics

1. Introduction


3.Feeding and digestion4. Ionic gradient, electrical potential





72/110

V


73/110

+ + + + +

+

+

+

+

+

+

+

+ + + + +

+

+

+

+

+

+

+

-

-

-

-

-

-

-

K+ 140 7 (mM)

Na+ 12 110 (mM)

Cl-

10 117 (mM)

P-

-

-

-

-

-

-

-

Cell

-

+

Anion

Cation

Vmi-o = -60 mV- - - - -

- - - - -

The separation of electric charge across a plasma membrane

(membrane potential) provides the electric force that drives

positive ions into a cell and negative ions out of a cell.


74/110

Na+

Cl-



A

Na+

Cl-+ -

Current


75/110


76/110

Membrane voltage

Membrane potential

http://www.cvphysiology.com/Arrhythmias/A007.htm

Membrane potential concept-Rice U

http://www.ruf.rice.edu/~bioslabs/bios415/mempot1.htm
http://www.cvphysiology.com/Arrhythmias/A007.htmhttp://www.ruf.rice.edu/~bioslabs/bios415/mempot1.htmhttp://www.ruf.rice.edu/~bioslabs/bios415/mempot1.htmhttp://www.cvphysiology.com/Arrhythmias/A007.htm


77/110

M b i t


78/110

Membrane resistance

Membranes act as barriers to the free diffusion

of ions.

Lipid bilayers would have very high resistance

(low conductance) to ions.

But, resistance to a specific ion can be lowered

by the opening ofprotein channels which

facilitate the movement of this specific ion.

Resistance =1

conductance

Variable resistor


79/110

Variable resistor


80/110

Outside Inside

[Cl-] [K+]

[K+

] [Cl-

]

Variable resistor

(K+ channel)

K+

K+K+

K+

K+

K+

capacitor

Cl-

Cl-

Cl-

Membrane capacitance


81/110

Membrane capacitance

Because they are very thin (100 ) and are

virtually impermeable to ions over most of

their surface areas,

biomembranes are able to violate the

principle of electroneutrality at the

microscopic level.

The ability of membranes to accumulate and

separate charges gives rise to the electrical

property of membrane capacitance.

( 1 -3 farad / cm2)

Different types of capacitors


82/110

Different types of capacitors


83/110


84/110

Outside Inside

[Cl-] [K+]

[K+

] [Cl-

]

Variable resistor

(K+ channel)

K+

K+K+

K+

K+

K+

capacitor

Cl-

Cl-

Cl-


85/110

Outside Inside

[Cl-] [K+]

[K+

] [Cl-

]

Variable resistor

(K+ channel)

K+

K+K+

K+

K+

K+

capacitor

Cl-

Cl-

Cl-


86/110

Ck < Ck (Chemical potential)

Vout > Vin (Electrical potential)

Charges (K+ and Cl-) are separated across

biomembranes at microscopic level.

V C


87/110

You have learned from physics that you

can equate gravitational potentialenergy and kinetic energy through :

mgh = mv2.

Similarly, you can equate chemicalpotential energy and electrical energy

through the Nernst Equation:

Ei-o =RTZF

ln C0C

i

RT

[7]


88/110

EKi-o=

RTZF

ln [7][140]

= - 75 mV

At equilibrium, when there is no net flow of K+

across the membrane,

Vm = EK

After the movement of K+ across themembrane through the K+ channels, the

changes in K+ concentrations in both sides are

negligible.


89/110

Solar energy/light





Heat

Heat

Heat

Heat


90/110

Summary on relationship between NKA and membrane potential

http://www.youtube.com/watch?v=iA-Gdkje6pg

Recall from Physics:
http://www.youtube.com/watch?v=iA-Gdkje6pghttp://www.youtube.com/watch?v=iA-Gdkje6pghttp://www.youtube.com/watch?v=iA-Gdkje6pghttp://www.youtube.com/watch?v=iA-Gdkje6pg


91/110

q = C.V

If you have an air compressor with the tank pressure at100PSI it will be filled with twice as many air molecules thanif its pressure was at 50PSI.

Looking at it another way, if you have an air compressor witha 5 gallon tank and another one with a 10 gallon tank andthey're both filled to 100PSI, the 10 gallon tank will havetwice as much air in it as the 5 gallon one.

C is analogous to the capacity of the tank,q is analogous to the quantity of air molecules it's

holding,

V is analogous to the tank pressure.

Recall from Physics:


92/110

q = C.V

where q = charges need to be separated andaccumulated across the capacitor.

C = capacitance

V = voltage built up across the capacitor

For a biomembrane of1 f / cm2 capacitance to buildup a voltage of 60 mV across it, the amount of ions tobe separated is:

q = C.V

= (1 x 10 6 F / cm2) . (6 x 10-2V)

= 6 x 10-8 coulombs / cm2


93/110

There are 96,500 coulombs of charge (1

faraday) in mole of a monovalent ion.

Hence,

= 6 x 10-8 coulombs /cm2

96,500 coulombs / mole ion

= 6 x 10 13 mole ion / cm2

Does it mean that Na+ and Cl- are


94/110

Does it mean that Na+ and Cl- are

perfectly impermeable and do not

contribute to Vm?

Note that75mV (EK) is close to60mV

(Vm) but not exactly the same.

The relative permeabilities of K+, Na+

and Cl- through biomembranes are

1 : 0.04 : 0.45

Aft k i th D G ld d i d


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After knowing these. DrGoldman derived

another equation:

Vm =RT

(+1)Fln

Pk[K]0 + PNa[Na]0 + PC1[Cl]i

Pk[K]i + PNa[Na]i + PC1[Cl]0

Substituting all the values into the

equation:

Vmi-o = 58 log10 60654

= -60.1 mV

+55 ENa


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-60-75

(Vm-ENa)Vm(i-o)

0

(mV)

(Vm-Ek)

EK

Resting memb. potential

Difference is small.Hence,e.m.f.k is

small. Though K+ channels are open,

net flux of K+ is small as it is close to

equilibrium.

Difference is large. Hence, e.m.f.Na is

large. Though e.m.f.Na is large, net

flux of Na+ is small because most Na+

channels are closed.

Formation of action potential


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Formation of action potential

Can the movement of Na+ in this case beregarded as diffusion?

No!!!

+ + + + + + + + + + + + +- - - - - - - - - - - - -

-

+

Transmission of

impulse

Na+

Na+

Axon

facilitated diffusion

Conclusion


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Conclusion

1. Protein channels in biomembranes behave asvariable resistors

(e.g. to K+, Na+).

2. Phospholipid regions of biomembranes act as

capacitors.

Usually capacitance is small (13 f / cm2).


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3. The concentration gradients of various ions(Na+, K+, Cl-) existing across the membrane

behaves as ionic batteries.

Energy is stored in the gradient as chemicalpotential.

4. At rest, biomembranes are selectively

permeable to K+.


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5. Movement of K+ down its chemical potential ( i

to o) gradient leads to a separation of charge

and an electrical potential gradient is built up

across the biomembrane.

6. Chemical potential can be equated to electrical

potential by the Nernst Equation.


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7. After the movement of K+, the concentrations

of K+ in the 2 compartments are insignificantly

affected.

8. At equilibrium, Vm = Ek.

9. At resting, Vm is slightly more positive than Ek.


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10. The polarity of Vm existing across a

membrane can be reverted by a change in the

selective permeability of the membrane.

11. At resting, although K+ channels are open,

e.m.f. is small as Vm Ek.


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12. However, at resting, e.m.f. Na+ is large as Vm is

very different from ENa.

Though e.m.f.Na is large, movement of Na+ is

negligible because most Na+ channels are

closed.

How does the movement of charged molecules differ from

uncharged molecules across an ion-selective membrane?


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g


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+

+

Mind Maps


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Mind Maps

Summarize information, act as mnemonicsQuickly identify and understand the structure of a

subject

Appreciate how pieces of information fit together

Provide a structure and encourages creative

problem solving

Hold information in a format that the human mindwill find easy to remember and quick to review


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1.Use single words or simple phrases.

2.Position the main idea/problem in the center.

3.Use lot of space so that things can be added

on later.

4.Use color to separate different ideas;personalize the map.

5.Look for relationships; cross-link with lines

and arrows; label the lines where applicable.

6.Create sub-center for sub-themes.

Pl b it i d t IVLE if


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Please submit your mind map to IVLE, if your

wish (not compulsory, no marking/grading),

so that you can learn from each other.

Please submit in Word format, and state your

name and email address.

GENERAL PHYSIOLOGY General

information and submission folder AY12-13(I)


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End

Documents

4 Membrane_ Ionic Gradient and Memb Potential Jan 2013