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Physiology of Cells 2002 > Lecture 4: Diffusion Potentials > Flashcards

Lecture 4: Diffusion Potentials Flashcards

1
Q

DIFFUSION IF ISOTONIC CELL

  • Is there a concentration gradient?
  • Is the membrane permeable?
  • what moves?
A
  • Is there a concentration gradient?
  • Yes out for potassium and organics
  • In for sodium and chloride
  • No for water
  • Is the membrane
    permeable?
  • Only to water
  • Nothing moves

ISOSMOTIC AND ISOTONIC

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2
Q

DIFFUSION IF OSMOSIS OF CELL

  • Is there a concentration gradient?
  • Is the membrane permeable?
  • what moves?
A
  • Is there a concentration gradient?
  • Yes for K, organics Na+ & Cl-
  • Yes for water into cell
  • Is the membrane permeable?
  • Only to water
  • Water enters cell, swells, may lyse

HYPOSOMOTIC AND HYPOTONIC

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3
Q

DIFFUSION IF UNCHARGED

  • Is there a concentration gradient?
  • Is the membrane permeable?
  • what moves?
A

Is there a concentration gradient?
- Yes in for urea
- No for water at the
start

  • Is the membrane permeable?
  • Yes to urea and water
  • Urea enters the cell

**ISOSMOTIC AND HYPOTONIC

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4
Q

Understanding Iso-Hypo-Hyper…Isotonic and Hyposmotic

A
  • Iso- means the same
  • Hypo- means less than
  • Hyper- means more than
  • Isotonic = the same tonicity
  • Hyposmotic = less osmolarity.
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5
Q

Ion movement in cells

if cell inside = 140mM K+ and 150mM A-

Outside = 140 mM Na+ and 110 mM Cl-

A

*If permeable to both Na+ and Cl- they would enter same as urea

*What if only permeable to sodium not to chloride?
*Na+ has a charge, accumulation of charge generates a voltage

*A VOLTAGE WILL MOVE CHARGES i.e. ion movement depends on concentration and voltage

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6
Q

A Contraction is signaled electrically

HOW? Example?

A
  • Cells are electrically charged.
  • Nerves and muscle use changes in charge to
    send electrical signals called Action Potentials.
  • Cardiac Muscle cells uses action potentials to co-ordinate contraction across the heart and activate contraction.
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7
Q

ACTION POTENTIALS - where is this going?
Nerve cells, sensory receptor, muscle, neurotransmitters, kidney+saliva+glands+mucous glands, gut? 6

A
  • Nerve cells use change in potential to carry signals.
  • Sensory receptor cells use change in potential to provide sensation, hearing ,vision etc
  • Muscle uses change in potential to signal contraction.
  • Release of neurotransmitters from nerves triggered by change in potential
  • Electrical currents used to move salts in kidney, saliva glands, mucous glands.
  • Absorption of food in gut linked to ion currents using co-transport.
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8
Q

What is Charge?

A
  • Charge (q), units coulombs (C).
  • Charge is to electricity like mass is to gravity.
  • Positive change repels positive charge and attracts negative charge.
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9
Q

Valence? equation?

A

Valance is charge on an ion given as z

z= − (qion/qelectron)

q = charge

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10
Q

Faradays constant?

A

Faradays constant (F) is charge per mole (96,485 C/mol).

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11
Q

charge of n moles of ions with valance z Equation.

A

q=zFn is charge of n moles of ions with valance z

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12
Q

What is Voltage? 4

A
  • Voltage (electrical potential, V) units volts (V)
  • Measures electrical potential that makes charges
    move.
  • Put two positive changes together makes a voltage that forces them apart.
  • Voltage is a bit like pressure in a fluid.
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13
Q

What is a Current?

A
  • Current (i) unit ampere (A)
  • Flow rate of charge one A is 1 C/s
  • Current is like flow in liquids

i = q/t

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14
Q

Understanding Charge separation:

diagram
* Na+ and Cl- (left side)
Na+ selective membrane
Na+ moves to right side through membrane
OVERTIME

LEFT IS NEGATIVELY CHARGED WHILST RIGHT UIS POSITIVELY CHARGED.

A
  • Diffusion gradient for sodium and chloride
  • Only permeable to sodium
  • Cl- stays behind, Na+ crosses membrane
  • Membrane now polarised, negative on left, positive on right
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15
Q

Understanding Charge Separation:

Selectively permeable membrane, ion movement…4

A
  • Selectively permeable membrane
  • One ion moves causing charge separation
  • Cells develop electrical charge and voltage across membrane
  • Ion movement now depends on voltage and concentration
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16
Q

Membrane Potential Qualitative:
* Is there a concentration gradient?
* is the membrane permeable
* Charged?
* Repels?

diagram*

outside: Cl- and Na+
150 mM NaCl = 3000 mOsmol/L
Permeable to Sodium and Water

ISOSMOTIC AND ISOTONIC

A
  • Is there a concentration gradient?
  • Yes in for Na+ and Cl-
  • Is the membrane permeable?
  • Yes to water and Na+
  • Accumulation of positive charge makes cell positive.
  • Cell positive repels sodium

ISOSMOTIC AND ISOTONIC

17
Q

Understanding Charge Separation: EXPLAIN

Diagram:
Beaker
left side: NEGATIVELY CHARGED WITH Na + and Cl right side: POSITIVELY CHARGED with Na+ and Cl-

movement
Chemical Gradient ——>
<——– Electrical gradient

A
  • Sodium entry down diffusion gradient will make right side positive.
  • At equilibrium positive potential will repel sodium as fast as it enters
  • Sodium entry stops
18
Q

Understaning GPE… equation?

KE …equation?

A
  • Pendulum has gravitational potential energy at top of swing
  • Falling turn GPE into kinetic energy
  • Kinetic energy turned back to GPE on upswing

GPE=mg* Δ h
KE =1/2mv^2

1/2mv2 =mgΔh
v2 =(2mgΔh) / m
v= (2g*Δh)^(1/2)

19
Q

Understanding Nernst Equation:

diffusion? concentration gradients? voltage? AND EQUATIONS

A
  • Molecules diffuse from high to low concentration.
  • Concentration gradients have chemical potential energy.
    𝜇𝑥 =𝑛𝑅𝑇 × 𝑙𝑛 ([𝑥]1/ [𝑥]2)
  • Voltage generates electrical potential energy
    𝐸𝑃𝐸 = 𝑞 × 𝑉
    𝜇𝑒 =𝑧𝐹𝑛×𝑉
20
Q

Nernst Equation at Equilibrium = 3 and equations

A

ue =−ux

znFV = −nRT * ln [x]1/ [x]2
1. At equilibrium energy per mole moved by diffusion is equal and opposite energy per mole moved by voltage.

  1. Nernst equation gives membrane potential at equilibrium.
    1 V = − RT/zF * ln [x]1/[x]2
  2. Assumes only one ion is permeable
    Nernst Equation

V = − (61/2) * log [x]1/log[x]2
At 37°C using log and in mV

At 20°C using log and in mV
1 V = −( 58/2) * log [x]1/[x]2

21
Q

Membrane Potential Quantitative

Diagram

15 Na+ mM inside
Outside Cl- and Na+
150nM Na+ outside
permeable to Sodium only
Mammal cell at body temp

A
  • Sodium will enter cell so answer must be positive.
  • V=-61/z log [Na+]in / [Na+]out
  • = - 61/1 log(15/150)
  • = - 61 log (0.1)
  • = - 61 (-1) = 61 mV
22
Q

Equilibrium Potentials..Ve, K+, Na+, Cl-

A

Ve is equilibrium potential.

  • Voltage is only that ion is permeable
  • For K+ = -61 log (140/5) ~ -90mV
  • For Na+ =-61 log (10/145) ~ +70 mV
  • For Cl- = -61/-1 log(6/106) ~ -75 mV
23
Q

Resting Membrane Potential. 6.

A
  • At rest most cells are permeable to potassium
  • Much less permeable to sodium or chloride.
  • Resting membrane potential is resting voltage from inside to out.
  • Typical resting potential -70 mV most cells
  • Increased permeability to x
  • Potential moves toward V for x.
24
Q

neuron….Resting Membrane Potential

A
  • Measurement close to predicted.
  • Error because not just permeable to potassium
25
Q
A
  • Capacitance (C, unit Faradays (F)) is relationship between charge and voltage.
    C = V/q

Capacitance for a typical cell ~1.3x10-11 F.
q = CV
* q=1.3x10-11(F)x0.07(V) = 9.1x10-13 C

n =9.1x10-13(C)/96 500(C/mol)
= 9.4x10-18 mol of K+ move out.

n =0.140(mol/L) x 4x10-12(L) = 5.6x10-13mol of K+ in cell
q = zFn
n=q/zF

  • i.e. only 0.0017% of cells K+ moves out
  • Concentrations change by nmol not mmol
26
Q

K+… Concentration and Electrical gradient for K+…. at Resting Membrane Potential

A

Large organic anions in cells cannot leave

  • At rest potassium leaves down concentration gradient.
  • Negative resting membrane potential develops
  • Membrane potential stops K+ leaving cell
27
Q

what next?

A
  • What happens if more than one ion is permeable?
  • Or if the ion permeability changes
  • What about cells that pump ions by active transport
  • Electrogenic potentials generated by active transport Na+ Cl-
28
Q

SUMMARY OF THIS LECTURE**

A
  • Selectively permeable membranes can produce charge separation.
  • Charge separation leads to a membrane voltage
  • Nernst equation gives the equilibrium potential if the
    membrane is only permeable to one ion.

*Changing concentration gradient will change equilibrium potential

*Resting membrane potential due to potassium permeability

  • Very few ions move to generate resting potential, no change in concentration

Physiology of Cells 2002 (24 decks)

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