PERMEABILITY PROPERTIES I:

ARTIFICIAL MEMBRANES Cargando, Debei

Fajardo, Laiza

Ferrer, Liezel

Pajarillaga, Shara

Ramos, Angeli

INTRODUCTION

MEMBRANE PERMEABILITY

Quality of a cell’s plasma membrane that allows substances to pass in and out of the cell

Cell membranes have SELECTIVE PERMEABILITY.

The membrane will allow certain substances to pass while forming a barrier against others.

Dependent upon the bilayer structure of the cell membrane

CELL MEMBRANE

barrier between the inside of the cell (ICF: cytoplasm and organelles) and the outside of the cell (ECF)

there is a constant and dynamic exchange of substances between the two fluids

CELL MEMBRANE

flexible lipid bilayer phospholipid

polar, hydrophilic head 2 hydrophobic hydrocarbon tails spontaneously bury the tails together and leave the hydrophilic

heads exposed automatically fixes itself when torn

3 major classes of lipid molecules: (1) phospholipids, (2) cholesterol, (3) glycolipids diff membranes have diff ratios of the 3 lipids

surface proteins functions: (1) cell surface receptors, (2) enzymes, (3) surface

antigens, (4) transporters also has hydrophilic and hydrophobic regions

hydrophilic region: help anchor the protein inside the cell membrane can be classified as (1) intrinsic / integral or (2) extrinsic / peripheral

IMPORTANCE OF MEMBRANE PERMEABILITY

the cells can extract the amino acids, fatty acids, sugars and vitamins it needs to carry out its daily functions

enables chemical messengers, such as hormones, to enter the cell and either trigger / inhibit some function of the cell as necessary

allows the exit and release of waste products after the cells create hormones, neurotransmitters,

proteins and other substances required by the body, MP allows these substances to exit the cell

prevents harmful substances from infiltrating the cell

ensures that the cell does not lose too much of its precious fluids and proteins at any one time

METHODOLOGY &

GUIDE QUESTIONS

Solution A

0.20 g NaCl

50 ml dH20

Solution B

0.20 g NaCl

50 ml

gelatin soln

WHAT IS THE PURPOSE OF GELATIN?

GELATIN

Comes from the thermal denaturation of collagen, isolated from animal skin and bones, with very dilute acid.

Gelatin is only partially soluble in cold water, however dry gelatin swells or hydrates when stirred into water. On warming to about 40°C gelatin that has been allowed to hydrate for about 30 minutes melts to give a uniform solution.

A protein food composed of 18 amino acids.

GELATIN

What is the purpose of the 5% gelatin solution in solution B?

The 5% gelatin solution simulates the inside of an animal cell. It contains proteins and peptides that are impermeable to the longganisa skin, which acts as the membrane.

Soln

A

Soln

B

Maintain distance

Soln BB

WHY LABEL SOLUTION BB DIFFERENTLY

FROM SOLUTION B?

Solution B → Solution BB

Concentration difference (permeating solute)

results in diffusion from area of high

concentration to low concentration

Solution BB has more Cl- ions because of

diffusion from solution A to B along the

concentration gradient

Soln A

0.5 ml

Soln A

0.5 ml

Soln A +

50 uL

Potassium

Chromate

+ Silver

Nitrate

25 uL

increments

WHY USE SILVER NITRATE?

Silver nitrate can react with the chloride ions of the NaCl in the solution.

Forms a while solid ppt -> AgCl-

Chemical reaction:

NaCl → Na+ + Cl-

AgNO3 + Cl- → AgCl- + NO3-

WHY USE POTASSIUM CHROMATE?

Potassium chromate was used because it indicates that there are no more chloride ions present in the solution. Excess silver nitrate (from the silver nitrate-chloride reaction) reacts

with potassium chromate

Product: silver chromate

(brick red ppt)

K2CrO4 →2K+ + CrO42+

Ag+ + CrO42+ → Ag2CrO4

-

DISCUSSION

Solution Amount of Silver

Nitrate (uL)

Computed moles of

Cl

A 725 ?

BB 250 ?

Conversion factor:

Each 50 µL portion of AgNO3

represent 1 mg of NaCl / mL

General Formula:

Molecula

r weight

Simple

conversion AgNO3 + Cl- AgCl- + NO3

-

COMPUTATIONS

For Soln A:

= 2.48 x 10 -4 mol Cl-

725

COMPUTATIONS

For Soln BB:

= 8.55 x 10 -5 mol Cl-

250

Solution Amount of Silver

Nitrate (uL)

Computed moles of

Cl

A 725 2.48 x 10 -4

BB 250 8.55 x 10 -5

GIBBS-DONNAN RULE

the presence of a nonpermeating charged solute on one side of a membrane results in an equilibrium in which each permeating charged solute is more concentrated on one side than the other

The final distribution of all ions will satisfy 3 requirements:

i. the total number of cations and anions on the same side of the semi-permeable membrane will be equal

# of cations = # of anions protein

# of cations = # of anions

ii. on the side containing the protein, the number of diffusible ANIONS present will be less and the number of diffusible CATIONS will be greater than on the other side of the semi-permeable membrane

# of cations

# of anions

protein

# of cations

# of anions

>

<

iii. the osmotic pressure on the side containing the protein anion will be slightly greater than on the side without protein anions

GIBBS-DONNAN EQUILIBRIUM IN SET-UP

Na+

Protein –

Na+

Cl –

Starting condition

membrane

Sol B Sol A

Initial concentrations (molar) N

a+

Pro

tein

–

Na+

Cl –

Na+

Protein—

Cl –

Na+

Cl –

Net diffusional movements during approach to equilibrium

membrane

Sol B Sol A

Final concentrations (molar)

Na

+

Na

+

Cl–

Na+

Cl –

Pro

tein

– C

l–

Sol BB Sol A

[Na]1 [Cl]1 = [Na]2 [Cl]2

Final concentrations (molar)

Na

+

Cl–

Sol BB Sol A

Pro

tein

– C

l–

Na

+

Solution Amount of Silver

Nitrate (uL)

Computed moles of

Cl

A 725 2.48 x 10 -4

BB 250 8.55 x 10 -5

HOW DOES THIS PHENOMENON AFFECT

THE GENERATION OF A MEMBRANE

POTENTIAL IN LIVING CELLS?

Aside from generating a concentration gradient, there is also a difference of electrical potential at equilibrium, with the nonpermeating solute having the charge of that solute.

Na+

Protein—

Cl –

Na+

Cl –

membrane

Sol B Sol A

Na+

Cl –

REFERENCES

http://www.biology4kids.com/files/cell_membrane.html

http://library.thinkquest.org/C004535/cell_membranes.html

http://www.biologymad.com/cells/cellmembrane.htm

http://www.wisegeek.com/what-is-membrane-permeability.htm

http://www.lsbu.ac.uk/water/hygel.html

http://www.gelatin.co.za/gltn1.html

http://www.gmap-gelatin.com/about_gelatin_comp.html