Experiment 2 (Group3)

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Text of Experiment 2 (Group3)

PERMEABILITY PROPERTIES I: ARTIFICIAL MEMBRANESCargando, Debei Fajardo, Laiza Ferrer, Liezel Pajarillaga, Shara Ramos, Angeli

INTRODUCTION

MEMBRANE PERMEABILITY Quality of

a cells plasma membrane that allows substances to pass in and out of the cell have SELECTIVE PERMEABILITY.

Cell membranes

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

Dependent

upon the bilayer structure of the cell

membrane

CELL MEMBRANEbarrier 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

phospholipidpolar, 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 proteinsfunctions: (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 40C 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.

Maintain distance

Soln B Soln A

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

0.5 ml Soln ASoln 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+ + ClAgNO3 + 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 ABB

Amount of Silver Nitrate (uL)

Computed moles of Cl

725250

??

General Formula:

Conversion factor: Each 50 L portion of AgNO3 represent 1 mg of NaCl / mL Simple conversion

Molecula r weight AgNO3 + Cl- AgCl- + NO3-

COMPUTATIONS

For Soln A:725

= 2.48 x 10 -4 mol Cl-

COMPUTATIONS

For Soln BB:250

= 8.55 x 10 -5 mol Cl-

Solution A BB

Amount of Silver Nitrate (uL) 725 250

Computed moles of Cl 2.48 x 10 -4 8.55 x 10 -5

GIBBS-DONNAN RULEthe 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 semipermeable 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

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