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Just like you , early investigators had lots of questions about the structure and chemical composition of the cell membrane and how these properties could account for differences in the membrane's permeability to different type of molecules.

At least one of these researchers, Ernest Overton of the University of Zurich, realized that systematic differences in the permeability of the membrane to solutes that varied in size, charge and lipid solubility (how well they dissolved in lipids relative to water) could provide insight into the membrane’s biochemical composition. That is, information about the membrane’s permeability to molecules of varied chemical properties could reveal biochemical properties of the biological molecules forming the membrane itself.

After investigating the permeability of a large variety of cell types to hundreds of different compounds, Overton eventually deduced the general chemical properties of the cell membrane and from this correctly predicted the type of biological molecule from which the membrane must be primarily formed (De Weer, 2000)! Interestingly, and as so often happens in science, Overton’s original research question had nothing to do with investigating properties of the cell membrane. Rather his pursuit of this question bloomed from research on heredity for which he needed a traceable material that would pass through the plant cell membrane (Eichman, 2007).

Unfortunately, Overton never published the detailed results of these studies so his data are no longer with us (De Weer, 2000). Data similar to Overton’s do exist, however, and an example taken from a paper published in 1937 based on work conducted on alga cells is presented in figure below.

Relationship between the permeability (log cm/hr) of the plasma membrane of cells of the alga Chara ceratophylla to non-ionic, organic solutes and the solute’s a) size as indicated by the relative size of the bubble (molecular mass; grams/mole); the larger the bubble the larger the solute and b) solubility in oil relative to water (log). Low values of oil to water solubility (ex. 0.001) indicate virtually no solubility in lipids and very high solubility in water. Increasing values indicate an increasing solubility in oil relative to water. Data from Collander (1937).

What do these data suggest to you about the biochemical properties of the cell membrane and, in turn, the type of biological molecule from which the cell membrane is constructed? To answer this question, review the figure above and work through the questions below.

1. a. Carefully review the figure legend, axes labels and the data presented. In a sentence or two, describe what relationship, if any, there is between membrane permeability and the oil to water solubility of a solute.

2. Describe what relationship, if any, there is between cell permeability and solute size. To answer this question, work through the series of questions below.

  • a) On a piece of paper, sketch what the above figure is expected to look like if permeability increases with increasing solute size. (Assume the relationship between permeability and solubility is the same as above.)
  • b) On a piece of paper, sketch what the above figure is expected to look like if permeability decreases with increasing solute size. (Assume the relationship between permeability and solubility is the same as above.)
  • c) Does the actual relationship between permeability and solute size match either hypothesis you sketched in response to parts a and b? Please explain.
  • d) What do the data presented in figure 1 and your answer to part c suggest about the relationship between cell permeability and solute size? Please explain in a sentence or two.

3. Consider what you know about hydrophobic and hydrophilic molecular interactions together with the results you described in questions 1 and 2 above. What do these results collectively suggest, if anything, about the type of biological molecules that form the cell membrane (i.e. the biochemical composition)? Please explain how the data support your conclusion.

4. An undisturbed cell membrane is generally impermeable to ions. Does your description of the cell membrane from question 3 account for this? Please explain.

5. If your description of the cell membrane cannot account for the observation that undisturbed cell membranes are generally impermeable to ions, please amend it so that it does.

6. Early on scientists knew that water, a very small polar molecule, could diffuse across the membrane although this problem was ignored for many years. Can your description of the properties of the cell membrane the account for the cell membrane’s permeability to water? Yes or no? Please explain.

    Works cited

  • Collander, R. 1937. The permeability of plant protoplasts to non-electrolytes. Transactions of the Faraday Society. 33:985-990.
  • De Weer, P. 2000. A century of thinking about cell membranes. Annual Review of Physiology. 62:919-926.
  • Eichman, P. 2007. (External Link) . SHiPS Resource Center for Sociology, History and Philosophy in Science Teaching

Questions & Answers

Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
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Brian Reply
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Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
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LITNING Reply
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LITNING
scanning tunneling microscope
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Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
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Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
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Adin Reply
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Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
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Kyle
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Joe
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research.net
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Introduction about quantum dots in nanotechnology
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Source:  OpenStax, Discovering the structure of the plasma membrane. OpenStax CNX. Oct 15, 2007 Download for free at http://cnx.org/content/col10470/1.1
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