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The Path to the Fluid Mosaic Model

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Onna W

on 10 April 2013

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Transcript of The Path to the Fluid Mosaic Model

The Path to the Fluid Mosaic Model Introduction References: The cell membrane is essential in separating the cell's contents and extracellular fluid, thus, creating a barrier. The cell membrane is composed of many proteins and a lipid bilayer. This also allows for the cell membrane to be semi-permeable, being highly selective of what is allowed to diffuse across the membrane. As a result, the cell membrane is vital for the cell to survive. Throughout the presentation, the contribution of each scientist that assisted with the development of the cell membrane is explained thoroughly. Figure 1: Benjamin Franklin
Image from :http:/www.biography.com/people/benjamin-franklin-9301234 Benjamin Franklin (1706 - 1790) Lord Rayleigh (1842 - 1919) Conclusion Neurotransmitters “Benjamin Franklin.” History. 1996-2013. Web. 6 April 2013. <http://www.history.com>
“Cell membrane is patterned like a patchwork quilt.” Max-Planck Gesellschaft. 2012. Web. 7 April 2013.
< http://www.mpg.de >
Edidin, Michael. “Lipids on the frontier: a century of cell membrane bilayers. 2003. Web.
5 April 2013. < http://www.uni-bonn.de >
Eichman, Philip. From the Lipid Bilayer to the Fluid Mosaic: A Brief History of Membrane Models.
SHiPS Resource Center for Sociology, History and Philosophy in Science Teaching. Web.
5 April 2013. < http://www1.umn.edu >
“George E. Palade EM Slide Collection.” Harvey Cushing/John Hay Whitney Medical Library.
Web. 6 April 2013. < http://library.medicine.yale.edu >
Harth, Richard. “New Membrane Research Takes Shape.” Illinois Institute of technology. 2012. Web.
4 April 2013. < http://www.iit.edu >
“History of the Study of Membranes.” Web. 5 April 2013. < http://www.willamette.edu/ >
“Lipids and Membranes.” 2012. Web. 5 April 2013. < http://saf.bio.caltech.edu >
"Lord Rayleigh - Biography". Nobelprize.org. Web. 6 Apr 2013 <http://www.nobelprize.org>
Scarc. “The Meyer-Overton Theory of Anesthesia.” The Pauling Blog. 2009. Web. 6 April 2013.
< http://paulingblog.wordpress.com >
Stark, Anne M. “ New look at cell membrane reveals surprising organization.” Lawrence Livermore
National Laboratory. Web. 8 April 2013. < www.llnl.gov >
Wightman, James. “Surface Chemistry Advances Have Come with Collaboration and, even, Gallantry.
Science From Virginia Tech. 2002. Web. 4 April 2012. < http://www.research.vt.edu/ > Agnes Pockels (1862 - 1935) Figure 5:
Image from: http://www.agnespockelslabor.de/en/agnes.html Charles Ernest Overton (1865 - 1933) Son of Samuel Charlesworth Overton and Harriet Jane Fox; closely related to Charles Darwin.
Working on doctorate degree in University of Zurich when Lord Rayleigh was experimenting on films.
Studied biology, especially botany, which is the study of plants.
Came up with 3 theories: lipid theory of cell permeability; lipid theory of narcosis; involvement of an Na+/K+ exchange in muscle & nerve excitability.
Found that substances that can pass through membrane was related to chemical nature.
Discovered that non polar substances pass quickly through membrane into cell.
Hypothesized similarities between fatty liquids and cell membranes as well as the transport through membranes depended on polarity of substance.
Did comparison of tested solutes led to conclusion that permeability not dependant on molecular size.
Plant and various animal cells shared same rapid permeability for lower alcohols, ether, chloroform, etc selective permeability appeared to be general property of all types of cells.
Investigated osmotic properties of cells & noticed in late 19th century that permeation of molecules through membranes related to partition coefficient b/e water & oil.
Overton’s rule forms the foundation of the solubility-diffusion permeability model.
Hypothesis led to theory, now called Overton’s lipod (or lipid) theory of plasma permeability.
Which involved a thin membrane surrounded by cells having properties of oil
-> He called the layers surrounding cells “lipoids”, which are made from lipids & cholesterol.
Was unable to finish proof of his theory, causing people to doubt his work, especially since he did not respond to critics about his theory. However, later studies confirmed Overton’s theory of plasma permeability.
Also carried out experiments involving muscle cells, which led to another hypothesis of muscle fibers becoming permeable to sodium and potassium ions.
-> This theory was proven fifty years later by by A. L. Hodgkin and A. F. Huxley, for which they were awarded the Nobel Prize in physiology or medicine in 1963.
Also came up with theory for anesthesia, which is called Meyer-Overton theory due to another scientists coming up with a similar theory at the time. The theory claims “Neurotransmittersd state and the pNeurotransmitter transporters are a class of membrane transport proteins that span the cellular membranes of neurons. Their primary function is to carry neurotransmitters across these membranes and to direct their further transport to specific intracellular locationsatient is rendered unconscious“(Scarc 4 June 2009). Irving Langmuir (1881 - 1957) Ernest Gorter (1881-1954) and F. Grendel
Ernest Gorter was a pediatrician and professor at University of Leiden
Francois Grendel was Gorter’s assistant.
They worked on many experiments together
In 1925, Gorter and Grendel published a paper on extracting lipids with acetone from red blood cells by spreading lipids as a monolayer on water.
Red blood cells, which they referred to as chromocytes, were used because red blood cells have no nucleus and other organelles.
Gorter and Grendel used a modified version of Langmuir’s trough to demonstrate that lipid mplecules could form bilayers as well as a monolayer.
This also helped them in showing that the surface area of the lipids extracted from the red blood cells was about twice the surface area of the cells itself.
As a result of the data collected and repeated studies with red blood cells from a variety of animals (ex: human, dogs, rabbit etc.) Gorter and Grendel concluded that chromocytes are covered by a layer of fatty substances that is two molecules thick. They also proposed that this double layer is constructed in a way that the two lipid bilayers are oriented with the polar head groups pointed towards the aqueous environment.
However, both scientists did not fully extract the lipids and the surface area of the red blood cells was underestimated, which caused in their results to be inaccurate. However, these two factors were able to cancel each other out, allowing for their conclusions to be correct.
Gorter and Grendel’s idea of a lipid bilayer became the basis for future models of the cell membrane structure. James Danielli. (1911-1984) Edmund. Newton Harvey (1887-1969), and Hugh Davson (1909-1996) 1935: First membrane model to be accepted by majority of scientists
James Danielli work was mostly related to biology, even though he was a trained physical chemist.
Danielli worked with Ernest Newton Harvey, who was an expert in the area of cell surface studies. While Danielli was working with Harvey, Hugh Davson was working as a physiologist at the University College in London.
Danielli found that oil droplets obtained from mackerel eggs can absorb proteins; this information was used later for determining tension at surface of mackerel egg oil.
The model was developed by Danielli and Davson.
The model was known as the “sandwich” model, which was a “sandwich” like model that consisted of lipids, arranged as a bilayer, in which the lipid heads were covered by proteins. Protein lined pores account for small molecules to move easily through the membrane.
In the published papers regarding this model, Danielli and Davson made some considerations such as: since the lipid layer consists of charged head groups or amphiphilic groups, this implies that the lipid membrane contains some water, hydrophobic molecules can go through membranes through the lipophilic liquid part, and many more.
Danielli and Davson also considered that proteins may arrange in a “mosaic” like pattern, however, they lacked the evidence to support such as idea. J. David Robertson (Unkown-1995) Figure 16: J. David Robertson
Image from: http://elprofedebiolo.blogspot.ca/2010/01/estructura-y-composicion-de-la-membrana.html George E. Palade (1912-2008) Figure 18 : George E. Palade
Image from: http://www.nndb.com/people/225/000130832/ Figure 20: Jonathan Singer & Garth Nicolson
Image from: http://elprofedebiolo.blogspot.ca/2010/01/estructura-y-composicion-de-la-membrana.html Born as John William Strutt to John James Strutt and Clara Elizabeth La Touche.
Awarded the Copley, Royal, and Rumford Medals of the Royal Society.
1904: Awarded Nobel Prize for "his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies". (“The Nobel Prize in Physics 1904: Lord Rayleigh”, 2013).
A century later after Benjamin Franklin’s experiment of dropping oil into water, Lord Rayleigh performed a similar experiment. He conducted his experiments in a round sponge bath. Lord Rayleigh placed a droplet of olive oil, approximately 0.81 mg, into a bath and the oil continued to spread until the surface area of the bath was entirely covered, which had a diameter of approximately 80cm to 100cm. He performed this numerous times to ensure that his results were accurate. Through this experiment, Lord Rayleigh was able to measure the thickness of a film of olive oil, which he proposed to be one molecule thick.
1890: Lord Rayleigh published his results about conducting a series of quantitative experiments involving olive oil and water. Lord Rayleigh’s published articles sparked the interest of a young German woman, Agnes Pockels.
Pockels wrote a letter to Lord Rayleigh describing the results of her own experiments. The letter was in German and he had his wife translate the letter to him. Once translated, the letter had mentioned a device designed by Pockels herself. This device was used to measure differences in surface tension between water while it contained different things.
Lord Rayleigh was impressed by Pockels work and continued to conduct more experiments, this time, with more accurate results, based on the information that Pockels had observed on her own. Also, he was so impressed by her work that he sent it to a scientific journal, Nature, to have her work published. Image from : http://www.ob-ultrasound.net/rayleigh.html Figure 3: Lord Rayleigh Son of Josiah Franklin and Abiah Folger.
“Benjamin Franklin is the only founding father to have signed all four of the key documents establishing in the U.S.: the Declaration of Independence (1776), the Treaty of Alliance with France (1778), the Treaty of Paris establishing peace with Great Britain (1783), and the U.S. Constitution (1787).” (“Benjamin Franklin” 1996 -2013).
Lived a very eventful life as he first started as a printer in Philadelphia and travelled between United States of America and Great Britain. During his travels, he acquired numerous titles for himself, such as a member of the Continental Congress to being president of the Supreme Executive Council of Pennsylvania. Not only was he a scientist, he was a politician, an author, and an inventor.
1757: He was sent by American House of Assembly of Philadelphia to Great Britain to fulfill a duty. A fleet of 96 ships travelled alongside Benjamin Franklin. Ships were rocking vigorously out at sea, except for two. He noticed and questioned the captain about it. The captain simply replied that the cooks dumped greasy water through scuppers to allow for a more calming effect of the boat during windy storms at sea. Curious, as all scientists are, he began to do experiments relating to this concept. Even though he did not agree with the concept of using grease to calm the ship, he had no other explanation for why that occurred the way it did.
Added a small amount of olive oil into a pond when he was staying in England.
He noticed that the oil spread in a thin film over the surface of water, until the portion of the pond was “as smooth as a looking glass”.
He also noticed that the oil did not mix with the water, thus, forming a think film over the water. Born in Venice to Theodor Pockels, Austrian soldier, and wife Adwine. Family is German, but father was stationed in Italy at the time.
Family moved to Braunschweig due to malaria outbreak and poor health, causing her father to retire early. Once there, Pockels attended school, which she discovered to have an interest in physics and often discussed it with her brother, Friedrich. However, at that time, girls did not enter university for education. When girls were allowed to attend school, Pockels was denied the option because she had to care for her parents, thus, spending most her life at home to care for her family. However, her brother provided her with news regarding the physics world.
One day, Pockels was washing dishes and an idea strikes her. She was curious about what happens to the water when washing dishes.
1880: Pockels began studying the effects of substances on water and surface tension.
"A rectangular tin trough, 70 cm. long, 5 cm. wide, 2 cm. high, is filled with water to the brim, and a strip of tin about 1 1/2 cm. wide laid across it perpendicular to its length, so that the under side of the strip is in contact with the surface of the water, and divides it into two halves. By shifting this partition to the right or left, the surface on either side can be lengthened or shortened in any proportion, and the amount of the displacement may be read off on a scale held along the front of the trough." (“Agnes Pockels – Making History at the Kitchen Sink”).
1891: Pockels wrote a letter in German to Lord Rayleigh, which he had translated. The letter described her research and experiments done in her kitchen. She had designed a device that consisted of a tin trough and a movable strip of tin on top. This device was used to measure differences in surface tension between water containing different things.
Through her results, she observed: how the surface tension of the water behaved, how surface tensions vary with different soluble elements, effects of solid bodies contacting the surface, and many more.
After Lord Rayleigh read Pockel’s letter, he sent it to a scientific journal, Nature, to have it published. In his letter to Nature, he mentioned that his work and Pockel’s were quite similar and the he would repeat or further improve his own experiments based on her research.
Pockel’s trough was later improved by Irving Langmuir, which is currently now called the Langmuir trough. However, Langmuir gave credit to Pockels when publishing his work.
1892-1899: Publication of other articles by Pockels.
1931: Awarded Laura Leonard Award (age 70). Wolfgang Ostwald published an article in tribute of Pockels’ work.
1932: Received honorary PhD from Technical University of Braunschweig.
1933: Publication of 16th and last article. Figure 7: Charles Ernest Overton
Image from: http://paulingblog.wordpress.com/tag/charles-ernest-overton/ Figure 9: Irving Langmuir
Image from: http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1932/langmuir-bio.html Jonathan Singer (1924-Present( and Garth Nicolson (Unknown) Figure 8: Solubility diffusion model; Circles represent lipid head groups while grey regions represent hydrophobic regions
Image from:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908771/figure/A002188F2/ American chemist & physicist
1932: Nobel prize for discoveries and investigations of surface chemistry.
1917: Published paper proposing that fatty acid molecules are oriented in such a way that the hydrocarbon chains are faced away from water while the polar groups are in contact with the surface of the water. When substance placed in water, hydrophobic ends will stay away from water while hydrophilic ends tend towards water.
Worked in laboratories of General Electric, did research on molecular monolayers as well as studied the works of Lord Rayleigh, and Agnes Pockels.
An assistant worked alongside Langmuir, Katherine Blodgett (1898 -1979).
With their joint research, Langmuir and Blodgett were both able to demonstrate what the orientation of monolayers would be when placed in hydrophilic solutions as well as stack monolayers to any thickness desired. That product is now known as the Langmuir-Blodgett film.
Langmuir also developed the Langmuir film balance to measure surface tension.
Used an improved model of Agnes Pockels’ trough that she developed in her kitchen, now referred to as Langmuir’s trough, to make measurements of surface areas occupied by known quantities of oil.
The Langmuir Trough is used to control the spreading of oil on a water surface. The barrier on the instrument is moved to cause a defined lateral pressure against the oil layers(Edidin 2003).
Katherine Blodgett (1898 -1979): first female to be hired at GE.
Was able to coat glass and reduce glare for many applications using lenses.
Assisted Irving Langmuir in developing a method to measure thickness of film. Figure 10: Katherine Blodgett
Image from: http://i1010.photobucket.com/albums/af222/shawncamp/BOS7/BOS-1920/img0006A.jpg Figure 11: The Langmuir Trough; used to control spreading of oil on water surface.
Image from: http://newton.ex.ac.uk/research/biomedical-old/membranes/images/X-Ray_diagram.jpg Figure 12: Red Blood Cells
Image from: http://topnews.in/healthcare/sites/default/files/red-blood-cells.jpg Figure 13: Lipid Bilayer; Circles represent hydrophilic heads and lines represent hydrophobic tails.
Image from: http://www1.umn.edu/ships/9-2/membrane.htm Figure 2: Modern video showing the oil water calming effect that Benjamin Franklin first did. Figure 4: Shows oil dropping into water.
Image from: http://www.wired.com/images_blogs/wiredscience/2009/11/oil_and_water-660x369.jpg Figure 6: Original trough designed by Agnes Pockels in her kitchen.
Image from: http://www.agnespockelslabor.de/en/xb-ap-rinne.jpg Figure 14: Danielli-Davson Model
Image from:http://www1.umn.edu/ships/9-2/membfig4.gif Figure 15: Danielli-Davson Model again.
Image from: http://avonapbio.pbworks.com/f/ddm.png 1957: J. David Robertson proposed a modified version of the membrane model.
He called it the “unit membrane” and was developed through studies conducted under electron microscope.
While observing the cell membrane under high magnification, Robertson noticed that there were two dark outer lines present and a lighter inner region.
The two outer darker lines are protein layers while the inner region is the lipid bilayer, according to the unit membrane model.
Also, Robertson came up with a statement regarding the cell membrane. The statement was meant to describe that cellular membranes are built with this similar structure.
During the 1960’s and early 1970’s, biologists would describe the membrane as a “lipo-protein sandwich”.
Overall, J. David Robertson confirmed most of the theories from previous scientists and built upon evidence and developed a better understanding of the cell membrane. Figure 17 : Two opposing plasma membranes showing double layer of membrane.
Image from: http://2.bp.blogspot.com/-ZgQfpyJXfnM/UQVIvt8ZCHI/AAAAAAAASPI/04GffQQPQSM/s640/la+membrana+celular.jpg American biochemists
1972: presented the model for cell membranes used today, the Fluid Mosaic Model.
The model still consists of the basic lipid bilayer structure, which was first proposed by Gorter and Grendel, but modified by Danielli and Davson.
Hydrophilic regions of the lipid bilayer face the aqueous medium whereas hydrophobic regions interact with other hydrophobic regions within the membrane.
The proteins however, are thought to be globular in shape and they float within the lipid bilayer, not forming layers that result in the sandwich type model.
Proteins contain channels, or pores, to allow for passage of molecules across membrane.
The proteins can either be embedded within the lipid bilayer or on the membrane surface (integral- embedded within membrane or peripheral proteins-loosely attached to the membrane surface).
Singer and Nicolson also suggested that the entire membrane is fluid with floating proteins that are free to move within the bilayer.
The mosaic portion of the model comes from a mosaic like pattern arrangement of proteins and other molecules of the cell membrane. Nobel prize for Medicine or Physiology in 1974
Also won the Albert Lasker award for Basic Medical Research and the American National Medal of Science.
1950's-1960's: George E. Palade mapped the structure of mitochondria and showed that microsomes are a part of the internal cellular transport system, endoplasmic reticulum.
When working at The Rockefeller University, Palade used biochemistry along with electron microscopy to establish and define the function of many organelles found in the cell and cytoplasm structures, which was later called ribosomes.
Palade also developed understanding for how organelles cooperate to enable protein secretion, endocytosis, and membrane biogenesis, which is the development of living things. Modern Researchers of the Cell Membrane Mary Kraft, Peter Weber, and Josha Simmerberg:
Used advanced molecule imaging method to allow researchers to look at cell membrane itself and map a lipid on mouse cell membranes.
Sphingolipids thought to associate with cholesterol to form domains.
Found that cells low on cholesterol still formed domains.
"We found that the presence of domains was somewhat affected by cholesterol but was more affected by the cytoskeleton -- the protein network underneath the membrane," Kraft said. (Stark).
"Cholesterol abundance is important. You change that, you tremendously change cell function," Kraft said. (Stark). Figure 19: Electron Microscope
Image from: http://www.zimbio.com/Cell+Membranes+and+Adhesion/articles/Y-j8gJXBMcZ/Davson+Danielli+Model+Singer+Nicolson+Fluid Figure 21: The Fluid Mosaic Model
Image from: http://3.bp.blogspot.com/_REiD9wQqwZ4/TNmCDqWIe5I/AAAAAAAAACk/IYyw7ICtz8E/s1600/Cell+Membrane.gif Max Planck researchers:
Performed comprehensive analysis of molecular structure of cell membrane.
Used advanced imaging to view cell membrane and proteins within them.
"Each protein in the cell membrane is located in distinct areas that adopt a patch- or network-like structure. The entire cell membrane thus consists of domains – like a kind of molecular patchwork quilt." ("Cell Biology" 2012).
Researchers able to show that lipids play a huge role in cell membrane.
Different lipids accumulate around certain protein anchors.
This helps explain how cell membrane can self organize. In conclusion, the cell membrane is essential as it plays a vital role in cellular processes. Without a cell membrane, nothing would hold the organelles and contents within the cell together, resulting in cells unable to exist. Since every biological thing is made up of cells, without them, there would be no life. Therefore, the cell membrane creates the structure of the cell and is highly specific in what the membranes allow to diffuse across. Neurotransmitters are the chemicals which allow the transmission of signals from one neuron to the next across synapses, which is a junction between two nerve cells across which a nerve impulse passes from an axon terminal to a neuron, muscle cell, or gland cell.
"Neurotransmitter transporters are a class of membrane transport proteins that span the cellular membranes of neurons. Their primary function is to carry neurotransmitters across these membranes and to direct their further transport to specific intracellular locations" ("Neurotransmitter Transporter" 2013).
Therefore, neurotransmitter transporters also require a cell membrane in order to function properly. Without it, the body would not be able to receive these signals, thus, failing to function. Contributed in 1774 Contributed in 1890: Contributed in 1880-1891 Contributed in 1895-1899: Contributed in 1917: Contributed in 1925: Contributed in 1935: Contributed in 1957: Contributed in 1950's-1960's Contributed in 1972:
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