Protein 5. Enzymes 6. Cell Respiration 9. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Natural Selection 3. Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. Because they could measure the actual size surface area of a red blood cell and knew approximately how many of those cells they had in their sample , they could calculate the total surface area that would have to be covered by membrane.
When the two numbers were compared, it was clear that the amount of lipid they had extracted could cover twice the area needed to enclose all the cells. Why would there be so much? Additional experiments showed that lipids could spontaneously form a bilayer when mixed with water Figure 1.
Together, these observations suggested that there may be a simple explanation for the results with the red blood cells. The plasma membrane of these cells likely consists of a double layer of lipid surrounding each cell. As it happens, Gortner and Grendel made some errors in their experiment.
They failed to completely extract all the lipids from the cells, and they also underestimated the total surface area of the individual red blood cells. However, because these two errors canceled each other out, their final conclusions turned out to be correct, regardless of their miscalculations. Thereafter, the idea of a lipid bilayer became the basis for future models of membrane structure. Sadava When the use of electron microscopy started to allow examination of the plasma membrane at high resolution, people noticed that the image clearly showed three layers, not two.
In a key paper, Stoeckenius provided clear pictures of the three-layer structure. He then described in both words and diagrams how the lipid bilayer results in a three-layer image.
As it turns out, the inner and outer edges of the bilayer have a different composition than the interior. Under the view of the electron microscope, the outsides of the lipid bilayer show up as two darker layers, whereas the hydrophobic interior stains less densely, thus showing three apparent "layers" outside layers are represented as blue in Figure 1C.
The first clues to lipid bilayer structure came from results with red blood cell membranes. The ultimate discovery that the plasma membrane is a lipid bilayer with hydrophobic and hydrophilic properties changed the way this structure was viewed. Its semipermeable and liquid nature provided the groundwork for understanding both its physical and biological properties.
Edidin, M. Lipids on the frontier: a century of cell-membrane lipids Nature Reviews : Molecular Cell Biology 4 : — Gortner, E. On bimolecular layers of lipoids on the chromacytes of blood. Journal of Experimental Medicine 41 , — Langmuir, I. The constitution and fundamental properties of solids and liquids II: Liquids. Journal of the American Chemical Society 39 , — Overton, E. The probable origin and physiological significance of cellular osmotic properties.
Vierteljahrschrift der Naturforschende gesselschaft 44 , 88— In Biological Membrane Structure , trans. Park, R.
Boston: Little Brown, Sadava, D. Cell Biology, Organelle Structure and Function. Boston: Jones and Bartlett, Stoeckenius, W. Structure of the plasma membrane: An electron-microscope study. Circulation 26 , — Cell Membranes. Microtubules and Filaments. Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes. Plant Cells, Chloroplasts, and Cell Walls.
Cytokinesis Mechanisms in Yeast. How Viruses Hijack Endocytic Machinery. Discovering the Lipid Bilayer. Discovery of the Giant Mimivirus. Endosomes in Plants. Mitochondria and the Immune Response. What is the phospholipid bilayer? Now, let's take a look at the factors that influence membrane fluidity! Factor 1: The length of the fatty acid tail The length of the fatty acid tail impacts the fluidity of the membrane. Factor 2: Temperature As temperature increases, so does phospholipid bilayer fluidity.
Factor 3: Cholesterol content of the bilayer Cholesterol has a somewhat more complicated relationship with membrane fluidity. Factor 4: The degree of saturation of fatty acids tails Phospholipid tails can be saturated or unsaturated. In summary! Health Professions.
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