Concept explainers
To write:
How the lipid bilayer creates the image of "railroad track".
Introduction:
Both the unicellular and multicellular organisms' cells are surrounded by the membrane known as plasma membrane or cell membrane. Plasma membrane can be defined as the cell outline or its borders, which give it a shape and determines the nature of its interaction with its environment.
Explanation of Solution
Any cell cannot live without a cell membrane due to the specific functions performed by it. They are necessary as like the DNA and proteins to the cell. The cell membrane is very flexible so that it can easily allow the specific substance to move inside and outside the cells. The surface of the plasma membrane carries markers, which allow the cells to recognize between the self and non-self during the tissue or organ formation. It is usually composed of proteins and phospholipids and exists as a lipid bilayer.
By using the electron micrographs, the bilayer structure of the cell membrane is defined. Cell membrane appears like two dense lines of the lipids which are separated by the intervening space. Morphologically this appears like a railroad track. This image formed by the binding of electron-dense heavy metals to the polar heads groups of the phospholipids which appear as dark or dense lines.
These lines are filled and separated by the lightly stained interior portion of the membrane, which consists of hydrophobic fatty acid chains. Phospholipids perform the function of barriers between the two aqueous compartments. Interior of the phospholipids is spaced by the hydrophobic fatty acids and impermeable to water soluble molecules.
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Hence, railroad track image is formed by the phospholipids as dark lines and hydrophobic fatty acids as the intervening space.
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