In cell biology, the biological membrane anatomy and functions are studied in detail. The overall plasma membrane functions (cell-to-cell recognition) depends on glycoproteins, and other carbohydrates present in the membrane. The percentage content of each of these components varies from one cell membrane to another. It basically consists of glycolipid, phospholipid, and cholesterol. In addition to the integral and membrane proteins, another major component is lipid. Since they are slightly exposed to the membrane parts of a cell, extraction of these proteins is possible through sophisticated laboratory procedures. They are attached to the hydrophilic lipid heads by hydrogen bonds or electrostatic bonds. If you analyze the model, you can identify them as those molecules that are projected slightly on the outer surface of the lipid bilayer. In contrary to the integral membrane proteins, peripheral ones are located at the periphery of the cellular membrane. Since the integral proteins are present within the lipid bilayer, their extraction is not possible. Amongst these, there are large protein molecules that extend on both sides of the phopholipid matrix, and collectively, they are known as tunnel proteins. As per the illustration of the model, almost 70% of the total proteins found in cell membrane are integral ones. The integral membrane proteins are present within the cell membrane. Formation of this bilayer is the base for the fluid mosaic model of the plasma membrane. Thus, the lipid bilayer is water repelling in nature, which allows the entry of only lipid soluble molecules. The result is a lipid bilayer with the polar and hydrophilic heads orienting outside, and the non-polar and hydrophobic tails pointing towards the inner side. The phospholipid layer folds upon itself due to its hydrophobic nature. In the membrane, the amphipatic lipid molecules arrange themselves in a specific manner. For your reference, the two integral components (lipid bilayer and proteins) of a cell membrane along with other substances are discussed below. Since the membrane contains various molecules (embedded protein, carbohydrate, cholesterol, etc), it is described as a mosaic. This is because of the sideways and lateral movements of protein and lipid molecules throughout the membrane, as per requirements of the cell. Regarding the term ‘fluid mosaic model’, the cell membrane is more like a fluid, rather than being a rigid or solid structure. In addition to cellular transport, cell membrane functions include recognition, adhesion, and signaling of cells. Hence, it is simply referred to as a semipermeable membrane. With reference to the model, the structure of this biological membrane is such that it only allows entry and exit of certain substances. It serves as a barrier between the cell interior and its surrounding. The plasma membrane is a unique component of both plant and animal cells. According to it, the cell membrane contains different types of protein and carbohydrate molecules embedded in a phospholipid bilayer. But, none of them are as acceptable as the fluid mosaic model. Besides this hypothesis, several theories pertaining to the plasma membrane structure have been developed. The model explains the structural components of biological membranes. In order to explain the structure and functions of biological membranes, the fluid mosaic model was proposed in 1972 by the researchers, S.J. This membrane not only serves as a protective covering for the cellular components, but also is a crucial structure for transportation of nutrients and communication between the cells. It holds true for both simple prokaryotic, as well as for the complex eukaryotic cells. The protoplasm of every living cell is enclosed by a plasma membrane.
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