The cell membrane structure-Fluid mosaic model.

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The cell membrane structure-Fluid mosaic model The cell membrane separates a watery cytoplasm from a watery external environment also known as ECF. The phospholipids are arranged in a double layer (lipid layer) with the hydrophilic heads facing outward (cytoplasm or ECF) and the hydrophilic tails turned in towards each other. The unsaturated fatty acids are not bonded to each other and form a fluid. Fluid Mosaic model. The term "fluid" is used because the phospholipid molecules and proteins that make up the membrane are free to drift around in fluid motion. The term "mosaic" is used to describe the position of the protein molecules. The molecules are placed randomly and there is no set pattern.


Some of the proteins extending into the ECF have carbohydrates attached (glycoprotein) The cell membrane has various functions. One of the most important is to isolate the cytoplasm from the external environment. In order to do this, the cells must be able to retain precious nutrients and eliminate wastes. Also, substances that are fat soluble (e.g. vitamins A, D and E) pass through easily but they are rare in the cell's environment because they are not water soluble. Substances which are water soluble such as salts, amino acids and sugars, cannot dissolve in lipids and so cannot pass through the bilayer. A second important function of the cell membrane is to regulate the flow of materials into and out of the cell.


Last, but not least, cell membranes have the function to communicate with other cells. For example, proteins (i.e. glycoprotein) that stick out of the ECF enable the cell to communicate with other cells. E.g. Glycoproteins on red blood cells determine blood type and serve as identification markers. Glycoproteins bind hormones such as insulin and trigger a metabolic change in the cell. Cholesterol is also found on within the cell membranes. Its function is to help keep membrane fluid. At low temperatures cholesterol keeps the phospholipids apart. This keeps the membrane fluid. At high temperatures (around 37C) it attracts the phospholipids and helps stabilize the membrane. The cell membrane is the only thing between a cell and its outside environment. It has the crucial role to play in the life of a cell: it must control what enters and leave s the cell.

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