CELL MEMBRANES (STRUCTURE)
The cell surface (plasma) membrane surrounds all cells and control what enters and leaves the cell. Membranes are visible at TEM microscope magnifications of x100,000. The distance across the membranes is about 7nm.
Membranes are made up of two phospholipid layers, plus protein. The polar heads are hydrophilic and are attracted toward the water and cytoplasm. The hydrocarbon tails are hydrophobic and are held together by weak hydrophobic bonds. Proteins are scattered throughout the membrane, and transmembrane proteins pass through from one side to the other. Carbohydrates are attached to proteins (Glycoproteins) and lipids (Glycolipids) This structure is called the fluid mosaic model.
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