Functions of plasma membrane
In all cells the plasma membrane has several essential functions to perform. These include transporting nutrients into and metabolic wastes out of the cell preventing unwanted materials from entering the cell. In short, the intercellular and intra cellular transport is regulated by plasma membrane. The plasma membrane maintains the proper ionic composition pH(~7.2) and osmotic pressure of the cytosol. To carry out all these functions, the plasma membrane contains specific trasport proteins that permit the passage of certain small molecules but not others. Several of these proteins use the energy relaeased by ATP hydrolysis to pump ions and other molecules into or out of the cell against concentration gradients. Small charged molecules such as ATP and amino acids can diffuse freely within the cytosol but are restricted in their ability to leave or enter it across the plasma membrane.
In addition to these universal functions, the plasma membrane has other important functions to perform. Enzymes bound to the plasma membrane catalyze reactions that would occur with difficulty in an aqueous environment. The plasma membranes of many types of eukaryotic cells also contain receptor proteins that bind specific signalling molecules like hormones, growth factors, neurotransmitters etc. leading to various cellular responses.
Like the entire cell, each organelle in eukaryotic cells is bounded by a unit membrane containing a unique set of proteins essential for its proper functioning.
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