This specificity helps to explain why human immunodeficiency virus (HIV) or any of the five types of hepatitis viruses invade only specific cells. Although they are highly specific, pathogens like viruses may evolve to exploit receptors to gain entry to a cell by mimicking the specific substance that the receptor is meant to bind.
Some recognition sites are used by viruses as attachment points. Receptors on the plasma membrane’s exterior surface interact with hormones or neurotransmitters, and allow their messages to be transmitted into the cell.
These metabolic pathways might be vital for providing the cell with energy, making specific substances for the cell, or breaking down cellular waste or toxins for disposal. For example, surface receptors of the membrane create changes in the interior, such as changes in enzymes of metabolic pathways. Each receptor is structured to bind with a specific substance. The plasma membrane also carries receptors, which are attachment sites for specific substances that interact with the cell. In addition, the surface of the plasma membrane carries markers that allow cells to recognize one another, which is vital as tissues and organs form during early development, and which later plays a role in the “self” versus “non-self” distinction of the immune response. These are the more obvious functions of a plasma membrane. The plasma membrane must be sufficiently flexible to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries.
Plasma membranes enclose the borders of cells, but rather than being a static bag, they are dynamic and constantly in flux. Cells exclude some substances, take in others, and excrete still others, all in controlled quantities. \)Ī cell’s plasma membrane defines the boundary of the cell and determines the nature of its contact with the environment.
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