We explain what the plasma membrane is and what its structure is like. In addition, the main functions of this lipid layer.
What is the plasma membrane?
It is called the plasma membrane, cell membrane, plasmalemma or cytoplasmic membrane to a double layer of lipids that covers and delimits the cells, serving as a border between the interior and exterior of the same, and also allowing a physicochemical balance between environment and cytoplasm cell phone.
The plasma membrane is not visible under amicroscope optical (yes under an electronic one), as it has an average thickness of 7.3 cubic nanometers. In the vegetables cells and of the mushrooms, said membrane is located below the cell wall.
Selective permeability is the main characteristic of the plasma membrane, that is, your ability to allow or deny entry of molecules determined to the cell, thus regulating the passage of Water, of nutrients or ionic salts, and keeping the cytoplasm always in optimal conditions in terms of electrochemical potential (negatively charged), pH or concentration is concerned.
The latter occurs through two elementary processes of absorption (orendocytosis) or expulsion (orexocytosis) of cellular substances, and can also release environment metabolic waste materials, the result of cellular respiration. For this, small vesicles are formed in the plasma membrane and serve as a means of cell transport.
An important dynamic in the case of cells usingle-celled organisms that use their membrane to wrap (orphagocyter) nutrients or prey, or to expel from amulticellular organism those harmful agents (such as lymphocytes or white blood cells).
Structure of the plasma membrane
The plasma membrane is composed of two layers of lipids, which orient their hydrophilic polar heads (that is, they have an affinity for water) towards the inside of the cell, keeping their hydrophobic parts (which reject water) in contact, in the manner of a sandwich. These lipids are primarily cholesterol, phosphoglycerides, and sphingolipids.
At the same time it owns about 20% of protein, that fulfill functions of connection, transport and catalysis: diverse forms of biochemical communication and cellular transport of nutrients and waste. Likewise, the membrane has various carbohydrates (sugars), in its outermost part, serving as support material and intercellular identification. These sugars represent only 8% dry of the weight of the total membrane.
Function of the plasma membrane
The plasma membrane has a number of different functions, such as:
- Delineate the cell. Define and protect the cell from its environment, separating the outside from the inside and one cell from another (in the case of cellular tissues). It is the first defense barrier in case of invading agents, such as virus.
- Nutrient administration. The selectivity of the membrane gives way to substances and denies it to the unwanted ones, serving as a filter and transport between the outside and the inside, since it also allows to dispose of toxins and metabolic waste (such as CO2).
- Preservation of life. By exchanging fluids and substances between the cytoplasm and the environment, the plasma membrane seeks to keep the concentration of water and other substances in the cytoplasm stable. This also implies conserving its pH level and its electrochemical charge.
- Cellular communication. Faced with certain stimuli from outside the cell, the plasma membrane is capable of reacting, transmitting information inside the cell and setting in motion certain biochemical processes: cell division, cell movement or the segregation of biochemical substances.
- Cell displacement. In some cases the cellular membrane it lengthens and allows the appearance of flagella (tails) or cilia (hairs) that allow the cell to move physically.