Plasma Membrane (Meaning and Explanation)

We explain what the plasma membrane is and what its structure is like. Furthermore, the main functions of this lipid layer.

What is the plasma membrane?

It is called plasma membrane, cell membrane, plasmalemma or cytoplasmic membrane a double layer of lipids that covers and delimits cells serving as a border between its interior and exterior, and also allowing a physicochemical balance between the environment and cell cytoplasm.

The plasma membrane is not visible under an optical microscope (it is visible under an electronic one), since It has an average thickness of 7.3 cubic nanometers. In plant and fungal cells, this membrane is located below the cell wall.

Selective permeability is the main characteristic of the plasma membrane I mean, its ability to allow or reject the entry of certain molecules into the cell, thus regulating the passage of water, nutrients or ionic salts, and always maintaining the cytoplasm in optimal conditions in terms of electrochemical potential (negatively charged), pH or concentration is concerned.

The latter occurs through two elementary absorption processes (or endocytosis) or expulsion (or exocytosis) of cellular substances, It can also release metabolic waste materials into the environment fruit of cellular respiration. To do this, small vesicles are formed in the plasma membrane and serve as a means of cellular transport.

An important dynamic in the case of cells or single-celled organisms that use their membrane to envelop (or phagocyter) nutrients or prey, or to expel harmful agents from a multicellular organism (as lymphocytes or white blood cells do).

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 same way. of a sandwich. These lipids are primarily cholesterol, phosphoglycerides and sphingolipids.

At the same time It has around 20% protein which 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.

Plasma membrane function

The plasma membrane has a different series of functions, such as:

Delimit 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 viruses.
Nutrient administration The selectivity of the membrane gives way to desired substances and denies them to unwanted ones, serving as a filter and transport between the outside and the inside, since it also allows the disposal 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 attempts to maintain a stable concentration of water and other substances in the cytoplasm. This also implies preserving its pH level and its electrochemical charge.
Cellular communication When faced with specific stimuli coming from outside the cell, the plasma membrane is capable of reacting, transmitting information to the interior of the cell and launching specific biochemical processes: cell division, cell movement or the segregation of biochemical substances.
Cellular movement In some cases the cell membrane elongates and allows the appearance of flagella (tails) or cilia (hairs) that allow the cell to physically move.