THE plasma membrane or plasmalemma it is a cellular envelope present in all living cells, whether they are prokaryotes or eukaryotes.
General characteristics of the plasma membrane
It is between 6 and 9 nm and, because it is so thin, it can only be seen through an electron microscope that magnifies thousands of times more than a light microscope.
Even under an electron microscope, the plasmalemma is only seen as a thin light layer between two darker lines that delimit the cell.
The most abundant components found in plasma membranes are the phospholipids and the proteins, that's why the constitution of the membrane is known as lipoprotein.
These molecules are extremely well organized in the plasma membrane, each phospholipid has a polar part (hydrophilic – with affinity for water) and a non-polar part (hydrophobic – repels water).
They are arranged in two layers, one next to the other, juxtaposed and with the hydrophobic parts in contact.
Encrusted in the lipid bilayer layer are proteins, which can be integral, that is, fully inserted into the membrane, or peripheral, housed only at the ends.
This membrane model is known as fluid mosaic and was proposed by Singer and Nicholson.
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In addition to involving, protecting and shaping, the plasma membrane plays an essential role in the exchange of substances between cells.
While phospholipids guarantee the structure of the membrane, proteins assume the role of transporters.
Fat-soluble substances are able to cross the plasma membrane through the lipid bilayer, whereas the larger substances, and even water, only cross the membrane through the proteins and tenuous channels present. in them.
Protein Functions
- Accession: proteins from adjacent cells can adhere to each other, “joining” the two cells together.
- Anchorage: function as cytoskeleton.
- Recipients: select the substances that will be received by the cell.
- Recognition: some membranes have glycoproteins that act as recognition markers for other cells.
- Transport: Proteins are directly involved in active membrane transport.
- enzymatic: some proteins can act alone in metabolic pathways.
Plasma Membrane Specializations
Plasma membranes coat living cells and in many of them they need to acquire some special feature, these adaptations are called membrane specializations. plasmatic. The four specializations are:
- eyelashes and scourges: are cell expansions with high mobility, work well in mobile cells (such as unicellular organisms or male gametic cells).
- Microvilli: Finger-like enlargement of the cell surface, released into the extracellular medium, causing the contact surface to be enlarged.
- demossomes: Provide greater fixation of the cell with its surroundings, each desmosome is composed of two halves, each of which belongs to one of the cells.
- Interdigitations: Communication of cells in a tissue, make a perfect fit of protrusions and recesses.
See too:
- prokaryote cell
- prokaryote cell
- animal cell
- plant cell
- Cytology
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