Cell junction
As cell contacts or cell connections ( engl. Cell junctions ) are called the direct points of contact of cells in tissues. All multicellular creatures form temporary or permanent cell contacts. The cell contacts are substantially formed by proteins, the cell adhesion molecules, on the one hand project from the cell surfaces and on the other hand form as intracellular anchor proteins cytoplasmic plaque. Their task is to hold together the fabric and allow cells to communicate with each other. Many of the cell adhesion molecules are transmembrane proteins, which protrude on both sides, the inside and outside of the cell membrane. These proteins can route signals from outside, for example from other cells into the interior, or to pass signals from the cell to the neighboring cells. Mediate cell adhesion molecules both contacts between cells and between cells and the extracellular matrix. A special feature are the channels forming transmembrane proteins of gap junctions, connexins and innexins. The cell contact generated from a certain cell density, cell contact inhibition.
- 3.1 adhesion proteins
- 3.2 anchor proteins
- 3.3 channel proteins
Differentiation of cell contacts
The cell contacts three major groups can be distinguished according to their function:
1 Occlusive compounds
Occlusive compounds (English: Occluding junctions ), also barriers contacts or impermeable compounds, bringing the cell interstices in close contact and control the flow of ions and molecules through the intercellular space.
- Zonula occludens or tight junction (mainly in vertebrates )
- Septate junction (mainly in invertebrates )
- Macula occludens
- Fascia occludens
2 -adhesive compounds
Adherent compounds, also adhesion compounds (English: Adhering junctions ) adhesion contacts or anchor links (English: Anchoring junctions ), the cells mechanically join. They allow so the intercellular cohesion, also called (cell) coherence. Two functional groups can be distinguished:
- Macula adherens ( desmosome = spot desmosome in the narrow sense )
- Adherens junctions (English: adherens junctions ) Adherens junction ( Gürteldesmosom )
- Punctum adhaerens ( Punktdesmosom )
- Fascia adherens ( Streifendesmosom )
- Hemidesmosome
- Focal adhesion
3 Communicating compounds
Communicating compounds (English: Communicating junctions ) or communication contacts allow the free flow of chemical or electrical signals ( ions and small molecules). Differences are:
- Gap junction ( Nexus )
- Synapse
- Plasmodesmos (with plants )
Purpose and function
The cohesion and communication between cells are the basic requirement for the development of complex organisms. Only then is a differentiation of the cells and thus a specialization of tissues allows to organs. The lipid bilayers of biological membranes are thin and can therefore be the major forces that are exerted on a cell cluster, not forward. Cell anchorage (English: Anchoring junctions ) solve this problem by connecting the cytoskeleton inside a cell with other cells or with the extracellular matrix.
Distinguishing the molecular structure
Adhesion proteins
The adhesion of adjacent cells is ensured by cell adhesion molecules (CAM ), the extracellular portions can connect to the same kind ( homophilic ) or with other types of CAMs ( heterophil ).
The molecular principles can be summarized as follows thereby simplified:
- Cadherins in the plasma membrane anchoring the cell to the plasma membrane of adjacent cells and are found in adherence compounds and desmosomes.
- Integrins in the plasma membrane anchor a cell with molecules of the extracellular matrix and are found in focal adhesions and hemidesmosomes.
Anchor proteins
- Claudine
Channel proteins
- Connexins