Cell junction
Encyclopedia
A cell junction is a type of structure that exists within the tissue
of a some multicellular organism
(- for example true for animal
s, but not plant
s, which possess plasmodesmata
instead). Cell junctions consist of protein complexes and provide contact between neighbouring cells
or between a cell and the extracellular matrix
. They also build up the paracellular barrier of epithelia and control the paracellular transport
. Cell junctions are especially abundant in epithelial
tissues.
In vertebrate
s, there are three major types of cell junctions:
Invertebrates have several other types of specific junctions, for example Septate junctions or the CeAJ (C. elegans
apical junction).
s. There are four main types: selectins, cadherins, integrins, and the immunoglobulin superfamily
.
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
of a some multicellular organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
(- for example true for animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, but not plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s, which possess plasmodesmata
Plasmodesmata
Plasmodesmata are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Species that have plasmodesmata include members of the Charophyceae, Charales and Coleochaetales , as well as all embryophytes, better known...
instead). Cell junctions consist of protein complexes and provide contact between neighbouring cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
or between a cell and the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
. They also build up the paracellular barrier of epithelia and control the paracellular transport
Paracellular transport
Paracellular transport refers to the transfer of substances between cells of an epithelium.It is in contrast to "transcellular transport", where the substances travel through the cell, passing through both the apical membrane and basolateral membrane....
. Cell junctions are especially abundant in epithelial
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
tissues.
In vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, there are three major types of cell junctions:
- Adherens junctionAdherens junctionAdherens junctions are protein complexes that occur at cell–cell junctions in epithelial tissues, usually more basal than tight junctions...
s and DesmosomeDesmosomeA desmosome , also known as macula adherens , is a cell structure specialized for cell-to-cell adhesion...
s (Anchoring Junctions) - Gap junctionGap junctionA gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells....
s (Communicating Junction) - Tight junctionTight junctionTight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates...
s (Occluding Junctions)
Invertebrates have several other types of specific junctions, for example Septate junctions or the CeAJ (C. elegans
Caenorhabditis elegans
Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
apical junction).
Cell junction molecules
The molecules responsible for creating cell junctions include various cell adhesion moleculeCell adhesion molecule
Cell Adhesion Molecules are proteins located on the cell surface involved with the binding with other cells or with the extracellular matrix in the process called cell adhesion....
s. There are four main types: selectins, cadherins, integrins, and the immunoglobulin superfamily
Immunoglobulin superfamily
The immunoglobulin superfamily is a large group of cell surface and soluble proteins that are involved in the recognition, binding, or adhesion processes of cells. Molecules are categorized as members of this superfamily based on shared structural features with immunoglobulins ; they all possess a...
.