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Encyclopedia > Gap junction

A gap junction is a junction between certain animal/plant cell-types that allows different molecules and ions to pass freely between cells. The junction connects the cytoplasm of cells. One Gap junction is composed of two connexons (or hemichannels) which connect across the intercellular space. Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, and are sometimes called the building blocks of life. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... An ion is an atom or group of atoms with a net electric charge. ... Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells. ... In biology, a connexon is an assembly of 6 proteins called connexins that forms a bridge between the cytoplasm of two adjacent cells. ...


In vertebrates, gap junction hemichannels are primarily homo- or hetero-hexamers of connexin proteins. Invertebrate gap junctions comprise proteins from the hypothetical innexin family. However, the recently characterized pannexin family, functionally similar but genetically distinct from connexins and expressed in both vertebrates and invertebrates, probably encompases the innexins. Groups Conodonta Hyperoartia Petromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish) Galeaspida Pituriaspida Osteostraci Gnathostomata (jawed vertebrates) Placodermi Chondrichthyes (cartilaginous fish) Acanthodii Osteichthyes (bony fish) Actinopterygii (ray-finned fish) Sarcopterygii (lobe-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Tetrapoda Amphibia Amniota Sauropsida/(Reptiles) Aves (Birds) Synapsida Mammalia... Connexins are four-pass transmembrane proteins, six of which assemble to form a channel, a connexon. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. ...


Gap junctions formed from two identical hemichannels are called homotypic, while those with differing hemichannels are heterotypic. In turn, hemichannels of uniform connexin composition are called homomeric, while those with differing connexins are hetermeric.


Generally, the genes coding for gap junctions are classified in one of three groups, based on sequence similarity: A, B and C (for example, GJA1, GJC1). However, genes do not code directly for the expression of gap junctions; genes can only produce the proteins which make up gap junctions (connexins). An alternative naming system based on this protein's molecular weight is also popular (for example: connexin43, connexin30.3).


Gap junctions are particularly important in the cardiac muscle: the signal to contract is passed efficiently through the gap junctions, allowing the heart muscle cells to contract in tandem. However, gap junctions are now known to be expressed in virtually all tissues of the body, with the exception of motile cell types such as sperm or erythrocytes. The heart and lungs (from an older edition of Grays Anatomy) The heart (Latin cor) is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions. ... A sperm cell attempts to penetrate an ovum coat to fertilize it. ... Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen to body tissues via the blood. ...

Contents


Overview of levels of organization

  1. DNA to RNA to Connexin protein.
  2. One connexin protein has four transmembrane domains
  3. 6 Connexins create one Connexon (hemichannel). When different connexins join together to form one connexon, it is called a heteromeric connexon
  4. Two hemichannels, joined together across a cell membrane comprise a Gap Junction.
When two identical connexons come together to form a Gap junction, it is called a homotypic GJ. When one homomeric gap junction and one heteromeric gap junction come together, it is called a heterotypic gap junction. When two heteromeric connexons join, it is also called a heteromeric Gap Junction.

Properties

  1. Allows for direct electrical transmission between cells
  2. Allows of second messengers, such as IP3, Ca+2
  3. Allows for any molecule smaller than 1,000 Dalton to pass through

Areas of Electrical Coupling

Neurons

There is not much coupling between neurons in the brain. Hot spots include the vestibular nucleus, the nucleus of Trigeminal Nerve and the inferior olivary nucleus. There has been some observation of weak neuron to glial cell coupling in the locus coeruleus, and in the cerebellum between Purkinje neurons and Bergman glial cells.


Connexin Proteins expressed in Neurons

  1. mCX26
  2. mCX43
  3. mCX36
  4. mCX57
  5. mCX45
  6. PX1
  7. PX2

See also


An electrical synapse is a mechanical and electrically conductive link between two abutting neurons that is formed at a narrow gap between the pre- and postsynaptic cells known as a gap junction. ... Another, unrelated ion channeling process is part of ion implantation. ... Junctional complexes (JC) are the connections between two epithelial cells. ...

Cell junctions
Adherens junction - Desmosome - Hemidesmosome - Gap junction - Tight junction

  Results from FactBites:
 
Gap junction - Wikipedia, the free encyclopedia (576 words)
In vertebrates, gap junction hemichannels are primarily homo- or hetero-hexamers of connexin proteins.
Gap junctions formed from two identical hemichannels are called homotypic, while those with differing hemichannels are heterotypic.
Gap junctions are particularly important in the cardiac muscle: the signal to contract is passed efficiently through the gap junctions, allowing the heart muscle cells to contract in tandem.
  More results at FactBites »

 
 

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