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| Gap junctions, also referred to as cell-to-cell channels, are present in most animal tissues and form aqueous channels between adjoining cells. Inorganic molecules as well as numerous [[Metabolites|metabolites]], such as [[Amino acids|amino acids and]] sugars, can pass through these channels. However, [[Macromolecules|macromolecules]], such as [[Proteins|proteins]] and [[Nucleic acids|nucleic acids]], cannot move across. Cell-to-cell channels allow communication between cells, including excitable cells. Gap junctions allow communication between cells in both directions. They also allow the spread of an extracellular signal; this is achieved by intracellular intermediaries, such as [[CAMP|cyclic AMP and]] [[Calcium|calcium ions]], moving between channels. <ref>Bruce Alberts et al, 2007. Molecular Biology of the Cell. 5th edition. USA: Garland Publishing Inc.</ref> One example of communication occurs in heart muscle cells, whereby a rapid flow of ions through these cells enables a speedy and coordinated response to a [[Stimulus|stimulus]], ultimately leading to contraction of the muscle. <ref>Berg J., Tymoczko J and Stryer L., 2007. Biochemistry. 7th edition. New York: WH Freeman</ref> <br>
| | See [[Gap Junction]] |
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| Specialised forms of [[Transmembrane proteins|transmembrane proteins]], called [[Connexins|connexins]], form gap junctions. Twelve connexin molecules assemble to form a gap junction. A single connexin molecule has four membrane spanning proteins. [[Connexons|Connexons]], also called hemichannels, are formed when six connexin molecules are arranged in a hexagonal structure; a cell-to-cell channel is formed when two connexons are aligned and joined together. <br>
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| Gap junctions differ from other membrane channels in a number of different ways. This includes cell-to-cell channels spanning across two membranes, instead of one, and channels forming between the cytoplasm of two cells, rather than to the extracellular matrix. <br>
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| An important point to note is that cell-to-cell channels are closed by high calcium and hydrogen ion concentrations; this mechanism protects healthy cells from damaged ones. <ref>Berg J., Tymoczko J and Stryer L., 2007. Biochemistry. 7th edition. New York: WH Freeman</ref><br>
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| = Refererences =
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| <references />
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Latest revision as of 09:30, 3 December 2016