Four Main Types of Junctions in Multicellular Organisms Essays

Four Main Types of Junctions in Multicellular Organisms Essays

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There are four main types of junctions in multicellular organisms, Anchoring Junctions, Occluding junctions, Channel-forming junctions and Signal-relaying junctions.

Anchoring junctions include cell-to-cell adhesion and cell-to-matrix adhesions, and are bound to the cytoskeleton filaments inside of a cell. (Cadherin & integrin proteins)
Cadherins bind with actin filaments to form adherens junctions and bind with intermediate filaments to form desmosomes, both of which are cell-to-cell adhesions. Integrins can also bind with actin filaments to form actin-linked cell-matrix adhesions or bind with intermediate filaments forming hemidesmosomes, both of which are cell-to-matrix adhesions.

Cadherins are so called as they utilize calcium ions to work properly. Without Ca+, most would fall apart while others also need the inclusion of trypsin, a protease, to completely cleave the cell adhesion molecules and separate the cell. This is often used when animal cells are split after growing in culture. Cadherins are utilized during embryo development. If anti-cadherin antibodies are added to the growth media of an embryo, then the cells will fall apart. Also, if a mutation has occurred in E-cadherin, then early in development an embryo will fall apart and die.
The first three cadherin types were named after the tissue that they were found in, although they were later found to be present in other tissues. E-cadherin was found in epithelial tissue, P-cadherin was found in the placenta and epidermis, and N-cadherin was found in the nerves and muscle tissue.
Cadherins have an extracellular motif that vary in number between each type. They then have a transmembrane domain and varying intracellular domains. The intracellular ...

... middle of paper ...

... to occur if the tight junctions are relaxed.
The main protein involved in tight junctions are claudins. The other proteins involved are tricellulin, which seals the junction between 3 adjoining cells, and occludin. The claudins on one cell form long chains and bind with claudins on neighboring cells to form a tight barrier between plasma membranes. The different observed permeabilities of the tight junctions can be attributed to the ratios of the different types of claudins used in the junction.
The entire complex of tight junctions, desmosomes and adherens form the junctional complex and are thought to help reinforce each other. For instance, if an anti-cadherin antibody is used to prevent adherens from forming, then the tight junctions will not form either. Also, tight junctions are oriented towards the apical end of the cell by Tjp, tight junction proteins.

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