Integral and peripheral membrane proteins

2018-12-09T20:48:26Z

180596106: added missing information and attached a picture showing the content of the page

=== Integral Membrane Proteins ===

These are [[Protein|proteins]] directly linked to the [[Plasma membrane|plasma membrane]] of [[Cells|cells]]. They are also considered as proteins that fully pass through the membrane ([[Carrier proteins|carrier proteins]] and [[Channel proteins|channel proteins]]). Transmembrane proteins can be single-pass, (pass through the membrane once), or mulitpass (pass through the membrane more than once). These [[Transmembrane proteins|transmembrane proteins]] have both [[Hydrophillic|hydrophilic]] and [[Hydrophobic|hydrophobic]] regions; they are [[Amphiphilic|amphiphilic]]<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2008) Molecular Biology of the Cell, 5th Edition, Pages 629-630, New York: Garland Science</ref>. The hydrophobic regions are the regions inside the lipid membrane, so they are kept away from water, whereas the hydrophilic regions are on either side of the membrane<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2008) Molecular Biology of the Cell, 5th Edition, Pages 630, New York: Garland Science</ref>. The hydrophobic regions interact with the hydrophobic tails on [[Phospholipid|lipids]] inside the membrane. The transmembrane domains are usually made up of [[Alpha-helix|alpha-helices]], although can be made up of [[Beta-sheet|beta-sheets]] rolled up into a [[Beta Barrel|beta-barrell]].

There is also a group of proteins that do not cross the lipid bilayer but are attached to only one side of it. That can be because:

*they have a hydrophobic segment that can dive into the [https://teaching.ncl.ac.uk/bms/wiki/index.php/Phospholipid phospholipid] layer
*they are attached [https://teaching.ncl.ac.uk/bms/wiki/index.php/Covalent covalently] to lipids of the bilayer
*they are bind via an [https://teaching.ncl.ac.uk/bms/wiki/index.php/Oligosaccharide oligosaccharide] linker(covalent interactions)<ref>Alberts B et al. Molecular Biology of the Cell. 6th ed., New York: Garland Science, Taylor &amp;amp;amp;amp;amp;amp;amp; Francis group, LLC. 2015</ref>

They do not readily disocciate with the cell membrane, and can therefore only be separated from the plasma membrane through the use of detergents (and other agents) to disrupt the plasma membrane.

=== Peripheral Membrane Proteins ===

These proteins are connected to the plasma membrane through intermediate [[Molecules|molecules]] (even integral proteins) by [https://teaching.ncl.ac.uk/bms/wiki/index.php/Noncovalent_bonds noncovalent ]interactions. They are released from the plasma membrane by agents that disrupts protein-protein interactions, e.g. by simply increasing the salt concentration of the buffer solution which the cells are suspended in. 

=== Membrane proteins association with lipid bilayer ===

====== [[Image:Membrane proteins and lipid bilayer.png|frame|left]]Figure 1. Various ways in which proteins associate with the lipid bilayer<ref>Alberts B et al. Molecular Biology of the Cell. 6th ed., New York: Garland Science, Taylor &amp;amp;amp;amp;amp;amp; Francis group, LLC. 2015</ref> ======

#single  α-helix
#multiple  α-helices
#β-barrel
#association by a hydrophobic face of the α-helix
#attached to a lipid
#attached via oligosaccharide linker
#8. membrane-associated proteins

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====== References ======

<references />

File:Membrane proteins and lipid bilayer.png

2018-12-09T20:25:51Z

180596106: Membrane proteins association with lipid bilayer

Membrane proteins association with lipid bilayer

The School of Biomedical Sciences Wiki - User contributions [en]

Integral and peripheral membrane proteins

File:Membrane proteins and lipid bilayer.png