Integral and peripheral membrane proteins

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=== Integral Membrane Proteins  ===
  
These are [[Proteins|proteins]] directly linked to the [[Plasma membrane|plasma membrane]] of [[Cells|cells]]; they do not have intermediate [[Molecules|molecules]] between them and the [[plasma membranes|plasma membranes]]. They are also considered as proteins that fully pass through the membrane ([[Carrier protein|carrier proteins]] and [[Channel protein|channel proteins]]).  
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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 multipass (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]].
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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:
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*they have a hydrophobic segment that can dive into the [[phospholipid|phospholipid]] layer
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*they are attached [[covalently|covalently]] to lipids of the bilayer
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*they are bind via an [[oligosaccharide|oligosaccharide]] linker(covalent interactions)<ref>Alberts B et al. Molecular Biology of the Cell. 6th ed., New York: Garland Science, Taylor  and; Francis Group, LLC. 2015</ref>.
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They do not readily dissociate 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  ===
 
=== Peripheral Membrane Proteins  ===
  
These proteins are connected to the plasma membrane through intermediate [[Molecules|molecules]] (even integral proteins) or proteins attached to only one side of the membrane; do not pass through the membrane <ref>Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002</ref>.<br>
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These proteins are connected to the plasma membrane through intermediate [[Molecules|molecules]] (even integral proteins) by [[noncovalent|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.
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=== Membrane proteins association with lipid bilayer  ===
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[[Image:Membrane proteins and lipid bilayer.png|frame|right|Figure 1. Various ways in which proteins associate with the lipid bilayer]]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 and Francis Group, LLC. 2015</ref>.  
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#single α-helix
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#multiple α-helices
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#β-barrel
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#association by a hydrophobic face of the α-helix
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#attached to a lipid
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#attached via oligosaccharide linker
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#8. membrane-associated proteins
  
=== Reference ===
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=== References ===
  
<references /><br>
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<references />

Latest revision as of 09:07, 10 December 2018

Contents

Integral Membrane Proteins

These are proteins directly linked to the plasma membrane of cells. They are also considered as proteins that fully pass through the membrane (carrier proteins and channel proteins). Transmembrane proteins can be single-pass, (pass through the membrane once), or multipass (pass through the membrane more than once). These transmembrane proteins have both hydrophilic and hydrophobic regions; they are amphiphilic[1]. 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[2]. The hydrophobic regions interact with the hydrophobic tails on lipids inside the membrane. The transmembrane domains are usually made up of alpha-helices, although can be made up of beta-sheets rolled up into a 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 do not readily dissociate 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 (even integral proteins) by 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

Figure 1. Various ways in which proteins associate with the lipid bilayer
Figure 1. Various ways in which proteins associate with the lipid bilayer[4].
  1. single α-helix
  2. multiple α-helices
  3. β-barrel
  4. association by a hydrophobic face of the α-helix
  5. attached to a lipid
  6. attached via oligosaccharide linker
  7. 8. membrane-associated proteins

References

  1. 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
  2. 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
  3. Alberts B et al. Molecular Biology of the Cell. 6th ed., New York: Garland Science, Taylor and; Francis Group, LLC. 2015
  4. Alberts B et al. Molecular Biology of the Cell. 6th ed., New York: Garland Science, Taylor and Francis Group, LLC. 2015
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