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The endoplasmic reticulum (ER) is a feature of all [[Eukaryotic_cells|eukaryotic cells]], thats main functions are its role in [[lipid|lipid]] and [[protein|protein]] biosynthesis and as a store for [[calcium|calcium]] within the cell. It is a network of internal membranes called cisternae which are continuous with the outer membrane&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p723</ref>. The ER can be rough ([[Rough endoplasmic reticulum|rough endoplasmic reticulum]]) in which [[ribosomes|ribosomes]] coat the surface of the ER&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724</ref>&nbsp;which synthesize [[proteins|proteins]] in the ER. In mammalian cells, synthesis of [[proteins|proteins]] is [[co-translational|co-translational]], which means [[proteins|proteins]] are captured from the [[cytosol|cytosol]] by the ER and imported into it before they are fully synthesized&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724</ref>. [[Cells|Cells]] that produce a lot of specific [[proteins|proteins]] to be secreted have an abundance of [[rough ER|rough ER]]&nbsp;<ref name="null">Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376</ref>. Modifications of proteins to be secreted such as [[glycosylation|glycosylation]] or formation of [[disulphide bonds|disulphide bonds]] take place in the lumen of the ER&nbsp;<ref name="null">Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376</ref>. The ER can also be smooth ([[smooth endoplasmic reticulum|smooth endoplasmic reticulum]]) which lack a coating of [[ribosomes|ribosomes]]. Transport vesicles bud off from the smooth ER, which carry the newly synthesized [[proteins|proteins]] and [[lipids|lipids]] and transport their contents to the [[Golgi apparatus|Golgi apparatus]]&nbsp;<ref name="null">Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p725</ref>. Here they are modified further, before being transported to their final destination&nbsp;<ref name="null">Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p15</ref>. As the ER is also a store of [[calcium|calcium]], the ER contains a [[calcium pump|calcium pump]] which transports [[calcium|calcium]] [[Ions|ions]] from the [[cytosol|cytosol]] into the ER lumen&nbsp;<ref name="null">Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p725</ref>. Cells which require rapid responses to extracellular signals, such as muscle cells, require transport of [[calcium|calcium]] [[ions|ions]] into the [[cytosol|cytosol]] from the ER (which is the uptaken back into the ER.) This is why muscle cells have many modified smooth ER, named the [[sarcoplasmic reticulum|sarcoplasmic reticulum]], so that [[calcium|calcium]] is available to trigger [[myofibril|myofibril]] contraction during muscle contraction&nbsp;<ref name="null">Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p726</ref>.<br>  
The endoplasmic reticulum (ER) is a feature of all [[Eukaryotic cells|eukaryotic cells]], thats main functions are its role in [[Lipid|lipid]] and [[Protein|protein]] biosynthesis and as a store for [[Calcium|calcium]] within the cell. It is a network of internal membranes called cisternae which are continuous with the outer membrane&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p723</ref>. The ER can be rough ([[Rough endoplasmic reticulum|rough endoplasmic reticulum]]) in which [[Ribosomes|ribosomes]] coat the surface of the ER&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724</ref>&nbsp;which synthesize [[Proteins|proteins]] in the ER. In mammalian cells, synthesis of [[Proteins|proteins]] is [[Co-translational|co-translational]], which means [[Proteins|proteins]] are captured from the [[Cytosol|cytosol]] by the ER and imported into it before they are fully synthesized&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724</ref>. [[Cells|Cells]] that produce a lot of specific [[Proteins|proteins]] to be secreted have an abundance of [[Rough ER|rough ER]]&nbsp;<ref name="null">Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376</ref>. Modifications of proteins to be secreted such as [[Glycosylation|glycosylation]] or formation of [[Disulphide bonds|disulphide bonds]] take place in the lumen of the ER&nbsp;<ref name="null">Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376</ref>. The ER can also be smooth ([[Smooth endoplasmic reticulum|smooth endoplasmic reticulum]]) which lack a coating of [[Ribosomes|ribosomes]]. Transport vesicles bud off from the smooth ER, which carry the newly synthesized [[Proteins|proteins]] and [[Lipids|lipids]] and transport their contents to the [[Golgi apparatus|Golgi apparatus]]&nbsp;<ref name="null">Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p725</ref>. Here they are modified further, before being transported to their final destination&nbsp;<ref name="null">Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p15</ref>. As the ER is also a store of [[Calcium|calcium]], the ER contains a [[Calcium pump|calcium pump]] which transports [[Calcium|calcium]] [[Ions|ions]] from the [[Cytosol|cytosol]] into the ER lumen&nbsp;<ref name="null">Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p725</ref>. Cells which require rapid responses to extracellular signals, such as muscle cells, require transport of [[Calcium|calcium]] [[Ions|ions]] into the [[Cytosol|cytosol]] from the ER (which is the uptaken back into the ER.) This is why muscle cells have many modified smooth ER, named the [[Sarcoplasmic reticulum|sarcoplasmic reticulum]], so that [[Calcium|calcium]] is available to trigger [[Myofibril|myofibril]] contraction during muscle contraction&nbsp;<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p726</ref>.<br>  


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

Revision as of 06:45, 30 November 2010

The endoplasmic reticulum (ER) is a feature of all eukaryotic cells, thats main functions are its role in lipid and protein biosynthesis and as a store for calcium within the cell. It is a network of internal membranes called cisternae which are continuous with the outer membrane [1]. The ER can be rough (rough endoplasmic reticulum) in which ribosomes coat the surface of the ER [2] which synthesize proteins in the ER. In mammalian cells, synthesis of proteins is co-translational, which means proteins are captured from the cytosol by the ER and imported into it before they are fully synthesized [3]. Cells that produce a lot of specific proteins to be secreted have an abundance of rough ER [4]. Modifications of proteins to be secreted such as glycosylation or formation of disulphide bonds take place in the lumen of the ER [4]. The ER can also be smooth (smooth endoplasmic reticulum) which lack a coating of ribosomes. Transport vesicles bud off from the smooth ER, which carry the newly synthesized proteins and lipids and transport their contents to the Golgi apparatus [4]. Here they are modified further, before being transported to their final destination [4]. As the ER is also a store of calcium, the ER contains a calcium pump which transports calcium ions from the cytosol into the ER lumen [4]. Cells which require rapid responses to extracellular signals, such as muscle cells, require transport of calcium ions into the cytosol from the ER (which is the uptaken back into the ER.) This is why muscle cells have many modified smooth ER, named the sarcoplasmic reticulum, so that calcium is available to trigger myofibril contraction during muscle contraction [5].

References

  1. ↑ Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p723
  2. ↑ Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724
  3. ↑ Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376 Cite error: Invalid <ref> tag; name "null" defined multiple times with different content
  5. ↑ Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p726


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