Endoplasmic Reticulum

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<sup></sup>The Endoplasmic Reticulum (ER) is an organelle found in all [[Eukaryotic cells|Eukaryotic cells]]. &nbsp;It is made up of a network of interconnected tubules and [[Cisternae|cisternae]] held together by the [[Cytoskeleton|cytoskeleton]]&nbsp;and is roughly 100nm in depth. The organelle has many distinct layers which fold and are shaped to create a maze-like structure.&nbsp;The ER and [[Nuclear membrane|nuclear membrane]] form and enclosed internal space called the [[ER lumen|ER lumen]]. &nbsp;The ER is involved in many general functions in the cell. &nbsp;Its main function is the synthesis of both [[Lipid|lipids]] and [[Proteins|proteins]] and serves as site of production for most of the cells organelles, including itself&nbsp;<ref>E Bittar, N Bittar, (1995) p190-211</ref>; Specialized Regions of ER serves as a store of [[Calcium|Ca]]<sup>[[Calcium|2+]]</sup><sup></sup><sup></sup>&nbsp;that is used in cell signalling and muscle contraction&nbsp;<ref>Alberts B, (2002) p723</ref>.  
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The Endoplasmic Reticulum (ER) is an organelle found in all [[Eukaryotic cells|Eukaryotic cells]]. It is made up of a network of interconnected tubules and [[Cisternae|cisternae]] held together by the [[Cytoskeleton|cytoskeleton]] and is roughly 100nm in depth. The organelle has many distinct layers which fold and are shaped to create a maze-like structure. The ER and [[Nuclear membrane|nuclear membrane]] form an enclosed internal space called the [[ER lumen|ER lumen]]. The ER is involved in many general functions in the cell. Its main function is the synthesis of both [[Lipid|lipids]] and [[Proteins|proteins]] and serves as a site of production for most of the cell's organelles, including itself<ref>E Bittar, N Bittar, (1995) p190-211</ref>.;Specialized Regions of ER serves as a store of [[Calcium|Ca<sup>2+</sup>]] that is used in cell signalling and muscle contraction<ref>Alberts B, (2002) p723</ref>.  
  
Distinct regions of the ER become highly specialized to meet the needs of the functional demands of the [[Cell|cell]]. &nbsp;There are three types are Endoplasmic Reticulum, [[Smooth Endoplasmic Reticulum|Smooth Endoplasmic Reticulum]] (SER), [[Rough Endoplasmic Reticulum|Rough Endoplasmic Reticulum]] (RER), and [[Sarcoplasmic Reticulum|Sarcoplasmic Reticulum]]. &nbsp;RER is coated in&nbsp;[[Ribosomes|ribosomes]] giving it its rough appearance and is involved in protein synthesis. Regions of ER that lack [[Ribosome|ribosomes]] are called SER, however most ER is usually partly smooth and partly rough. The SER is where the vesicles carrying newly synthesied proteins bud off &nbsp;as well as various other metabolic processes like drug detoixification, carbohydrates and steroid metabolism and Ca<sup>2+</sup> regulation<ref>Alberts B, (2002)</ref>.&nbsp;Sarcoplasmic Reticulum is modified smooth ER specialised for the pumping and storing of [[Calcium|Ca]]<sup>[[Calcium|2+]]</sup> storage <ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2002) Molecular Biology of the Cell, Fifth Edition, New York, Garland Science.</ref>&nbsp;<ref>Lodish H, (2003) Molecular Cell Biology, 5th Edition. W. H. Freeman</ref>&nbsp;<ref>Bittar E, Bittar N (1995). Cellular Organelles, Elsevier Science, P190-211</ref>.  
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Distinct regions of the ER become highly specialized to meet the needs of the functional demands of the [[Cell|cell]]. There are three types are Endoplasmic Reticulum, [[Smooth Endoplasmic Reticulum|Smooth Endoplasmic Reticulum]] (SER), [[Rough Endoplasmic Reticulum|Rough Endoplasmic Reticulum]] (RER), and [[Sarcoplasmic Reticulum|Sarcoplasmic Reticulum]]. RER is coated in [[Ribosomes|ribosomes]] giving it its rough appearance and is involved in protein synthesis. Regions of ER that lack [[Ribosome|ribosomes]] are called SER, however, most ER is usually partly smooth and partly rough. The SER is where the vesicles carrying newly synthesised proteins bud off as well as various other metabolic processes like drug detoxification, carbohydrates and steroid metabolism and Ca<sup>2+</sup> regulation<ref>Alberts B, (2002)</ref>. Sarcoplasmic Reticulum is modified smooth ER specialised for the pumping and storing of [[Calcium|Ca]]<sup>[[Calcium|2+]]</sup> storage<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2002) Molecular Biology of the Cell, Fifth Edition, New York, Garland Science.</ref><ref>Lodish H, (2003) Molecular Cell Biology, 5th Edition. W. H. Freeman</ref><ref>Bittar E, Bittar N (1995). Cellular Organelles, Elsevier Science, P190-211</ref>.  
  
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>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>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>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>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>
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The endoplasmic reticulum (ER) is a feature of all [[Eukaryotic cells|eukaryotic cells]], its 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<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<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724</ref>. ,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<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]]<ref>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<ref>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]] <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<ref>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<ref>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<ref>Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p726</ref>.  
  
 
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Latest revision as of 20:41, 6 December 2018

The Endoplasmic Reticulum (ER) is an organelle found in all Eukaryotic cells. It is made up of a network of interconnected tubules and cisternae held together by the cytoskeleton and is roughly 100nm in depth. The organelle has many distinct layers which fold and are shaped to create a maze-like structure. The ER and nuclear membrane form an enclosed internal space called the ER lumen. The ER is involved in many general functions in the cell. Its main function is the synthesis of both lipids and proteins and serves as a site of production for most of the cell's organelles, including itself[1].;Specialized Regions of ER serves as a store of Ca2+ that is used in cell signalling and muscle contraction[2].

Distinct regions of the ER become highly specialized to meet the needs of the functional demands of the cell. There are three types are Endoplasmic Reticulum, Smooth Endoplasmic Reticulum (SER), Rough Endoplasmic Reticulum (RER), and Sarcoplasmic Reticulum. RER is coated in ribosomes giving it its rough appearance and is involved in protein synthesis. Regions of ER that lack ribosomes are called SER, however, most ER is usually partly smooth and partly rough. The SER is where the vesicles carrying newly synthesised proteins bud off as well as various other metabolic processes like drug detoxification, carbohydrates and steroid metabolism and Ca2+ regulation[3]. Sarcoplasmic Reticulum is modified smooth ER specialised for the pumping and storing of Ca2+ storage[4][5][6].

The endoplasmic reticulum (ER) is a feature of all eukaryotic cells, its 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[7]. The ER can be rough (rough endoplasmic reticulum) in which ribosomes coat the surface of the ER[8]. ,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[9]. Cells that produce a lot of specific proteins to be secreted have an abundance of rough ER[10]. Modifications of proteins to be secreted such as glycosylation or formation of disulphide bonds take place in the lumen of the ER[11]. 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 [12]. Here they are modified further, before being transported to their final destination[13]. 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[14]. 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[15].

References

  1. E Bittar, N Bittar, (1995) p190-211
  2. Alberts B, (2002) p723
  3. Alberts B, (2002)
  4. Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P. (2002) Molecular Biology of the Cell, Fifth Edition, New York, Garland Science.
  5. Lodish H, (2003) Molecular Cell Biology, 5th Edition. W. H. Freeman
  6. Bittar E, Bittar N (1995). Cellular Organelles, Elsevier Science, P190-211
  7. Alberts, Johnson, Lewis, Raff, Roberts, Walter(2008)Molecular Biology of the Cell,5th Edition, New York: Garland Science p723
  8. Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724
  9. Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p724
  10. Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376
  11. Lodish,Berk,Kaiser,Krieger,Scott,Bretscher,Ploegh,Matsudaira(2008) Molecular Cell Biology,6th Edition,New York:W.H.Freeman and Company p376
  12. Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p725
  13. Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, Matsudaira(2008) Molecular Cell Biology,6th Edition, New York: W.H.Freeman and Company p15
  14. Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p725
  15. Alberts,Johnson,Lewis,Raff,Roberts,Walter(2008)Molecular Biology of the Cell,5th Edition,New York:Garland Science p726
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