Difference between revisions of "Smooth endoplasmic reticulum"

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'''Definition'''
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=== Definition ===
  
''noun''
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'''noun'''
  
(cell biology) (A part of) [[endoplasmic reticulum]] that is [[tubular]] in form (rather than sheet-like) and lacks [[ribosomes]], and is associated with [[lipid]] synthesis, [[carbohydrate]] metabolism, [[calcium]] concentration, [[drug]] [[detoxification]], and attachment of [[receptor]]s on [[cell membrane]] [[proteins]]
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''plural: smooth endoplasmic reticula''
  
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(''cell biology'') (A part of) [[endoplasmic reticulum]] that is [[tubular]] in form (rather than sheet-like) and lacks [[ribosomes]], and is associated with [[lipid]] synthesis, [[carbohydrate]] metabolism, [[calcium]] concentration, [[drug]] [[detoxification]], and attachment of [[receptor]]s on [[cell membrane]] [[proteins]]
  
 
'''Supplement'''
 
  
The [[endoplasmic reticulum]] (ER) is an organelle made up of a network of flattened sacs or tubules. The membranes of the ER are connected to the [[nuclear membrane]] and run through the cytoplasm. There are two types of ER: (1) the rough endoplasmic reticulum (rER) and (2) the smooth endoplasmic reticulum (sER).
 
  
The sER is seen connected to the [[nuclear envelope]], and consists of [[tubule]]s and [[vesicle]]s that branch forming a [[network]] to increase surface area for the action or storage of key [[enzymes]]. Its functions include [[lipid]] synthesis, [[carbohydrate]] metabolism, [[calcium]] concentration, [[drug]] [[detoxification]], and attachment of [[receptor]]s on [[cell membrane]] [[proteins]]. It contains the [[enzyme]] Glucose-6-phosphatase (which converts glucose-6-phosphate to [[glucose]]), a step in [[gluconeogenesis]]. A specialized form of SER (called [[sarcoplasmic reticulum]]) occurs in [[muscle]] cells where [[calcium]] ions are stored. It is also abundant in [[hepatocytes]] to process and detoxify [[lipophilic]] drugs. In muscle cells, the smooth endoplasmic reticulum is called [[sarcoplasmic reticulum]].
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== Details ==
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=== Overview ===
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Endoplasmic reticulum is one of the most prominent organelles of a eukaryotic cell. The endoplasmic reticulum (ER) is an [[organelle]] that occurs as interconnected network of flattened sacs or tubules (called [[cisterna]]e) in the cytoplasm. The membranes of the ER are connected to the outer [[nuclear envelope]]. They may also extend into the cell membrane. The ER is one of the three components of the GERL system, in which the Golgi apparatus and the lysosomes are the other components. It is found in different cell types. However, it is absent in red blood cells and spermatozoa. There are two kinds of ER: the rER, or the [[rough endoplasmic reticulum]], and the sER, or the [[smooth endoplasmic reticulum]].
  
  
''Abbreviation / Acronym:'' sER
 
  
''Synonym(s):''  
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=== Characteristics ===
* [[agranular endoplasmic reticulum]]
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The sER is seen connected to the [[nuclear envelope]], and consists of [[tubule]]s and [[vesicle]]s that branch forming a [[network]] to increase surface area for the action or storage of key [[enzymes]]. The sER, as opposed to the [[rough endoplasmic reticulum]], does not have [[ribosomes]] on its surface, thus the name ''smooth''.
''Compare:''  
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=== Type(s) ===
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A specialized type of SER occurs in [[muscle]] cells where [[calcium]] ions are stored. It releases calcium ions during muscle contraction and absorb them during relaxation. The regulation of calcium ion level has to be regulated. Too much calcium inside the cell could lead to ''calcification'' and hardening of intracellular structures, and eventually to cell death. In muscle cells, this smooth endoplasmic reticulum is referred to as ''[[sarcoplasmic reticulum]]''.
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=== Biological functions ===
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The major functions of sER include [[lipid]] synthesis, [[carbohydrate]] metabolism, regulation of intracellular [[calcium]] concentration, [[drug]] [[detoxification]], and attachment of [[receptor]]s on [[cell membrane]] [[proteins]]. In carbohydrate metabolism, the sER contains the [[enzyme]] ''glucose-6-phosphatase'' that converts glucose-6-phosphate to [[glucose]], a step in [[gluconeogenesis]]. In drug detoxification, the sER is capable of detoxifying lipophilic drugs. Thus, it can be seen abundant in [[hepatocyte]]s. Other specialized cells with abundant sER are cells of [[sebaceous gland]]s and [[gonad cell]]s (e.g. [[testes]] and [[ovaries]]). At the cellular level, sER is involved in the ''intracellular transport'' of materials. For instance, it [[transport]]s the products of the rER to other [[cell]] parts like [[Golgi apparatus]].
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=== Common biological reactions  ===
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==== Lipid synthesis and transport ====
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sER is the major site of lipid synthesis, particularly at the ''membrane contact sites'' (MCS). MCS are areas where ER membranes make close contact with other cytoplasmic organelles, such as [[Golgi]], [[mitochondria]], [[lysosome]]s, [[peroxisome]]s, [[endosome]]s, [[chloroplast]]s, and [[plasma membrane]], and allow the transfer of substances. In particular, contact sites between ER and mitochondria allow the synthesis of [[phospholipid]]s.
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== Supplementary ==
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=== Abbreviation(s) ===
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* sER
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=== Synonym(s) ===
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* agranular endoplasmic reticulum
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== Further reading ==
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=== Compare ===
 
* [[rough endoplasmic reticulum]]
 
* [[rough endoplasmic reticulum]]
''See also:''
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=== See also ===
 
* [[endoplasmic reticulum]]
 
* [[endoplasmic reticulum]]
 
* [[sarcoplasmic reticulum]]
 
* [[sarcoplasmic reticulum]]
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© Biology Online. Content provided and moderated by '''[https://www.biology-online.org/about/ Biology Online Editors]'''
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Latest revision as of 23:59, 17 August 2019

Definition

noun

plural: smooth endoplasmic reticula

(cell biology) (A part of) endoplasmic reticulum that is tubular in form (rather than sheet-like) and lacks ribosomes, and is associated with lipid synthesis, carbohydrate metabolism, calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins


Details

Overview

Endoplasmic reticulum is one of the most prominent organelles of a eukaryotic cell. The endoplasmic reticulum (ER) is an organelle that occurs as interconnected network of flattened sacs or tubules (called cisternae) in the cytoplasm. The membranes of the ER are connected to the outer nuclear envelope. They may also extend into the cell membrane. The ER is one of the three components of the GERL system, in which the Golgi apparatus and the lysosomes are the other components. It is found in different cell types. However, it is absent in red blood cells and spermatozoa. There are two kinds of ER: the rER, or the rough endoplasmic reticulum, and the sER, or the smooth endoplasmic reticulum.


Characteristics

The sER is seen connected to the nuclear envelope, and consists of tubules and vesicles that branch forming a network to increase surface area for the action or storage of key enzymes. The sER, as opposed to the rough endoplasmic reticulum, does not have ribosomes on its surface, thus the name smooth.


Type(s)

A specialized type of SER occurs in muscle cells where calcium ions are stored. It releases calcium ions during muscle contraction and absorb them during relaxation. The regulation of calcium ion level has to be regulated. Too much calcium inside the cell could lead to calcification and hardening of intracellular structures, and eventually to cell death. In muscle cells, this smooth endoplasmic reticulum is referred to as sarcoplasmic reticulum.


Biological functions

The major functions of sER include lipid synthesis, carbohydrate metabolism, regulation of intracellular calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins. In carbohydrate metabolism, the sER contains the enzyme glucose-6-phosphatase that converts glucose-6-phosphate to glucose, a step in gluconeogenesis. In drug detoxification, the sER is capable of detoxifying lipophilic drugs. Thus, it can be seen abundant in hepatocytes. Other specialized cells with abundant sER are cells of sebaceous glands and gonad cells (e.g. testes and ovaries). At the cellular level, sER is involved in the intracellular transport of materials. For instance, it transports the products of the rER to other cell parts like Golgi apparatus.


Common biological reactions

Lipid synthesis and transport

sER is the major site of lipid synthesis, particularly at the membrane contact sites (MCS). MCS are areas where ER membranes make close contact with other cytoplasmic organelles, such as Golgi, mitochondria, lysosomes, peroxisomes, endosomes, chloroplasts, and plasma membrane, and allow the transfer of substances. In particular, contact sites between ER and mitochondria allow the synthesis of phospholipids.


Supplementary

Abbreviation(s)

  • sER

Synonym(s)

  • agranular endoplasmic reticulum


Further reading

Compare

See also



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