Endoplasmic reticulum

It is a bag-shaped membranous structure surrounded by a single membrane, and its shape and size are not uniform. It is found in almost all cytoplasm. The rough endoplasmic reticulum is one in which ribosomes, which are ribonucleoprotein particles, are attached to the surface of the endoplasmic reticulum, and the smooth endoplasmic reticulum is one in which ribosomes are not attached. The rough endoplasmic reticulum is the site of protein synthesis, and is found in many cells with secretory functions. Ergastoplasma, as seen under an optical microscope, corresponds to a cluster of rough endoplasmic reticulum. Messenger RNA (ribonucleic acid) that receives information from nuclear DNA (deoxyribonucleic acid) attaches to the ribosomes of the rough endoplasmic reticulum, and transfer RNA carries amino acids from the cytoplasm according to the information. Using these amino acids as materials, the rough endoplasmic reticulum synthesizes proteins specific to that cell. On the other hand, the smooth endoplasmic reticulum is a branched and anastomosed tubular structure, in which enzymes necessary for the function are localized. These enzymes are involved in functions such as glycolysis and detoxification in the liver, steroid hormone synthesis in the gonads and adrenal glands, hydrochloric acid secretion in gastric glands, and calcium uptake and release in striated muscle.

[Yasushi Kobayashi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

一重膜で包まれ、袋の形をした膜状構造で、形や大きさは一定せず、ほとんどすべての細胞質内に存在する。小胞体の表面にリボ核タンパク粒子であるリボゾームが付着しているものを粗面小胞体とよび、リボゾームが付着していないものを滑面小胞体とよぶ。粗面小胞体はタンパク合成の場で、分泌機能をもつ細胞に多く含まれる。光学顕微鏡でいうエルガストプラズマは粗面小胞体の集塊に相当する。核DNA（デオキシリボ核酸）の情報を受け取った伝令RNA（リボ核酸）は粗面小胞体のリボゾームに付着し、転移RNAは情報に従って細胞質からアミノ酸を運ぶ。このアミノ酸を材料として、粗面小胞体はその細胞に特有なタンパクを合成する。一方、滑面小胞体は、分岐、吻合(ふんごう)した管状を呈し、この中には機能に応じて必要な酵素が局在している。それらの酵素は、肝の解糖と解毒、性腺(せいせん)や副腎(ふくじん)のステロイドホルモン合成、胃腺の塩酸分泌、横紋筋のカルシウムの取り込みと放出などの働きに関係がある。

［小林靖夫］

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