Endoplasmic reticulum

The endoplasmic reticulum (ER) is a part of a transportation system of the <a href="/facts/Eukaryote/SkwyPLMA">eukaryotic cell</a>, and has many other important functions such as <a href="/facts/Protein_folding/rf3nR2Y1">protein folding</a>. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for "little net". It is a type of <a href="/facts/Organelle/vhDFnGbs">organelle</a> made up of two subunits – rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER). The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as <a href="/facts/Cisterna/RKBv0AmH">cisternae</a> (in the RER), and tubular structures in the SER. The membranes of the ER are continuous with the outer <a href="/facts/Nuclear_membrane/IwRQ5BVL">nuclear membrane</a>. The endoplasmic reticulum is not found in <a href="/facts/Red_blood_cell/Kggpq8Jh">red blood cells</a>, or <a href="/facts/Spermatozoa/sTG4GWc0">spermatozoa</a>.
There are two types of ER that share many of the same <a href="/facts/Protein/Jxmagu3E">proteins</a> and engage in certain common activities such as the synthesis of certain <a href="/facts/Lipid/TdQR87HX">lipids</a> and <a href="/facts/Cholesterol/TnfPlYc1">cholesterol</a>. Different types of <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a> contain different ratios of the two types of ER depending on the activities of the cell. RER is found mainly toward the nucleus of the cell and SER towards the cell membrane or plasma membrane of cell.
The outer (<a href="/facts/Cytosol/VyXgygWm">cytosolic</a>) face of the RER is studded with <a href="/facts/Ribosome/CF2u2gtg">ribosomes</a> that are the sites of <a href="/facts/Protein_synthesis/P4IcGjPd">protein synthesis</a>. The RER is especially prominent in cells such as <a href="/facts/Hepatocyte/USpvDz1n">hepatocytes</a>. The SER lacks ribosomes and functions in <a href="/facts/Lipid/TdQR87HX">lipid</a> synthesis but not <a href="/facts/Metabolism/WxDrm8k5">metabolism</a>, the production of <a href="/facts/Steroid_hormone/WDtHmcTl">steroid hormones</a>, and <a href="/facts/Detoxification/SQzAYKQj">detoxification</a>. The SER is especially abundant in mammalian <a href="/facts/Liver/Rtp4Fk2b">liver</a> and <a href="/facts/Gonad/36BUam2x">gonad</a> cells.
The ER was observed by <a href="/facts/Light_microscopy/GpHlElDS">light microscopy</a> by Garnier in 1897, who coined the term ergastoplasm. The lacy membranes of the endoplasmic reticulum were first seen by <a href="/facts/Electron_microscopy/XtaBktwF">electron microscopy</a> in 1945 by <a href="/facts/Keith_R._Porter/f1CG8nRW">Keith R. Porter</a>, <a href="/facts/Albert_Claude/VsexEX6k">Albert Claude</a>, and Ernest F. Fullam.

Endoplasmic reticulum open-in-new

Endoplasmic reticulum