The ER was observed by light microscopy by Garnier in 1897, who coined the term ergastoplasm. The SER is especially abundant in mammalian liver and gonad cells. The SER lacks ribosomes and functions in lipid synthesis but not metabolism, the production of steroid hormones, and detoxification. The RER is especially prominent in cells such as hepatocytes. The outer ( cytosolic) face of the RER is studded with ribosomes that are the sites of protein synthesis. RER is found mainly toward the nucleus of cell and SER towards the cell membrane or plasma membrane of cell. Different types of cells contain different ratios of the two types of ER depending on the activities of the cell. The two types of ER share many of the same proteins and engage in certain common activities such as the synthesis of certain lipids and cholesterol. The endoplasmic reticulum is not found in red blood cells, or spermatozoa. The membranes of the ER are continuous with the outer nuclear membrane. ![]() The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae (in the RER), and tubular structures in the SER. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( RER), and smooth endoplasmic reticulum ( SER). The endoplasmic reticulum ( ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. ![]() Dark small circles in the network are mitochondria. Micrograph of rough endoplasmic reticulum network around the nucleus (shown in the lower right-hand area of the picture). Cytosol (fluid that contains organelles with which, comprises cytoplasm).
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