Intro | Cytoplasm | Endoplasmic Reticulum | Golgi Complex | Microtubules | Mitochondria | Nucleus | Plasma Membrane | Ribosomes
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Endoplasmic Reticulum (ER) is an extensive system of parallel and folded membranes found within a neuron. Rough endoplasmic reticulum is covered with ribosomes, the site of protein synthesis, whereas smooth endoplasmic reticulum (without ribosomes) is the site for lipid synthesis. Proteins produced within rough ER will be exported (secreted) outside of the neuron, used within the cell to guide the production of neurotransmitters, or used within the plasma membrane of the neuron. The endoplasmic reticulum forms a network of tubes that isolate, modify, store, and transport newly synthesized proteins and lipids to other locations within the cell.
The membrane of rough endoplasmic reticulum (rER) is continuous with the nuclear membrane, a relationship which likely aids in the transport of ribosomes from the nucleolus within the nucleus to the membrane of the endoplasmic reticulum where they produce proteins (Arms & Camp, 1995). The protein modifications that take place within rER include the removal of unwanted amino acids, the folding of proteins into more complex structures (such as the alpha-helix or beta pleated-sheet), and the addition of sugars. Smooth endoplasmic reticulum (sER) is merely a continuation of rER with the absence of ribosomes. In addition to lipid synthesis, sER is involved in the synthesis of steroid hormones and the detoxification of drugs.
Arms, K. & Camp, P. (1995), Biology (4th ed.). New York: Harcourt Brace College Publishers.