Processes of the ER (RER and SER)

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Processes of the ER (RER and SER)
2013-11-12 11:30:06
Cell Bio Processes

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  1. N-linked glycosylation
    • -          the first seven sugars (5 mannose and 2-N-acetylglucosamine) are transferred one at a time by glycosyltransferase to dolichol phosphate, a phospholipid that is anchored to the ER membrane by a lipid anchor on the cytoplasmic side.
    • -          Dolichol phosphate then gets flipped across the membrane, and the remaining sugars (four mannose and three glucose residues) are added on the luminal side of the membrane
    • -          Once these sugars are added, an enzyme called oligosaccharylstransferase will transfer this oligosaccharide to the asparagines residue of a growing polypeptide chain. The asparagines residue is  Asp-X (any amino acid except proline)-Serine or Threonine
  2. Cholesterol synthesis (SER):
    • -          through a series of processes, acetate will be converted to cholesterol
    • -          two enzymes that take part in this are HMG-CoA reductase and squalene synthesase
    • -          The enzymes that are part of the process will contain their active sites in the cytoplasm, where the final product will end up
  3. Storage of Calcium Ions (SER)
    • -          calcium ions are stored in the SER, giving the SER a new name—the sarcoplasmic reticulum
    • -          When an impulse travels along tubular networks via a motor neuron, it will travel to the interior of the cell to the SR
    • -          This action potential will cause the calcium gates to fly open and the calcium ions to be released into the cytoplasm
    • -          At the end of the action potential, resting potential causes the calcium gates to close and calcium ions to be pumped (active transport) back into the SR
  4. Steroid synthesis in Adrenal Cortex  (SER)
    • -          cholesterol will enter the mitochondria of the adrenal cortex to begin the pathway
    • o   acetate can also begin the pathway by entering the SR of the adrenal cortex and being converted to cholesterol, which will then enter the pathway
    • -          Shuttling of intermediates back and forth between organelles must occur for its proper configuration
    • -          All cells of the adrenal cortex will carry out the pathway to progesterone. However, if making cortisol, the pathway continues in the mitochondria of the inner cortex. If making corticosterone or aldosterone, the pathway will continue in the mitochondria of the glomerulosa
    • Golgi Apparatus
    • Constitutive Pathway