• Smooth Endoplasmic Reticulum (SER)
  • Involved in synthesis and processing of hydrophobic compounds (lipids, phospholipids, cholesterol derivatives)
  • Contains enzymes for steroid and phospholipid biosynthesis (e.g., 21-hydroxylase)
  • Key in steroidogenesis, particularly in steroid-producing cells (adrenals, gonads, liver)
  • Associated with conditions like virilization due to androgen-secreting tumors and paraneoplastic syndromes
• Rough Endoplasmic Reticulum (RER)
  • Characterized by numerous ribosomes on its outer membrane
  • They synthesize secretory proteins, the integral membrane proteins of the nucleus and cell membrane, and proteins within the ER, Golgi network, and lysosomes.
• Free ribosomes remain floating in the cytosol throughout protein synthesis. They are responsible for translating proteins found within the cytosol, nucleosol, peroxisome matrix, and nuclear-encoded mitochondrial proteins