Cell Structure: Endoplasmic Reticulum and Golgi Apparatus Study Notes

  1. Discuss the appearance of the endoplasmic reticulum in the cell.
    The endoplasmic reticulum (ER) is an elaborate membrane system that can occupy up to 50% of the total membrane surface area in animal cells. It extends from the nuclear envelope nearly to the plasma membrane, consisting of interconnecting channels or tubules that may expand to form flattened discs known as cisternae.

  2. Discuss the role of smooth ER in cell activities including lipid production and detoxification.
    The Smooth Endoplasmic Reticulum (SER) is agranular, lacking attached ribosomes, and is well-developed in cells that secrete lipids and steroids (e.g., adrenal cortex cells, Leydig cells, follicular cells). Its functions include lipid synthesis, steroid synthesis and secretion, carbohydrate metabolism, and detoxification (such as drug breakdown). It also plays a role in calcium ion accumulation, notably as the sarcoplasmic reticulum in muscle cells.

  3. Describe the structure of rough ER and explain its role in protein production.
    The Rough Endoplasmic Reticulum (RER) is characterized by granulation due to attached ribosomes on its surface. It is abundant in cells involved in protein synthesis. Its primary role in protein production involves synthesizing and transporting two main types of proteins:

    • Water-soluble proteins that enter the ER lumen for release elsewhere.

    • Prospective transmembrane proteins that remain embedded in the ER membrane.
      Examples include digestive enzymes, hormones, plasma membrane proteins, neurotransmitters, and lysosomal enzymes. Proteins undergo post-translational processing (e.g., folding) within the RER cisternae and are then primarily transported to the Golgi Apparatus.

  4. Describe examples of specialized ER such as the sarcoplasmic reticulum.
    A specialized form of smooth ER is the sarcoplasmic reticulum, found in muscle cells. It is particularly responsible for the storage and release of Ca2+^{2+} during muscle contraction through excitation-contraction coupling.

  5. List the four major functions of the Golgi apparatus in the cell including the production of primary lysosomes.
    The four major functions of the Golgi apparatus are:

    1. Processing newly synthesized secretory products, including proteins, glycoproteins, and mucopolysaccharides.

    2. Acting as a redistribution center for cell membranes by facilitating lipid transport.

    3. Production of primary lysosomes.

    4. Synthesis of carbohydrates, including polysaccharides and glycosaminoglycans (GAGs).

  6. Describe the structure and function of peroxisomes in the cell.
    Structure: Peroxisomes are rounded organelles, 0.5 - 1.0 µm in diameter, bounded by a single membrane. They contain oxidative enzymes involved in reactions for breaking down compounds, and they remove hydrogen peroxide (H<em>2<em>2O</em>2</em>2) by catalase.
    Function: They play a crucial role in fatty acid breakdown (β-oxidation) and metabolizing various substances. Defects in peroxisomes can lead to severe abnormalities, such as Zellweger syndrome.

  7. Discuss the presence of secretory and zymogen granules in certain classes of cells.
    Specialized cells possess secretory granules, which are vesicles designed for rapid secretion of substances like proteins (e.g., insulin) upon signaling by chemical messengers. These secretory vesicles arise from the trans-face of the Golgi Apparatus and release their contents into the extracellular space via exocytosis. While the note specifically mentions secretory granules, zymogen granules are a type of secretory granule observed in cells that store inactive enzyme precursors for later release.