Lecture Notes: Components and Functions of the Endomembrane System

Overview of the Endomembrane System

• Definition: A group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins.
• Components:
  • Nuclear envelope
  • Lysosomes
  • Vesicles
  • Endoplasmic reticulum (ER)
  • Golgi apparatus
  • Plasma membrane

Membrane and Protein Synthesis

• Membrane Proteins:
  • Synthesis begins at the rough endoplasmic reticulum (Rough ER) using ribosomes.
  • Proteins may be modified within the Rough ER.
  • Proteins are transported to the Golgi apparatus via vesicles.

Endoplasmic Reticulum (ER)

• Structure:
  • Interconnected membranous sacs and tubules.
  • Continuous with the nuclear envelope.
• Types of ER:
  • Rough ER:
    • Contains ribosomes on its surface.
    • Functions in protein synthesis and modification.
    • Can produce phospholipids.
  • Smooth ER:
    • Lacks ribosomes.
    • Synthesizes lipids, carbohydrates, and steroids.
    • Detoxifies drugs and poisons.
    • Stores calcium, particularly in muscle cells.

Golgi Apparatus

• Function:
  • Acts as the cell’s post office for sorting and tagging proteins.
  • Receives vesicles on the CIS face from the ER.
  • Modifies proteins by adding carbohydrates (glycosylation).
  • Packages proteins for their specific destinations.
  • Produces lysosomes.

Lysosomes

• Function:
  • Digest large biomolecules, old organelles, and pathogens.
  • Enzymes are produced in the Rough ER and modified in the Golgi.
• Pathways:
  • Involved in endocytosis and phagocytosis.
  • Breaks down materials in phagolysosomes.

Cellular Processes Involving the Endomembrane System

• Endocytosis:
  • Cells engulf large particles or pathogens.
  • Involves the formation of vacuoles that fuse with lysosomes.
• Exocytosis:
  • Release of digested materials or secretion from the cell.

Upcoming Topics

• Next video will cover the cytoskeleton and intercellular connections in animal and plant cells.