Lecture Notes: Components and Functions of the Endomembrane System

Overview

• Endomembrane System: A group of membranes and organelles within a cell that modify, package, and transport lipids and proteins.
• Components include:
  • Nuclear envelope
  • Lysosomes
  • Vesicles
  • Endoplasmic Reticulum (ER) - Rough and Smooth
  • Golgi Apparatus
  • Plasma membrane
• Membranes are interchangeable, facilitating protein and lipid transport.

Protein Synthesis and Transport

• Rough ER:
  • Site of synthesis for membrane/secretion proteins via ribosomes.
  • Modifies proteins, example: attaching carbohydrates.
  • Proteins bud from ER in vesicles, first stop is the Golgi apparatus.
• Golgi Apparatus:
  • Modifies proteins further, adding carbohydrates.
  • Functions as the "post office," sorting and tagging proteins for delivery.
  • Proteins exit through the trans face, ready for the cell membrane or secretion.

Endoplasmic Reticulum (ER)

• Structure: Interconnected membranous sacs/tubules, continuous with nuclear envelope.
• Types:
  • Rough ER:
    • Ribosomes attached, synthesizes proteins.
    • Sometimes modifies proteins; produces phospholipids too.
    • Associated with the nuclear envelope.
  • Smooth ER:
    • No ribosomes, synthesizes lipids.
    • Detoxifies medications/poisons.
    • Stores calcium, especially in muscle cells.

Lysosomes

• Function: Break down biomolecules (carbohydrates, lipids, proteins, nucleic acids) and old organelles.
• Production:
  • Digestive enzymes made in rough ER, modified in Golgi.
  • Vesicle fuses with Golgi, becomes lysosome.

Cellular Processes

• Endocytosis: Process of taking substances into the cell.
• Phagocytosis: Type of endocytosis for larger particles.
  • Involves formation of a vacuole/vesicle.
  • Fuses with lysosome, forming a phagolysosome.
  • Breakdown of contents, release through exocytosis.

Summary

• Endomembrane System crucial for cell function and involved in protein and lipid modification and transport.
• Next session will cover the cytoskeleton and intercellular connections in animal and plant cells.