Overview
This lecture explains the endomembrane system in animal cells, focusing on the pathways of protein processing, lipid synthesis, and cellular transport.
The Endomembrane System
- The endomembrane system is a network of internal membranes in the cell.
- Its main functions include protein processing and various metabolic activities.
Endoplasmic Reticulum (ER)
- The ER is part of the endomembrane system and comes in two types: rough and smooth.
- Rough ER is covered with ribosomes, which synthesize proteins.
- Smooth ER lacks ribosomes and is where lipids are made.
Protein Synthesis and Transport
- Ribosomes on the rough ER produce proteins that grow inside the ER.
- Completed proteins exit the rough ER in vesicles that bud off from its membrane.
- Some vesicles fuse with the Golgi apparatus for further protein processing.
Golgi Apparatus and Vesicle Transport
- The Golgi apparatus processes and modifies proteins received from the ER.
- Finished proteins are packaged into vesicles that pinch off from the Golgi.
- Vesicles are transported along cytoskeleton tracks within the cell.
Vesicle Roles: Secretion and Digestion
- Some vesicles fuse with the plasma membrane to secrete contents outside the cell.
- Other vesicles, called lysosomes, contain digestive enzymes.
- Lysosomes can fuse with worn-out organelles, like mitochondria, to break them down.
Cellular Activity and Energy
- Each cell is highly active, requiring millions of ATP molecules every minute to function.
Key Terms & Definitions
- Endomembrane System — a network of internal membranes involved in protein and lipid processing.
- Endoplasmic Reticulum (ER) — an organelle with rough (ribosome-covered) and smooth (ribosome-free) regions.
- Rough ER — ER with ribosomes; site of protein synthesis.
- Smooth ER — ER without ribosomes; site of lipid synthesis.
- Vesicle — a small, membrane-bound sac that transports materials in the cell.
- Golgi Apparatus — organelle that processes and packages proteins for transport.
- Lysosome — a vesicle containing digestive enzymes for breaking down waste.
- Cytoskeleton — network of protein fibers that help transport vesicles.
Action Items / Next Steps
- Review diagrams of the endomembrane system for visual understanding.
- Read textbook section on organelles involved in protein and lipid processing.