Overview
This lecture introduces organelles and cellular compartmentalization, focusing on their definitions, membrane structures, and their roles in differentiating prokaryotic and eukaryotic cells.
Definition and Types of Organelles
- Organelles are specialized structures within a cell, each with a specific function.
- Not all important cell structures are organelles (e.g., cell wall, cytoskeleton, cytoplasm).
- Prokaryotes have some organelles, but none are surrounded by membranes (no membrane-bound organelles).
Membrane Classification of Organelles
- Non-membrane-bound organelles: ribosomes, centrioles, microtubules.
- Single-membrane-bound organelles: Golgi apparatus, lysosomes, vacuoles, vesicles, smooth and rough endoplasmic reticulum.
- Double-membrane-bound organelles: nucleus, mitochondria, chloroplasts.
- Only eukaryotic cells have membrane-bound organelles; prokaryotes do not.
Compartmentalization in Eukaryotes
- Eukaryotic cells are compartmentalized due to their membrane-bound organelles.
- Compartmentalization allows protection (e.g., nucleus protects DNA), and mRNA editing before translation.
- Prokaryotes lack nuclear membranes, so their DNA and mRNA are not compartmentalized or protected similarly.
- Compartmentalization enables concentration of enzymes, localized pH/solute environments, and storage of dangerous substances.
- Lysosomes store destructive enzymes safely within their membrane-bound compartment.
Key Terms & Definitions
- Organelle — a cell structure specialized for a specific function within the cell.
- Membrane-bound organelle — an organelle surrounded by one or two membranes (found only in eukaryotes).
- Compartmentalization — division of the cell into specialized, membrane-bound regions for different functions.
Action Items / Next Steps
- Review more detailed cell structure content in section A2.2.
- Memorize which organelles are non-membrane-bound, singly membrane-bound, and double-membrane-bound.