Overview
This lecture covers the structure, types, identification, and functions of key eukaryotic cell organelles: nucleus, endoplasmic reticulum (ER), and Golgi apparatus. It also highlights differences between membrane-bound and non-membrane-bound organelles.
Types of Organelles
- Organelles are cell structures with specific functions.
- Membrane-bound organelles have their own membrane (e.g., nucleus, ER, Golgi apparatus).
- Non-membrane-bound organelles lack a surrounding membrane.
Nucleus Structure and Identification
- The nucleus is a double membrane-bound organelle with nuclear pores, nucleolus, and chromatin.
- Chromatin is linear DNA wrapped around histone proteins.
- Under a light microscope, the nucleus may appear as a dark area; under an electron microscope, structural details like the double membrane and nucleolus are visible.
- Light microscopes show color, while electron microscopes produce black and white images.
Nucleus Functions
- Contains genetic information (chromatin).
- Site of transcription for protein synthesis.
- Nucleolus within the nucleus produces ribosomes.
Endoplasmic Reticulum (ER)
- ER is a single membrane organelle with a fluid-filled space called cisternae, forming a network structure.
- Rough ER has ribosomes on its surface; smooth ER does not.
- Both ER types cannot be seen under a light microscope due to their small size.
- Rough ER is often located next to the nuclear membrane.
Functions of ER
- Smooth ER synthesizes and transports lipids and steroids.
- Rough ER synthesizes and transports proteins (ribosomes on rough ER synthesize proteins; rough ER helps transport them in vesicles).
Golgi Apparatus Structure and Identification
- Golgi apparatus is a single membrane organelle with curved, stacked membranes (cisternae), surrounded by vesicles.
- Forms a stack (not a network like ER) and appears curved under an electron microscope.
- Not visible under light microscope due to thin membranes.
Golgi Apparatus Functions
- Produces lysosomes.
- Packages and modifies proteins (e.g., creating glycoproteins by combining carbohydrates and proteins).
- Packages hydrolytic enzymes into lysosomes.
Key Terms & Definitions
- Organelle — a specialized structure within a cell with a distinct function.
- Membrane-bound organelle — an organelle surrounded by its own membrane.
- Nucleus — double membrane organelle containing DNA, site of transcription.
- Nucleolus — structure in the nucleus responsible for ribosome production.
- Chromatin — DNA wrapped around histone proteins.
- Endoplasmic reticulum (ER) — single membrane organelle (rough with ribosomes, smooth without).
- Golgi apparatus — single membrane organelle with stacked, curved membranes.
- Vesicle — small vacuole for transport within a cell.
Action Items / Next Steps
- Practice drawing and identifying organelles as required in exams.
- Review next chapters on histone proteins (chapter 5) and nuclear pores/transcription (chapter 6).