Overview
This lecture reviews the main organelles of the eukaryotic cell, their functions, structural details, and special features such as endosymbiosis and the cytoskeleton.
Nucleus and Nucleolus
- The nucleus stores genetic information and is surrounded by two lipid bilayer membranes.
- The nucleolus, found inside the nucleus and not membrane-bound, is responsible for ribosome synthesis.
Endoplasmic Reticulum (ER)
- The smooth ER (no ribosomes) synthesizes carbohydrates and lipids.
- The rough ER (with ribosomes) synthesizes proteins.
Golgi Complex
- The Golgi complex modifies and packages lipids and proteins into vesicles for delivery within or outside the cell.
Vesicular Organelles
- Lysosomes digest cellular fragments and food particles.
- Peroxisomes produce hydrogen peroxide and help metabolize carbohydrates.
Mitochondria and Chloroplasts
- Mitochondria synthesize ATP and are known as the "powerhouse of the cell."
- Chloroplasts carry out photosynthesis and contain structures called thylakoids and grana.
- Both have double membranes, bacterial-like DNA, and their own bacterial-type ribosomes, supporting the endosymbiosis theory.
Endosymbiosis Theory
- Mitochondria and chloroplasts originated from bacteria engulfed by ancient eukaryotic cells.
- Cells with only mitochondria became animals or fungi; those with both became algae or plants.
Additional Structures
- The extracellular matrix (like glycocalyx) can form protective capsules in some fungi.
- The cell membrane in eukaryotes is fundamentally similar to that in prokaryotes.
Cytoskeleton and External Appendages
- The cytoskeleton consists of three filament types: microtubules (dynamic, for movement/division), intermediate filaments (static, maintain structure).
- External appendages include flagella and cilia, both used for movement.
- Eukaryotic flagella are structurally different from bacterial flagella and function more like oars.
Key Terms & Definitions
- Nucleus — Organelle storing genetic information, surrounded by two membranes.
- Nucleolus — Non-membrane-bound region in the nucleus for ribosome synthesis.
- Endoplasmic Reticulum — Network for synthesizing proteins (rough) and lipids/carbohydrates (smooth).
- Golgi Complex — Organelle modifying and packaging molecules.
- Lysosome — Organelle for digestion.
- Peroxisome — Organelle producing hydrogen peroxide and metabolizing carbohydrates.
- Mitochondrion — Organelle synthesizing ATP.
- Chloroplast — Organelle for photosynthesis.
- Endosymbiosis — Origin of organelles from engulfed bacteria.
- Cytoskeleton — Network of filaments for support and movement.
- Flagella/Cilia — External structures for movement.
Action Items / Next Steps
- Review the structure and function of each organelle.
- Understand evidence supporting the endosymbiotic origin of mitochondria and chloroplasts.
- Learn the differences between eukaryotic and prokaryotic structures, especially flagella.