Overview
This lecture introduces the cell as the fundamental unit of life, covering cell theory, organelle structure and functions, and the historical development of cell biology.
Cell Theory and Historical Development
- The cell is the basic unit of life.
- All living organisms are made up of cells.
- New cells arise from pre-existing cells (Omnis cellula e cellula).
- Robert Hooke discovered cells in cork in 1665.
- Anton van Leeuwenhoek observed "animalcules" using improved microscopes.
- Schleiden and Schwann concluded plants and animals are composed of cells.
- Rudolf Virchow added the concept that cells arise from other cells.
Major Parts of the Cell
- Plasma membrane: Separates cell interior from the environment and controls material exchange.
- Cytoplasm: Jelly-like fluid (cytosol) containing organelles, primarily water, proteins, and salts.
- Nucleus: The control center containing DNA and directing cell activity.
Plasma Membrane Structure
- Composed of a fluid mosaic of phospholipids, cholesterol, and proteins.
- Phospholipid bilayer with hydrophobic tails inward and hydrophilic heads outward.
- Cholesterol stabilizes membrane; proteins aid transport and recognition.
Cytoplasm and Cytosol
- Cytosol suspends organelles and provides space for metabolic reactions.
- Contains enzymes for waste breakdown and supports cell expansion and movement.
Nucleus and Nuclear Components
- Enclosed by a double membrane with pores for exchange.
- Contains nucleolus (ribosome synthesis) and chromosomes (DNA).
Endomembrane System Organelles
- Endoplasmic Reticulum (ER): Rough ER (protein modification), Smooth ER (lipid synthesis, detoxification).
- Ribosomes: Sites of protein synthesis, found free or attached to ER.
- Golgi Apparatus: Modifies, sorts, and packages molecules from the ER for storage or export.
- Vacuoles: Store substances; plant vacuoles also break down molecules.
- Lysosomes: Digest and recycle cellular materials, important for autophagy.
- Peroxisomes: Detoxify harmful substances and break down fatty acids.
- Centrosomes/Centrioles: Organize microtubules for cell division.
Energy-Producing Organelles
- Mitochondria: Powerhouse of the cell, site of ATP production via cellular respiration.
- Chloroplasts (plants/algae): Site of photosynthesis, converting sunlight into chemical energy.
Chloroplast Structure
- Double membrane with outer, inner, and thylakoid systems.
- Thylakoids (stacked as grana) contain chlorophyll for light absorption.
- Stroma contains enzymes, DNA, and ribosomes.
Key Terms & Definitions
- Cell Theory — Principle stating all organisms are made of cells, and all cells arise from pre-existing cells.
- Organelle — Specialized structure within a cell that performs a specific function.
- Phospholipid bilayer — Double layer making up cell membranes.
- Ribosome — Organelle synthesizing proteins.
- Mitochondria — Organelle producing ATP.
- Chloroplast — Organelle for photosynthesis in plants and algae.
- Lysosome — Organelle for digesting cellular waste.
- Endoplasmic Reticulum — Network for protein and lipid synthesis.
- Golgi Apparatus — Modifies and packages proteins/lipids.
- Cytosol — Fluid portion of cytoplasm.
- ATP — Molecule acting as the main energy currency of the cell.
Action Items / Next Steps
- Draw and label each part of a plant and animal cell on short bond paper.
- Reflect: Why are cells generally small in size?