Overview
This lecture covers Chapter 3, focusing on cell theory, cell structure, functions of cell organelles, membrane transport, cell junctions, and basic metabolism.
Cell Theory and Types
- Cell theory states all living organisms are made up of cells, and new cells arise from pre-existing cells.
- The origin of the first cell is unknown, making parts of cell theory a theory rather than a law.
- Cells vary in shape (e.g., nerve cells are star-shaped, red blood cells are round, plant cells are rectangular).
- Cells are small due to surface-area-to-volume ratio, which aids efficient exchange of materials.
Microscopy and Cell Classification
- Compound light microscopes and electron microscopes (scanning and transmission) are used to view cells.
- Scanning electron microscopes show 3D surfaces; transmission electron microscopes show internal structures.
- Prokaryotes (bacteria, archaea) lack nuclei; eukaryotes (plants, animals, fungi, protists) have nuclei and organelles.
Cell Structures and Membrane
- Both prokaryotes and eukaryotes have plasma (cell) membranes and cytoplasm.
- Plasma membrane is a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrate chains (glycoproteins, glycolipids).
- Fluid mosaic model describes the flexible, moving arrangement of membrane molecules.
Membrane Transport Mechanisms
- Diffusion: Molecules move from high to low concentration (no membrane required).
- Osmosis: Water moves from high to low concentration through a selective membrane.
- Facilitated diffusion: Molecules move across membrane via proteins, no energy required.
- Active transport: Molecules move against concentration gradient, requiring ATP (e.g., sodium-potassium pump).
- Endocytosis (phagocytosis, pinocytosis, receptor-mediated): Bulk material enters cell.
- Exocytosis: Bulk material exits cell.
Organelles and Cell Function
- Nucleus contains DNA and controls protein synthesis.
- Endoplasmic reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies.
- Ribosomes synthesize proteins.
- Golgi apparatus modifies, sorts, and packages proteins/lipids.
- Lysosomes contain enzymes for digestion and cell cleanup ("suicide bag").
- Vesicles transport substances within or out of the cell.
- Mitochondria are the "power plant" making ATP via cellular respiration.
Cytoskeleton and Cell Junctions
- Cytoskeleton provides support and movement (microtubules, intermediate filaments, actin filaments).
- Cilia and flagella aid movement; 9+2 microtubule structure.
- Extracellular matrix (e.g., collagen) supports cells outside the membrane.
- Cell junctions: adhesion (attach cytoskeletons), tight (barrier), and gap (communication, e.g., in heart cells).
Metabolism and Enzymes
- Metabolism: all chemical reactions in the cell.
- Enzymes (proteins) lower activation energy and speed up reactions, acting on substrates to form products at the active site.
- Coenzymes (vitamins) and cofactors (minerals) help enzyme function.
- Glycolysis occurs in the cytoplasm (anaerobic); aerobic respiration occurs in mitochondria, producing ATP.
- Fermentation is anaerobic respiration.
Key Terms & Definitions
- Prokaryote — cell without a nucleus or organelles.
- Eukaryote — cell with a nucleus and organelles.
- Phospholipid bilayer — double-layered structure of the cell membrane.
- Diffusion — movement of molecules from high to low concentration.
- Osmosis — diffusion of water through a selective membrane.
- Facilitated diffusion — passive transport via membrane proteins.
- Active transport — energy-requiring movement of substances across membrane.
- Endocytosis/Exocytosis — bulk transport into/out of cells.
- Organelle — membrane-bound cell structure with specific function.
- Enzyme — protein that speeds up reactions without being changed.
Action Items / Next Steps
- Review and memorize the structure and functions of all major organelles.
- Study types of membrane transport and their differences.
- Read about the functions of cell junctions, cytoskeleton, and extracellular matrix.
- Prepare for quizzes on cell theory, microscopy, membrane structure, and metabolism.