Cell Biology
Every living thing is made of cells. Understanding them is the foundation of all biology.
🏗️ Cell Structure
Cells have a membrane that separates them from their environment, cytoplasm (the fluid inside), and in eukaryotes, a nucleus that houses DNA. Prokaryotic cells (bacteria) have no nucleus; eukaryotic cells (animals, plants, fungi) do.
⚙️ Organelles
The nucleus stores DNA. Mitochondria produce ATP (energy). The endoplasmic reticulum makes and transports proteins. The Golgi apparatus packages and ships them. Ribosomes build proteins. Lysosomes break down waste. Chloroplasts (in plants) perform photosynthesis.
⚡ ATP and Energy
Adenosine triphosphate (ATP) is the universal energy currency of cells. Cellular respiration converts glucose into ATP: C6H12O6 + 6O2 → 6CO2 + 6H2O + ~38 ATP. Mitochondria are the main site of this process.
🔄 Cell Division
Mitosis produces two identical daughter cells for growth and repair. Meiosis produces four genetically unique gametes (sperm/eggs) for reproduction. Cancer is essentially uncontrolled cell division caused by mutations in growth-regulating genes.
🧱 Cell Membrane
The phospholipid bilayer controls what enters and leaves the cell. The fluid mosaic model describes it as a dynamic structure with embedded proteins that act as channels, receptors, and transporters.
📡 Cell Signaling
Cells communicate via chemical signals (hormones, neurotransmitters). A signal binds to a receptor, triggering a cascade of reactions inside the cell. This is how insulin controls blood sugar, and how neurons fire.