Introduction to Cell Biology – Study Notes
1. What Is Cell Biology?
- Definition: The branch of biology that studies the structure, function, and behavior of cells—the basic units of life.
- Scope:
- Cellular components (organelles, membranes, cytoskeleton)
- Cellular processes (metabolism, signaling, division)
- Inter‑cellular interactions and tissue organization
- Why It Matters: All living organisms are made of cells; understanding cells explains development, disease, biotechnology, and evolution.
2. The Cell Theory (Foundational Principles)
| Principle |
Description |
| 1. All living things are composed of cells |
Cells are the universal building blocks of life. |
| 2. The cell is the basic unit of structure and function |
All physiological processes occur within or because of cells. |
| 3. All cells arise from pre‑existing cells |
Cell division (mitosis, meiosis) is the mechanism of reproduction. |
| 4. (Modern addition) Cells contain hereditary information that is passed on during cell division. |
DNA is the genetic material housed in the nucleus (eukaryotes) or nucleoid (prokaryotes). |
3. Major Types of Cells
| Feature |
Prokaryotic Cells |
Eukaryotic Cells |
| Nucleus |
No true nucleus; DNA in nucleoid region |
Membrane‑bound nucleus |
| Size |
0.1–5 µm |
10–100 µm |
| Organelles |
Few (ribosomes, sometimes thylakoids) |
Many (mitochondria, ER, Golgi, lysosomes, etc.) |
| Cell Wall |
Usually peptidoglycan (bacteria) or pseudo‑peptidoglycan (archaea) |
Plants & fungi: cellulose or chitin; animals: none |
| Examples |
Bacteria, Archaea |
Animals, plants, fungi, protists |
4. Cellular Structures & Their Functions
4.1 Plasma Membrane
- Composition: Phospholipid bilayer with embedded proteins, cholesterol (eukaryotes), glycolipids.
- Functions:
- Selective barrier & transport (diffusion, facilitated transport, active pumps)
- Cell signaling (receptors)
- Cell adhesion & recognition
4.2 Cytoplasm
- Cytosol: Aqueous matrix containing ions, metabolites, enzymes.
- Cytoskeleton:
- Microfilaments (actin) – cell shape, motility, cytokinesis.
- Intermediate filaments – mechanical support.
- Microtubules – chromosome segregation, intracellular transport, cilia/flagella.
4.3 Nucleus (eukaryotes)
- Nuclear envelope: Double membrane with pores.
- Chromatin: DNA + histone proteins.
- Nucleolus: Ribosomal RNA synthesis & ribosome assembly.
4.4 Organelles (selected)
| Organelle |
Primary Role |
| Mitochondria |
ATP production via oxidative phosphorylation; apoptosis regulation. |
| Chloroplasts (plants & algae) |
Light‑dependent reactions & Calvin cycle → photosynthesis. |
| Endoplasmic Reticulum (ER) |
Rough ER – protein synthesis & folding; Smooth ER – lipid synthesis, detoxification, Ca²⁺ storage. |
| Golgi Apparatus |
Modification, sorting, and packaging of proteins/lipids |