- Cell Theory Tenets: Proposed by Schleiden and Schwann (1839), modified by Virchow (1855). State: (1) All living organisms are made of cells. (2) The cell is the structural/functional unit of life. (3) All cells arise from pre-existing cells. Exceptions: Viruses, Viroids, Prions (lack protoplasm/cellular structure).
- Prokaryotic vs. Eukaryotic Cells:
• Prokaryotes: No membrane-bound nucleus (naked DNA in nucleoid region). Lacks double-membranous organelles. Ribosomes are 70S. Cell wall contains peptidoglycan (in bacteria). Examples: Bacteria, Cyanobacteria (Blue-green algae), Mycoplasma (PPLO - smallest living cell, lacks cell wall).
• Eukaryotes: Defined nucleus with nuclear membrane. Double-membrane organelles (mitochondria, plastids) present. Ribosomes are 80S (cytoplasm) & 70S (organelles). Examples: Protists, Fungi, Plants, Animals. - Cell Wall & Cell Membrane:
• Cell Wall: Rigid, fully permeable, non-living outer layer. Present in Plants (cellulose), Fungi (chitin), Bacteria (peptidoglycan). Absent in Animals.
• Cell Membrane: Semi-permeable, living, fluid-like phospholipid bilayer with embedded proteins. Described by the Fluid Mosaic Model (Singer & Nicolson, 1972).
Cell BiologyCell Biology
Master cell structures, prokaryotes vs. eukaryotes, organelles (mitochondria, chloroplasts, lysosomes), chromosome classifications, and key mechanisms of cell division (Mitosis & Meiosis) for competitive exams.Master cell structures, prokaryotes vs. eukaryotes, organelles (mitochondria, chloroplasts, lysosomes), chromosome classifications, and key mechanisms of cell division (Mitosis & Meiosis) for competitive exams.
Chronological Evolution of Cell Biology
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Cell Biology Core Study Notes
Thoroughly review cell discovery milestones, organelles and their vital functions, chromosome types, and comparison of cell division pathways.
1. Cell Theory, Prokaryotic vs. Eukaryotic Cells & Cell Walls
2. Structure & Function of Cell Organelles (Mitochondria, Chloroplasts, Lysosomes)
Eukaryotic cells contain specialized subcellular components called organelles. Their roles and properties are highly tested in competitive exams:
| Organelle | Membrane Status | Key Discoverer / Term | Core Function & Exam Notes |
|---|---|---|---|
| Mitochondria | Double Membrane | Kölliker (discovered), Benda (coined term) | Powerhouse of the Cell: Site of aerobic respiration (Krebs Cycle, Electron Transport). Synthesizes ATP. Contains circular DNA and 70S ribosomes (Semi-autonomous). Shows maternal inheritance. |
| Plastids (Chloroplast) | Double Membrane | Schimper (coined Chloroplast) | Kitchen of the Cell: Found in plants. Contains chlorophyll pigment. Site of photosynthesis (Light reaction in Thylakoid/Grana; Dark reaction in Stroma). Semi-autonomous (own DNA/70S ribosomes). |
| Ribosome | Non-Membranous | George Palade (discovered Palade particles) | Protein Factory: Composed of RNA (rRNA) and proteins. Site of protein synthesis. Smallest organelle. Found free in cytoplasm or bound to Rough Endoplasmic Reticulum (RER). |
| Lysosome | Single Membrane | Christian de Duve | Suicidal Bags: Rich in acid hydrolases (active at pH ~5). Autophagy, cell debris cleaning, cell digestion under pathological conditions. |
| Endoplasmic Reticulum (ER) | Single Membrane | Porter, Claude & Fullam | Rough ER (RER): Has ribosomes; involved in protein folding/transport. Smooth ER (SER): Lacks ribosomes; synthesizes lipids/steroid hormones, detoxifies drugs/toxins in liver. |
| Golgi Apparatus | Single Membrane | Camillo Golgi | Director of Macromolecular Traffic: Packaging, sorting, and chemical modification of proteins and lipids. Site of glycoprotein and glycolipid formation. Contributes to lysosome formation. |
| Nucleus | Double Membrane | Robert Brown (1831) | Brain of the Cell: Contains genetic material (DNA/chromatin). Houses the nucleolus (site of active rRNA synthesis and ribosome subunit assembly). Bounded by a porous nuclear envelope. |
3. Chromosome Classifications & Cell Division (Mitosis vs. Meiosis)
- Chromosome Anatomy & Centromere Classifications: Chromosomes are thread-like structures containing chromatin (DNA + Histone proteins). Based on the location of the **Centromere** (primary constriction), they are classified into:
• Metacentric: Centromere in the middle; forms two equal arms (V-shape during anaphase).
• Sub-metacentric: Centromere slightly away from the center; one arm is slightly shorter (L-shape during anaphase).
• Acrocentric: Centromere close to one end; one arm is extremely short, the other is long (J-shape during anaphase).
• Telocentric: Centromere at the terminal end; possesses only one arm (I-shape / rod-shape during anaphase). - Mitosis (Equational Division): Occurs in somatic cells. Results in two identical diploid (2n) daughter cells.
• **Prophase:** Chromatin condenses into chromosomes; spindle fibers form; nucleolus and nuclear envelope disappear.
• **Metaphase:** Chromosomes line up at the cell's equator. Studied for karyotype analysis.
• **Anaphase:** Sister chromatids split at centromere and pull to opposite poles (shortest phase).
• **Telophase:** Nuclear membranes reform around two sets of chromosomes; chromosomes decondense. - Meiosis (Reductional Division): Occurs in germ/reproductive cells. Reduces the chromosome number by half to produce four haploid (n) gametes. Consists of Meiosis I (reductional) and Meiosis II (equational).
• **Prophase I (Highly Tested sub-stages):**
1. Leptotene: Chromatin threads condense.
2. Zygotene: Pairing of homologous chromosomes (**Synapsis**) occurs, forming a bivalent (synaptonemal complex).
3. Pachytene: Non-sister chromatids of homologous chromosomes exchange genetic material (**Crossing over** mediated by *recombinase* enzyme).
4. Diplotene: Synaptonemal complex dissolves; homologous chromosomes separate slightly but remain connected at cross points called **Chiasmata**.
5. Diakinesis: Chiasmata move to chromosome ends (terminalization); nuclear envelope disintegrates.
Practice Zone: 50 Questions
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