Cell Biology – Quick‑Study Notes
(For B.Pharm Admission – Biology)
1. Simple Explanation
Cell biology is the study of the structure, function, and behaviour of cells – the basic units of life. In pharmacy, understanding cells helps you grasp how drugs interact at the microscopic level, how they are absorbed, distributed, metabolised, and how they exert therapeutic or toxic effects.
2. Key Points
| Topic | What to Know | Why It Matters in Pharmacy |
|---|---|---|
| Cell Types | • Prokaryotic (bacteria, fungi) – no nucleus. • Eukaryotic (human, plant, animal) – nucleus & membrane‑bound organelles. |
Antibiotics target bacterial cells; human cells are drug targets. |
| Cell Structure | • Plasma membrane – lipid bilayer + proteins. • Cytoplasm – gel‑like matrix. • Nucleus – DNA, nucleolus. • Mitochondria – ATP generation. • Ribosomes – protein synthesis. • Endoplasmic reticulum – rough (protein) & smooth (lipid). • Golgi apparatus – protein sorting. • Lysosomes – hydrolysis. |
Drug molecules must cross membranes, bind to receptors, or be metabolised by organelles. |
| Cell Membrane Composition | Phospholipids (head & tails), cholesterol, proteins (integral, peripheral). | Determines drug permeability & transporter interactions. |
| Transport Mechanisms | • Passive: diffusion, osmosis, facilitated diffusion. • Active: ATP‑driven pumps (Na⁺/K⁺‑ATPase). • Endocytosis / Exocytosis |
Drug absorption (GI, blood‑brain barrier) and efflux (P‑gp pumps). |
| Cell Cycle | G₁ → S → G₂ → M → G₀. | Chemotherapeutic agents target rapidly dividing cells (e.g., cancer). |
| Signal Transduction | Receptors (GPCR, RTK, ion channel), second messengers (cAMP, Ca²⁺), kinases, phosphatases. | Many drugs are agonists/antagonists of receptors or modulate signalling pathways. |
| Apoptosis & Necrosis | Apoptosis (programmed cell death) vs necrosis (uncontrolled). | Desired drug effect: induce apoptosis in cancer cells; avoid necrosis in healthy tissue. |
| Cell–Cell Interaction | Gap junctions, adherens junctions, integrins. | Targeted therapies (e.g., monoclonal antibodies) may disrupt tumour micro‑environment. |
| Cellular Metabolism | Glycolysis, Krebs cycle, oxidative phosphorylation, β‑oxidation. | Metabolic pathways are drug targets (e.g., statins inhibit HMG‑CoA reductase). |
| Cellular Quality Control | Protein folding (chaperones), proteasome, autophagy. | Misfolded proteins linked to drug side effects; proteasome inhibitors used in multiple myeloma. |
3. Worked Example – Drug Transport Across the Plasma Membrane
Scenario: A lipophilic drug (Drug X) needs to reach intracellular receptors.
Goal: Determine how Drug X crosses the cell membrane and estimate its rate of passive diffusion.
Step‑by‑Step
| Step | Description | Key Formula / Concept |
|---|---|---|
| 1. Identify drug properties | Drug X is lipophilic, low ionization at physiological pH. | Lipophilicity → high membrane permeability. |
| 2. Use Fick’s Law for passive diffusion: [ J = -P \times (C_{\text{outside}} - C_{\text{inside}}) ] | (J) = flux (mol cm⁻² s⁻¹), (P) = permeability coefficient. | |
| 3. Estimate (P) using the solubility‑diffusion model: [ P = \frac{D \times K}{h} ] | (D) = diffusion coefficient, (K) = partition coefficient (lipophilicity), (h) = membrane thickness (~5 nm). | |
| 4. Assume: (D = 1 \times 10^{-5},\text{cm}^2,\text{s}^{-1}), (K = 100). | Then (P = \frac{1 \times 10^{-5} \times 100}{5 \times 10^{-7}} = 2 \times 10^3,\text{cm},\text{s}^{-1}). | |
| 5. Calculate flux if (C_{\text{outside}} = 10^{-6},\text{mol cm}^{-3}), (C_{\text{inside}} \approx 0). | (J = -2 \times 10^3 \times (10^{-6}) = -2 \times 10^{-3},\text{mol cm}^{-2},\text{s}^{-1}). | |
| 6. Interpret | Drug X crosses rapidly; passive diffusion is the dominant route. |
Take‑away: Lipophilic drugs cross membranes quickly via passive diffusion; their plasma concentration and partition coefficient largely determine intracellular exposure.
4. Quick Revision Summary
| Topic | Quick Facts |
|---|---|
| Cell Types | Prokaryotes: no nucleus; eukaryotes: nucleus + organelles |
| Membrane | Phospholipid bilayer + cholesterol + proteins |
| Transport | Diffusion, osmosis, facilitated diffusion, active pumps, endocytosis |
| Cell Cycle | G1‑S‑G2‑M‑G0; targets for chemotherapeutics |
| Signalling | Receptors → second messengers → kinases → cellular response |
| Apoptosis | Programmed, caspase cascade; drug‑induced in cancer |
| Metabolism | Glycolysis → Krebs → oxidative phosphorylation; drug targets |
| Quality Control | Chaperones, proteasome, autophagy; implicated in drug side‑effects |
Tip for Exam:
- Relate each