Medical Applications of Cell Biology

1. Antibiotic Design (70S vs 80S Ribosome Selectivity)

• Streptomycin, tetracycline → target 30S subunit of 70S ribosomes → kill bacteria, safe for humans (80S cytoplasmic ribosomes unaffected)
• Erythromycin, chloramphenicol → target 50S subunit → inhibit bacterial protein synthesis
• Penicillin → targets peptidoglycan synthesis (bacterial cell wall) → no target in human cells → selective toxicity
• Limitation: Mycoplasma (no cell wall) is resistant to penicillin

2. Lysosomal Storage Disorders

• Tay-Sachs disease: deficiency of hexosaminidase A in lysosomes → accumulation of $GM_{2}$ ganglioside in neurons → neurodegeneration
• Gaucher disease: deficiency of glucocerebrosidase → lipid accumulation in macrophages
• Treatment: enzyme replacement therapy (ERT) — inject functional enzyme that is targeted to lysosomes

3. Cancer Biology — Cell Division Gone Wrong

• Unchecked cell division when cell cycle controls fail
• Colchicine (spindle poison, disrupts tubulin → microtubules) → used in cytogenetics to arrest cells in metaphase for chromosome analysis
• Vincristine/Vinblastine (plant alkaloids) → antitumor drugs that disrupt microtubule polymerization → arrest mitosis in cancer cells

4. Plasmids in Recombinant DNA Technology

• Plasmids used as vectors to introduce foreign genes into bacteria
• Example: Human insulin gene inserted into plasmid → transformed into E. coli → E. coli produces human insulin at scale
• Antibiotic resistance genes on plasmids used as selectable markers

5. Endosymbiotic Theory and Mitochondrial Medicine

• Mitochondrial DNA mutations → mitochondrial diseases (MELAS, MERRF)
• These diseases affect tissues with highest energy demand (brain, muscle, heart)
• Mitochondrial DNA is maternally inherited → inheritance pattern differs from nuclear DNA

Biotechnology Connections