FR Exam 3

1. Transformation, Transduction, Conjugation

Transformation is the uptake of free (“naked”) DNA from the environment by a bacterium. Transduction is DNA transfer via a bacteriophage that carries bacterial DNA between cells. Conjugation involves direct cell-to-cell contact using a sex pilus to transfer plasmid DNA.

2. PCR Steps

PCR includes denaturation, annealing, and extension. Denaturation separates DNA strands with high heat. In annealing, cooler temperatures allow primers to bind to DNA, and extension uses DNA polymerase to build new strands. A thermocycler controls the start and stop of each step by precisely changing the temperature.

3. Pathogenesis (3 stages)

Exposure is when a pathogen first contacts the host, which is needed to start an infection. Adhesion lets it stick to host cells so it can colonize, like E. coli in the intestines. Invasion allows it to enter tissues and multiply, spreading the infection and completing its life cycle, as seen with Listeria.

4. Koch’s Postulates

The pathogen must be isolated and grown in pure culture. It must cause the same disease in a healthy host. The same pathogen must then be re-isolated from the newly infected host.

5. Exception to Koch’s Postulates

HIV cannot be tested in healthy humans, so the postulate requiring the pathogen to cause disease in a healthy host can’t be fulfilled. Some pathogens, like Treponema pallidum, also can’t be grown in pure culture, making that postulate difficult to meet.

6. Drug Development

Fungi and helminths are eukaryotic like human cells, so they have fewer unique drug targets. Viruses replicate inside host cells, making them difficult to target without harming the host. Bacteria are prokaryotic and have unique structures, making them easier to target.

7. Selective Toxicity

Penicillin targets bacterial cell wall synthesis. Human cells do not have cell walls, so they are not affected. This makes the drug selectively toxic to bacteria.

8. Antibiotic Resistance

Sub-therapeutic antibiotic use allows resistant bacteria to survive and reproduce. One mechanism is β-lactamase production, which breaks down β-lactam antibiotics. This prevents the drug from working effectively.

9. Public Health (HIV)

For HIV, antiretroviral therapy (ART) reduces viral replication and improves survival. Public health measures like testing and education on safe practices help prevent new infections and ensure early treatment, lowering both mortality and morbidity.