Microorganisms, Viruses, Immunology and Biotechnology
This domain of the Basque PAU Biology exam combines microbiology, virology, immunology and biotechnology. You should distinguish cellular microorganisms from viruses, explain exponential growth, compare innate and adaptive immunity, and describe core recombinant-DNA techniques.
Microorganisms and viruses
- Bacteria are prokaryotic and reproduce by binary fission; growth follows lag, log, stationary and death phases.
- Exponential growth: N = N0 × 2^n, where n is the number of generations.
- Viruses are acellular, with a nucleic acid genome and a protein capsid; they are obligate intracellular parasites. Some have envelopes or reverse transcriptase.
- Lytic cycles destroy the host cell; lysogenic cycles integrate viral DNA and can later enter the lytic cycle.
Immunology
- Innate immunity includes physical barriers, phagocytes, inflammation and complement; it is fast and non-specific.
- Adaptive immunity involves B lymphocytes, antibodies, T lymphocytes and memory cells; it is specific and slower on first exposure.
- Vaccination produces active immunity and memory; passive immunity transfers antibodies and is short-lived.
Biotechnology
- Recombinant DNA uses restriction enzymes, plasmids, DNA ligase and transformation.
- PCR uses denaturation, primer annealing and extension, usually with Taq polymerase.
- Gel electrophoresis separates DNA by size; CRISPR-Cas9 allows targeted genome editing.
Worked example
A bacterial culture starts with 100 cells and has a generation time of 20 minutes. After 2 hours, the number of generations is 120 ÷ 20 = 6. N = 100 × 2^6 = 100 × 64 = 6400 cells. If the question asks for population growth after 3 hours, use 9 generations and obtain 51,200 cells. The reasoning is exponential doubling, not linear addition.
Traps
- Antibiotics do not treat viral infections because viruses lack bacterial targets.
- Viruses are not cells and do not carry out metabolism independently.
- The primary immune response is slower and produces less antibody than the secondary response.
- PCR requires primers and a thermostable polymerase; it is not simply heating DNA.
- In exponential growth, n is the number of generations, not the number of minutes.