Quick questions on Pathogens and disease management (bacteria, viruses, vaccines, antibiotics): VCE Biology Unit 4

Bacteria. Single-celled prokaryotes with a cell wall (containing peptidoglycan), a circular chromosome and 70S ribosomes. They reproduce asexually by binary fission, often every 20 to 30 minutes in ideal conditions. Bacteria cause disease by releasing toxins (cholera, tetanus, diphtheria) or by damaging host tissues directly (tuberculosis, strep throat).

A vaccine trains the adaptive immune system without causing disease. Vaccine types include:

When a high proportion of a population is immune, the pathogen has too few susceptible hosts to spread. Transmission chains break and outbreaks die out. Unvaccinated people (infants, immunocompromised patients, vaccine non-responders) are indirectly protected.

Antibiotics are drugs that kill or stop the growth of bacteria. They target bacterial structures absent from human cells:

Antiviral drugs target steps in the viral replication cycle:

Antibiotic resistance is a textbook example of natural selection:

Single-celled prokaryotes with a cell wall (containing peptidoglycan), a circular chromosome and 70S ribosomes. They reproduce asexually by binary fission, often every 20 to 30 minutes in ideal conditions. Bacteria cause disease by releasing toxins (cholera, tetanus, diphtheria) or by damaging host tissues directly (tuberculosis, strep throat).

Acellular particles consisting of genetic material (DNA or RNA, single or double stranded) inside a protein capsid, sometimes surrounded by a lipid envelope taken from the host membrane. Viruses are obligate intracellular parasites: they cannot reproduce without a host cell. They attach to specific receptors on host cells, inject or release their genome, hijack the cell's ribosomes and machinery to make new virions, and exit by lysis or budding.

Single-celled eukaryotes with a nucleus and membrane-bound organelles. They cause diseases mostly in tropical regions: Plasmodium (malaria, transmitted by mosquitoes), Giardia (intestinal infection), Trypanosoma (sleeping sickness). Many have complex life cycles involving multiple hosts.

Eukaryotes with a chitinous cell wall, mostly multicellular (hyphae forming a mycelium) but some single-celled (yeasts). Fungal pathogens include Candida (thrush), Tinea (ringworm, athlete's foot) and Aspergillus (lung infections in immunocompromised people). Fungi are harder to treat than bacteria because their cells are biochemically similar to ours.

Misfolded versions of normal cellular proteins (not organisms at all). Prions cause normal proteins to misfold into the same abnormal shape, forming aggregates that destroy brain tissue. Diseases include Creutzfeldt-Jakob disease, mad cow disease (bovine spongiform encephalopathy) and scrapie in sheep.

The vaccine presents antigens to the immune system. Helper T cells, B cells and cytotoxic T cells with matching receptors activate and proliferate. Plasma cells secrete antibodies and memory B and T cells persist for years.

Prescribe antibiotics only when needed, complete the full course, use narrow-spectrum drugs where possible, develop new antibiotics, vaccinate to reduce infections, and improve hygiene and infection control.

Bacteria are cells; viruses are not. Antibiotics work on bacteria, antivirals on viruses.

Most vaccines cannot cause disease. Live attenuated vaccines very rarely cause mild forms in immunocompromised people.