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

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.

Identify the five major groups of pathogens and give one Australian disease example for each. [5 marks]

A new strain of Streptococcus is resistant to penicillin. (a) Identify two mechanisms by which resistance can arise. (b) Predict the effect of restricting penicillin use on resistance allele frequency over 12 months.

Refer to vaccination. (a) Distinguish active from passive immunisation. (b) Explain how an mRNA vaccine generates antibodies without containing the pathogen.