Pathogens: virus vs bacterium sim
Turn scale models of a virus and a bacterium on their turntables, work out their real sizes from the magnification, then step hour by hour through a virus taking over a host cell while bacteria divide next to it, and compare runs with and without an antibiotic.
Pathogens: the structure of viruses and bacteria, how a virus takes over a host cell, and why antibiotics kill bacteria but not viruses · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Pathogens: virus vs bacterium, a model. Two scale models stand on turntables: drag either turntable sideways to turn its model all the way round. The virus model is a ball 60 mm across (a protein coat with spike proteins) a real virus magnified 600,000 times (the real one is about 100 nm, or 0.1 µm, across); the bacterium model is a rod 120 mm long with a flagellum and pili, a real bacterium magnified 60,000 times (the real one is about 2 µm long). Magnification = image size / actual size, with 1 mm = 1000 µm and 1 µm = 1000 nm. At the same magnification the virus model would be only 6 mm across: a bacterium is about 20 times longer than this virus. The close-ups show what each one does, one hour per click. A virus is not a cell: it is genetic material inside a protein coat, and it can reproduce only inside a host cell. It attaches, its genetic material gets in, and the host cell makes copies of the genetic material and the protein coats; new viruses are put together and the cell bursts, releasing them (100 in this model). A bacterium is a single cell (cell wall, cell membrane, cytoplasm, circular DNA with no nucleus, plasmids, ribosomes, often a slimy capsule and a flagellum); it divides in two. An antibiotic kills bacteria, for example by damaging their cell walls, but has no effect on viruses: they have no cell wall and use the host cell's own parts, inside the cell. Simplified on purpose: timings are illustrative (one hour per step; real virus cycles take from under an hour to a day or more, and in ideal conditions some bacteria divide every 20 minutes); in this model each bacterium divides once an hour, and from the hour after the antibiotic 3 in every 4 bacteria die each hour; one virus and one host cell; 100 new viruses per cell is illustrative (real viruses release from tens to thousands). The close-ups are not to scale with each other or with the models, and viruses are drawn far larger than real next to the host cell (about 20 µm across); drawn bacteria, viruses and copies show roughly how many there are, not real numbers. Real viruses vary in shape: some have no spikes, and some inject their genetic material and leave the coat outside, as here, while others enter whole and lose their coat inside.
- Pointer: which way the model faces
- Close-ups: what each pathogen does, one hour per click (not to scale)
- Graph: solid line bacteria, dashed line virus particles
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