Non-cellular forms of life
Viruses are a non-cellular form of life. They were first discovered in 1892 by D. I. Ivanovsky while studying tobacco mosaic disease, in fluid that had passed through a filter that holds back bacteria; in 1917 F. d’Herelle described the bacteriophage, a virus that infects bacteria. A virus consists of a nucleic acid (DNA or RNA) and a protein coat around it, the capsid. Viruses have no metabolism of their own and no protein-making machinery, so they multiply only inside a living cell: they are intracellular parasites. A virus first binds to a receptor protein on the cell surface and then brings its genome into the cell; the cell is forced to make new virus particles and is often destroyed. Viruses cause influenza, measles, rubella, rabies, hepatitis A and B and COVID-19; vaccination and hygiene are important against them, while antibiotics do not act on viruses.
“The virus path”. Put the cards in order: 1) binding to the receptor, 2) entry of the genome, 3) making new virus proteins and genomes, 4) assembly of particles, 5) release from the cell. A pair of students retells the steps in their own words.