Genome
A few thousand to over a million bases. Influenza has eight RNA segments; parvoviruses are tiny single-strand DNA.
Biology here is a borrowed timetable. The particle binds, the genome enters, host ribosomes translate viral proteins, new genomes are copied, and progeny leave by budding or lysis.
Latent viruses can sit as nucleic acid for years. That is persistence, not 'the virus is a bacterium hiding in a spore'.
Parts
Capsid
Protein box or helix. Protects nucleic acid and often determines the first binding step.
Envelope (some families)
A lipid bilayer taken from the host. Soap and alcohol disrupt many enveloped respiratory viruses on skin and surfaces.
Surface glycoproteins
Haemagglutinin, spike, gp120 — teaching names for locks that fit particular cells. They are also vaccine antigens.
No ribosomes
Protein synthesis is 100% host. That is why antibiotics aimed at bacterial 70S ribosomes do not 'treat a virus'.
Packaged enzymes (some)
Some virions carry a polymerase because the host cell has no matching copy machine. Description only — not an engineering list.
Life cycle
1Attach
A protein matches a receptor — sialic acids for some influenza strains, ACE2 for SARS-CoV-2 in textbooks.
2Enter and uncoat
Endocytosis or membrane fusion delivers the genome. The capsid opens; the instruction set is now inside.
3Replicate with the host
Viral genomes are copied and proteins assembled. Cells may die, pause, or keep working while particles form.
4Release
Budding through membranes or bursting the cell. Transmission to the next host is ecology — droplets, contact, vectors — not a lab protocol.
Headlines that say a virus 'mutated overnight' usually mean a large infected population plus selection, not a cartoon costume change.
Keep exploring
More in Tree of microbes
Bacteria
Single-celled prokaryotes with cell walls ? the oldest widespread life form, and both partners and pathogens.
Familiarity 95Fungi
A eukaryotic kingdom of yeasts, moulds and mushrooms — chitin walls, external digestion, partners of plants.
Familiarity 80Archaea
A prokaryotic domain that is not bacteria — methanogens, extremophiles and no known human pathogens.
Familiarity 35Bacteriophages
Viruses that infect bacteria — Earth's most abundant biological entities, and a concept-level idea in medicine.
Familiarity 42Protozoa
Motile unicellular eukaryotes — a teaching grade that includes pond ciliates and a minority of serious parasites.
Familiarity 58