viirustes

Viirustes are submicroscopic infectious agents that replicate only inside living cells. They consist of genetic material made of DNA or RNA enclosed in a protein coat called a capsid; some also have a lipid envelope derived from the host cell membrane. Outside a host, viirustes cannot reproduce and are not considered living organisms in the traditional sense.

In terms of structure and genome, viirustes vary widely. Their genomes can be double-stranded or single-stranded DNA or RNA, and their size ranges from about 20 to 300 nanometers. They attach to specific receptors on a host cell surface and enter by endocytosis or membrane fusion. Once inside, they commandeer the host’s machinery to replicate their genome and assemble new virions, which leave the cell by lysis or budding.

Classification of viirustes is based on genome type, structure, and replication strategy. The Baltimore classification groups viruses by genome type (DNA or RNA, single- or double-stranded) and replication method. Structural differences include icosahedral or helical capsids, and the presence or absence of an outer envelope. Replication location often differs, with DNA viruses frequently targeting the nucleus and RNA viruses usually replicating in the cytoplasm; retroviruses use reverse transcription.

Ecologically, viirustes are ubiquitous and include bacteriophages that infect bacteria, playing a key role in microbial ecosystems and horizontal gene transfer. In medicine and agriculture, viruses are studied for vaccines and antiviral therapies, as well as for applications like phage therapy and gene delivery research. Not all viirustes cause disease; many interact with hosts in neutral or beneficial ways, shaping evolution and ecology across communities.