noncellular

Noncellular refers to entities that lack cellular organization and are not composed of cells. In biology, the term is commonly applied to biological agents that do not have cellular structure, such as viruses, viroids, and prions. The concept contrasts with cellular life, which consists of cells that carry out metabolism, growth, and reproduction within a defined cellular boundary.

Viruses are the most widely cited noncellular agents. They consist of genetic material—DNA or RNA—encapsulated in a protein coat, and sometimes enveloped by lipids. Outside a host cell, viruses have no independent metabolism and cannot replicate; they require living cells to produce new viral particles. Viroids are even simpler, consisting of small circular RNA molecules without protein coats that infect plants and rely on host enzymes for replication. Prions are infectious proteins that propagate by inducing the misfolding of normal proteins, lacking nucleic acids entirely and not encoding genetic information themselves. Together, these examples illustrate how noncellular agents achieve propagation and pathogenicity without cellular machinery.

The term noncellular is sometimes used interchangeably with acellular, though acellular is the more precise term in many scientific contexts, particularly in virology and microbiology. The designation highlights differences in biology, life status, and replication strategy, and it informs areas such as disease control, biosafety, and the study of pathogen evolution. The noncellular classification also acknowledges entities that challenge conventional definitions of life, prompting ongoing discussion in biology and philosophy.