prokaryo

Prokaryo, a shorthand for prokaryote, refers to unicellular organisms that lack a nucleus and other membrane-bound organelles. The term is used for members traditionally grouped into Bacteria and Archaea. Prokaryotes are one of the two major cellular lineages alongside eukaryotes.

They have a nucleoid where the genome resides, typically a single circular chromosome, and often plasmids. They possess a cell envelope consisting of a plasma membrane and, in many species, a cell wall. External structures such as flagella, fimbriae, or a protective capsule may be present. They lack mitochondria, chloroplasts, and other membrane-bound organelles.

Genetics and reproduction: Their genomes are generally small and haploid, and reproduction is mainly by binary fission. Horizontal gene transfer occurs through transformation, transduction, and conjugation, enabling rapid adaptation.

Metabolism and ecology: Prokaryotes show diverse metabolisms, including photoautotrophy, chemotrophy, and mixotrophy. They occupy nearly every habitat and play key roles in nutrient cycling, decomposition, and symbiotic associations. Some are pathogens, while many are beneficial to humans and ecosystems.

Classification and evolution: Historically, prokaryotes were grouped into Bacteria and Archaea, separate from the eukaryotic domain. Phylogenetic studies based on conserved genes, including 16S rRNA, support deep divisions between these lineages. The label prokaryote is a convenience rather than a strict clade.

Relevance: Prokaryotes are central to microbiology, medicine, and industry; they include model organisms, producers of antibiotics and enzymes, and agents in fermentation and biotechnological processes.