What cellular structure is characteristic of prokaryotes?

Prokaryotes are defined by several distinguishing characteristics, one of which is the absence of a nucleus. In prokaryotic cells, the genetic material is not enclosed within a membrane-bound structure, which is a fundamental difference from eukaryotic cells that possess a true nucleus. Instead, prokaryotic DNA is typically found in a single circular chromosome located in a region called the nucleoid. This structural simplicity allows prokaryotes to reproduce and carry out cellular processes without the compartmentalization seen in more complex cells.

Cell walls and other structures can be found in both prokaryotic and eukaryotic organisms, but the presence of a nucleus is a definitive feature that separates these two groups. While many prokaryotes indeed have cell walls made of peptidoglycan (in bacteria), this feature is not exclusive to them, as some eukaryotic cells, like plants and fungi, also have cell walls. Membrane-bound organelles, like mitochondria and the endoplasmic reticulum, are characteristic of eukaryotic cells, further differentiating them from prokaryotes that lack these structures altogether. Therefore, the defining characteristic that clearly identifies prokaryotes is their lack of a nucleus