Prokaryot

A prokaryote is a unicellular organism that lacks a true nucleus and membrane-bound organelles. Prokaryotes comprise two major domains, Bacteria and Archaea, and they are among the earliest forms of life. They are found in nearly every habitat on Earth, from soil and water to extreme environments such as acidic hot springs and deep-sea vents.

Cell organization and genetics: The genetic material of a prokaryote is typically a single circular chromosome located in the nucleoid region. Many also carry smaller circular DNA molecules called plasmids. Prokaryotic cells have a cell membrane and usually a rigid cell wall; in many bacteria the wall contains peptidoglycan, whereas archaeal walls may be composed of pseudopeptidoglycan or other polymers. Most prokaryotes possess 70S ribosomes. Some lack a cell wall, while others have external structures such as capsules, flagella, or pili for movement and attachment.

Reproduction and genetics: Prokaryotes reproduce primarily by asexual binary fission, enabling rapid population growth. Genetic variation arises through mutations and horizontal gene transfer mechanisms, including transformation, transduction, and conjugation, which mix genetic material between cells.

Metabolism and ecology: They display a wide range of metabolisms, including photosynthesis, chemosynthesis, and heterotrophy. Prokaryotes play crucial roles in nutrient cycles (carbon, nitrogen, sulfur) and in ecological processes such as decomposition, symbiosis, and bioremediation. While some species are pathogens, many prokaryotes are beneficial or neutral to other organisms.

Classification and significance: Historically grouped as prokaryotes, modern taxonomy recognizes two domains, Bacteria and Archaea, with eukaryotes distinct from them. Prokaryotes are central to biology and medicine, influencing health, industry, and environmental science.