prokaryote

prokaryote, any organism that lacks a distinct nucleus and other organelles because of the absence of internal membranes. Bacteria are among the best-known prokaryotic organisms. The lack of internal membranes in prokaryotes distinguishes them from eukaryotes.

Physical features

The prokaryotic cell membrane is made up of phospholipids and constitutes the cell’s primary osmotic barrier, regulating the movement of substances into and out of the cell. The cytoplasm contains ribosomes, which carry out protein synthesis, translating genetic information into proteins, and a double-stranded deoxyribonucleic acid (DNA) chromosome, which is usually circular and is located in a nucleoid region rather than enclosed within a nucleus. Many prokaryotes also contain additional circular DNA molecules called plasmids, with additional dispensable cell functions, such as encoding proteins to inactivate antibiotics. Some prokaryotes have flagella. Prokaryotic flagella are distinct in design and movement from the flagella found on some eukaryotes.

Evolutionary significance and metabolic diversity

Prokaryotes are classified into two major domains, Bacteria and Archaea, which differ in genetic makeup, membrane chemistry, and biochemical pathways despite sharing a simple cellular structure without a nucleus. These groups represent the earliest forms of life on Earth, emerging more than 3.5 billion years ago, and played a central role in shaping the planet’s environment. Through activities such as photosynthesis and nitrogen fixation, prokaryotes transformed Earth’s atmosphere and enabled the evolution of more complex organisms; they are also linked to the origin of eukaryotic cells through ancient symbiotic relationships.

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Bacteria: The bacterial cell

Prokaryotes exhibit extensive metabolic diversity, employing a wide range of energy and nutritional strategies, including phototrophy and chemotrophy, as well as autotrophic and heterotrophic modes of growth. They may use oxygen or alternative electron acceptors such as nitrate or sulfate, and many are capable of fermentation or of switching between metabolic pathways depending on environmental conditions. Some prokaryotes play specialized roles in biogeochemical cycles, including nitrogen fixation and sulfur metabolism, and many—particularly among the archaea—are adapted to extreme environments. Prokaryotes reproduce primarily by binary fission but also engage in horizontal gene transfer through conjugation, transformation, and transduction, processes that enhance genetic diversity and facilitate rapid adaptation.

Medical significance and applications

Prokaryotes are medically significant owing to their role in disease and to their formation of the human microbiome. Certain bacteria are pathogenic, collectively causing a wide range of infectious diseases. Some also contribute to the development of antimicrobial resistance, posing major public health challenges. As part of the normal microbiota, many prokaryotes are also essential to human health, supporting numerous processes, including digestion, metabolism, and immune function.

Prokaryotes also have important applications in medicine, industry, agriculture, and environmental management. They serve as key tools in genetic engineering and synthetic biology, being used in the production of antibiotics, vaccines, recombinant proteins, and probiotics. An example is the use of Escherichia coli to manufacture human insulin. The gene responsible for insulin production is inserted into bacterial plasmids, enabling the bacteria to generate large amounts of insulin, which can then be purified and used to treat diabetes mellitus.

In industry and food production, prokaryotes drive fermentation processes and are used to produce enzymes and biofuels. Environmentally, they play critical roles in bioremediation and wastewater treatment, while in agriculture they enhance soil fertility through nitrogen fixation and function as biofertilizers and biopesticides.

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