Prokaryotes unicellular organisms that lack a true nucleus and membrane-bound organelles . Their genetic material is not enclosed in a nuclear membrane but instead is found in a single circular DNA molecule located in the nucleoid cell .
Main Characteristics of Prokaryotes: Feature Description Cell Type Simple, unicellular Nucleus Absent (DNA is in nucleoid)Organelles No membrane-bound organelles (e.g., mitochondria , ER)DNA Single circular chromosome Size Small (typically 0.1–5 μm) Cell Wall Present in most (e.g., made of peptidoglycan in bacteria) Reproduction Asexual (usually by binary fission ) Ribosomes Present (70S, smaller than eukaryotic 80S)
Major Groups of Prokaryotes: Bacteria Found in many environments (soil, water , human gut) Can be beneficial (gut flora, yogurt fermentation) or pathogenic (e.g., E. coli , Streptococcus ) Cell walls contain peptidoglycan Archaea Often found in extreme environments (hot springs, salt lakes) Do not have peptidoglycan in their cell wallsGenetically and biochemically more similar to eukaryotes than bacteria Functions and Importance: Decomposers : Recycle nutrients in ecosystems.Nitrogen fixation : Convert atmospheric nitrogen into forms usable by plants.Symbiosis : Live in mutualistic relationships (e.g., gut microbiota in humans).Industrial uses : Used in biotechnology (e.g., insulin production, fermentation).Medical relevance : Some cause diseases, but many are essential to health.Prokaryotes vs. Eukaryotes Feature Prokaryotes Eukaryotes Nucleus Absent Present DNA Structure Circular, no histones (except in archaea) Linear, packaged with histones Size Small (0.1–5 µm) Larger (10–100 µm) Organelles None Membrane-bound (e.g., mitochondria) Cell Division Binary fission Mitosis or meiosis Examples Bacteria, Archaea Animals, plants, fungi, protists
Summary Table: Property Description Cell Structure Simple, no nucleus DNA Single circular molecule in nucleoid Organelles None membrane-bound Ribosomes 70S (smaller than eukaryotic) Reproduction Binary fission Types Bacteria and Archaea Importance Ecological, medical, industrial
