Bacteria

Bacteria are single-celled prokaryotic organisms whose cells lack a nucleus and membrane-bound organelles. They include an immense diversity of forms, metabolisms, and ecological roles.

Prokaryote: An organism whose cells lack a nucleus and other membrane-bound organelles. Bacteria are prokaryotes, alongside archaea.
Peptidoglycan: A mesh-like polymer of sugars and amino acids that forms the bacterial cell wall. Its presence and organization distinguish major bacterial groups and guide antibiotic action.
Human microbiome: The community of microorganisms living in and on the human body, together with their genes and interactions. Bacteria make up a large part of these communities and influence health.
Archaea: A domain of single-celled prokaryotes distinct from bacteria in genetics, cell chemistry, and evolutionary history. Archaea also lack nuclei, but they are not bacteria.
Bacterial cell wall: A rigid layer outside the bacterial cell membrane, usually containing peptidoglycan. Its structure gives many bacteria shape and makes them targets of antibiotics.
Bacterial chromosome: The main DNA molecule carrying a bacterium’s essential genetic information, usually located in the nucleoid. Unlike a eukaryotic nucleus, the nucleoid is not enclosed by a membrane.
Antibiotic: A substance that kills bacteria or inhibits their growth. Antibiotics treat bacterial infections, but resistance can make them ineffective.
Eukaryote: An organism whose cells contain a nucleus and membrane-bound organelles. Eukaryotic cells have internal compartments absent from bacterial cells.
Bacterial binary fission: A form of cell division in which one bacterial cell replicates its DNA and splits into two cells. This is the usual mode of bacterial reproduction.
Plasmid: A small DNA molecule that replicates separately from a cell’s chromosome. Plasmids can carry traits such as antibiotic resistance and move between bacterial cells.

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