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A prokaryote (/ p r oʊ ˈ k ær i oʊ t,-ə t /; less commonly spelled procaryote) [1] is a single-celled organism whose cell lacks a nucleus and other membrane-bound organelles. [2] The word prokaryote comes from the Ancient Greek πρό (pró), meaning 'before', and κάρυον (káruon), meaning 'nut' or 'kernel'. [3]
The DNA of a prokaryotic cell consists of a single circular chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid. Most prokaryotes are the smallest of all organisms, ranging from 0.5 to 2.0 μm in diameter. [1] [page needed] A prokaryotic cell has three regions:
The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea.
Bacteria can be classified on the basis of cell structure, cellular metabolism or on differences in cell components, such as DNA, fatty acids, pigments, antigens and quinones. [117] While these schemes allowed the identification and classification of bacterial strains, it was unclear whether these differences represented variation between ...
[3] [4] In the three-domain model, the first two are prokaryotes, single-celled microorganisms without a membrane-bound nucleus. All organisms that have a cell nucleus and other membrane-bound organelles are included in Eukarya and called eukaryotes. Non-cellular life, most notably the viruses, is not included in this system.
Image of the mitotic spindle in a human cell showing microtubules in green, chromosomes (DNA) in blue, and kinetochores in red. [citation needed] Cells are broadly classified into two main categories: simple non-nucleated prokaryotic cells and complex nucleated eukaryotic cells. Due to their structural differences, eukaryotic and prokaryotic ...
One example of infection of a virus constituting as extrachromosomal DNA is the human papillomavirus . The HPV DNA genome undergoes three distinct stages of replication: establishment, maintenance and amplification. HPV infects epithelial cells in the anogenital tract and oral cavity. Normally, HPV is detected and cleared by the immune system.