The structure of prokaryotic and eukaryotic cells
There are two basic cell types: prokaryotic and eukaryotic cells.
cell, nucleus, bacterium, flagellum, cilium, cell wall, plasmid, nuclear membrane, cytoskeleton, endoplasmic reticulum, polysaccharide, peptide, DNA, chromosome
Every living organism on Earth is built up of one or more cells. Based on their cell structure, organisms can be grouped as prokaryotes and eukaryotes.
Prokaryotes are unicellular organisms that lack a cell nucleus, while the cells of Eukaryotes have a membrane-bound nucleus.
Prokaryotic and eukaryotic cells differ in several respects. Such differences are their size and structure: prokaryotic cells are about ten times smaller and much simpler in structure than eukaryotic cells.
The genetic material of prokaryotic cells consists of a single circular chromosome which is not separated from other parts of the cell by a nuclear membrane.
These simple cells do not have any membrane-bound organelles or a cytoskeleton either. The cytoplasm is surrounded by a cell membrane, which, in turn, is covered by a polysaccharide and peptide cell wall that provides external protection for the cells. Prokaryotic cells may have one or numerous appendages extending from their surface. These can be cilia, flagella or pili.
Bacteria (formerly: Eubacteria) and Archea are the two main groups of prokaryotes.
Eukaryotic cells have real nuclei, that is, the genetic material is enclosed by a membrane. The nucleus contains several linear chromosomes.
These cells also contain membrane-bound cell organelles besides the nucleus. The most important of these are the mitochondria and the chloroplasts, the latter characteristic of plant cells only.
The endoplasmic reticulum, connected to the cell nucleus, also plays an important role in the cell: this is the site of protein synthesis.
The cytoplasm of all eukaryotic cells is surrounded by a cell membrane, but only plant and fungal cells have cell walls.
Eukaryotes are usually grouped in four kingdoms: unicellular eukaryotes (protozoa), fungi, plants and animals.
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