Sinauer Associates ; Search term The Origin and Evolution of Cells Cells are divided into two main classes, initially defined by whether they contain a nucleus. Prokaryotic cells bacteria lack a nuclear envelope ; eukaryotic cells have a nucleus in which the genetic material is separated from the cytoplasm. Prokaryotic cells are generally smaller and simpler than eukaryotic cells ; in addition to the absence of a nucleus, their genomes are less complex and they do not contain cytoplasmic organelles or a cytoskeleton Table 1.
Konstantin Mereschkowski proposed a symbiotic origin for cells with nuclei. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton The terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C.
In his work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes.
However he mentioned this in only one paragraph, and the idea was effectively ignored until Chatton's statement was rediscovered by Stanier and van Niel. Plants had thus inherited photosynthesis from cyanobacteria.
This helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organellesmitochondria and chloroplasts. Wheeler renamed this the Archaea.
Dring suggested that the eukaryotic cell's nucleus came from the ability of Gram-positive bacteria to form endospores. In and later papers, Thomas Cavalier-Smith proposed instead that the membranes of the nucleus and endoplasmic reticulum first formed by infolding a prokaryote's plasma membrane.
In the s, several other biologists proposed endosymbiotic origins for the nucleus, effectively reviving Mereschkowski's theory. Eukaryotic DNA is divided into several linear bundles called chromosomeswhich are separated by a microtubular spindle during nuclear division.
Internal membrane[ edit ] The endomembrane system and its components Eukaryote cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system.
Many cells ingest food and other materials through a process of endocytosiswhere the outer membrane invaginates and then pinches off to form a vesicle.
Alternatively some products produced by the cell can leave in a vesicle through exocytosis. The nucleus is surrounded by a double membrane commonly referred to as a nuclear membrane or nuclear envelopewith pores that allow material to move in and out.
It includes the rough endoplasmic reticulum where ribosomes are attached to synthesize proteins, which enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the smooth endoplasmic reticulum.
For instance, lysosomes contain digestive enzymes that break down most biomolecules in the cytoplasm. Many protozoans have contractile vacuoles, which collect and expel excess water, and extrusomeswhich expel material used to deflect predators or capture prey.
In higher plants, most of a cell's volume is taken up by a central vacuole, which mostly contains water and primarily maintains its osmotic pressure.
Mitochondria and plastids[ edit ] Simplified structure of a mitochondrion Mitochondria are organelles found in all but one [note 1] eukaryote.
Mitochondria provide energy to the eukaryote cell by converting sugars into ATP.A critical step in the evolution of eukaryotic cells was the acquisition of membrane-enclosed subcellular organelles, allowing the development of the complexity characteristic of these cells.
The organelles are thought to have been acquired as a result of the association of prokaryotic cells with the . Some of the oldest cells on Earth are single-cell organisms called bacteria. Fossil records indicate that mounds of bacteria once covered young Earth.
Some began making their own food using carbon dioxide in the atmosphere and energy they harvested from the sun. This process (called photosynthesis.
The Evolution of Eukaryotic Cells Getty/Stocktrek Images As life on Earth started to undergo evolution and become more complex, the simpler type of cell called a prokaryote underwent several changes over a long period of time to become eukaryotic cells.
Eukaryotic cells boast their own personal "power plants", called mitochondria. These tiny organelles in the cell not only produce chemical energy, but also hold the key . The Endosymbiotic Theory is the accepted mechanism for how eukaryotic cells evolved from prokaryotic cells. Learn more. The Endosymbiotic Theory is the accepted mechanism for how eukaryotic cells evolved from prokaryotic cells.
Learn more. Endosymbiotic Theory. Search the site GO. Animals and Nature. Evolution History of Life on Earth Basics. In evolution of eukaryotic cells Organisms with a nucleus may have evolved as long ago as billion years, but how the first nuclear membrane arose remains a mystery.