The Basics Eukaryotic Cells Eukaryotic cells are cells with membrane-bound organelles and a nucleus.
Reproduction[ edit ] Bacteria and archaea reproduce through asexual reproductionusually by binary fission. Genetic exchange and recombination still occur, but this is a form of horizontal gene transfer and is not a replicative process, simply involving the transference of DNA between two cells, as in bacterial conjugation.
DNA transfer[ edit ] DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has been mainly studied in bacteria. In bacteria, gene transfer occurs by three processes.
These The evolution of eukaryotic cells from 1 bacterial virus bacteriophage -mediated transduction2 plasmid -mediated conjugationand 3 natural transformation. Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, rather than an adaptation of the host bacteria.
Conjugation in the well-studied E. Infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA conjugation also appears to be an accidental process rather than a bacterial adaptation.
Play media 3D animation of a prokaryotic cell that shows all the elements that compose it Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium. Unlike transduction and conjugation, transformation is clearly a bacterial adaptation for DNA transfer, because it depends on numerous bacterial gene products that specifically interact to perform this complex process.
About 40 genes are required in Bacillus subtilis for the development of competence. Sociality[ edit ] While prokaryotes are considered strictly unicellular, most can form stable aggregate communities.
Also, as with multicellular eukaryotes, these changes in expression often appear to result from cell-to-cell signalinga phenomenon known as quorum sensing. Biofilms may be highly heterogeneous and structurally complex and may attach to solid surfaces, or exist at liquid-air interfaces, or potentially even liquid-liquid interfaces.
Bacterial biofilms are often made up of microcolonies approximately dome-shaped masses of bacteria and matrix separated by "voids" through which the medium e.
The microcolonies may join together above the substratum to form a continuous layer, closing the network of channels separating microcolonies. This structural complexity—combined with observations that oxygen limitation a ubiquitous challenge for anything growing in size beyond the scale of diffusion is at least partially eased by movement of medium throughout the biofilm—has led some to speculate that this may constitute a circulatory system  and many researchers have started calling prokaryotic communities multicellular for example .
Differential cell expression, collective behavior, signaling, programmed cell deathand in some cases discrete biological dispersal  events all seem to point in this direction. However, these colonies are seldom if ever founded by a single founder in the way that animals and plants are founded by single cellswhich presents a number of theoretical issues.
Most explanations of co-operation and the evolution of multicellularity have focused on high relatedness between members of a group or colony, or whole organism. If a copy of a gene is present in all members of a group, behaviors that promote cooperation between members may permit those members to have on average greater fitness than a similar group of selfish individuals  see inclusive fitness and Hamilton's rule.
Should these instances of prokaryotic sociality prove to be the rule rather than the exception, it would have serious implications for the way we view prokaryotes in general, and the way we deal with them in medicine.
Environment[ edit ] Phylogenetic ring showing the diversity of prokaryotes, and symbiogenetic origins of eukaryotes Prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types.
For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarcticastudied in cryobiology or as hot as undersea hydrothermal vents and land-based hot springs.
Prokaryotes live in nearly all environments on Earth.
Some archaea and bacteria are extremophilesthriving in harsh conditions, such as high temperatures thermophiles or high salinity halophiles. Symbiotic prokaryotes live in or on the bodies of other organisms, including humans.
Classification[ edit ] Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes InCarl Woese proposed dividing prokaryotes into the Bacteria and Archaea originally Eubacteria and Archaebacteria because of the major differences in the structure and genetics between the two groups of organisms.
Archaea were originally thought to be extremophiles, living only in inhospitable conditions such as extremes of temperaturepHand radiation but have since been found in all types of habitats.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. 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 . 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.
Mitochondria and chloroplasts have striking similarities to bacteria cells. They have their own DNA, which is separate from the DNA found in the nucleus of the cell.
And both organelles use their DNA to produce many proteins and enzymes required for their function. The origin of the eukaryotic cell is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine; Knoll () suggests they developed approximately – billion years ago.
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 .