Eukaryote

Heliozoan Acanthocystis turfacea

Lower eukaryotes or eukaryotes ( Eukaryota / Eukaryonta / Eucarya / Eukarya; εὖ to ancient Greek eu, good, genuine ' and κάρυον Karyon, nut ') are all living together whose cells have a nucleus. The group of organisms that lack a cell nucleus are called prokaryotes. In addition to bacteria and archaea eukaryotes are one of the three domains in the classification of living things.

Features

The cells of the eukaryotes usually have a diameter of 10-30 microns. They are substantially greater than those of prokaryotes, generally, their volume is about 100 - to 10,000 -fold. For the smooth functioning of cellular processes over long distances within the cell, a higher level of organization and a division of the cell space into compartments ( enclosed spaces ) as well as transport between these compartments is low. For this reason, eukaryotic cells are structured by means of cell organelles, which perform like the organs of a body different functions. The eponymous organelle is the nucleus with the main component of the genetic material of eukaryotic cells. Other genes depending on the type in the mitochondria - organelles that make energy through chemical reactions available - and plastids - photosynthetic organelles driving - before. The intracellular transport are the organelles of the endomembrane system.

Structure and form of eukaryotic cells is given by the cytoskeleton, which also serves as the moving. It is composed of microtubules, microfilaments and intermediate filaments. Some eukaryotes, such as plants and fungi, have cell walls that enclose the cells outside of the cytoplasmic membrane and determine its shape.

Another special feature of eukaryotes lies in the protein biosynthesis: Unlike prokaryotes, eukaryotes able to produce using the same DNA information by alternative splicing of different proteins.

Multicellularity

Eukaryotes can be unicellular or multicellular organisms. These consist of a larger number of cells with a common metabolism, with specific cell types take over certain tasks. Most known multicellular organisms are eukaryotes, including plants, animals and multicellular fungi.

System

In biological classification, the eukaryotes form one of the three domains, ie, the highest categories for the classification of living things. Writing, the current classification of eukaryotes was by Adl et al. Erected in 2005. They divided the eukaryotes into six groups, often called " supergroup " called, instead of a classical concept of rank:

• Amoebozoa, one-celled organisms that are characterized generally by an amoeboid shape
• Opisthokonta to which animals and fungi are
• Rhizaria, unicellular organisms, the fine as a characterizing feature of pseudopods, called pseudopodia have
• Archaeplastida to which the plants are
• Chromalveolata, they include mainly various photosynthetically active groups, which are generally referred to as algae
• Excavata, unicellular organisms that are flagellated by a majority. The name derives from the typical cell shaped mouth ( cytostome ) with a pronounced mouth pit ( " excavater " type).

Taxa of uncertain position ( incertae sedis ):

• Camera lens, a Geißeltierchenart and the only member of the genus camera
• Ancyromonas
• Apusomonadidae
• Centrohelida
• Collodictyonidae
• Spironemidae
• Kathablepharidae
• Picozoa

Also still out as incertae sedis at Adl:

• Stephanopogon: The genus was found in 2008 near the Heterolobosea ( excavata ).

History of development

The oldest macroscopic, multicellular, eukaryotic fossils are 2.1 billion years old ( Gabonionta ). This single-celled eukaryotic origins are even older.

Little is known about the exact evolutionary history of eukaryotes, but it is thought that they evolved in parallel to bacteria and archaea and are not descended from any of these taxa. Morphological and genetic studies, however, show that the archaea eukaryotes apparently are closer than the bacteria, so these two domains may have had a common ancestor. The similarities include the transcription which is carried out at archaea using complex with RNA polymerase ten subunits. Bacteria possess a polymerase which is formed of only five subunits. The translation is similar to that of eukaryotes.

It is not known whether eukaryotes their size before capture of organelles possessed (which this necessitated due to the negative surface- to-volume ratio ) or could purchase these only after the increase in their level of organization. The most popular theory on the origin of the organelles is the endosymbiont theory that states that mitochondria and chloroplasts evolved from bacteria, which Incorporation of in the early eukaryotes. The membrane structure of these organelles, the presence and the structure of the genetic material and ribosomes as well as the relatively high autarky compared to other cell structures - chloroplasts and mitochondria can not be formed by the cell, but multiply by division - in favor of this theory. For the explanation of the origin of mitochondria, a bacterium has been found from the group of rickettsia recently, showing a relatively large genetic match with them. This bacterium is a pathogen, it moves into a host cell and parasite in it. It is questionable whether other organelles such as the endoplasmic reticulum have evolved after the endosymbiotic theory of prokaryotes. Some researchers assume at least that the nucleus is caused by immigration or incomplete phagocytosis of a bacterium or an archaeon.

After the development of the organelles, especially the mitochondria, the eukaryotes were now able to accelerate their metabolism and development as well as to optimize its energy efficiency.