Organisms with cellular structure are combined into an empire cell, or prokaryotic (from the Greek Carion -. Engine). The body has a cellular structure. In the cell, simultaneously present both forms of nucleic acids – RNA and DNA. There ribosome. Capable of self-reproduction. There metabolism. Independently synthesized enzymes.
A typical cell structure, typical of most organisms, there was not immediate. In the cell, the earliest representatives of the contemporary organisms (prokaryotes or non-nuclear) cytoplasm and nuclear material with the DNA has not yet been separated from each other.
According to the presence or absence of the nucleus cellular organisms are divided into three subempire: nuclear-free (prokaryotes), mesokaryotes and nuclear (eukaryotic) (from Greek protos – first and eu – in fact, real.).
Prokaryotes are single-celled organisms that do not contain a limited nuclear membrane.
Superkingdom (subempire) prokaryotes include three kingdoms: Archaebacteria, Shizomycophyta and Cyanophyta. For prokaryotes are the cyanobacteria (blue-green algae), actinomycetes, bacteria, mycoplasma, Rickettsia and viruses.
Superkingdom prokaryotes: the main features
- Single-celled prokaryotic organisms (Bacteria Monera): general information
- Genome prokaryotes
- Archaebacterial or Archaebacteriobionta
- These bacteria (Bacterlobionta)
Structure and Physiology
Amino acids: carbon catabolism: cystine
Prokaryotes superkingdom includes three kingdoms: Archaebacteria, Shizomycophyta and Cyanophyta. For prokaryotes are blue-green algae, actinomycetes, bacteria, mycoplasma, Rickettsia and viruses.
Subempire of mesokaryotes
These include representatives of a single type – armored flagellates – dinoflagellates. In contrast to prokaryotes, they have a separate kernel. Unlike eukaryotic DNA in a closed ring. These long running parallel rings threadlike DNA can be twisted like bundles, forming a kind of chromosomes. It appears mitosis.
Mesokaryotes – not the ancestors of eukaryotes. This is – a side branch of evolution, the first attempt to build a cell in which the cytoplasm and nucleus separated from each other.
The main features of eukaryotes:
- the cell is divided into the cytoplasm and the nucleus;
- most of the DNA is concentrated in the nucleus. This nuclear DNA is responsible for most of cell life processes, and for the transmission of hereditary daughter cells;
- Nuclear DNA is split into multiple threads, not closed in the ring;
- these threads extend linearly within the chromosomes are clearly visible during mitosis;
- there is always the mitochondria (in green plants, there is also the plastid);
- there mitosis;
- It attaches to the sexual process;
- recombination of hereditary material provided by meiosis and sexual process;
- gametes are formed;
- flagella are real;
- characterized by digestive vacuole;
- not capable of free nitrogen fixation.
Reliable eukaryotic fossils date back to the age of 1.4 billion. Years. There are ambiguously interpreted findings age 2.0 billion. Years. Eukaryotes are divided into three kingdoms: plants, fungi and animals.
Eukaryotic cells: origin
At the beginning of the XX century, Russian botanists Famintsin and Merezhkovsky hypothesized that cells of green plants (eukaryotes) gained plastids the symbiosis of chlorophyll-deficient cells with blue-green cells. This hypothesis simbiogenetic origin of eukaryotic cells ahead of its time, was a half-forgotten and once again attracted attention in the middle of the XX century. In addition to nuclear DNA in a small quantity of eukaryotic cell found in the mitochondria, the plastids, centrioles, base flagella.
Electron microscopic comparison of the structure of flagella and centrioles says certitude of their relationship. The basis of these organelles is always eleven tubes, nine of which are arranged circumferentially and are two in the center. It was found that extranuclear DNA flagella and centrioles alone is capable of reduplicated. It was found that the mitochondrial DNA, plastid, apparently, and flagella and centrioles filamentous structure is connected in the ring as in typical prokaryotes. All these facts made it possible at the end of the 60s to return to the hypothesis of the origin of eukaryotic cells simbiogenetic.
This hypothesis was developed by the American researcher Lynn Margulis. According to this hypothesis, the primary cell of large irocariotic bacteria entering into symbiosis with the cells of blue-green, acquired plastids. Symbiosis with heterotrophic prokaryotic cells led to transform them into the mitochondria. Spirochetal symbiosis with bacteria could lead to the emergence of flagella on the one hand, and to the transformation of a portion of these cells in spirochetal centrioles – other. Biochemical, genetic, electron-microscopic data of recent years make the hypothesis L. Margulis more reasonable. However, while this hypothesis does not explain the origin of the eukaryotic nucleus, which could occur due to the complexity of nuclear material. In any case, the dual nature of nuclear DNA and the DNA of cytoplasmic organelles and surprising similarities with last prokaryotic DNA evidence that symbiosis has played a prominent role in the emergence of eukaryotic cells.