Eukaryotic cell
Eukaryotic cells —from the Greek eu, 'good,' and karyon, 'nut' 39;— are the cells of eukaryotic organisms, which are characterized by always presenting a cytoplasm compartmentalized by lipid membranes and an organized cell nucleus. This cell nucleus is covered by a nuclear envelope that contains deoxyribonucleic acid or DNA, necessary for the development and functioning of the organism. Eukaryotic cells are thus distinguished from prokaryotic cells, which lack a defined nucleus and whose genetic material is dispersed in the cytoplasm. Organisms made up of eukaryotic cells are called eukaryotes.
The evolutionary step from prokaryotes to eukaryotes meant the great leap in complexity of life and the most important after the origin of life. Without the complexity that eukaryotic cells acquired, further steps such as the appearance of multicellular organisms would not have been possible; life would probably have limited itself to conglomerate bacteria. In fact, with the exception of prokaryotes (from which they come), the four remaining kingdoms (animals, plants, fungi and protists) are the result of this qualitative leap. The success of these eukaryotic cells made possible the subsequent adaptive radiations of life, which have led to the great variety of species that exist today.
Organization
Eukaryotic cells have a cytoplasm organized into compartments, with separate or interconnected (semimembranous) organelles, limited by biological membranes that have the same nature as the plasma membrane. The nucleus is the most notable and characteristic of the compartments in which the protoplasm, that is, the active part of the cell, is divided. In the nucleus is the genetic material, DNA. DNA is distributed in multiple chromosomes and linked to proteins, mainly to chromosomal proteins called histones, and it carries all the necessary information for all processes to be carried out, both intracellular and outside the cell, that is, in the organism itself..
In the protoplasm there are three main components to know: the plasmatic membrane, the cell nucleus and the cytoplasm, made up of everything else. Eukaryotic cells are endowed in their cytoplasm with a complex, highly structured and dynamic cytoskeleton, made up of microtubules and various protein filaments. In addition, there may be a cell wall, which is typical of plants, fungi and multicellular protists, or some other type of external covering to the protoplasm.
For its comparison with the prokaryotic cell, see the Comparative Table
Physiology
Although eukaryotic cells demonstrate incredible diversity in their form, they share the fundamental characteristics of their cellular organization, summarized above, and a great homogeneous catalysis in relation to their biochemistry (composition), and metabolism, which contrasts with the immense heterogeneity that prokaryotes (bacteria in the broad sense) present in this area.
Eukaryotic cells initially contain mitochondria, organelles that they would have acquired by endosymbiosis from certain primitive bacteria, which gives them the ability to develop an aerobic metabolism. However, in some eukaryotes of the protista kingdom, mitochondria have disappeared secondarily in the course of evolution, generally deriving to other organelles, such as hydrogenosomes.
Some eukaryotes perform photosynthesis, unlike animal cells, thanks to the presence in their cytoplasm of organelles called plastids, which derive by endosymbiosis from bacteria of the group called cyanobacteria (blue algae).
Origin of the eukaryotic cell
The origin of eukaryotes is a complex process that has a prokaryotic origin. Although there are several theories that explain this process, according to most studies it was produced by endosymbiosis between various prokaryotic organisms, where the main proto-eukaryotic ancestor is of the archean type and the mitochondria and chloroplasts are of bacterial origin. The incorporation of other prokaryotic organisms is debatable. The most widespread theory in this regard is serial endosymbiosis, postulated by Lynn Margulis. The endosymbiotic theory (endo means internal and symbiont refers to the mutually beneficial relationship between two organisms). This interpretation does not extend to the origin of the nuclear membrane, which would have been established from an invagination of the cell membrane.
Eukaryotic Organisms
Eukaryotic organisms make up the Eukaryota domain, which includes the best-known organisms, divided into four kingdoms: Animalia (animals), Plantae (plants), Fungi (Fungi) and Protista (which cannot be classified within the first three kingdoms).). They include the vast majority of morphologically recognizable extinct organisms that paleontologists study. Examples of eukaryotic disparity range from a dinoflagellate (a photosynthesizing single-celled protist), a tree such as a sequoia, a squid, or a cluster of mushrooms (fungal reproductive organs), each with distinct cells and, in the case of multicellular, often highly varied. In summary, Eukaryota includes multicellular organisms distributed in the kingdoms: Animalia, Plantae and Fungi, and there are also unicellular (microscopic) organisms, among which are microsporidia, protozoa (amoeboids, flagellates, ciliates), yeasts, some fungi and molds.
Differences between eukaryotic cells
There are various types of eukaryotic cells, among which the cells of animals and plants stand out. Fungi and many protists do, however, have some substantial differences.
Animal Cells
Animal cells make up the tissues of animals and are distinguished from plant cells in that they lack cell walls and chloroplasts and have smaller and generally more abundant centrioles and vacuoles. Due to the lack of a rigid cell wall, animal cells can take on a variety of shapes and can even engulf other structures.
Plant cells
The distinctive characteristics of plant cells are:
- A large central vacuola (delimited by a membrane, the tonoplast), which maintains the form of the cell and controls the movement of molecules between cytosol and sap.
- A cellular wall composed of cellulose and in many cases, lignine, which is deposited by the protoplast on the outside of the cell membrane. This contrasts with the cellular walls of the fungi, which are made of chin, and that of the procariots, which are made of peptidoglycan.
- Plasmodesms, link pores on the cell wall that allow the cells of the plants to communicate with the adjacent cells. This is different from the hiff network used by the fungi.
- Plasts, especially chloroplasts containing chlorophyll, the pigment that gives the plants its green color and that allows them to take photosynthesis.
- The groups of plants without scourges (including conifers and plants with flower) also lack the centrioles that are present in the animal cells. These can also be found in animals of all types, that is, in a mammal in a bird or in a reptile.
Fungal cells
Fungal cells, for the most part, are similar to animal cells, with the following exceptions:
- A cell wall made of chin.
- Lower definition between cells. The cells of the upper fungi have porous separations called septos that allow the passage of cytoplasm, orgoulos, and sometimes nuclei. Primitive fungi do not have such divisions, and each organism is essentially a giant supercell. These fungi are known as coenocytics.
- Only the most primitive mushrooms, Chytridiomycota, have scourges.
Cells of Protista Organisms
Some Protista organisms are made up of a single cell that can reach macroscopic sizes (the unicellular organism Syringammina fragilissima reaches 20 cm in diameter).
| Typical animal cell | Typical vegetable cell | |
|---|---|---|
| Basic structures |
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| Orgánulos |
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| Additional structures |
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Playback
Eukaryotic cells can reproduce in three different ways, mainly:
- Bipartition: The kernel is divided into two and then the cell is divided into two of the same size.
- Gemation: The core is divided into two, one moves to the membrane and forms a separate yolk. Forming two cells of different size.
- Sporulation: The core is divided repeatedly and surrounded by membrane forming cells called sporas.
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