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What is the meaning of Plastid? Concept and Definition of Plastid


Definition, concept, meaning, what is plastid


1. Concept of plastid

The plastos, plastids or plastids are organelles eukaryotic, plants and algae. Its main function is the production and storage of important chemical compounds used by the cell. Thus, they play an important role in processes such as photosynthesis, the synthesis of lipids and amino acids, determining the color of fruits and flowers, among other functions.
There are two types of plastos clearly differentiated, according to the structure of their membranes: the primary plastos, which are found in most plants and algae; and secondary, more complex plastos encountered in plankton.


The primary plastos are own evolutionary branch that includes the red algae, green algae and plants. There are secondary plastos which have been acquired by endosymbiosis by other evolutionary lineages and which are modified forms of plastidiadas eukaryotic cells.
The plants plastos are presented as relatively large organelles, of generally numerous and ellipsoidal shape. In a square millimeter section of a sheet, there may be more than 500,000 chloroplasts. In protists are often unique structures, which are more or less widely spread over the cytoplasm. Limited for the remainder of the cytoplasm are two structurally different membranes. They are often coloured by nature liposoluble pigments. Like mitochondria, they have circular and naked DNA. The plastos of eukaryotic groups are remarkably diverse. Those that appear on the plants offer a proper reference.
They appear delimited by sheath plastidial, formed by two membranes, the outer plastidial membrane and plastidial inner membrane. The space between the two, called space intraplastidial, has a differential composition and is counterpart of the Periplasmic space of bacteria.
The interior space of the chloroplast, the stroma contains flattened vesicles called thylakoids, whose lumen or cavity is sometimes continued with periplastidial space, especially in youth chloroplasts (proplastids). The thylakoid membranes, more or less parallel, stretching form locally piles called grana (granum-Latin neutral plural). The thylakoid membranes are the photosystems, complexes of proteins and pigments responsible for photosynthesis light phase.
Processes of the dark phase of photosynthesis, with the fixing of carbon (Calvin cycle) occur in dissolution in the stroma, taking advantage of the power set as ATP in the thylakoid membranes during the light phase.
In the stroma is the DNA plastidial, a reduced version of the bacterial chromosome, which comes from a catalog of genes limited carrier. As it is common in bacteria, the Green plasto presents their DNA in the form of a single circular chromosome. The genetic information of the plastidial chromosome directs the formation of a limited number of proteins, the rest are imported from the cytoplasm. For protein synthesis the plastid boasts its own Ribosomes which are, logically, prokaryotic (bacterial) type. The plastos multiply by bipartition, once duplicate DNA plastidial.
In plant cells chloroplasts move and orient themselves increasingly of the most appropriate way to capture the light.

2. Definition of plastid

A plastid is an organelle present in the cells of eukaryotic type, whose purpose is to generate and accumulate certain chemical substances.
Typical organisms such as algae, plants and plankton, the plastids (which are also known as plastids or plastos) are essential in the synthesis of amino acids, in photosynthesis and in other processes.
In organisms that reproduce sexually, the plastids are transmitted via the gametes. They have a particular DNA (called DNA plastidial) and have Ribosomes of reduced size in comparison to the Ribosomes in the cytoplasm.
According to its origin and structure, it is possible to differentiate between the plastids of primary and secondary plastids. The primary plastids are present in terrestrial plants and algae green and red, while the secondary plastids are found in Brown algae and other organisms. Another classification, developed according to the location of the plastids, speaks of amiloplastos, proplastidos, leucoplastos, and chromoplasts.
It is important to emphasize that, although the plastids are typical of plants, there are animals that can present secondary plastids in their cells. That is the case of corals, which belong to the phylum of the phylum Cnidaria.
It should be noted, on the other hand, that the plastids are part of the activity that allows the cells to store proteins, lipids and carbohydrates, substances that are necessary for their subsistence and development. The plastids may also carry pigments that determine the staining of the organism in question, carotenoids and chlorophyll.

3. Meaning of plastid

Plastids. The plastids are typically plant cell organelles. They are characteristic of plant cells part. Each plastid is surrounded by a double membrane. Within this double membrane we have the stroma that is the watery substance contained in the plastid.


It's reaction areas rich in lipoid, limited against the Central cytoplasm by a very delicate double membrane. They are often coloured by fat soluble pigments (lipocromas) and serve in anabolism as organs of the photosynthetic uptake of carbon and condensation of the starch. In this case you are called chromatophores.


They are involved in the synthesis and storage of Organics such as carbohydrates, lipids and proteins. You can take different pigments such as chlorophyll and carotenoids (red, yellow or orange pigment).

Pigments possessing the plastids

By pigments possessing the plastids, are of the following classes:
Chloroplasts: (chlorine = green): plastids of green, for wearing a Green pigment called chlorophyll.
Chromoplasts: (chrome = color) plastillos, pigments as the red pigment (lecopeno) yellow (Xanthophyll) orange (carotene). They are that give color to flowers and fruits of many plants.
Leucoplastos: (leucos = white) colorless plastids which serve as Center of stored certain cytoplasm materials such as starch (amiloplastos).
Oleoplastos: Stored and colorless plastids from droplets of oils such as peanuts, Castor, etc.


All plastids, which in its juvenile phase (the so-called proplastids) contain up to 3% of its dry weight in DNA and in adult State always have more than 1% of it, multiply by bipartition. In some plastids of algae DNA is observed in the form of filamentous structures in exactly certain sites, which, moreover, are «empty» in the electron microscope. The proplastids still relatively small, equipped with (juvenile) meristematic cells ameboid movement, growing together with these cells up to several times greater than the initial and, through the formation of creases in its inner membrane can acquire a considerable inner surface, in which the photosynthetic pigments are placed neatly. The senile plastids often contain lipid droplets: the so-called plastoglobulos.


In sexual reproduction, the plastids are transmitted through the gametes from generation to generation. Often only the ovocelula contains them. as the male gameta is very poor in plasma, certain pigments mutations linked to the plastids are transmitted in such cases. only through maternal (plastidial inheritance). In this connection, the plastids contain DNA specific plastidial, which does not exist in the cell nucleus.
In the photosynthetically active, in the cyanobacteria, blue and lacking bacteria's core. Photosynthesis pigments are not still located in special organelles, but they are located in a peripheral cromatoplasma, whose structure, however, can be recognized as a provision laminar apart, such that this case, is itself exclusively of chromatophores.
Algae of higher organization, the form of chromatophores presents a great diversity. Next to large plates and overwhelmed in propeller tape are given forms reticular (Oedogonium), star-shaped section (Euastrum), and other desmidiales. cupuliformes and irregularly lobed (Rhodochorton)


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