It is called chloroplast yet organelle present in the cells of plants, where the photosynthesis (the metabolism process that allows certain organisms to synthesize organic substances using sunlight as an energy source).
Bounded by two membranes, chloroplasts have vesicles called thylakoids that house the molecules capable of transforming the light energy from the sun's rays into chemical energy. One of these molecules is the chlorophyll .
The chloroplast outer membrane has a good amount of protein calls porinas . In the inner membrane, however, the porins are smaller. Inside the chloroplast you can recognize the stroma , a cavity where carbon dioxide is fixed. Thylacoids, with chlorophyll, carotenoids and other pigments with photosynthetic capacity, are also found inside.
In chloroplast it is also possible to recognize the plastoglobes , protected by a membrane which is similar to the one that covers the thylakoids, from which they emerge. In the plastoglobes there are different organic molecules, among which some lipids are especially common. It should be noted that all the functions of the plastoglobulin molecules have not yet been specified.
The photosynthesis It is carried out in two phases, each one developed in different sectors of the chloroplast. The call luminous phase It is produced in the membrane that surrounds thylakoids, where the elements that convert light energy into chemical energy are found. The dark phase , meanwhile, is generated in the stroma. There an enzyme is responsible for fixing carbon dioxide.
The content of the cell is divided into several compartments and this phenomenon represents an organizational level challenge due to the concept known as protein traffic , which, in a cell eukaryotic , regulate:
* classification signals , a reduced number of amino acids that form a compound known as peptide, which in this case indicates with lysosomal enzymes of the mannose-phosphate group the proteins that are secreted;
* receivers that warn said signals and move the proteins in which they are contained to the relevant compartments.
The importation of proteins by means of one or more external membranes that act as limits occurs in four cell organelles: chloroplast, nucleus, peroxisomes and mitochondria . An example can be seen in the proteins that import these organelles in the rough endoplasmic reticulum, which have amino acid sequences that serve as "domicile" so that the receivers located in the outer membrane recognize them.
While in the rough endoplasmic reticulum the importation of proteins is carried out almost contemporary to translation, in the other organelles it occurs after the synthesis is completed in the ribosomes free of the cytoplasmic matrix (the so-called cytosol). In the specific case of chloroplasts, proteins can reach a series of well-defined subcompartments: internal and external envelope membranes; intermembranous space; stroma; thylakoidal membrane; thylakoid light.
The mechanisms that chloroplast uses to import proteins are very similar to those of mitochondria, although the evolution of their translocations has been different.
It is important to mention that chloroplasts are present, beyond plants, in certain animals that acquire them through different processes, such as kleptoplasty , an endosymbiosis that consists of plastids being assimilated by organisms that do not have them.
The kleptoplasty has the objective that the organisms that acquire the plastids can make use of their capacity autotroph This behavior has been observed in almost all sacoglossous mollusks and in certain dinoflagellates.