In cell biology, the nucleolus or nucleolus is a core region regarded as an organelle. The main function of the nucleolus is the production and assembly of ribosomal components. The nucleolus is roughly spherical and is surrounded by a layer of condensed chromatin. The nucleolus is the most prominent heterochromatic regions of the nucleus. There is no membrane separating the nucleolus from the nucleoplasm.
The nucleoli are made of protein and ribosomal DNA (rDNA). The rDNA is a fundamental component since it is used as a template for transcription of ribosomal RNA, to incorporate new ribosomes. Most of the animal and plant cells have prominent nucleoli, although there are certain cell types that do not. In addition to the nucleolus takes place the production and maturation of ribosomes, and most of the ribosomes found within it. Also, is believed to have other roles in ribosome biogenesis.
The nucleolus is fragmented in division (although it can be seen in mitotic metaphase). After separation of the daughter cells by cytokinesis, nucleolus fragments merge again around the nucleolus organizer regions of chromosomes.
The nucleolus is fragmented in division (although it can be seen in mitotic metaphase). After separation of the daughter cells by cytokinesis, nucleolus fragments merge again around the nucleolus organizer regions of chromosomes.
Number and Structure:
The number of nucleoli is quite variable depending on cell type studied. Even within the same cell type, can provide important variations in quantity. Most cells have one or two nucleoli, although they can reach to many such as amphibian oocytes, which have come to find a thousand nucleoli.
Morphologically, the nucleolus is usually spherical but can adopt irregular shapes. Usually found in the center of the nucleus or slightly shifted to the periphery. Its size can also be very variable but usually ranges between one and two microns. The nucleolus is divided into two parts: Part
amorphous: there is little dense to electrons consists of interconnected spaces with each other and which are among the most dense. Is equivalent to the nucleoplasm.
Dense part: how the nucleolonema. This part shows the electron dense, but there are different regions depending on their degree of density:
fibrillar centers or Central Zone: the region with lower density. It consists of a network of fibrils of 4-5 nm thick. The form is usually globular, with a diameter of 50 nm to one micron. The number and size of the central regions is variable and depends on cellular activity and the need for production of more ribosomes. In a cell with large central areas there is more activity in another cell with little activity. DNA fibrils may occur and some RNA. This region is the DNA of the nucleolar organizer and some proteins and enzymes involved in transcription. These regions are not essential. Dense fibrillar components
Fibrilar or party, is the most dense. Are ribonucleoprotein fibrillar structures with a thickness of 8-10 nm. These are regions with DNA and ribosomal RNA formed and to which proteins bind. Normally surround the central area, and its size reflects the amount of rRNA that is occurring.
granular region: there is less dense to electrons than the more dense fibrillar and the fibrillar center. It consists of granular structures of 25 nm in diameter that correspond to ribosomal subunits that are forming. In some cases occur dense mass of DNA associated with nucleolus (nucleolus-associated heterochromatin). The granular components are small granules with a diameter of about 15 nm. They usually occur forming a mass surrounding the fibrillar complex and bind the central area with dense fibrillar component.
Morphologically, the nucleolus is usually spherical but can adopt irregular shapes. Usually found in the center of the nucleus or slightly shifted to the periphery. Its size can also be very variable but usually ranges between one and two microns. The nucleolus is divided into two parts: Part
amorphous: there is little dense to electrons consists of interconnected spaces with each other and which are among the most dense. Is equivalent to the nucleoplasm.
Dense part: how the nucleolonema. This part shows the electron dense, but there are different regions depending on their degree of density:
fibrillar centers or Central Zone: the region with lower density. It consists of a network of fibrils of 4-5 nm thick. The form is usually globular, with a diameter of 50 nm to one micron. The number and size of the central regions is variable and depends on cellular activity and the need for production of more ribosomes. In a cell with large central areas there is more activity in another cell with little activity. DNA fibrils may occur and some RNA. This region is the DNA of the nucleolar organizer and some proteins and enzymes involved in transcription. These regions are not essential. Dense fibrillar components
Fibrilar or party, is the most dense. Are ribonucleoprotein fibrillar structures with a thickness of 8-10 nm. These are regions with DNA and ribosomal RNA formed and to which proteins bind. Normally surround the central area, and its size reflects the amount of rRNA that is occurring.
granular region: there is less dense to electrons than the more dense fibrillar and the fibrillar center. It consists of granular structures of 25 nm in diameter that correspond to ribosomal subunits that are forming. In some cases occur dense mass of DNA associated with nucleolus (nucleolus-associated heterochromatin). The granular components are small granules with a diameter of about 15 nm. They usually occur forming a mass surrounding the fibrillar complex and bind the central area with dense fibrillar component.
Function:
The main function of the nucleolus is the biosynthesis of ribosomes from their DNA to form components of ribosomal RNA. Is related to protein synthesis. In cells with a intense protein synthesis many nucleoli.
addition, recent studies have described the nucleolus as responsible for the trafficking of small RNA segments. The nucleolus also participates in the maturation and transport of RNA to its final destination in the cell. Although the nucleolus disappears
divisive current studies say that regulates the cell cycle.
addition, recent studies have described the nucleolus as responsible for the trafficking of small RNA segments. The nucleolus also participates in the maturation and transport of RNA to its final destination in the cell. Although the nucleolus disappears
divisive current studies say that regulates the cell cycle.
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