cell nucleus - a mandatory structure of each eukaryotic organism.This organelle performs a variety of functions, but its main purpose - is the storage and transmission of hereditary genetic material.
Virtually every cell in the human body has a nucleus.The only exceptions are red blood cells and platelets.Most of the mononuclear cells, but, for example, neurons and muscle fibers may have several of these organelles.The core of the cell may have a different size - the largest nuclear structures in the female egg.
cell nucleus: structure
kernel has a fairly complex structure and consists of the nuclear envelope, chromatin, nucleolus and nucleoplasm.Let's look at each part in more detail.
- Karioteka or nuclear envelope - a structure that separates the internal environment of the nucleus from the cytoplasm.This shell is composed of an outer and inner membrane, between which there is so-called the perinuclear space.Interestingly, the outer membrane shell passes directly into the granular endoplasmic reticulum membrane, so ESR cavity and core tanks interconnected.A shell has nuclear pores, closed aperture.They are designed for penetration of large molecules, as well as for the exchange of substances between karyoplasm and cytoplasm.
- karyoplasm - homogenous substance, which fills the inner cavity of the nucleus.It contains the nucleolus and chromatin.
- Chromatin - the genetic material of cells.Its structure is a nucleosome unit, which is a DNA strand is wound on a specific protein - histone.In the cell, there are two states of the genetic material.Heterochromatin a representing a small, dense granules osmophilic.Euchromatin or loosened chromatin - are areas in which active synthetic processes occur.During cell division the chromatin condenses to form chromosomes.
- nucleolus - a small oval structure that is made up of strands of RNA and protein molecules.It is here that the formation of ribosomal subunits.The nucleus may be one or more nucleoli, but you can see them only in dividing cells.
cell nucleus: function
functions of the cell nucleus can be determined by reading the structure.First, the kernel is responsible for the transfer of genetic information set during cell division, both mitosis and meiosis.During mitosis daughter cells receive a gene which is identical to the parent cell.During meiosis (the formation of human gametes) each cell receives only half the chromosomes - a complete set of chromosomes is formed only after the merger with the sexual cells of other organisms.
In addition, the cell nucleus is responsible for one of the most important steps in metabolism - protein synthesis.The fact that it is formed in the core information, or messenger RNA.Then it goes into the endoplasmic reticulum, is attached to the ribosome and serves as a model for the formation of the amino acid sequence of the peptide molecule.
And as has been said, in the core of the synthesis of ribosomal subunits.
cell nucleus: the origin
To date, there are several very different hypotheses, by which scientists try to explain how it is formed in the cell nucleus.But, unfortunately, none of these allegations has not yet found the actual confirmation.
There is a theory that the nucleus as a cell structure formed as a result of the symbiosis of bacterial cells and archaea.Other scientists believe that the core - is the result of infection of cells of a specific virus.
most complete explanation contains a so-called ekzomembrannaya hypothesis.According to her, in the course of evolution, there is another cell outside the cell membrane.In this old inner membrane into a shell core - over time, it has a complicated system, and then it began to concentrate cavity molecule chromatin.
