Structure and function of cells in the process of evolution undergone a number of changes.The emergence of new organelles preceded by changes in the atmosphere, lithosphere and the young planet.One of the major acquisitions was the cell nucleus.Eukaryotic organisms have received, due to the presence of isolated organelles significant advantages over prokaryotes and quickly came to dominate.
cell nucleus, the structure and functions of which are slightly different in different tissues and organs, improved the quality of the biosynthesis of RNA and the transmission of hereditary information.
Origin
Today there are two main hypotheses on the formation of a eukaryotic cell.According to the theory of symbiotic organelles (such as mitochondria or flagella) were once separate prokaryotic organisms.The ancestors of modern eukaryotes swallowed them.As a result, it formed a symbiotic organism.
kernel at the same time formed as a result of inward protrusion portion of the cytoplasmic membrane.It was necessary to purchase a cell on the path of development of a new way of eating, phagocytosis.Grab food accompanied by an increase in the mobility of the cytoplasm.Genofory represent the genetic material of a prokaryotic cell and attached to the walls, got into a zone of strong "trends" and in need of protection.As a result, it formed a deep invagination of the membrane portion containing attached genofory.This hypothesis is proved by the fact that the shell of the nucleus is inextricably linked to the cytoplasmic membrane of the cell.
There is another version of events.According to the hypothesis of the origin of the viral core it is formed as a result of the infection of the cells of ancient Archaea.It penetrated DNA virus and eventually got complete control over life processes.Scientists consider this theory more correct result lot of arguments in its favor.However, to date there is no conclusive evidence for any of the existing hypotheses.
One or more
Most of the modern eukaryotic cell has a nucleus.The vast number contains only one such organelle.There are, however, and the cells that have lost the core because of some functional features.These include, for example, the red blood cells.There are also cells with two (ciliates), and even multiple cores.
structure of the cell nucleus
Regardless of the characteristics of the organism, the structure of the core is characterized by a set of typical organelles.From the inner space of the cell is partitioned off by a double membrane.The inner and outer layers of it in some places merge, forming the pores.Their function is the exchange of substances between the cytoplasm and the nucleus.
space filled organelles karyoplasm also called nuclear juice or nucleoplasm.It is located chromatin and nucleolus.Sometimes the last of these organelles of the cell nucleus is not present in a single copy.Some of the organisms nucleoli, conversely, are absent.
membrane
nuclear membrane lipids formed and consists of two layers: external and internal.In fact, it's the same cell membrane.The core communicates with the channels of the endoplasmic reticulum through the perinuclear space and a cavity formed by two layers of cladding.
outer and inner membrane have their own characteristics in the structure, but on the whole are quite similar.
closest to the cytoplasm
outer layer passes into the membrane of the endoplasmic reticulum.Its main difference from the last - a significantly higher concentration of proteins in the structure.The membrane, in direct contact with the cytoplasm of the cell covered with a layer of ribosomes to the outside.On the inside of the membrane, it is connected by numerous pores, is a relatively large protein complexes.
inner layer
appeal to the cell nucleus membrane, in contrast to the exterior, smooth, not covered by ribosomes.It limits karyoplasm.A characteristic feature of the inner membrane - layer nuclear lamina lining it by contacting the nucleoplasm.This particular protein structure supports the shape of the shell, is involved in the regulation of gene expression, and promotes attachment of chromatin to the nuclear membrane.
Metabolism
interaction nucleus and cytoplasm through nuclear pores.They are quite complex structures formed by 30 proteins.The number of pores on one core may be different.It depends on the type of cell, organ or organism.Thus, a human cell nucleus can have from 3 to 5000 pores, some frogs it reaches 50 000.
main function of pore - metabolism between kernel space and the rest of the cell.Some molecules penetrate the pores passively without additional energy input.They have a small size.Transporting large molecules and supramolecular complexes requires a certain amount of energy consumption.
From karyoplasm get synthesized in the cell nucleus in the RNA molecule.In the opposite direction is transported proteins required for intranuclear processes.
nucleoplasm
Nuclear juice is a colloidal solution of proteins.It is limited to the core and the shell surrounds the chromatin and nucleolus.Nucleoplasm - viscous liquid in which various substances are dissolved.These include enzymes and nucleotides.The first essential for DNA synthesis.Enzymes involved in transcription and DNA replication and repair.
juice nuclear structure varies depending on the state of the cell.Two of them - stationary and occurs during the division.The first characteristic of the interphase (the time between the divisions).Thus nuclear sap different uniform distribution and unstructured nucleic acids DNA molecules.During this period there is genetic material in the form of chromatin.The division of the cell nucleus is accompanied by the transformation of chromatin into chromosomes.At this time, changing the structure of karyoplasm: genetic material acquires a certain structure, the nuclear envelope breaks down and mixed with karyoplasm cytoplasm.
Chromosomes
main functions of nucleoprotein structures converted at the time of division of chromatin - storage, sale and transfer of genetic information, which contains the cell nucleus.Chromosomes are characterized by a particular form: divided into parts or shoulders the primary constriction, also called tselomeroy.According to its location there are three types of chromosomes:
- rod-shaped or acrocentric: they are characterized by placing tselomery almost at the end, one shoulder turns out very little;
- raznoplechie submetacentric or possess arms of unequal length;
- -equal or metacentric.
set of chromosomes in a cell is called a karyotype.Each type it is fixed.At the same time different cells of one organism can contain diploid (double) or haploid (single) set.The first embodiment is characteristic of the somatic cells in the main body components.Haploid - the privilege of sex cells.Somatic human cells contain 46 chromosomes, the sex - 23.
diploid chromosomes pair up.Same nucleoprotein structures within the couple, called alleles.They have the same structure and perform the same functions.
structural unit of the chromosome is the gene.It is a portion of a DNA molecule encoding a specific protein.
nucleolus
cell nucleus has one organelle - a nucleolus.It does not separate from karyoplasm membrane, but it is easily seen during the study cells with a microscope.Some of the core may have multiple nucleoli.There are those in which like organelles lacking altogether.
The shape resembles the nucleolus sphere is small enough.It is composed of various proteins.The main function of the nucleolus - the synthesis of ribosomal RNA and ribosomes themselves.They needed to create polypeptide chains.The nucleoli are formed around specific regions of the genome.They are called nucleolar organizer.It contains genes of ribosomal RNA.Nucleolus, among other things, is a place with the highest concentration of protein in the cell.Some of the proteins necessary to perform the functions organelle.
As part of the nucleolus are two components: granular and fibrillar.The first is a maturing ribosomal subunit.In the fibrillar center of the synthesis of ribosomal RNA.The granular component surrounds fibrillary located in the center of the nucleolus.
cell nucleus and its functions
role played by the kernel, is inextricably linked to its structure.The internal structure of organelle jointly implement the most important processes in the cell.Here is located the genetic information that determines the structure and function of cells.The kernel is responsible for the storage and transmission of genetic information carried out during mitosis and meiosis.In the first case, a subsidiary of the parent cell receives an identical set of genes.As a result, formation of meiotic germ cells with a haploid set of chromosomes.
Another important function of the nucleus - the regulation of intracellular processes.It is carried out by monitoring the synthesis of proteins responsible for the structure and function of cellular elements.
Effect on protein synthesis is another expression.The core controlling processes inside the cell, it combines all the organelles in a single system with a well-functioning mechanism works.Failures it usually leads to cell death.
Finally, the kernel is the site of synthesis of ribosomal subunits, which are responsible for the formation of the same protein from amino acids.Ribosomes are essential in the process of transcription.
eukaryotic cells is a more perfect structure than prokaryotic.The emergence of self-membrane organelles possible to increase the efficiency of intracellular processes.Forming the core, surrounded by a double lipid membrane, it played in the evolution of a very important role.Protection of genetic information membrane allowed the ancient single-celled organisms to learn new ways of life.Among them was the phagocytosis, which is one of the versions has led to a symbiotic organism, who later became the ancestor of the modern eukaryotic cell with all its characteristic organelles.The cell nucleus, the structure and function of some of the new structure will enable the oxygen metabolism.The result was a radical change in the Earth's biosphere, it laid the foundation for the formation and development of multicellular organisms.Today, eukaryotic organisms, which include people, dominate the planet, and nothing portends changes in this regard.
