cell nucleus - its most important organelle, storage and playback of hereditary information.This membrane structure, which occupies 10-40% of the cells, whose functions are very important for the life of eukaryotes.However, even without the presence of the core implementation of genetic information available.An example of this process is the vital activity of the bacterial cells.However, features of the structure of the nucleus and its mission is very important for a multicellular organism.
location in the cell nucleus and its structure
kernel is located deep in the cytoplasm and in direct contact with rough and smooth endoplasmic reticulum.It is surrounded by two membranes between which the perinuclear space.Inside the nucleus is present matrix, chromatin and some nucleoli.
some mature human cells do not have nuclei, and others operate in a strong inhibition of its activity.In general, the structure of the nucleus (the scheme) is presented as a nuclear cavity bounded karyotheca of cells containing the chromatin and nucleoli, fixed in the nucleoplasm nuclear matrix.
structure karyotheca
for the convenience of the cell nucleus, the latter should be seen as bubbles bounded by shells from the other bubbles.The core - a bottle of genetic information in the cell thickness.From its cytoplasm he shielded bilayer lipid membrane.Core shell structure similar to the cell membrane.In fact, they differ only the name and number of layers.Without all this, they are the same in structure and function.
karyotheca structure (nuclear membrane) two-layer: it consists of two lipid layers.The outer layer bilipidny karyotheca direct contact with the rough endoplasmic reticulum of the cell.Internal karyotheca - with the contents of the nucleus.Between the outer and inner kariomembranoy there perinuclear space.Apparently, it was formed due to electrostatic phenomena - repulsive portions glycerol residues.
function of the nuclear membrane is to create a mechanical barrier between the nucleus and cytoplasm.The inner membrane of the nucleus serves as a fixing nuclear matrix - chain protein molecules that support the three-dimensional structure.The two nuclear membranes have special pores: through them to the ribosomes in the cytoplasm messenger RNA leaves.The thickness of the core are several nucleoli and chromatin.
internal structure of the nucleoplasm
avilable kernel allow you to compare it with the cell.Inside the nucleus is also present a special environment (nucleoplasm) submitted a sol gel, colloidal solution of proteins.Inside it has nucleoskeleton (matrix) submitted fibrillar proteins.The main difference consists in that the core contains mostly acidic proteins.Apparently, such a reaction environment need to preserve the chemical properties of nucleic acids and biochemical reactions.
nucleolus
structure of the cell nucleus can not be complete without the nucleolus.He is the helical ribosomal RNA, which is in the process of maturation.Later, from her get a ribosome - organelle required for protein synthesis.The structure of the nucleolus are two components: the fibrillar and globular.They differ only by electron microscopy and have their membranes.
fibrillar component is at the center of the nucleolus.It is a type of ribosomal RNA strand, which will be collected from the ribosomal subunit.If we consider the core (the structure and function), it is obvious that one will subsequently be formed by granular component.This same ripening ribosomal subunit, which are in the later stages of its development.Of these, soon formed the ribosome.They are removed from the nucleoplasm through nuclear pores karyotheca and fall onto the membrane of rough endoplasmic reticulum.
Chromatin and chromosomes
Structure and function of the cell nucleus is organically linked: it is present only those structures that are necessary for the storage and playback of hereditary information.Also there karioskelet (matrix core) whose function is to maintain the form of organelles.However, the most important part of the nucleus is chromatin.This chromosome, playing the role of card indexes of different groups of genes.
Chromatin is a complex protein that consists of the quaternary structure of the polypeptide coupled to a nucleic acid (RNA or DNA).The plasmids chromatin bacteria also present.Almost a quarter of the total weight up chromatin histones - proteins responsible for "packaging" hereditary information.This feature of the study biochemistry and biology.The structure of the nucleus difficult just because of the presence of chromatin and processes, alternating his spiralization and uncoiling.
presence of histones and makes it possible to condense complement strand of DNA in a small place - in the cell nucleus.It is as follows: histones to form nucleosomes, which are entities such as beads.H2B, H3, H4 and H2A - a main histone proteins.The nucleosome is formed by four pairs of each of the presented histones.Thus histone H1 is a linker: it is related to the DNA at the site of entry e in the nucleosome.DNA packaging is the result of "winding" linear molecule 8 histone protein structure.
structure of the nucleus, the scheme of which is presented above, it requires a solenoidpodobnoy DNA structure, equipped to histones.The thickness of the conglomerate is about 30 nm.This structure can be compacted and then to take up less space and less subject to mechanical damage, will inevitably arise in the process of living cells.
chromatin fractions
structure, the structure and function of the cell nucleus fixated on whether to support dynamic processes helix and uncoiling of chromatin.Because there are two major fraction thereof: the helical much (heterochromatin) and malospiralizovannaya (euchromatin).They are separated both structurally and functionally.In heterochromatin DNA is well protected from any impacts, and can not be transcribed.Euchromatin protected weaker, but the genes may be doubled for protein synthesis.The most common sites of heterochromatin and euchromatin are alternated throughout the entire length of the chromosome.
Chromosomes
cell nucleus, the structure and functions of which are described in this publication contains the chromosomes.This is a complex and densely packed chromatin, which can be seen in the light microscope.However, this is only possible if the slide on the stage of the cell is mitotic or meiotic division.One of the stages is a helix of chromatin to form chromosomes.Their structure is very simple: chromosome has a telomere, and two arms.Each multicellular organism of one species identical structure of the nucleus.Table chromosomes he also similar.
Implementation of core functions
main features of nuclear structure are linked to the performance of certain functions and the need to control them.The core acts as the repository of genetic information, then there is some sort of card index to record a series of amino acids of proteins that can be synthesized in the cell.Then, to perform a function the cell must synthesize the protein structure is encoded in a gene.
kernel to "understand" what exactly is necessary to synthesize the protein at the right time, there is a system of external (membrane) and internal receptors.Information from them comes to the core by means of molecular transmitters.Most often this is accomplished through the adenylate cyclase mechanism.Thus influence on cell hormones (epinephrine, norepinephrine), and some drugs with a hydrophilic structure.
second mechanism is an internal transfer of information.He is peculiar to lipophilic molecules - corticosteroids.This material bilipidnuyu penetrates the cell membrane and directed to the nucleus, where it interacts with its receptor.As a result of activation of the receptor complex located on the cell membrane (cyclase mechanism) or karyotheca, triggered activation reaction of a particular gene.He is replicated on the basis of its construction messenger RNA.Later, the structure of the final synthesized protein that performs a function.
core of multicellular organisms
in multicellular organisms core structural features are the same as in the single-celled.Although there are some nuances.The first multicellular implies that the number of cells will be allocated its own specific function (or more).This means that some genes are permanently despiralizovany, while others are inactive.
For example, in the cells of adipose tissue protein synthesis will go inactive, but because most of the helical chromatin.And in cells, for example, exocrine pancreatic protein synthesis processes are constantly.Because of their chromatin despiralizovan.In those areas, the genes are replicated more often.This important key feature: the chromosome set of the cells of the body of the same.Only because of differentiation functions in some tissues off from work, and often other dispiralized points.
enucleated cells of the body
existing cells, the structural features of the kernel which may not be considered, because they are a result of their livelihoods or inhibit its function, or just get rid of him.The simplest example - red blood cells.This blood cells, the nucleus of which is present only in the early stages of development, when synthesized hemoglobin.As soon as it is sufficient to transfer the amount of oxygen, the kernel is removed from the cells, in order to ease her not to interfere with oxygen transport.
In general, the red blood cell is the cytoplasmic bag filled with hemoglobin.A similar structure is also characteristic of the fat cells.The structure of the cell nucleus adipocytes extremely simplified, it is reduced and shifted to the membrane, and the processes of protein synthesis the most oppressed.These cells also resemble "bags" filled with fat, even though, of course, a variety of biochemical reactions therein slightly larger than erythrocytes.Platelets also have no nucleus, but they should not be regarded as full-fledged cells.This cell debris were required to implement the processes of hemostasis.
