cell wall

Cells (cell) are prokaryotes and Eukaryotes The structure and function of the The basic unit . In addition to the virus, all living organisms are made of cells, cellular core structure according to the different degree of differentiation, the cells can be divided into prokaryotic and eukaryotic cells of two types. Whether by forming the nucleus to distinguish. Cell wall (cellwall) is the outer layer of cells outside the cell membrane, cell wall thickness often due to organization, function varies. Plants, fungi, algae and Prokaryote (in addition to Mycoplasma With the L shaped bacteria ( The lack of the bacterial wall )) have a cell wall, and Animal Cells do not have cell walls. The cell wall structure is loose, the outside world can enter the cell through the cell wall, cell wall has Quantouxing.
cell wall

cell wall brief introduction

 plant cell plant cell
Fossil Research shows that about 3 billion 500 million years ago the earth was out Prokaryotic cells , about 12 ~ 1 billion 400 million years ago to appear Eukaryotic cells . About the origin of eukaryotic cells, there are two main hypotheses: one is "endosymbiont hypothesis", that the prokaryotic eukaryotic cells originated from several parts of the different symbiotic aerobic bacteria, penetrate Heterotrophic anaerobic Prokaryotes into Mitochondrion , Blue-green algae Penetrate into Chloroplast , Spiral Penetrate into Flagellum and cilia One is " plasma membrane The inpocketed hypothesis ", that the ancient prokaryotic organism with the volume increased, plasma membrane infolding occurred and the formation of endoplasmic reticulum, and Nuclear membrane At the same time, caused by the nucleus; DNA replication into many copies, around DNA plasma membrane infolding, finally formed a double membrane organelles, such as mitochondria and chloroplasts. The shape and size of the cells with different biological and different, even the same species in different parts of the cell morphology is not the same. There are usually separate free cells spherical Or spherical, but due to cell surface tension
 Peptidoglycan Peptidoglycan
or Protoplasm The viscosity and uniformity of cell shape, sometimes also will change. Composition of tissue cells by mechanical stress and directional constraints between adjacent cells, often appear in different forms. Generally speaking, cell morphology and physiological function Closely related. The different cell size disparity, the general bacterial cell diameter of 0.5 to 1.5 microns to 5 microns long, 1, Seed plant The young cell diameter of about 5 to 25 microns, mature cell diameter was 15 ~ 65 micron. The higher animal cells than in plant cells is small, but Egg cell Generally, the largest known cell is an ostrich egg, a diameter of about 5cm. Some neuronal processes can reach more than 1 meters. The smallest cell for Mycoplasma cells, only 0.1 m in diameter. Single cell biology Consisting of a cell. The number of cells in multicellular organisms vary greatly. When a person was born about 1014 or one million billion cells; adult is about 1014 * 16 or 1600 trillion
 The cell wall of gram positive bacteria The cell wall of gram positive bacteria
A cell, nearly 100 types. Although the biological cell types, but has substantially the same basic construction, eukaryotic cells SUBMICROSTRUCTURE Can be divided into surface structure and the internal structure of the two most. The surface structure comprises a cell membrane and the outer membrane material layer, such as cell wall of plant cells and some Animal cells The cell coat; the internal structure includes the nucleus and cytoplasm. The nucleus by nuclear membrane, Karyoplasms The nucleolus, and Chromatin Form。 Translucent colloidal solution of undifferentiated cytoplasm called matrix; fine structure of all kinds of special feature called organelles, such as mitochondria, plastids, Er Ribosomaland Golgi, lysosome , Centrosome , microtubule And microfilaments, and Flagellum and cilia Etc.; the cytoplasm often contain many metabolites formed particles, such as starch grains, starch grains, fat drops, Glycogen Grain, a matter referred to after. A cell is a unit of activity, the basic process of life activities, such as Material metabolism And the conversion of energy, movement, development, reproduction and genetics, is the foundation to realize the cell structure.

cell wall structure

The cell wall is divided into 3 layers, namely the cell layer (middle), The primary wall And the secondary wall. The cell layer of the adjacent cells together form tissue. The primary wall in the cell layer on both sides, all plant cells are. Inside the secondary wall in the primary wall, and divided into (S1), (S2), (S3) 3 layer in the inner layer, sometimes also can appear a layer. This thick wall, water and nutrients can not be through. Tuberculate layer of the secondary wall of some plants, but also has a special structure such as differentiation. Pit Nodulers and etc.. The pit is intercellular substance circulation area, and the tumor is layer projections on the secondary wall.
The structure of the cell wall is generally divided into the following three layers
1 cell layer: the cell layer is in cell division The formation of new cells, two adjacent cells is shared by a layer of thin film. It is the main component of soft colloidal pectin. The cell layer Both the adjacent cell adhesion together, but also squeezing the buffer between the cells, it will not hinder Cell growth .
2: in the primary wall cell Telophase The cell layer was formed after protoplast
 Under electron microscope, the cell walls of plants Under electron microscope, the cell walls of plants
The secretion of cellulose, Hemicellulose And a small amount of pectin, adding in the cell layer, constitute the primary cell wall. The primary wall is elastic, along with the increasing area of cell growth. The cell wall formation in cell growth, called the primary wall, plant cells have The primary wall .
3: to stop the growth of secondary wall cells, protoplasts continued to produce cellulose and other substances, add in the primary wall inside the cell wall, cell wall thickening, thickening of secondary wall called this part. Add in the secondary wall inside the primary wall, secondary cell wall is thicker, the inner of the cavity wall is smaller. Secondary wall Only in some cells in plants. Thick wall Fiber cell , Stone cell , Tracheid A secondary wall thickening and vessel etc..
A major component of the cell wall is cellulose, it formed the framework of the cell wall, containing other substances. stay electron microscope See, this framework consists of a layer of cellulose Microfilament Referred to as. Microfibril The composition, each layer of microfibrils is basically arranged in parallel, each additional layer, microfibril alignment orientation is different, so between the layers array cross into the net. The space between the microfibrils are usually filled with other substances.
In addition, in some Plant cuticle The cell wall, often with wax, Horny , Corky . In the cell wall of some mature and thick, often deposited lignin. stay Gramineae , Equisetaceae Silicon containing epidermal cell wall of plants. In the cell wall of fungi in there chitin .
There are pits on the cell wall, because in the process of cell growth, cell growth and secondary wall with time
 Secondary wall Secondary wall
Stretch, but wall thickening is not uniform, formed a lot of thin wall area, called the primary pit field; cell secondary wall thickening, is not uniform, usually in the primary pit field site not thickened, cell wall structure on the formation of pits. The adjacent cell wall. Pit Often formed corresponding to pitpair. Grain hole Single pit and Bordered pit Two. There are usually many Plasmodesmata From the pit, plasmodesmata and cytoplasmic endoplasmic reticulum connected to communication material exchange between cells, is conducive to the transport of water. Therefore, the pits on the cell wall is the intercellular communication channel, so that the whole plant can become the organic unity in life.
The formation of a new cell wall is the equatorial plane in telophase on the division of the mother cell to form a film body. stay Chromosome To The poles When, Golgi With the separation of the microtubule vesicle set in equator On the surface of a Cell plate . The polysaccharide substance deposition is gradually formed in the new cell plate The cell layer . The intracellular synthesis of some cellulose Microfibril Deposition on both sides of the cell layer, appeared in the primary wall. When the cells mature to stop the growth of a new layer of cellulose and Hemicellulose And the lignin added in the primary wall, secondary wall was built. The primary wall each add a layer of micro fiber arrangement direction can be different (vertical or horizontal), staggered mesh formed irregular, growth for multi network. Such thickening results, the mechanical support of the entire plant is the foundation.

cell wall Form

Cell wall The cell layer Basically consists of pectin.
If plant tissue The use of pectin pectinase Broken down, the cells will discrete, this is because the primary wall is made of water, Hemicellulose , pectin, cellulose, protein and lipid composition. The average value of the various components of coleoptile, leaf and stem, wool and other primary wall table. Composition of cell wall components, is about 90% of polysaccharide, about 10% proteins, enzymes and fatty acids. The polysaccharides in the cell wall is mainly cellulose and hemicellulose and pectin Class, they are composed of glucose, Arabia sugar , Galacturonic acid Such as polymerization. Secondary cell wall There are a lot of Lignin .
The extracellular matrix of the animal in a sense is the cell wall, its chemical composition is Collagen protein , Adhesion protein And glycosaminoglycan and Proteoglycan .
 Plant and animal cell map Plant and animal cell map
The cell wall of bacteria The main component is Peptidoglycan .
The main component of fungal cell wall in chitin Cellulose, glucan Mannan, etc., these polysaccharides are Monosaccharide Polymer.

cell wall formation

The cell wall is formed with a variety of organelles result. The formation of a new cell wall began in late anaphase or early cell division. When cells divide, between two groups of chromosomes, which is in the mother cell Equatorial plate (not real) on the surface, there are many different sizes of secretion Vesicle (secretoryvesicles) irregular together in one piece, these vesicles by Golgi apparatus And ER secretion and the formation of various sugars, which is rich in the structure of cell wall and cell, they exist with the equatorial plate in the vertical direction of microtubule movement, gradually neatly arranged into pieces, composed of phragmoplasts (phragmoplast). Phragmoplast The vesicle membrane fusion and connected to the cell membrane, which Inclusion Together constitute the cell plate, this is the embryonic form of the middle structure. Cell plate, Golgi apparatus Vesicular transport The wall building material released into the plasma membrane, in order to enrich the new form of the wall. When the cell plate has the pectin and a small amount of cellulose molecules constantly filling and mixing occurs in the middle, in the middle on both sides have been deposition of cellulose and hemicellulose and other substances into the primary wall soft, then the two sub cell form. Since then, most cells inside the primary wall and delamination, directed deposition of cellulose molecules, they clearly Jingwei cross reinforcement, this is the important basis to improve support ability of plants. Directional layered deposition of cellulose molecules and microtubule related activities, Colchicine (colchicine) can prevent the formation of microtubules, targeted inhibition of cellulose molecular arrangement. Another important role of microtubules is to make some channel reservation cell plate on the newly formed, even involved in filament formation between cells, the protoplasm can keep in touch in two sub cells.
Therefore, the formation of the cell wall is gradually completed in the process of cell division, growth and differentiation of life in. In the formation of new cell division and cell wall, in addition to Golgi apparatus And, er microtubule Participate in, and a variety of auxin and enzymes The role of all activities but also rely on the mitochondria to provide energy, which reflects the characteristics to complete the activities of life with each other in different parts of cells.

cell wall type

cell wall The cell wall of bacteria

The cell wall of bacteria The main ingredient is Peptidoglycan (peptidoglycan), also called Peptidoglycan (mucopetide). Cell wall mechanical strength Depends on the existence of peptidoglycan. The synthesis of peptidoglycan is unique in prokaryotes. Peptidoglycan is n- acetyl glucosamine and n- acetyl acid cell two Amino sugar The connection of polysaccharide formation by stent spaced -1.4 beta glycosidic bond. In the n- acetyl Muramic acid Connect the four peptide side chain molecules, Peptide A peptide or polypeptide chain between the bridge link, composed of a mechanical mesh structure is very strong. Peptidoglycan supports of various bacterial cell walls are the same in the four peptide Side chain The composition and its connection with strain .
Usually by Gram staining of bacterial cell wall technology can be divided into two types, gram positive and gram negative (G+) (G-). Gram staining (Gram stain) is Denmark Doctor gram (Hans Christian Gram) in 1884 by table 2-3 are procedures for bacterial staining results for different color can be divided into two types of bacteria, called the gram positive and negative.
Gram positive bacteria The four peptide side chain Amino acid Composed of d- C -d- Valley -r-l- -d- Lai C. At the beginning of the end of a synthetic peptide d- alanine residues. The bridge is a 5 peptide glycine peptide cross-linking and end Side chain Third lysine connection, the other end in transpeptidases under the action of another five peptide side chain terminal d- and alanine off, connected with the side chain fourth d- alanine. From the X-ray examination showed polysaccharide chain of peptidoglycan is a hard and a long rod spiral curl, due to its spiral, connected on the chain to extend to all directions, the crosslink subject to certain restrictions, only nearby Peptide It can be crosslinked. But the bridge is Staphylococcus peptide
 The cell wall of bacteria The cell wall of bacteria
There are long. Plasticity The distance between the chains, can also be cross-linked, crosslinking rate reached 90%, forming a three-dimensional reticular structure is strong and compact. Four peptide side chains of amino acids in gram negative Escherichia coli was third Two amino Pimelic acid (DAP) replaced by chain is directly connected with the four adjacent peptide side chain d- alanine, and cross-linking rate is low, there is no five peptide called formation Two-dimensional The plane structure, so the structure is gram positive Staphylococcus and birch.
Bacterial cell wall is tough and elastic, protection of bacterial resistance to hypotonic environment, under the environment where within 5 ~ 25 of the atmosphere osmotic pressure And, the bacteria in low permeability under the environment of the cell is not easy to rupture; inherent form of cell wall to maintain bacteria play an important role; soluble allows moisture and a diameter of less than 1nm Small molecule The freedom, and The exchange of material Related; cell wall with multiple epitopes, determines the antigenicity of bacteria.
The bacterial cell wall structure
Who can destroy peptidoglycan structure or inhibit the synthesis of material, can damage the cell wall and the deformation of bacteria or killing bacteria, such as lysozyme (lysozyme) can link between cut off between the peptidoglycan n- acetyl glucosamine and n- n-acetylmuramicacid beta -1.4 glycosidic bond with glycosidic bond, destroy peptidoglycan support, caused by bacterial lysis. Penicillin and cephalosporin can turn to peptidase and bacterial cell wall synthesis competition process, the link between inhibition of four peptide side chain d- alanine and five peptide bridges, so that bacteria can not complete cell wall synthesis, can lead to the death of bacteria. Human and animal cells without cell wall structure, there is no peptidoglycan, so lysozyme And penicillin on The cells of the body No Toxic effect . In addition to the basic ingredients of peptidoglycan, gram positive bacteria and Gram negative bacteria Also each has its special structure components.
 The cell wall of gram positive bacteria The cell wall of gram positive bacteria
Gram positive bacteria cell wall of the cell wall is thick, the chemical composition is simple, there are 90% peptidoglycan and teichoic acid 10%. The cell wall by a thick layer of peptidoglycan and teichoic acid, interspersed among them. Teichoic acid is divided into two categories, one category and peptidoglycan molecules covalently, said wall teichoic acid, the other is across the peptidoglycan layer associated with the cell membrane, called lipoteichoic acid or lipoteichoic acid. Between cell wall and plasma membrane space called the periplasmic space.
The cell wall of gram negative bacteria than gram positive bacteria of the cell wall of the cell wall is thin, the chemical composition is relatively complex, can be divided into two layers, for the peptidoglycan layer and thin membrane. There are obvious space in the outer membrane and cytoplasmic membrane, called the periplasmic space. As the main component of the outer membrane lipid
 The cell wall of gram negative bacteria The cell wall of gram negative bacteria
Sugar (lipopolysaccharide, LPS) LPS by the core polysaccharide, O and lipid composition of specific branched chain A. In addition also contain phospholipid membrane protein and polysaccharide. The outer lipid and polysaccharide composition of the outer membrane, known as the LPS layer, it is closely connected with lipid.
Yeast cell wall Yeast cell wall The 0.1~0.3 thickness m, weight Cell dry weight The 18%~30% is mainly composed of D- dextran and D- mannan two kinds of polysaccharide composition, containing a small amount of protein, fat and minerals. About an equal amount of dextran and Mannan Total cell wall dry weight
 cell wall cell wall
85%. When Cell senescence After the cell wall weight will be doubled. Although it has certain toughness, but its tenacity to keep the shape of special yeast. Its chemical composition is more special, mainly by yeast cellulose, it's like a sandwich structure. The outer layer of the cell wall mannan, accounting for about 40%~45% of dry weight. The middle layer is a layer of protein molecules, accounting for about 10% of the dry weight of the cell wall. Some of them are in combination with cell wall enzyme form. The inner layer is glucan .
Yeast glucan is an insoluble polymer backbone to a branch, beta -1, 6 glycosidic bond, branched to beta -1, 3 glycosidic bond. As the inner layer material of the cell wall, maintaining cell wall strength, when cells in hypertonic environment and contraction, it can maintain cell elasticity.

cell wall The cell wall of plant cells

The main component of the cell wall of plant cells is cellulose and pectin . Plant cell wall Is the difference between plant cells in animal cells is one of the main features. Consists of three parts:
1, the cell layer
The cell layer Also called mesoglea. Located between two adjacent cells, two adjacent cells shared by a layer of film, as the main component of pectin. Help the adjacent cell adhesion together, and can squeeze the buffer between cells.
2, the primary wall
The primary wall cell division, initially secreted by protoplasts of cell wall formation. In all living cells of plants. Be located The cell layer Inside. Usually thin, about 1 to 3 microns thick. With greater plasticity, which enables the cell to maintain a certain shape, but also with the cell growth and extension. The main components of cellulose, hemicellulose, and protein structure. Cells in the primary wall formation, if no new wall accumulation, the primary wall is their permanent cell wall. Such as the parenchyma cells.
3, secondary wall
In the part of plant cell growth stopped, the primary wall inside the cell wall to accumulation layer. Located between the plasma membrane and the primary wall. The main component is cellulose, and often have wood there. Are usually thick, about 5 to 10 microns, and hard, the cell wall has great mechanical strength. With most of the secondary wall cells at maturity, Protoplast Death. Fiber and stone cell is a typical secondary cell wall. In plants Protoplast culture When used with pectinase and cellulase The enzyme mixture processing plant tissue to damage The cell layer And remove the cell wall cellulose, get naked protoplast free.

cell wall Fungal cell wall

The main component of fungal cell wall in chitin.
Fungal cell wall thickness of about 100~250nm, which accounted for 30% of the dry matter cells. The main component of the cell wall polysaccharide, followed by protein and lipid. In different groups of fungi in different types of cell wall polysaccharides. Fungal cell wall polysaccharides are mainly chitin ( chitin ), cellulose, glucan Mannan, etc., these polysaccharides are Monosaccharide The polymer, such as chitin is composed of acetyl N- Grape Glucosamine molecules, with B -1, 4 grape polysaccharide glycosidic. Cell wall components with low fungal cellulose, yeast by dextran, and higher fungi in chitin The main. A group of fungal cell wall and is not fixed, in the different growth stage, cell wall components are significantly different.

cell wall function

1, the maintenance of cell shape, cell growth, cell wall increased control cells mechanical strength , and bear the protoplast due to internal vacuole The water generated by turgor pressure, so that the cells have a certain shape, which not only protect Protoplast The role, but also to maintain the natural shape and plant organ. In addition, the wall in control of cell growth, cell elongation and expansion because the premise is to make the cell wall relaxation and irreversible stretching.
2, material transport and information transmission of the cell wall to allow Ion , Polysaccharide Other small molecules and low molecular weight Protein By and large molecular or microbial resistance to external. Therefore, the cell wall is involved in material transportation, reduce Transpiration To prevent water loss ( Secondary wall The surface of the wax, etc.), plant water potential regulation and a series of physiological activities. The cell wall pits or plasmodesmata is affected by cell physiological age and metabolic activity intensity, so the transport of cell wall in the intercellular substance has a moderating effect. In addition, the cell wall is chemical signals (hormones, growth regulator etc.), Physical signal ( Air waves And the pressure transfer medium and channel).
3, some oligosaccharides defense and resistance in the cell wall can induce phytoalexins (phytoalexin) formation, they also have regulatory effects on other physiological processes, which can modulate activity of oligosaccharide fragments called oligosaccharin (Oligosaccharin). A G Glucoside Oligosaccharin applied to soybean cells, will inhibit the growth of fungi responsible for the synthesis of the antibiotic gene Activation and antibiotics. A variety of functional oligosaccharide complex, such as some Protease inhibitor The induced factor, play a role in plant resistance to pest damage; some Oligosaccharin can make plants produce allergic death caused the illness, the original can not be further diffusion; and Oligosaccharin is involved in the regulation of plant Morphogenesis . In the cell wall Extensin In addition to serve as structural components, and disease resistance function. Such as cucumber resistant varieties is a fungal infection, the cell wall hydroxyproline The content increased faster than sensitive varieties.
4, the function of other enzymes in the cell wall are widely involved in cell wall High polymer Synthesis, transfer, hydrolysis And transporting extracellular material into cells and defense etc..
5, participate in the interaction between cells adhesion That is " Plasmodesmata ".
The study found that the cell wall is also involved in plant and Rhizobia symbiosis nitrogen fixation The mutual recognition, in addition, in the cell wall Polygalacturonase and lectin May also participate in Stock And scion grafting The reaction in the process of recognition. It should be noted that not all cells of the cell wall has the function of cell wall function of each cell is determined by the specific composition and structure.