The outer layer of cells.

cells that form the fabric of flora and fauna are significant differences in size, shape, constituent elements.However, they all found similarities in the basic features of growth, metabolism, life activity, irritability, ability to variability development.Next, consider the more the structure of plant cells (Table main components will be given at the end of the article).

Brief History

With osmotic shock in 1925 Gorter and Grendel got empty shells of red blood cells, their so-called "shadow".They piled into a stack, defining their surface area.With the use of acetone were isolated lipids.It was also determined the number of erythrocytes per unit area.Despite the uncertainty in the calculations, it was launched accidentally correct result and open the lipid bilayer.

General

study of the development and growth of the tissue elements of flora and fauna deals with biology.The structure of the plant cell is a complex of three inextricably linked to each other components:

• kernel.It is separated from the cytoplasm by means of a porous membrane.It contains the nucleolus, the nuclear sap and chromatin.
• cytoplasm and a set of specialized structures - organelles.The latter, in particular, carry the plastids, mitochondria, and Golgi apparatus, lysosomes, the cell center.Organelles present time.Apart from these, there are also temporary formation, called inclusions.
• structure that forms the surface - the shell of the plant cell.

Features surface apparatus

have white blood cells and unicellular organisms sheath cells provides the penetration of water, ions, molecules of other small compounds.The process in which there is penetration of solid particles, called phagocytosis.If no drops of liquid compounds, we speak of pinocytosis.

organelles

They are present in eukaryotic cells.With organelles associated biological transformations that occur in the cell.Their covers double diaphragm - the plastids and mitochondria.They contain their own DNA, as well as the machine that synthesizes the protein.Reproduction is carried out by division.In the mitochondria, except ATP, the protein is synthesized in small quantities.Plastids present in plant cells.Their reproduction is carried out by division.

membrane

a mistake to assume that the outer layer of cells - is the cytoplasm.The membrane is elastic molecular structure.The outer layer of cells called the surface unit, by which the separation of the contents from the external environment.There are different functions of the cell membrane.One of the main tasks is to ensure the integrity of the item.Inside the structure are also present, sharing a cell for so-called compartments.These closed areas or compartments called organelles.Inside they maintain certain conditions.The functions include regulation of cell membrane exchange between the medium and the cell.

membrane

What is the structure of the cell membrane?Cell membrane - a bilayer (double) class of lipid molecules.Most of them represents a complex type lipids - phospholipids.The hydrophobic molecules are present (tail) and hydrophilic (head) part.When the shell is formed by cells tails inward, and head - in the opposite direction.Membranes - this invariabelnye structure.The shell of the animal cell has many similarities with the element of flora.The thickness of the membrane - the order of 7-8 nm.Biological outer layer of cells includes various protein compounds: poluintegralnye (one end submerged in the external or internal lipid layer), integral (permeates), surface (adjacent to the inner sides of which are either on the outside).Some proteins is the connecting point of the membrane and inside the cell cytoskeleton and the outer wall (if present).Some integrated compounds play a role of ion channels, receptors and transporters varied.

Protective task

cell membrane structure largely determines its activities.In particular, the membrane is selectively permeable.This means that the degree of permeability of molecules through the membrane depends on their size, chemical properties, electrical charge.The main function performed by the outer layer of cells, called a barrier.Through it provides selective, adjustable, active and passive exchange connections with the environment.For example, the shell provides protection peroxisome cytoplasm of dangerous peroxides.

Transport

Through the outer layer of cells of the transition substances.Due to the transportation service provided by nutrients, elimination of the end products of metabolism, the secretion of various substances, the formation of ionic ingredients.Furthermore, the cell maintains an optimal pH and ion concentration is necessary for the enzymes.If required the particles for some reason, can not pass through the bilayer of phospholipids, for example, in connection with the hydrophilic, since the membrane is hydrophobic in, or because of their large size, they can cross the membrane by means of special transporters (carrier proteins)by endocytosis or proteins channels.During passive transport compound tested outer layer of cells without expenditure of energy by diffusion down a concentration gradient.One variant of this process is considered to facilitate the implementation.In this case, the material helps to cross the outer cell layer of any specific molecule.It may be present channel which is capable of transmitting only one type of material.For active transport requires energy.This is due to the fact that in this case the movement takes place back to the concentration gradient.On the membrane in this case there are special pumps proteins, including ATPase which actively pumped into the cell and potassium ions, sodium pumps.

Other tasks

outer layer of cells performs matrix function.This ensures a certain mutual position and orientation of membrane protein compounds and their optimum interaction.Due to the mechanical function provides autonomous cells and internal structures, as well as connections to other cells.Of great importance in this case the representatives of the flora are wall structures.Animals to ensure the mechanical function depends on the intercellular substance.Membranes operate and energy problem.In the process of photosynthesis in chloroplasts and cell respiration in the mitochondria in their walls are activated by energy transfer system.In these, as in many other cases, proteins are involved.One important function of the receptor is considered.Some proteins that are found in the membrane are receptors.Due to these molecules the cell can receive one or more signals.For example, steroids, circulate through the bloodstream, affect only those target cells that have receptors corresponding to one or the other hormones.There are also neurotransmitters.These chemicals provide a pulse transmission.They also have links with specific target proteins.The membrane components are often enzymes.Hence the enzymatic function of the cell membrane.The plasma membranes of epithelial elements intestinal digestive present compound.The outer layer of cells are generated and held biopotentials.

ion concentration

With the membrane is supported by the inner content of K + ion at a higher than the outside level.The concentration of Na + is considerably lower than the outside.This is of particular importance, as is provided so the potential difference across the wall and generation of nerve impulses.

Marking

present on the membrane antigens that act as some "shortcuts".Marking allows you to identify the cell.Glycoproteins - proteins docked to them oligosaccharide branched side chains - play the role of "antenna".Since the configuration of the side chains are countless, it is possible for each group of cells to make their mark.With them there is some recognition of the other elements, which in turn allows them to act in concert.This happens, for example, the formation of tissues and organs.By the same mechanism of the immune system work done on recognition of foreign antigens.

composition and structure

As mentioned above, cell membranes are composed of phospholipids.However, besides these structures are present in cholesterol and glycolipids.The latter are lipids docked them carbohydrates.Glycolipids and phospholipids, mainly forming cell membranes, composed of 2 long carbohydrate hydrophobic "tails".They are associated with a hydrophilic, charged "head".Due to the presence of cholesterol membrane has the required level of rigidity.The compound occupies the space between the hydrophobic lipid tails, thus preventing their bending.In this regard, those membranes in which lower cholesterol, more flexible and soft, but where it is greater on the contrary, greater stiffness and brittleness in the walls.Furthermore, the compound acts as a stop preventing movement of the cells in the cell polar molecules.Of particular importance are proteins that penetrate the membrane and are responsible for its various properties.Or that the shell of the plant cell is determined by the composition of proteins and their orientation.

of annular lipids

These compounds are close to the protein.However, of annular lipids are more streamlined and less mobile.Their composition contains fatty acids with greater saturation.Lipids leaves the membrane with protein compound.None of annular elements of membrane proteins will not function.Often, asymmetric membranes.In other words, this means that the layers have a different composition of lipids.In the external contain mostly glycolipids, sphingomyelin, phosphatidylcholine, fosfatidilnozitol.The inner layer is present fosfatidilnozitol, phosphatidylethanolamine and phosphatidylserine.The transition from one level to another specific molecule more difficult.However, it may well happen spontaneously.It happens about once every six months.Daylight can also be done with the help of proteins and flippaz skramblazy.When the outer layer fosatidilserila, macrophages take a defensive stance and focus their activity on the destruction of the cells.

organelles

These sites can be single and closed or connected with each other, separated by membranes hyaloplasm.Odnomembrannymi considered periksisomy organelles, vacuoles, lysosomes, Golgi apparatus, endoplasmic reticulum.By dvumembrannym include plastids, mitochondria, nucleus.As for the structure of membranes in the various organelles wall differ in composition of proteins and lipids.

selective permeability through cell membranes slowly diffuse fatty and amino acids, ions and glycerol, glucose.In doing so, the walls are actively regulate the process by skipping some and holding other substances.To enter the compound in the cell, there are four main mechanism.These include endo- or exocytosis active transport, osmosis and diffusion.The last two have passive and does not require energy consumption.But the first two - are active.For them, energy is needed.In the passive transport is caused by selective permeability of integral proteins - specific channels.The membrane is permeated by them through.These channels are formed in some way pass.Proteins have their elements Cl, Na, K. With regard to the concentration gradient, the molecules of elements moving within the cell thereof.Against the background of irritation occurs disclosure channel sodium ions.They, in turn, begin to rapidly enter the cell.This is accompanied by an imbalance in the membrane potential.However, after he recovers.Potassium channels remain open forever.Ions enter the cell through these slowly.

In conclusion

Below are brief tasks and structure of the plant cell.The table also contains information about the composition and the biological element.