Cells that form the tissues of representatives of flora and fauna have significant differences in size, shape, and constituent elements. However, all of them show similarities in the main features of growth, metabolism, vital activity, irritability, the ability to change, and development. Next, let's take a closer look at the structure of a plant cell (a table of the main components will be given at the end of the article).
Brief historical background
With the help of osmotic shock in 1925, Grendel and Gorter obtained empty erythrocyte shells, their so-called "shadows". They were stacked in a pile, determining their surface area. Lipids were isolated using acetone. Their number per unit area of erythrocytes was also determined. Despite the errors in the calculations, the correct result was accidentally deduced and the lipid bilayer was discovered.
General information
Biology is the study of the development and growth of tissue elements of representatives of flora and fauna. The structure of a plant cell is a complexthree inextricably linked components:
- The core. It is separated from the cytoplasm by a porous membrane. It contains the nucleolus, nuclear sap and chromatin.
- Cytoplasm and a complex of specialized structures - organelles. The latter, in particular, include plastids, mitochondria, lysosomes and the Golgi complex, the cell center. Organelles are always present. In addition to them, there are also temporary formations called inclusions.
- The structure that forms the surface is the shell of the plant cell.
Features of the surface apparatus
In leukocytes and unicellular organisms, the cell membrane provides the penetration of water, ions, small molecules of other compounds. The process during which the penetration of solid particles occurs is called phagocytosis. If drops of liquid compounds fall, then they speak of pinocytosis.
Organoids
They are present in eukaryotic cells. Biological transformations that occur in the cell are associated with organelles. They are covered by a double membrane - plastids and mitochondria. They contain their own DNA, as well as a protein-synthesizing apparatus. Reproduction is by division. In mitochondria, in addition to ATP, protein is synthesized in a small amount. Plastids are present in plant cells. Their reproduction is carried out by division.
Membrane
It is a mistake to assume that the outer layer of the cell is the cytoplasm. The membrane is a molecular elastic structure. The outer layer of the cell is calledsurface apparatus, through which the separation of the contents from the external environment is carried out. There are different functions of the cell membrane. One of the main tasks is to ensure the integrity of the entire element. Inside, there are also structures that divide the cell into so-called compartments. These closed zones are called organelles or compartments. Within them, certain conditions are maintained. The function of the cell membrane is to regulate the exchange between the environment and the cell.
Membrane
What is the structure of the cell membrane? The cell membrane is a bilayer (double) of lipid class molecules. Most of them are lipids of a complex type - phospholipids. Molecules contain hydrophobic (tail) and hydrophilic (head) parts. When the cell membrane is formed, the tails are turned inward, and the heads are turned in the opposite direction. Membranes are invariable structures. The shell of an animal cell has many similarities with an element of a representative of the flora. The membrane thickness is about 7-8 nm. The biological outer layer of the cell includes various protein compounds: semi-integral (at one end immersed in the outer or inner lipid layer), integral (penetrating through), surface (adjacent to the inner sides or located on the outer side). A number of proteins are the junction points of the membrane and cytoskeleton inside the cell and the outer wall (if present). Some integral compounds act as ion channels, various receptors and transporters.
Defensive task
The structure of the cell membrane largely determines its activity. In particular, the membrane has selective permeability. This means that the degree of permeability of molecules through the membrane depends on their size, chemical properties, and electric charge. The main function that the outer layer of the cell performs is called the barrier. Due to it, a selective, regulated, active and passive exchange of compounds with the environment is ensured. For example, the membrane of peroxisomes protects the cytoplasm from dangerous peroxides.
Transportation
Through the outer layer of the cell there is a transition of substances. Due to transport, the delivery of nutritional components, the elimination of the end products of the metabolic process, the secretion of various substances, and the formation of ionic ingredients are ensured. In addition, the optimal pH and the concentration of ions necessary for the functioning of enzymes are maintained in the cell. If for some reason the necessary particles cannot pass through the phospholipid bilayer, for example, due to hydrophilic properties, since the membrane is hydrophobic inside, or because of their large size, they can cross the membrane through special transporters (carrier proteins), by endocytosis or by protein channels. In the process of passive transport, compounds pass through the outer layer of the cell without energy costs by diffusion along the concentration gradient. Lightweight implementation is considered one of the options for this process. In this case, a specific molecule helps the substance to cross the outer layer of the cell. She canthere is a channel that is able to pass substances of only type 1. Active transport requires energy. This is due to the fact that the movement in this case occurs inversely to the concentration gradient. In this case, the membrane contains special pump proteins, including ATPase, which quite actively pumps potassium ions into the cell and pumps out sodium ions.
Other tasks
The outer layer of the cell performs a matrix function. This ensures a certain mutual arrangement and orientation of membrane protein compounds, as well as their optimal interaction. Due to the mechanical function, the autonomy of the cell and internal structures, as well as connection with other cells, is ensured. In this case, the walls of structures are of great importance in representatives of the flora. In animals, the provision of mechanical function depends on the intercellular substance. Membranes also perform energy tasks. In the process of photosynthesis in chloroplasts and cellular respiration in mitochondria, energy transfer systems are activated in their walls. In them, as in many other cases, proteins take part. One of the most important is the receptor function. Some proteins that are found in the membrane are receptors. Thanks to these molecules, the cell can perceive certain signals. For example, steroids circulating in the bloodstream affect only those target cells that have receptors corresponding to certain hormones. There are also neurotransmitters. These chemicalconnections provide impulse transmission. They also have an association with specific target proteins. Membrane components are often enzymes. Hence the enzymatic function of the cell membrane. Digestive compounds are present in the plasma membranes of the intestinal epithelial elements. Biopotentials are generated and conducted in the outer layer of the cell.
Ion concentration
With the help of the membrane, the internal content of the K+ ion is maintained at a higher level than outside. At the same time, the Na+ concentration is significantly lower than on the outside. This is of particular importance because it provides a potential difference across the wall and the generation of a nerve impulse.
Marking
There are antigens on the membrane that act as some kind of "labels". The marking allows the cell to be identified. Glycoproteins - proteins with oligosaccharide branched side chains attached to them - play the role of "antennas". Since there are countless configurations of side chains, it is possible to make a marker for each group of cells. With the help of them, some elements are recognized by others, which, in turn, allows them to act in concert. This happens, for example, during the formation of tissues and organs. According to the same mechanism, the immune system works to recognize foreign antigens.
Composition and structure
As mentioned above, cell membranes are composed of phospholipids. However, in addition to them, the structure containscholesterol and glycolipids. The latter are lipids with attached carbohydrates. Glyco- and phospholipids, which mainly form cell membranes, consist of 2 long hydrophobic carbohydrate "tails". They are associated with a hydrophilic, charged "head". Due to the presence of cholesterol, the membrane has the necessary level of rigidity. The compound occupies the free space between the lipid hydrophobic tails, thus preventing their bending. In this regard, those membranes in which there is less cholesterol are more flexible and soft, and where there is more of it, on the contrary, there is more rigidity and fragility in the walls. In addition, the compound acts as a stopper that prevents the movement of polar molecules from cell to cell. Of particular importance are proteins that penetrate the membrane and are responsible for its various properties. One or another shell of a plant cell has proteins defined in composition and orientation.
Annular lipids
These compounds are found next to proteins. However, annular lipids are more ordered and less mobile. They contain fatty acids with a higher saturation. Lipids leave the membranes together with the protein compound. Without annular elements, membrane proteins will not work. Often the shells are asymmetric. In other words, this means that the layers have different lipid compositions. The external contains mainly glycolipids, sphingomyelins, phosphatidylcholine, phosphatidyl nositol. The inner layer contains phosphatidyl nositol,phosphatidylethanolamine and phosphatidylserine. The transition from one level to another specific molecule is somewhat difficult. However, it may well happen spontaneously. This happens about once every six months. The transition can also be carried out with the help of flippase and scramblase proteins. When phosphatidylseryl appears in the outer layer, macrophages take a defensive position and direct their activity to destroy the cell.
Organelles
These areas can be single and closed or connected to each other, separated by membranes from the hyaloplasm. Perixisomes, vacuoles, lysosomes, the Golgi apparatus, and the endoplasmic reticulum are considered single-membrane organelles. The double membranes include plastids, mitochondria, and the nucleus. As for the structure of membranes, the walls of different organelles differ in the composition of proteins and lipids.
Selective permeability
Through cell membranes slowly diffuse fatty and amino acids, ions and glycerol, glucose. At the same time, the walls themselves actively regulate this process, passing some and retaining other substances. There are four main mechanisms for the entry of a compound into a cell. These include endo- or exocytosis, active transport, osmosis and diffusion. The last two are passive in nature and do not require energy costs. But the first two are active. They need energy. With passive transport, selective permeability is determined by integral proteins - special channels. The membrane is permeated through them. These channels form a kind of passage. There are own proteins for the elementsCl, Na, K. As for the concentration gradient, the molecules of the elements move into the cell from it. Against the background of irritation, sodium ion channels open. They, in turn, begin to abruptly enter the cell. This is accompanied by an imbalance in the membrane potential. However, he recovers after that. Potassium channels always remain open. Ions enter the cell slowly through them.
In closing
The tasks and structure of a plant cell are briefly presented below. The table also contains information about the composition of the biological element.
| Types of elements | Composition and functions |
| Plant cells | Made of fiber. Provides scaffolding and protection. |
| Bioelements | Very thin and elastic layer - glycocalyx includes proteins and polysaccharides. Provides protection. |
