Features, structure and functions of cell membranes

In 1972, a theory was put forward, according to which a partially permeable membrane surrounds the cell and performs a number of vital tasks, and the structure and functions of cell membranes are significant questions regarding the proper functioning of all cells in the body. Cell theory was widely spread in the 17th century, together with the invention of a microscope. It became known that plant and animal tissues consist of cells, but because of the low resolving power of the device it was impossible to see any barriers around the animal cell. In the 20th century, the chemical nature of the membrane was studied in more detail, it was found that its basis is composed of lipids.

Structure and function of cell membranes

The cell membrane surrounds the cytoplasm of living cells, physically separating the intracellular components from the external environment. Mushrooms, bacteria and plants also have cell walls that provide protection and prevent the passage of large molecules. Cellular membranes also play a role in the formation of the cytoskeleton and attachment to the extracellular matrix of other vital particles. This is necessary in order to keep them together, forming the tissues and organs of the body. The structural features of the cell membrane include permeability. The main function is protection. The membrane consists of a phospholipid layer with embedded proteins. This part is involved in such processes as cell adhesion, ionic conductivity and signaling systems and serves as an attachment surface for several extracellular structures, including the wall, glycocalyx and internal cytoskeleton. The membrane also preserves the potential of the cell, working as a selective filter. It is selectively permeable to ions and organic molecules and controls the movement of particles.

Biological mechanisms involving the cell membrane

1. Passive diffusion: some substances (small molecules, ions), such as carbon dioxide (CO2) and oxygen (O2), can penetrate through the plasma membrane by diffusion. The shell acts as a barrier to certain molecules and ions, they can concentrate on both sides.

2. Transmembrane protein channels and transporter: nutrients, such as glucose or amino acids, must enter the cell, and some metabolic products must leave it.

3. Endocytosis is the process by which molecules are absorbed. A small deformation (invagination) is created in the plasma membrane, in which the substance to be transported is swallowed. This requires energy and, thus, is a form of active transport.

4. Exocytosis: occurs in various cells to remove undigested residues of substances brought by endocytosis to secrete substances such as hormones and enzymes, and transport the substance completely through the cell barrier.

Molecular structure

A cell membrane is a biological membrane consisting primarily of phospholipids and separating the entire cell from the external environment. The process of formation occurs spontaneously under normal conditions. To understand this process and correctly describe the structure and functions of cell membranes, as well as properties, it is necessary to evaluate the nature of phospholipid structures for which structural polarization is intrinsic. When phospholipids in the cytoplasmic aquatic environment reach a critical concentration, they combine into micelles, which are more stable in the aquatic environment.

Membrane properties

• Stability. This means that, after formation, the disintegration of the membrane is unlikely.
• Strength. The lipid membrane is sufficiently reliable to prevent the passage of a polar substance, and the dissolved border (dissolved in ions, glucose, amino acids) and much larger molecules (proteins) can not pass through the formed boundary.
• Dynamic nature. This is perhaps the most important property, if we consider the structure of the cell. The cell membrane can undergo various deformations, it can fold and bend and not collapse. In special circumstances, for example, when merging vesicles or budding, it can be disturbed, but only for a while. At room temperature, its lipid constituents are in a constant, chaotic motion, forming a stable fluid boundary.

Liquid mosaic pattern

Speaking about the structure and function of cell membranes, it is important to note that in the modern view the membrane as a liquid mosaic model was considered in 1972 by the scientists Singer and Nicholson. Their theory reflects three basic features of the membrane structure. Integral membrane proteins contribute to the mosaic pattern for the membrane, and they are capable of lateral movement in the plane due to the volatile nature of the lipid organization. Transmembrane proteins are also potentially mobile. An important feature of the membrane structure is its asymmetry. What is the structure of the cell? Cell membrane, nucleus, proteins and so on. The cell is the basic unit of life, and all organisms consist of one or many cells, each of which has a natural barrier separating it from the environment. This outer boundary of the cell is also called the plasma membrane. It consists of four different types of molecules: phospholipids, cholesterol, proteins and carbohydrates. The liquid mosaic pattern describes the structure of the cell membrane as follows: flexible and elastic, resembling a vegetable oil in consistency, so that all individual molecules simply float in a liquid medium, and they are all capable of moving sideways within this shell. Mosaic is something that contains many different details. In the plasma membrane it is represented by phospholipids, cholesterol molecules, proteins and carbohydrates.

Phospholipids

Phospholipids constitute the basic structure of the cell membrane. These molecules have two different ends: the head and tail. The head end contains a phosphate group and is hydrophilic. This means that it is attracted to water molecules. The tail consists of hydrogen and carbon atoms, called chains of fatty acids. These chains are hydrophobic, they do not like to mix with water molecules. This process resembles what happens when you pour vegetable oil into the water, that is, it does not dissolve in it. Features of the structure of the cell membrane are associated with the so-called lipid bilayer, which consists of phospholipids. Hydrophilic phosphate heads are always located where there is water in the form of intracellular and extracellular fluids. The hydrophobic tails of phospholipids in the membrane are organized in such a way that they are kept away from water.

Cholesterol, proteins and carbohydrates

Hearing the word "cholesterol", people usually think that this is bad. However, in fact, cholesterol is a very important component of cell membranes. Its molecules consist of four rings of hydrogen and carbon atoms. They are hydrophobic and occur among hydrophobic tails in the lipid bi-layer. Their importance is to maintain a consistency, they strengthen the membrane, preventing the crossing. Cholesterol molecules also keep phospholipid tails from coming into contact and hardening. This ensures fluidity and flexibility. Membrane proteins function as enzymes to accelerate chemical reactions, act as receptors for specific molecules or transport substances through the cell membrane.

Carbohydrates, or saccharides, are found only on the extracellular side of the cell membrane. Together they form a glycocalyx. It provides damping and protection of the plasma membrane. Based on the structure and type of carbohydrates in the glycocalysis, the body can recognize the cells and determine whether they should be there or not.

Membrane Proteins

The structure of the cell membrane of an animal cell can not be imagined without such a significant component as a protein. In spite of this, they may be considerably inferior in size to another important component - lipids. There are three types of basic membrane proteins.

• Integral. They completely cover the bi-layer, cytoplasm and extracellular environment. They perform transport and signaling functions.
• Peripheral. Proteins are attached to the membrane by electrostatic or hydrogen bonds in their cytoplasmic or extracellular surfaces. They are involved mainly as a means of attachment for integral proteins.
• Transmembrane. They perform enzymatic and signaling functions, and also modulate the basic structure of the lipid bi-layer of the membrane.

Functions of biological membranes

The hydrophobic effect, which regulates the behavior of hydrocarbons in water, controls the structures formed by membrane lipids and membrane proteins. Many properties of membranes are provided by carriers of lipid bi-layers, which form the basic structure for all biological membranes. Integral membrane proteins are partially hidden in the lipid bi-layer. Transmembrane proteins have a specialized organization of amino acids in their primary sequence.

Peripheral membrane proteins are very similar to soluble, but they are also bound to membranes. Specialized cell membranes have specialized cell functions. How does the structure and function of cell membranes affect the body? On how the biological membranes are arranged, the provision of the functionality of the whole organism depends. From intracellular organelles, extracellular and intercellular membrane interactions, structures are created that are necessary for the organization and performance of biological functions. Many structural and functional features are common to bacteria, eukaryotic cells and enveloped viruses. All biological membranes are built on a lipid bi-layer, which causes a number of common characteristics. Membrane proteins have many specific functions.

• Controlling. Plasma cells membranes determine the boundaries of cell interaction with the environment.
• Transport. Cell intracellular membranes are divided into several functional blocks with different internal composition, each of which is supported by the necessary transport function in combination with permeability of control.
• Signal transduction. The fusion of membranes provides a mechanism for intracellular vesicular alerting and preventing various kinds of virus from freely entering the cell.

Meaning and conclusions

The structure of the outer cell membrane affects the entire body. It plays an important role in protecting integrity, allowing the penetration of only selected substances. It is also a good base for fixing the cytoskeleton and cell wall, which helps in maintaining the shape of the cell. Lipids constitute about 50% of the mass of the membrane of most cells, although this index varies depending on the type of membrane. The structure of the outer cell membrane of mammals is more complex, there are four basic phospholipids. An important property of lipid bi-layers is that they behave like two-dimensional liquids in which individual molecules can freely rotate and move in lateral directions. Such fluidity is an important property of membranes, which is determined depending on temperature and lipid composition. Due to the hydrocarbon ring structure, cholesterol plays a role in determining the fluidity of the membranes. The selective permeability of biological membranes for small molecules allows the cell to control and maintain its internal structure.

Considering the structure of the cell (cell membrane, nucleus, and so on), we can conclude that the body is a self-regulating system that, without outside help, can not harm itself and will always look for ways to restore, protect and properly function each cell.