Publication of facilities: features, types and examples
Dacilitated Diffusion Definition Biology Expansion of facilities is a physical phenomenon that involves the transport of particles, ions or liquids across a membrane and in favor of the gradual stabilization of its stability and thanks to the participation of the structure which is said to move. ۔
In this type of transport, the motion of the particles is always in favor of their concentration gradient, i.e., they travel across a membrane from a region where their concentration is “higher” in another region where it “Less” happens.
The contribution of chemical energy is not required to initiate or maintain the movement of easily dispersed particles. Various amino acids, carbohydrates (polysaccharides), ions and gases enter the cells through diffusion.
The cell membranes are responsible for “separating” the cytosol content from the formal module, and are “selectively capable” for different substances according to their properties. This is possible thanks to the presence of carrier proteins that form channels or holes for the entry or exit of particles.
Some molecules require energy to transport, as they are against their concentration gradient. Others enter through the common medium (pass the membrane freely) and others are passed down its slope through channels or holes (facilitation).
Features facilitated spread
To define a convenient spread, we can mention some of its features.
Most molecules travel from one cell of the membrane to another through proteins that are “embedded” in the cell membrane, acting as “channels”.
- The movement of substances is always subject to the same direction: from a place where their concentration is high to a low concentration.
No energy is expended to move the transport particles.
For this type of transport, there must be a membrane between the two parts.
- The particles move into the unmade cell. However, the structure of these molecules inside and outside the cells is designed so that it does not happen automatically.
- In general, molecules are easily transported to molecules that, due to their physical and / or chemical properties, cannot cross the cell membrane freely.
Types of facilitation
To date, 3 different types of easy spread have been described. These vary according to the properties of the proteins that “facilitate” transportation and are:
Propagation through protein channels
This involves sharing special proteins to move the molecules, which are basically in a liquid state. These proteins are known as “channel” proteins and form a kind of “pore” through which water molecules or small ions pass rapidly.
Propagation through closed channel proteins
Channel-forming proteins also participate in this type of transport, but they have a “gate” molecular system that regulates the entry of substances.
Consequently, in order for any substance to enter through the “closed” channel protein, substances must be bound at specific locations in the channel peptide sequence, so it is important to identify the transport of the molecule.
Thus, the entry or exit of matter is possible only when the transport proteins “experience” a stimulus (chemical, thermal, electrical or mechanical signal) that allows the channel to open, which is otherwise always open. Is.
There are different types of these proteins, which they classify according to the ions or molecules they carry. For example, there are channels of sodium (Na +), calcium (Ca +), glucose (C6H12O6) and others.
Propagation by carrier proteins
Such propagation is by proteins that transport ions or macromolecules across the plasma membrane. An important feature of this transfer is that binding to the transfer of molecules causes the transformation of transporter proteins.
Instead of maintaining a closed gate that opens in response to a stimulus (as in the previous case), transporter proteins mediate transport only when they are bound to transport subsystems and process Change their shape during
They are proteins that specialize in transporting the required amount of molecules to the cell, and are thus highly selective carriers.
Examples of facility publishing
Channel proteins, also known as aquaporns, are the most representative example of a protein involved in transport by easy dispersion, as they move water molecules from the outer cell to the medium-sized distance through the channels that carry them. Create .
Cells use aquaporins in plant roots and stems to absorb water quickly and efficiently.
Animal cells also contain aquaporins, but in smaller amounts than plant cells (many protozoa have rich vacuole membranes, for example, aquaporins).
Vertical animal neurons have sodium channels that are activated to open by chemical signals that allow this ion to enter. These channels are a perfect example of the “closed” channels we mentioned earlier.
Another example of easy circulation through closed “gate” channels is the transport of glucose through the membrane.
Glucose molecules have sizes and properties that prevent them from crossing the cell membrane, for example, “small” channels such as aquaporins.
Furthermore, cells must maintain an internal concentration of this solution in a harsh location, as the energy requirements for their metabolism are not always available. This means that not all glucose that enters the cell should enter the cell.Dacilitated Diffusion Definition Biology
The transport mechanism of these molecules involves the sharing of transporter proteins that are easily catalyzed to initiate transport and when they bind to the molecules that are perceived to transport them. The shape changes.
There are many ion channels that are transport proteins that work to spread easily.Dacilitated Diffusion Definition Biology
For example, in the case of potassium (K +) and chlorine (CL) ions, which are large ions with specific functions and effects inside the cell, their entry is often combined with the emission of other ions.
The inward and outward path of these ions is controlled and many facilitated diffusion ion channels are activated only when stimulated by the ion exchange effect, which uses a catalyst directly on the carrier protein.
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