There are substances that a cell needs to have inside or, on the contrary, substances that must be eliminated by expelling them outside, but either because they are very large, because they have an electrical charge or because to do so it is necessary to overcome a concentration gradient, they cannot cross the cell membrane.
Active transport and mass transport are mechanisms that cells have developed to be able to act in these cases, whether they are small molecules or large proteins or bacteria.
Next, in the following FastlyHealarticle, we will explain what the definition of active transport is , in turn, we will tell you what the main methods of mass transport are.
What is active transport
The term active transport refers to the molecular movement that occurs from a region with low concentration to one of high concentration, crossing the cell membrane, although it can also occur in a direction opposite to a gradient or any other obstructing factor, although it is frequently a gradient of concentration.
This movement of molecules through the cell occurs within the cell membrane because of a chemical energy that makes the cell able to admit large molecules that it could not otherwise. The transporter molecules that are housed in the cell are linked to the molecules that must be carried inside the cell, facilitating active transport, in the same way that some enzymes do, which act as small chemical detonations that facilitate the passage of the different substances across the cell membrane.
active and passive transport
The difference between active and passive transport is that, while the latter uses kinetic energy and molecular entropic nature to move them down a gradient, active transport uses the energy of cells to make them move against a gradient. gradient or any other type of resistance, such as polar repulsion.
Normally, active transport is associated with the accumulation in high degrees of molecular concentrations required by the cell, such as glucose, amino acids or ions. In fact, the glucose uptake process that occurs inside the human intestines is a good example of active transport.
Depending on the energy used for transportation, we can divide it into two different categories; primary active transport and secondary active transport . The primary is the one that consumes chemical energy during the process, while the secondary uses the energy of some type of electrochemical gradient.
The ways in which a macromolecule crosses the cell membrane can be of a very different nature, for that reason, depending on the way it does it, the active transport process receives one name or another. The mechanism by which the molecule crosses the cell membrane is called mass transport and can be in the following ways:
- Endocytosis : In this system, the molecules enter a vesicle that inserts itself into the cell without it crossing the cell membrane.
- Pinocytosis : Unlike the previous one, in this case the membrane undergoes an invagination that, enveloping the molecule, introduces it into the cell, as you can see in the illustration above.
- Phagocytosis : The cell causes a folding of its membrane, with which it embraces and encompasses the molecule, as you can see in the drawing below.
- Exocytosis : This procedure is the opposite of phagocytosis, in this case the molecule is inside the cell and it is close to the cell membrane. Once there, the molecular envelope fuses and the rest is expelled out of the cell.
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