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Active Transport Types and Examples

In cellular biology, the term active transport is used to define the movement of the molecules around the plasma membrane from the lower concentration area to the higher concentration area; that is, the action is generally against the concentration gradient. For the process of active transport to take place, it requires energy. Active transport is divided into three categories:

  • Primary active transport where adenosine triphosphate (ATP) is used.
  • Secondary active transport where the electrochemical gradient is used.
  • Bulk transport

Active transport

Active cellular transport

Active Transport

In active cellular transport, cellular energy moves the particles against a gradient, polar repulsion, and many other resistances. It collects a high concentration of molecules required by the cells, like ions, amino acids, and glucose. Active cellular transport occurs both in human beings and plants as well.
Example

  • Uptake of glucose ions in the intestine of human beings.
  • Uptake of mineral ions in the root hairs of different plants.

Not all molecules are allowed to move across the plasma membrane. For example, transmembrane proteins permit the movement of the substances because the membrane's phospholipid bilayer is selectively permeable and enables specific substances to move against the direction of a concentration gradient.

In addition, there is a fine distinction between active transport and passive transport. A mode of active transport requires energy to move the molecules against the concentration gradient. In contrast, in passive transport, no energy is needed to move the substances in the direction of the concentration gradient.

Transporters

There are two kinds of transporters that are involved in transporting substances.

  • Antiporter: It transports a substrate in a direction across the membrane, while another substrate gets co-transported simultaneously in the opposite direction.
  • Symporter: It transports two substrates in the same direction at the same time together.

Both the antiport and symport are related to secondary active transport. To transport the molecules from lower concentration to higher concentration, select transmembrane carrier proteins. These proteins have receptors on their surfaces that bind to only selected molecules transported across the cell membrane.

Sodium-Potassium pump: The process where sodium gets hauled out of the cell, and potassium is actively transported inside the cell. In human beings, active transport often occurs in the lining of the small intestine. The membrane potential is maintained by the movement of three Na+ ions far from the cell and two K+ ions inside the cells.

To extract the mineral salt from the diluted solution present in the soil, active transport of the salts occurs against the direction of its concentration gradient.

Primary active transport

In this process, metabolic energy is directly used to transport the molecules through the cell membrane. The molecules that get transferred via primary active transport are Na+, Mg+, K+, etc. Generally, ion channels are needed for these molecules to cross the membrane. The main enzyme that performs the active transport is transmembrane ATPase. Redox energy and photon energy are other forms of energy that are required for primary active transport.

The various types of primary active transport are:

  • P-type ATPase
  • F-ATPase
  • V-ATPase
  • ABC transporter

Secondary active transport

It is also called coupled transport. In this method of transport, the coupling of ATP does not occur. Instead, the electrochemical potential difference gets created by pumping ions in and out of the cells. An ion or a molecule moves in the direction of the electrochemical gradient but against the concentration gradient from the higher concentration to the lower the engagement that elevates the entropy creating energy for the metabolism. In humans, the Na+ ions get co-transported across the membrane so that its electrochemical gradient is used as a power in the active transport of another ion against the gradient.

Bulk transport

The biologists recognise two forms of bulk transports that transport materials in and out of the cells via vesicles.

  • Endocytosis: is a process where substances are brought inside the cell. It consists of pinocytosis and phagocytosis. Therefore, it is a kind of active transport.
  • Exocytosis: It is removing substances from the cell by fusing a cell membrane and vesicle membrane.

Model of active transport

The hydrogen ions are transported against the electrochemical gradient via ATP Hydrolysis. When phosphorylation occurs in a carrier, the protein binds to hydrogen ions, which transports in contrast to the electrochemical gradient. Hydrolysis of the phosphate group bound, which then releases the hydrogen ion, restores the carrier protein to its original shape.

 

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