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Active transport definition and its kinds

Ever wonder how molecules, substances, minerals or water move from one part of the cell to the other part of the cell? The cell is considered a living body where movement or the transfer of substances required in one part of the cell is possible. This process of substance movement is called active transport. Of course, the cell has membranes covering or protecting it from its external surrounding but that doesn’t mean it cannot live. Although, concentration gradient or other factors possibly block or act against these movements but that still doesn’t make the process of active transport across cell membranes impossible

Molecules travel from regions where their concentration is either low, for instance within the cell itself to regions with high concentration e.g. outside the cell by a way of active transport. It is also possible to see or observe movements from high concentration regions to regions with very low concentration. Active transport is normally connected with gathering high concentrations of molecules needed by the cell. These molecules can be any of the following:

  • ions
  • glucose
  • amino acids

With the development of science, there are two distinct types of active transport occurring within the cells. These two types of molecule transport include the following:

  • Primary active transport of molecules
  • Secondary active transport of molecules

Primary active transportation of molecules is that process or processes that involve the use of chemical energy, such as the chemical energy derived from adenosine triphosphate (ATP). This kind of transport is also known as direct active transport. This is so because it uses metabolic energy as its mode of active transportation of molecule to the cell as well as from the cell and also across a cell membrane

Most of the enzymes that perform such kind of active transportation are the so-called transmembrane ATPases. A well-known primary ATPase that is said to be universal to all animal life is the sodium-potassium pump. This Na+- K+ pump serves the sole purpose of maintaining the cell potential during the process of active transport

There are other source or point of energy that can be used for primary active transport. They include:

  • Redox energy
  • Photon or light energy

An example of primary active transportation using redox energy is a mitochondrial electron transport chain which uses the reduction energy of NADH to transport protons across the inside of the mitochondrial membrane against their concentration gradient. A good example of primary active transport are the proteins that are involved in photosynthesis. These proteins use the energy of photons to create a proton gradient across the thylakoid membrane as well as generating a reduction power in the form of NADPH

Secondary active transportation involves the use of some electrochemical gradients to achieve the process of molecule transportation within any cell. This form of active transport is also called the coupled transport or simply as cotransport

The secondary form of active transport involves the use of energy in order to be able to transfer molecules across the cell membrane. Nevertheless, there is no direct coupling of ATP as found in primary active transportation rather, it depends on the electrochemical potential difference that was created by pumping ions inside and outside of the cell. Permitting one ion or a molecule to move down an electrochemical gradient. This moves against the concentration gradient where it is more concentrated to regions where it is less concentrated increasing entropy and can serve as a source of energy for metabolism


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