Why do cells pump things like protons against their electrochemical gradients?
What will be an ideal response?
Answer: Electrochemical gradient is define as the difference in charge and chemical concentration across a membrane.
To move substances against the membrane’s electrochemical gradient, the cell utilizes active transport which requires energy. The energy is harvested from adenosine triphosphate (ATP) generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements. Much of a cell’s supply of metabolic energy may be spent maintaining these processes. Active transport is the movement of a substance across a cell membrane against its concentration gradient (from low to high concentration) facilitated by ATP conversion. There are two mechanism of active transport are following:
- Primary active transport, which is directly dependent on ATP, moves ions across a membrane and creates a difference in charge across that membrane.
- Secondary active transport, created by primary active transport, is the transport of a solute in the direction of its electrochemical gradient and does not directly require ATP.
As in one of the case that is proton pumping against electrochemical gradient is through Proton pump. Proton pump is a membrane-integrated enzymatic complex which is able to mobilize protons to generate a proton gradient across the membrane.
Humans have a gastric hydrogen potassium ATPase or H+/K+ ATPase that also belongs to the P-type ATPase family. This enzyme functions as the proton pump of the stomach, primarily responsible for the acidification of the stomach contents.
Proton gradient constitutes a fundamental energy reservoir. The proton pump plays an important role in cell respiration and photosynthesis. The electron transport chain in cell respiration generates an electrochemical potential which is coupled to the proton pumps located in the inner mitochondrial membrane. In mitochondrial electron transport chain, each of the complexes I, III and IV acts as a proton pump that uses the free energy of electron flow as the deriving force to transport H+ from mitochondrial matrix to the outside of the IMM (inner mitochondrial membrane) against the gradient of H+. This results in generation of electrochemical H+ gradient across the inner mitochondrial membrane (IMM) since outside and inside of the IMM becomes electropositive and electronegative due to accumulation of H+ in intermembrane space. The H+ gradient thus generated is utilized to form ATP from ADP and Pi. Since IMM is impermeable to H+, the protons flow back from intermembrane space into matrix down the electrochemical H+ gradient through proton channel in Fo component of F1-Fo particles (i.e. ATP synthase). The passage of H+ via proton channel is coupled with phosphorylation of ADP to ATP by F1 component of ATP synthase enzyme of IMM. The Fo and F1 components of ATP synthase coordinate with each other and couple the disappearance of H+ gradient with ATP synthesis
This proton gradient is an energy reservoir because it is the driver for the generation of chemical energy (ATP), or any secondary transport system associated to it, such as the transport of nutrients, the maintenance of the ionic homeostasis of cells.
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