How Ion Pumps Maintain Membrane Potential?

Advertisements
Advertisements

Related Posts:


A proton pump. Proton pumps are electrogenic pumps that store energy by generating voltage (charge separation) across membranes. A proton pump translocates positive charge in the form of hydrogen ions. The voltage and H+ concentration gradient represent a dual energy source that can drive other processes, such as the uptake of nutrients. Most proton pumps are powered by ATP hydrolysis.
Source: Urry, Lisa A.. Campbell Biology (p. 138). Pearson Education. Kindle Edition.

How Ion Pumps Maintain Membrane Potential? (Campbell Biology)

All cells have voltages across their plasma membranes. Voltage is electrical potential energy —a separation of opposite charges. The cytoplasmic side of the membrane is negative in charge relative to the extracellular side because of an unequal distribution of anions and cations on the two sides. The voltage across a membrane, called a membrane potential, ranges from about -50 to -200 millivolts (mV). (The minus sign indicates that the inside of the cell is negative relative to the outside.)

The membrane potential acts like a battery, an energy source that affects the traffic of all charged substances across the membrane. Because the inside of the cell is negative compared with the outside, the membrane potential favors the passive transport of cations into the cell and anions out of the cell. Thus, two forces drive the diffusion of ions across a membrane: a chemical force (the ion’s concentration gradient, which has been our sole consideration thus far in the chapter) and an electrical force (the effect of the membrane potential on the ion’s movement). This combination of forces acting on an ion is called the electrochemical gradient.

In the case of ions, then, we must refine our concept of passive transport: An ion diffuses not simply down its concentration gradient but, more exactly, down its electrochemical gradient. For example, the concentration of Na+ inside a resting nerve cell is much lower than outside it. When the cell is stimulated, gated channels open that facilitate Na+ diffusion. Sodium ions then “fall” down their electrochemical gradient, driven by the concentration gradient of Na+ and by the attraction of these cations to the negative side (inside) of the membrane. In this example, both electrical and chemical contributions to the electrochemical gradient act in the same direction across the membrane, but this is not always so. In cases where electrical forces due to the membrane potential oppose the simple diffusion of an ion down its concentration gradient, active transport may be necessary.

Some membrane proteins that actively transport ions contribute to the membrane potential. An example is the sodium-potassium pump. The pump does not translocate Na+ and K+ one for one, but pumps three sodium ions out of the cell for every two potassium ions it pumps into the cell. With each “crank” of the pump, there is a net transfer of one positive charge from the cytoplasm to the extracellular fluid, a process that stores energy as voltage. A transport protein that generates voltage across a membrane is called an electrogenic pump. The sodium-potassium pump appears to be the major electrogenic pump of animal cells. The main electrogenic pump of plants, fungi, and bacteria is a proton pump, which actively transports protons (hydrogen ions, H+) out of the cell. The pumping of H+ transfers positive charge from the cytoplasm to the extracellular solution. By generating voltage across membranes, electrogenic pumps help store energy that can be tapped for cellular work. One important use of proton gradients in the cell is for ATP synthesis during cellular respiration, as you will see in Concept 9.4. Another is a type of membrane traffic called cotransport.

Source:

Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html

Advertisements
Advertisements

Related Research

Research Article: Quantitative in vivo mapping of myocardial mitochondrial membrane potential

Date Published: January 16, 2018 Publisher: Public Library of Science Author(s): Nathaniel M. Alpert, Nicolas Guehl, Leon Ptaszek, Matthieu Pelletier-Galarneau, Jeremy Ruskin, Moussa C. Mansour, Dustin Wooten, Chao Ma, Kazue Takahashi, Yun Zhou, Timothy M. Shoup, Marc D. Normandin, Georges El Fakhri, Cecilia Zazueta. http://doi.org/10.1371/journal.pone.0190968 Abstract: Mitochondrial membrane potential (ΔΨm) arises from normal function of … Continue reading

Research Article: Combining Membrane Potential Imaging with l-Glutamate or GABA Photorelease

Date Published: October 11, 2011 Publisher: Public Library of Science Author(s): Kaspar E. Vogt, Stephan Gerharz, Jeremy Graham, Marco Canepari, Olivier Jacques Manzoni. http://doi.org/10.1371/journal.pone.0024911 Abstract: Combining membrane potential imaging using voltage sensitive dyes with photolysis of l-glutamate or GABA allows the monitoring of electrical activity elicited by the neurotransmitter at different sub-cellular sites. Here we describe … Continue reading

Research Article: Correction: Quantitative in vivo mapping of myocardial mitochondrial membrane potential

Date Published: February 8, 2018 Publisher: Public Library of Science Author(s): unknown. http://doi.org/10.1371/journal.pone.0192876 Abstract: Partial Text   Source: http://doi.org/10.1371/journal.pone.0192876  

Research Article: Versatile Membrane Deformation Potential of Activated Pacsin

Date Published: December 7, 2012 Publisher: Public Library of Science Author(s): Shih Lin Goh, Qi Wang, Laura J. Byrnes, Holger Sondermann, Ludger Johannes. http://doi.org/10.1371/journal.pone.0051628 Abstract: Endocytosis is a fundamental process in signaling and membrane trafficking. The formation of vesicles at the plasma membrane is mediated by the G protein dynamin that catalyzes the final fission step, … Continue reading

Research Article: A Potential Role for Bat Tail Membranes in Flight Control

Date Published: March 30, 2011 Publisher: Public Library of Science Author(s): James D. Gardiner, Grigorios Dimitriadis, Jonathan R. Codd, Robert L. Nudds, Brock Fenton. http://doi.org/10.1371/journal.pone.0018214 Abstract: Wind tunnel tests conducted on a model based on the long-eared bat Plecotus auritus indicated that the positioning of the tail membrane (uropatagium) can significantly influence flight control. Adjusting tail … Continue reading