A polarized membrane is a lipid membrane that has a positive electrical charge on one side and a negative charge on another side, which produces the resting potential in living cells. Whether or not a membrane is polarized is determined by the distribution of dissociable protons and permeant ions inside and outside the membrane that travel passively through ion channel or actively via ion pump, creating an action potential.[1][2][3]
Structure and composition
editPolarized membranes consist of a phospholipid bilayer, with embedded membrane proteins that aid in molecular transport and membrane stability as well as lipids that primarily aid in structure and compartmentalization of membrane proteins. The bilayer aspect of the membrane is due to the amphiphilic nature of the phospholipids that comprise the membrane. These phospholipids contain a hydrophilic head region with a phosphate bonded to a variety of functional groups. This head region is localized to face the extracellular space outside of the cell as well as the intracellular, cytosolic region of the cell. The hydrophobic phospholipid tail region consists of a chain of carbon molecules bound to hydrogen with two categories: saturated or unsaturated. [4]
Mechanisms of polarization
editThe polarization of cellular membranes are established and maintained through the active and passive transport of ions across the membrane through membrane proteins, specifically channel proteins and ion pumps. These proteins maintain an electrochemical gradient by pumping certain ions in and out of the cell. This gradient of ions lead to a positive charge on one side and a negative charge on the other. [5]
The primary mechanism for generating this electrochemical gradient is the activity of the sodium-potassium pump (Na/K ATPase), which utilizes active transport to pump two potassium (K+) ions into the cell and three sodium (Na+) ions out of the cell per cycle. This is a P-class protein, meaning it is phosphorylated in the process and utilizes adenosine triphosphate (ATP) as an energy source. [6]
Ion channels, which are specific in which ions are allowed to pass through them, are also crucial to polarization and maintaining polarization. Voltage-gated ion channels are activated or deactivated in response to a change in membrane potential, allowing various ions to flow down their concentration gradient based on the channel's specificity. These channels are crucial in the propagation and transduction of action potentials in the nervous system, when transient activation and deactivation of said ion channels enable signal transduction. [7]
See also
editReferences
edit- ^ "Membrane Channels". Cell Biology. Elsevier. 2017. pp. 261–284. doi:10.1016/b978-0-323-34126-4.00010-4. ISBN 978-0-323-34126-4.
- ^ Nicholls, David G.; Ferguson, Stuart J. (2013). "Quantitative Bioenergetics". Bioenergetics. Elsevier. pp. 27–51. doi:10.1016/b978-0-12-388425-1.00003-8. ISBN 978-0-12-388425-1.
- ^ McCormick, David A. (2014). "Membrane Potential and Action Potential". From Molecules to Networks. Elsevier. pp. 351–376. doi:10.1016/b978-0-12-397179-1.00012-9. ISBN 978-0-12-397179-1.
- ^ "Chemical Foundations". Molecular Cell Biology. W.H. Freeman and Company. 2016. pp. 22–44. ISBN 1464183392.
- ^ Molecular Cell Biology. W.H. Freeman and Company. 2016. ISBN 1464183392.
- ^ Skou, Jens Christian (1957). "The influence of some cations on an adenosine triphosphatase from peripheral nerves". Bio- chimica et Biophysica Acta. 23: 394–401. doi:10.1016/0006-3002(57)90343-8.
- ^ Martin, Robert (2011). From Neuron to Brain. Oxford University Press. ISBN 0878936092.
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