Potassium channel / K channel

Everything in this video is take from the following website:
www.garlandscience.com/garland...
The bacterial potassium channel is a multipass transmembrane protein in the plasma membrane. It is built from four identical subunits that are arranged symmetrically. A pore in the center of the protein allows selective passage of potassium ions across the membrane.
Four rigid protein loops, one contributed by each subunit, form a selectivity filter at the narrowest part of the pore. This structure is responsible for the channel's high degree of selectivity for potassium ions over sodium ions.
In the selectivity filter, carbonyl groups line the walls of the pore. These carbonyl groups are spaced precisely to interact with an unsolvated potassium ion, balancing the energy required to remove its hydration shell. Passage of a sodium ion through the channel is energetically unfavorable because the sodium is too small for optimal interaction with the carbonyl groups.

[@dannichols6261]

It's very good that the text of the presentation is included, thank you, that's helpful. But I think it could use a little elaboration. I'll do so, but please correct me if I include errors. All ions in water electrostatically attract water molecules into a hydration shell around them, with the size of that shell depending on the charge of the ion. The selectivity filter functions in relation to this larger hydration shell around the ions. Potassium ions are larger than sodium ions, and when the larger K ion with a correspondingly larger hydration shell enters the selectivity filter section, that filter section is sized so that portions of it are just the right size to interact with and remove the hydrating ('solvating') water molecules, allowing the now 'naked' K ions to continue through the smaller exit portion of the pore. Na ions, which are themselves smaller than K ions, have a correspondingly smaller hydration shell than that of K, so when a Na ion gets to the selectivity filter, the water molecules in the Na hydration shell cannot be reached by the portions of the selectivity filter which would otherwise remove the water molecules, so the Na ion retains its hydration shell, which is then in composite (Na ion plus hydration shell) too large to pass through the pore of the K channel, so it doesn't. (This wikipedia may be helpful, en.wikipedia.org/wiki/Potassium_channel , and this may be more helpful: pdb101.rcsb.org/motm/38 , near the bottom of the page, at ' Exploring the Structure '. )

[@abbyhe4284]

Really helpfu!!!

[@marloncendron611]

I might be wrong on this, but the smaller the atom, the greater is its electric field and thus the bigger is its hydration shell. Since Na+ is smaller than K+, its hydration shell is bigger.

[@arwahadi7861]

This was amazing, thank you!

[@muntahajabbar3747]

thanku its was too helpful and beautifully shown,easy to understand

[@sanahilal6179]

Perfect! Thanks loads

[@potatochip190]

Perfect!

[@carol-annenicol8022]

Very useful! :)

[@durlabhbhaya2676]

Very nice 3d model makes very easy too learn this topic

[@davidlejenkins]

I don't remember the K channel being provided in my cable package.

[@khoshalsaidy526]

Wtf was this??🤔😟😡