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Topic: Electronegativity and Cell membrane potential  (Read 20315 times)

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Offline Bioionic

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Electronegativity and Cell membrane potential
« on: April 21, 2008, 12:23:31 AM »
Looking at the periodic chart and going down, the electronegativity goes down, ie Na = .9 and K = .8 From the definition electronegativity is the ability to attract electrons. So is that to say the more electronegative would actually be the more positively charged? I ask because I am getting confused with the K pump in a neuron cell. It seems as though the side that has more Na ions is more positive than the membrane side with K ions.

Or put another way. If you had a Sodium atom on one side of a membrane, and a potassium on the other side, and were some how able to place a meter across each membrane, which side would read more positive? I am still trying to relate this to the membrane potential of a neuron.

I have also been thinking that the proteins on the inner membrane side effect the negative state of the inner membrane.
I think I am just missing a small piece to the puzzle.  Would someone care to assist?

Thanks in advance.

Offline nj_bartel

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Re: Electronegativity and Cell membrane potential
« Reply #1 on: April 21, 2008, 01:07:11 AM »
An element doesn't have to be charged to be electronegative.  Take for example the element Fluorine:  it has seven valence shell electrons, so it strongly desires an eighth to satisfy the octet rule.  Thus, it is strongly electronegative.

Offline Bioionic

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Re: Electronegativity and Cell membrane potential
« Reply #2 on: April 21, 2008, 01:15:29 AM »
But then, what causes the -70mv membrane potential of a neuron.  One side has Na+ the other side has K+.  The K+ are allowed to reach equillbrium, yet the Na side is more +?

Offline Arkcon

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Re: Electronegativity and Cell membrane potential
« Reply #3 on: April 21, 2008, 07:41:20 AM »
Briefly, more than one Na+ and K+ ion are involved in a living cell's membrane potential.  And like nj_bartel: explained to you, the electronegativity of an element is a physical constant related to it's likelihood of acquiring a charge, measured relative to hydrogen.  The concept charge caused by a bunch of ions, separated by a membrane, has nothing in common, except for some of the same syllables.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Yggdrasil

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Re: Electronegativity and Cell membrane potential
« Reply #4 on: April 21, 2008, 09:27:26 AM »
Electronegativity is an atoms ability to attract electrons to itself in a chemical bond.  Since sodium and potassium ions are not covalently bonded to anything, the concept of electronegativity is not relevant here.  Both ions will have full +1 charges.

The way the sodium-potassium pump works is that it pumps 3 sodium ions out of the cell, and 2 potassium ions in, leading to a sodium gradient, a potassium gradient, and an electrical gradient (since the net result is pumping one positive charge out of the cell).  These three gradients allow the neuron to very precisely control its electrochemical state and perform the tasks needed to generate action potentials:

1)  The sodium gradient allows cells to depolarize by opening sodium channels.
2)  The potassium gradient allows cells to hyperpolarize opening potassium channels.
3)  The electrical gradient creates a membrane potential that can be sensed by voltage-gated channels.

All three of these concepts (depolarization, hyperpolarization, and voltage-sensing) are crucial to action potentials.

Offline Bioionic

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Re: Electronegativity and Cell membrane potential
« Reply #5 on: April 21, 2008, 11:00:51 AM »
Thanks for the response.  So let me see if I got this. On one side of the membrane are K+ ions, the other side is Na+ ions. A potassium channel allows K+ ions to move freely between the membranes, until equillibrium of K+, so one side has more +1 ions than the other side, resulting in a net potential of -70 mv.
Is that about right?
I found the Na/K pump that you were talking about.  However is the pump on the neuron is a gated pump.  Is this a different kind.  I found a animation that discusses the type I am talking about.
http://www.blackwellpublishing.com/matthews/channel.html

It seems the deeper I dig the more confused I get.
« Last Edit: April 21, 2008, 07:41:30 PM by Bioionic »

Offline Bioionic

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Re: Electronegativity and Cell membrane potential
« Reply #6 on: April 21, 2008, 08:36:37 PM »
Okay, now I think I got it.
Initially, the Na-K pump allows 3 Na ions to leave the cell, and 2 K+ ions to enter the cell. 
Now the Na and K concentration gradients are high.  There are more K+ ion channels than Na+ channels, so more K+ ions leaves the cell, thus making the inside of the cell more negative with respect to the outside.  Once the K and Na ions reach equillibrium, there is a -70 mv resting potential.
Did I miss anything?

Thanks

Offline Yggdrasil

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Re: Electronegativity and Cell membrane potential
« Reply #7 on: April 21, 2008, 08:42:53 PM »
I wouldn't say that the Na+ and K+ are at equilibrium.  They are at steady state.

Also, the number of channels isn't important.  It is the number of open channels that is important.

Offline Bioionic

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Re: Electronegativity and Cell membrane potential
« Reply #8 on: April 25, 2008, 02:39:16 AM »
Thanks for the assistance.

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