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the -70mV is mostly generated by the leaking K+ and only a small portion is because of the "-" macromolecules like dna and proteins right?
Neuron resting potential
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According to Cliffs AP Bio book, the "-" comes form the negativity of the larger ions found inside the cell, not from K+. K+ may make it that specific mV, but doesn't account for the overall negative charge.
Someone correct me if I'm wrong...my DAT is on Monday!
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yeah, i posted this question because i was reading cliffs, BUT, that's a high school ap study guide, remember, most ap classes haven't taught students about Na+/K+ channels.
From my 3rd year physiology notes, i noticed that a majority is coming from Potassium leakage and the negative molecules also contribute, though not as significant as cliffs claim
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Basically, the primary source of intracellular "-" charge comes from proteins, which have a net negative charge at cellular pH. The off-setting positive charge comes from cations found within the cell (Ca and K).
I this instance, the proteins can be considered immobile, so the intracellular negative charges aren't really fluctuating much (I'm discarding any other negative ions like Cl, which can be considered negligible for the sake of resting membrane potential).
As the Na/K/ATPase pumps one net cation out of the cell, this builds up a net negative charge inside. Also, as leaky K gates allow potassium to flow out, this contributes even more to the net negative number.
Eventually, there are a ton of potassium ions around the cell on the outside, and there are a relatively fewer number inside. This difference in numbers creates a chemical gradient (think diffusion). The chemical gradient wants the potassium to flow back into the cell (from high to low), but there is no way for that to happen. What actually happens is that the potassium essentially stops leaking out, stabilizing the membrane potential around -70mV.
Therefore, not only is the electrical gradient important when thinking about the charge distribution, but the chemical gradient is just as important for explaining why the number can be somewhat stabilized at -70.
Hope this helps, and good luck!
I this instance, the proteins can be considered immobile, so the intracellular negative charges aren't really fluctuating much (I'm discarding any other negative ions like Cl, which can be considered negligible for the sake of resting membrane potential).
As the Na/K/ATPase pumps one net cation out of the cell, this builds up a net negative charge inside. Also, as leaky K gates allow potassium to flow out, this contributes even more to the net negative number.
Eventually, there are a ton of potassium ions around the cell on the outside, and there are a relatively fewer number inside. This difference in numbers creates a chemical gradient (think diffusion). The chemical gradient wants the potassium to flow back into the cell (from high to low), but there is no way for that to happen. What actually happens is that the potassium essentially stops leaking out, stabilizing the membrane potential around -70mV.
Therefore, not only is the electrical gradient important when thinking about the charge distribution, but the chemical gradient is just as important for explaining why the number can be somewhat stabilized at -70.
Hope this helps, and good luck!
The negative charge inside a cell is due to negatively charged large molecules inside the cell, yes. This has nothing to do with the "-" sign of resting membrane potential.
This sign is simply due to sign convention derived from the resting membrane potential equation, E=(constant)log([x]o/[x]i). The fact that the concentration of K+ inside is much higher than outside the cell gives the log term and therefore the calculated potential a negative value. Consequently the resting membrane potential of Na+ is positive (much more Na+ outside than inside). The standard potential of K+ is around -90mV, Na around +70mV. These values are derived solely from the concentration gradient across the cell membrane.
Now, the ACTUAL resting membrane potential is influenced by the permeability of the cell membrane to each ion. It is mostly impermeable to Na+ but leaky to K+, so the actual resting membrane potential hovers near the K+ standard potential, usually at about -70mV (the physical movement of 3/2 cations through the Na/K pump constributes a little to this as well).
This mechanism also explains what happens during depolarization. When a neuron cell depolarizes during an action potential, it does so by opening Na+ channels. This increases Na+ permeability across the membrane, which shifts the cell membrane potential closer to the standard Na+ potential of +70mV. This is a simplified example, as there are many different ion channels that contribute to the depolarization/repolarization of the cell membrane potential.
Sorry for the overly-involved post
This sign is simply due to sign convention derived from the resting membrane potential equation, E=(constant)log([x]o/[x]i). The fact that the concentration of K+ inside is much higher than outside the cell gives the log term and therefore the calculated potential a negative value. Consequently the resting membrane potential of Na+ is positive (much more Na+ outside than inside). The standard potential of K+ is around -90mV, Na around +70mV. These values are derived solely from the concentration gradient across the cell membrane.
Now, the ACTUAL resting membrane potential is influenced by the permeability of the cell membrane to each ion. It is mostly impermeable to Na+ but leaky to K+, so the actual resting membrane potential hovers near the K+ standard potential, usually at about -70mV (the physical movement of 3/2 cations through the Na/K pump constributes a little to this as well).
This mechanism also explains what happens during depolarization. When a neuron cell depolarizes during an action potential, it does so by opening Na+ channels. This increases Na+ permeability across the membrane, which shifts the cell membrane potential closer to the standard Na+ potential of +70mV. This is a simplified example, as there are many different ion channels that contribute to the depolarization/repolarization of the cell membrane potential.
Sorry for the overly-involved post
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