Nov 17, 2009
259
0
Status
Pre-Medical
ION Intracellular Conc. mMol Extracellular Conc. mMol
Na+ 10 142
K+ 140 4
Cl- 4 110
Ca2+ 0.0001 2.4
------------------------------------------------------

I realize that the OUTSIDE of a cell has a higher potential (+ charged). However, when I net the charges of the intra and extra-cellular environment, I see that the intracellular environment has "relative voltage" of 10 + 140 - 4 = +146.

For the extracellular Conc. is 142+4-110 + 2(2.4) = +41

Therefore, the INSIDE of the cell has more positive charges. Please explain why, in reality, the inside has a charge of -0.70 mV.
 

normtheniner

7+ Year Member
Aug 20, 2010
499
43
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Attending Physician
ION Intracellular Conc. mMol Extracellular Conc. mMol
Na+ 10 142
K+ 140 4
Cl- 4 110
Ca2+ 0.0001 2.4
------------------------------------------------------

I realize that the OUTSIDE of a cell has a higher potential (+ charged). However, when I net the charges of the intra and extra-cellular environment, I see that the intracellular environment has "relative voltage" of 10 + 140 - 4 = +146.

For the extracellular Conc. is 142+4-110 + 2(2.4) = +41

Therefore, the INSIDE of the cell has more positive charges. Please explain why, in reality, the inside has a charge of -0.70 mV.
If I remember correctly from cell biology proteins within the cell are negatively charge with contribute to that negative charge. Also, nuclear material (DNA/RNA) are negatively charged as well due to the phosphate group.
 
OP
Z
Nov 17, 2009
259
0
Status
Pre-Medical
That's not intuitive at all. So it sounds like all the cell really needs to do to have a negative voltage inside is to simply *NOT* create a Na or K ion gradient, but to simply close the cell up, and be agnostic to Na/K.
 

WhiteWashed

10+ Year Member
7+ Year Member
Mar 26, 2008
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That's not intuitive at all. So it sounds like all the cell really needs to do to have a negative voltage inside is to simply *NOT* create a Na or K ion gradient, but to simply close the cell up, and be agnostic to Na/K.

Just think of all that ADP/ATP with those high negative phosphate groups, combine that with DNA negativity and the fact that there are more acidic Amino Acids than basic and you are bound to have a negative intra-cellular charge.
 
Sep 5, 2010
59
0
Status
ION Intracellular Conc. mMol Extracellular Conc. mMol
Na+ 10 142
K+ 140 4
Cl- 4 110
Ca2+ 0.0001 2.4
------------------------------------------------------

I realize that the OUTSIDE of a cell has a higher potential (+ charged). However, when I net the charges of the intra and extra-cellular environment, I see that the intracellular environment has "relative voltage" of 10 + 140 - 4 = +146.

For the extracellular Conc. is 142+4-110 + 2(2.4) = +41

Therefore, the INSIDE of the cell has more positive charges. Please explain why, in reality, the inside has a charge of -0.70 mV.
Umm.. This is my take on it, I may be totally wrong but thats science lol...

You calculated the relative extracellular charge and not the relative extracellular voltage. Charge and voltage are not the same. To calculate the voltage you would use the Nernst Equation :)() which gives you an approx. value of the membrane potential:

E = 59.2mV ln ([out]/[in]) = 59.2 ln ([142+4-100]/[10+140-4]) = 59.2 ln ([46]/[146]) = -68 mV.....
*you mention the inside has a charge of "-0.70 mV", you probably meant -70mV.

I'm not taking Ca2+ into account since the relative conc is small compared to the others.

I think you're just confused with the resting potential = voltage, and what you are calculating is the relative charge on the two sides... Hopefully, I'm making sense...
 
OP
Z
Nov 17, 2009
259
0
Status
Pre-Medical
Umm.. This is my take on it, I may be totally wrong but thats science lol...

You calculated the relative extracellular charge and not the relative extracellular voltage. Charge and voltage are not the same. To calculate the voltage you would use the Nernst Equation :)() which gives you an approx. value of the membrane potential:

E = 59.2mV ln ([out]/[in]) = 59.2 ln ([142+4-100]/[10+140-4]) = 59.2 ln ([46]/[146]) = -68 mV.....
*you mention the inside has a charge of "-0.70 mV", you probably meant -70mV.

I'm not taking Ca2+ into account since the relative conc is small compared to the others.

I think you're just confused with the resting potential = voltage, and what you are calculating is the relative charge on the two sides... Hopefully, I'm making sense...

You're totally on the right track, and that's all that counts in my eyes. There are short-comings to your approach, but that's OK. For example, you should only use 0.05912 when using base 10 logs. What's super important to me is that I shouldn't conflate Q-charge with V-volts.

Moreover, NERNST equation! This is a great way for me to learn that a little better.

Thank you very much.
Thanks so much.
 
Sep 5, 2010
59
0
Status
You're totally on the right track, and that's all that counts in my eyes. There are short-comings to your approach, but that's OK. For example, you should only use 0.05912 when using base 10 logs. What's super important to me is that I shouldn't conflate Q-charge with V-volts.

Moreover, NERNST equation! This is a great way for me to learn that a little better.

Thank you very much.
Thanks so much.
lol.. I highly doubt they'll put Nernst calculations on the MCAT.. If they do, they're hating lol

But yeah glad to be of service :)