Hot answers tagged cell-membrane
8
That quasi-travesty is the Nernst equation in $\log_{10}$ for a positive monovalent ion at physiological temperatures (37 degrees celsius), but they've hidden all that from you. Shame on them.
The canonical form of the Nernst equation, for an ion $S$ is
$$
E_{S} = \frac{RT}{z_{S}F}\ln{\frac{[S]_{out}}{[S]_{in}}}
$$
where $R$ is the gas constant, $T$ is ...
8
This 1969 Steensland paper seems to suggest that the membranes of halophiles are stabilized by sodium ions and they rapidly denature at lower-salt conditions (2.2 vs. 4.3 M). The protein composition of the membrane was generally acidic, stabilized by all the Na+.
As far as what the role of the halophile membrane is in sheltering the cell from the high ...
7
Transmembrane proteins are inserted into the membrane in the ER in a rather complicated system, there is a whole chapter about translocation of proteins in "Molecular Biology of the Cell".
The proteins are moved through an aqueous pore in the Sec61 complex, which explains how charged parts of a protein are moved across the membrane.
The parts of a ...
7
I couldn’t find a value for this but I have calculated an efficiency of 84 %.
Caution: this seems too high to me, so I show below my calculation, fully dissected, in case anyone can spot an error.
First of all the parameters. Ion concentrations are:
internal Na+ = 12 mM;
external Na+ = 140 mM;
internal K+ = 140 mM;
external K+ = 5 mM;
and membrane ...
5
The System intracellular/membrane/extracellular space is well described by the model of a Concentration cell (see more on Wikipedia). The equation you mentioned is also called the Nernst equation.
$$
E_{ion}= 62mV \biggl(\log\frac{[ion]_{outside}}{[ion]_{inside}}\biggr)= \frac{k_B T}{z e} \biggl(\ln\frac{[ion]_{outside}}{[ion]_{inside}}\biggr)
$$
where ...
4
Early histochemical work indicated that the internal surface of the lysosomal membrane has a glycocalyx - a layer of polysaccharide, presumed to have a protective role.
Neiss, W. F. (1984) A coat of glycoconjugates on the inner surface of the lysosomal membrane in the rat kidney. Histochemistry 80, 603–608
Subsequently it was found that major membrane ...
3
For an organism (think single-celled) living in just the right kind of environment, it might just be possible to survive using only facilitated diffusion, at least as far as small molecules are concerned. This kind of organism would have to maintain exactly the right concentration of the molecules it wants to keep or get rid of, based on the external ...
3
Bilayer components will 'flip-flop' at measurable rates, but these are very different for different lipid classes. Here are the results of an experiment using fluorescently-labelled analogues.
Bai, JN and Pagano, RE (1997) Measurement of spontaneous transfer and transbilayer movement of BODIPY-labeled lipids in lipid vesicles. Biochemistry 36:8840-8848 ...
3
The extracellular cue signal must be relayed to the cell by Rho family of GTPases, like in the case of filopodia and lammelipodia. This causes local actin polymerization leading to extension of pseudopodium.
For a casual reference you can check the wikipedia page on Rho family of GTPases. Cell biology books like MBOTC also have information on mechanism of ...
2
According to Gerry Joyce: "Life is a self-sustained chemical system capable of undergoing Darwinian evolution."
From a meta-analysis of 123 definitions of life: "Life is metabolizing material informational system with ability of self-reproduction with changes (evolution), which requires energy and suitable environment."
According to Alexander Oparin: “Any ...
2
No, silicon oil couldn't block an ion channel. Oil is a nonpolar substance, just like the membrane lipids, so if you can get your oil to that cell, it will mix with the lipids within the membrane. The ion channel, which sits in the membrane, too, is rather closed to the membrane interior and opens to the inside and outside of the cell which, contrarily, is a ...
2
Firstly, demyelination has got nothing to do with membrane integrity of the neuron. Demyelination causes the current to "leak" through the ion-channels and thus causing loss of signal.
There is an old article which reports a study on membrane integrity of RBCs of MS patients but there seems to be no connection.
It has been proven that neurons do secrete ...
2
The absolute answer would depend on a lot of factors, but the basics of it would be that - Yes, the volume does change and Yes, it would have an affect on the membrane potential.
By adding mass to any liquid solution, you are changing the volume. Plain and simple. Liquids are not compressible, and the only way to maintain volume while adding mass would be ...
1
Diffusion is always a passive process that doesn't require energy. Therefore it would seem that A is correct, B doesn't really make a whole lot of sense. In the case of the cell membrane diffusion will often be in the form of 'facilitated diffusion' through carrier proteins, however the transport is still not active.
1
I think, given Alan's answer the question you might be asking is something like
'do compounds become concentrated in the lipid bilayer', as opposed to achieving high concentration inside the cell after diffusing through the membrane as he describes.
This could certainly happen (if that's what you're thinking), but usually won't for I think two reasons.
...
1
I interpret your question to refer to the movement of a lipid-soluble molecule that is therefore able to diffuse into cells down a concentration gradient. I think that you are asking whether as the gradient collapses, some of these molecules would "stay in the bilayer".
You are thinking about the diffusion process in the wrong way. There will always be a ...
1
I'm no electrophysiologist, but I do know that the membrane potential is determined by the distribution of ions across the membrane: mostly Na+, K+, Ca2+ and Cl-.
An uncharged molecule will only influence membrane potential if it has an effect upon the distribution of these ions. One example of such a molecule is valinomycin, a neutral ionophore which ...
1
Well, without the details of your experiment to cross-check with the sugar and H2O content of your average grape, I'd say the saturated solution probably approximated the natural molarity of sugar in the grape. At least to the point it didn't make any advese effects noticeably on your time scale.
That seems the most apparent solution to me. I suppose it's ...
1
Life is a physical entity that creates copies of itself,sometimes in a slightly changed form.
That's it.
A cell is not the basic unit of a life but a large number of molecules that have bonded together to reap the benefits of specialization.
Like what is happening today, humans coming together to form a society which collectively starts to function like a ...
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