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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

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 ...


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 ...


6

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 ...


5

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 ...


4

Although the Wikipedia page on dermatographism refers to "weak membranes" it cites no source for this, and like Chris, I haven't found any mention of this in a quick look at the literature. Histamine is usually released from mast cells in response to specific stimuli by a degranulation reaction (internal vesicles fusing with the surface membrane to release ...


4

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 ...


4

It depends on the concentration, but at higher concentration the detergent molecules build so called micelles, where the hydrophobic "tail" is orientation into the inner part and the hydrophilic "head" is orientated to the outside. This allows the micelle also to fuse with the membrane and then to desintegrate it. This illustration from the Wikipedia shows ...


3

The membrane is dispersed by detergents. But the detergents, under the right concentrations and conditions (salt, pH, et) form micelles with smaller curvature than the lipids that compose cell membranes. With some luck, they can form a small hydrophobic micelle bubble around the protein. This figure is depicts detergent micelles around a membrane ...


3

Conductance is the inverse of resistance, and measures how much of a given substance flows throught a channel. In this context, it means how many calcium ions enter the cell in a period of time. There are at least two ways potassium channels may prevent the calcium to enter in the cell. 1) Potassium intake by ion channels decrease the membrane potential, ...


3

Thanks to studies on animal behavior and on histamine dection in the Central Nervous System, researchers found out the "histaminergic system". It's thought that histamine-containing neurons regulate sleep-wake cyrcle, immunity, memory, body temperature, drinking, feeding rhythms. By the way, knockout rats who lack of histamine system don't show big defects ...


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 ...


3

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 ...


3

According to wikipedia, cardiolipin is found in two places, the inner mitochondrial membrane, and bacterial membranes. Given the endosymbiotic origin of mitochondria, it makes sense that they would retain some remnant of their bacterial ancestry. But more importantly, cardiolipin plays a role in the enzymatic functions of mitchondrial membranes. Cardiolipin ...


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

It is important to note that osmotic pressure is a colligative property, which means that it does not depend on the identity of the solutes, but simply their concentration. This also means that in considering the grape, we have to estimate the concentration of all solutes, not just the one you used to make the (possibly) hypertonic solution. I'll assume the ...


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 ...


2

Cell membranes (not cell walls) are composed of a double layer of phospholipids. The lipids are orientated in the way, that the hydrophilic part of the molecule is oriented to the outside and the inside of the cell and the hydrophobic tail to the inside of the membrane. See the figure from the Wikipedia: Embedded in the bilayer are transport proteins, ...


2

What one thinks, no matter how intuitive it may appear is not particularly relevant in science. The inductance associated with a neural axon has been well documented since Cole (1966). Its role in the propagation of neural signals is developed extensively in http://neuronresearch.net/hearing/pdf/7Projection.pdf#page=39 . The actual development begins ...


1

There are several types of channels, but probably the type you are referring to is voltage gated ion channels. The state in which these channels are, open or closed, depends on the action potential across the cell membrane. If the potential is at the correct energy for the channel to be open it will remain open allowing a steady flow of ions through. Once ...


1

The processes that occur at the ER membrane in eukaryotic cells take place directly at the bacterial plasma membrane. Phospholipids are synthesised and inserted at the plasma membrane, and there is a protein translocation apparatus for translocation of proteins into the periplasmic space and insertion of transmembrane proteins into the plasma membrane.


1

Your confusion is caused by the assumption that Na+ always leaves the cell and K+ always enters. The Na+/K+ pump is there to maintain membrane potential and relative Na+ and K+ ion concentrations stable inside. When an action potential (AP) is generated, sodium channels open and sodium rushes inside to depolarize the cell( 1st phase of AP). Next, the sodium ...


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 ...



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