Questions tagged [cell-membrane]

A selectively-permeable biological membrane that separates the interior of all cells from the outside environment.

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Why lipophilic molecules can pass phospholipid bilayer, in spite of 2 hydrophilic layers?

It is commonly told that, hydrophobic/ lipophilic/ nonpolar molecules can quite easily pass phospholipid bilayer, and hydrophilic (polar or ionic) molecules can't pass (when no protein aid that); ...
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Why do cell membranes have a lipid bilayer instead of a monolayer?

Many cells have a cell membrane composed of two layers of lipids. Why is it that they have two layers and not just one? What purpose do this arrangement serve?
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Domains in cell membrane

How is movement of proteins and lipids between different domains of cell membrane prevented? Why is the noncytosolic layer not able to do lateral movements between domains but cytosolic layer is able ...
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How is membrane capacitance related to the increased speed of saltatory conduction?

Here is the original question which inspired my question. As explained by the answers there, the reason saltatory conduction in myelinated neurons is faster than non-myelinated conduction is because ...
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Why don't the heads of phospholipid bilayers repel hydrophobic molecules?

What I Think I Know: Hydrophilic and hydrophobic things repel each other. Since the cell membrane contains hydrophobic tails, it is difficult for hydrophilic molecules to pass through the cell ...
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Inductance in cell

In an animal cell, especially neuron and in particular its axon, while there is electrical resistance and capacitance mechanism in the cell, which play essential roles in the cable theory model of ...
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Are large cell bodies of neurons harder to depolarize than small cell bodies of neurons?

In order for the axon to initiate an action potential, we know that the axon initial segment must be brought to threshold. So my question is as follows: Say we have the minimum charge input, "X", ...
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How do ion channels transport only specific ions?

Ion channels, such as $Na^+$ channels and $K^+$ channels, are higly specific for ion permeability. But how do these channels achieve and maintain this specificity? Like how does a $K^+$ channel ...
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What is the difference between organelle membranes?

Cells and organelles are contained in lipid bilayers. I'm particularly interested in eukaryotic organelle bilayers and the biophysicochemical differences between them. Many papers assume a ...
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How do lipid-soluble substances diffuse through the cell membrane?

It’s said that water-soluble substances can diffuse through cell membrane with less ease than lipid-soluble substances because the former encounters impedance in the hydrophobic region of the ...
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Why doesn't the cell membrane just…break apart?

Forgive me if this is a silly question. I can't understand the basics. Why doesn't the cell membrane just break apart? What's keeping the layers in the phospholipid bilayer together? I know that the ...
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Why should phospholipid non-polar tails be “protected” in the membrane bilayer?

lipids are arranged within the membrane with polar head towards the outer side and non polar tails towards inner side, this ensures that the non polar tail is protected from aqueous environment. My ...
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Why do larger diameter myelinated axons have greater conduction velocities than small diameter myelinated axons?

A canonical statement I have frequently read is that "large diameter axons conduct action potentials at faster velocities than small diameter axons". After recently learning the effect of increased ...
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Can general soap kill bacteria?

I have read that general soap can kill bacteria by opening holes in the bacterial membrane. http://questions.sci-toys.com/node/90 However, I found some articles as well saying that it cannot. http:/...
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Why does K+ move out of the cell?

I was reading this page: Equilibrium Potentials when I found the following example at the end of the page: "If the K+ equilibrium potential is –90 mV and the membrane potential is –70 mV, in what ...
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At What Rate Do Ions Leak Out of a Plasma Membrane Segment That Has No Ion Channels?

In reading about the purpose of myelin during action potential propagation, I came across a point of confusion. From what I understand, one of the primary "benefits" of myelin is that it aids in ...
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Permeability of Plasma Membrane

I’m having trouble grasping why small polar molecules can cross the hydrophobic region of the membrane and not ions. Won’t the polar molecules be attracted to the watery extracellular medium and not ...
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Problems understanding membrane potential

I understand that membrane potential is the difference of the extracellular and intracellular ionic charges, due to their concentrations. We say that the extracellular space has a charge of 0 and then ...
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Simple diffusion of lipid-soluble molecules through phospholipid bilayer — does anything get “stuck” in transit?

It's a pretty elementary concept, and when I first learned of it I don't think I had the foundations to even think of such a question, but I found myself the other day thinking about the amphipathic ...
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Neuronal membrane resting potential for large cells

I'm reading Medical Physiology by Boron and Boulpaep (a really terrific book). In the chapter Electrophysiology of the Cell Membrane, section Membrane Potential Is Generated by Ion Gradients, Not ...
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How efficient is the sodium-potassium pump ?

I am reading about transportation of ions in a cell. It is necessary to transport sodium back out and potassium back in, against their electrochemical gradient. This task is carried out by sodium-...
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Are cells really the basic unit of all life? [closed]

Please see comments as to the appropriateness of this question on biology SE. All known life on Earth is made up of cells. It is thus safe to say that all known life is characterized by the presence ...
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What is the lipid membrane of SARS-CoV-2 made of?

SARS-CoV-2 is an enveloped virus: in structural diagrams it is drawn with membrane glycoprotein (M), envelope protein (E) and spike protein (S) embedded in a lipid membrane. What specifically is the ...
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Is plasma membrane permeable to sucrose

I searched a lot in the net but don't found a clear answer. I just want to know if plasma membrane is permeable to sucrose.
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How are lipid-coated mRNA-based vaccines transported into cells for expression?

In CNN's video Scientist says Coronavirus vaccine could be ready by 2021 after about 00:25 'Robin Shattock, the Head of Mucosal Infection and Immunity at Imperial ...
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Understanding what passes through and doesn't pass through the plasma membrane [duplicate]

I have difficulty in understanding the reason why certain molecules can pass through phospholipid bilayers. Firstly, I understand that the outer layer of the lipid bilayer is hydrophilic - my ...
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How does soap affect membrane permeability? Which component of the membrane does it affect?

In a lab we used distilled water + 3 drops of soap to examine how beetroot would be affected by it. I believe the beetroots membrane denatured and a red pigment leaked from it. However, I cannot ...
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ATP stoichiometry of the Na+/K+ pump

The Na+/K+ ATPase pump exports 3 Na+ for every 2 Ka+ imported. This process is ATP dependent, but I have not been able to find how many ATPs are required in each translocation. What is the ...
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“Most bacteria have at least one cell wall”

In the first answer to How do we find antibiotics? @Ashafix claims that Most bacteria have at least one cell wall Does this mean that there are bacteria with more than one cell membrane? Which are ...