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

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What would happen if a cell is poked by a fine needle? [on hold]

I had seen this question in an exam: A living cell has a protoplasm which is water based and demarcated by a lipid bilayer membrane. If a cell is pierced to 1/5th of its diameter with a very sharp ...
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Difference between protein channels, protein carriers and protein pumps?

I'm revising for my biology exam and I don't fully comprehend the difference between protein channels, carriers and pumps. I know that: Protein channels do not require ATP (passive transport) The ...
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28 views

Why does uniprot sometimes not label single-pass transmembrane proteins as “anchors”?

Currently, section 3a) of unitprot TRANSMEM reference page divides single-pass transmembrane proteins into 4 types: ...
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Mitochodrial osmotic flux

If you incubate mitochondria in isosmotic solution of Tris/EGTA and KCH3COO solution with rotenone, no swelling occurs at first - i.e. no ions enter the matrix so water doesn't follow to compensate ...
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85 views

Relationship between turgor pressure and osmotic pressure?

I would like to know if there is a relationship between osmotic pressure (inside and outside of a cell) and turgor pressure. If so, is there a way to formalize it mathematically? Thank you in ...
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Cellular concentractions, why do they remain constant?

The GHK equation indicates that at its resting potential there is no net current flowing into or out of the cell. However, if we consider the current due to just one ion, then this will be none-zero ...
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80 views

At what point during an action potential are the sodium potassium pumps working?

I'm trying to understand how all of the potentials during an action potential are created. My question specifically is about the sodium potassium pumps, however I would also be grateful if someone ...
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51 views

How does membrane potential vary between intraceullar membranes and the cellular membrane?

Question Does each type of membrane have a different membrane potential? I'm especially interested in answers that can cite academic papers that have attempted to measure membrane potentials. ...
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1answer
62 views

Is there any way to make protein pass through cell membrane?

Protein cannot pass cell membrane because it's a large molecule. Until now, is there any technique that can make protein pass through the cell membrane in vivo? I want to create a protein-drug that ...
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1answer
40 views

What does uniprot consider “unambiguous” evidence for the subcellular domain of a protein?

Uniprot has annotation for subcellular location of protein domains. This topological domain information of proteins is under the TOPO_DOM flag. In most cases the ...
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Mechanism of Octoxynol-10 as a preservative in vaccines

I noticed that the Fluarix Quad flu shot this season contains Octoxynol-10 rather than Thimerosal as a preservative. I am not expert in this area, so I did a Google search of "Octoxynol-10", and ...
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38 views

Rate of potassium/sodium transport

Assume that the plasma membrane of a cell was suddenly permeable to the same degree to both Na+ and K+ and that each responded to a concentration gradient of the same magnitude. Would you expect these ...
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1answer
31 views

What happen if we inject restriction enzyme into the blood

Just a curious question, if we extract restriction enzyme and inject it to our body, what happen? Does antibody recognize and block it? Can restriction enzyme pass over cell membrane and destroy the ...
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2answers
98 views

Blebbistatin effect on vesicles

Blebbistatin is a drug that specifically inhibits the assembly of myosin in the cytoskeleton. What effect would you expect blebbistatin to have on intracellular vesicles? ...
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39 views

Lipid-soluble vs. water-soluble substances through the membrane

It’s said that water-soluble substances can enter the cell membrane with less ease than lipid-soluble substances because the former encounters impedance in the hydrophobic region of the phospholipid ...
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84 views

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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4answers
111 views

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. ...
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1answer
27 views

How is the Concept of Simple Diffusion Possible

How can a substance pass through a lipid membrane in a cell through simple diffusion? In order for something to be able to go through the membrane, in simple diffusion, it must be hydrophobic, or non ...
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1answer
268 views

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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1answer
89 views

Description of the paramaters in the packing parameter?

For a phospholipid, the critical packing parameter is given by: $$P=\frac{v}{a_0l_c}$$ And I know that $v$ is the volume of the hydrocarbon tail. $l_c$ is the critical length of the hydrocarbon ...
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1answer
94 views

Membrane Permeability to Pyruvate

Pyruvate seems to pass easily through the outer membrane of the mitochondrion but has difficulty entering the inner membrane (and gets in by H+ symport). I have two questions: (1) what property of ...
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1answer
165 views

How can a polar molecule pass through polar channels of proteins in the cell membrane?

To transport a polar molecule through the nonpolar cell membrane, a protein with a polar channel is needed to allow it to diffuse. However, if the molecule is polar and the channel is polar, wouldn't ...
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1answer
61 views

Which step in endocytosis requires ATP?

Everybody seems to agree that endocytosis is an energy-using process, and as such requires ATP hydrolysis. However, which particular step requires it? More precisely, which 'molecular machine' ...
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1answer
38 views

How reliable is SwissProt topology?

I am using TOPO_DOM annotations from uniprot databases to characterise the orientation of transmembrane features. Is SwissProt topology experimentally validated, ...
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1answer
64 views

Can Nanodiscs be used to study membrane energetics?

Nanodiscs have changed they way we can study the structures, insertion, and functions of transmembrane proteins. Below is an image of a nanodisc bilayer. The key difference, as far as I can tell, ...
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29 views

What is internal symmetry in membrane proteins?

I have come across the term "internal symmetry" in the context of membrane proteins, but have never found a satisfactory definition. I'm struggling to figure out exactly what this term means... What ...
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1answer
37 views

Which hydrophobicity scales are best for detecting transmembrane regions, and why?

There are many hydrophobicity scales for protein analysis. Broadly, I gather the differences between them are from the experimental method to acquire the data and the normalisation (or lack thereof) ...
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What are all of the currently known variations of the G zipper motif?

The G zipper motif is found in transmembrane proteins at an above random frequency and there are models explaining how it might help with multiple transmembrane intra-membrane helix bundle assembly. ...
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203 views

What is the transmembrane 'Positive-Inside Rule' nowadays? Has the definition changed over time?

First definition. Two publications by von Heijne in 1989 and 1992 coined the 'Positive-Inside rule' and showed it's practical value in topology prediction of transmembrane helices. It was clearly ...
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1answer
2k views

Bacterial capsule vs. slime wall

I've read that the bacterial capsule protects the bacterium from phagocytes and prevents water (and nutrients, possibly?) leakage from the bacterium. A less organized and less dense version is called ...
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3answers
2k views

Why don't phospholipid bilayers dissolve?

I just started learning about the structure and composition of cell's membrane and there is something that I fail to understand. The membrane is composed of a phospholipid bilayer. The phospholipid ...
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2answers
197 views

What are multicell spheroids?

I'm from a maths background and I'm doing some research on mathematical models of cancer. I've come across alot of literature mentioning "multicell spheroids" in the context of avascular tumours. I ...
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1answer
276 views

How did the endoplasmic reticulum come to be?

Organelles are sub-cellular compartments in cells. However prokaryotes don't use organelles to organise their intracellular space. Evolutionarily, there is evidence that mitochondria and ...
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1answer
110 views

What recovers normal polarisation after hyperpolarisation?

I have been taught that a Na+/K+ pump helps to recover normal polarisation after hyperpolarisation in neurons. I could not find out how it does that, since I've also been taught that such a pump moves ...
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1answer
193 views

Why do some proteins “use” a beta barrel structure instead of alpha helices in transmembrane space?

Most proteins are fixed in the membrane by alpha helices. But some use beta barrels. Wikipedia describes beta barrels as used for porins, preprotein translocases, and lipocalins. To me, a coiled coil ...
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3k views

Difference between facilitated diffusion and secondary active transport in cells

Specifically, what is the difference between facilitated diffusion carrier processes (passive transport) and secondary active transport co-transport processes (active transport)? They seem to be the ...
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1answer
98 views

Microalgae without cell walls?

Most microalgae have rigid cell walls. Dunaliella Salina is a pretty famous example of an algae with no cell wall, but just a plasma membrane. Are there any other microalgae without a cell wall?. I ...
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1answer
178 views

Why does a “cascade” of events happen during signal transduction?

I've been watching some videos on signal transduction and it says that because there are enzymes being activated by the signal, then there is a "cascade" which happens afterwards...I don't understand ...
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2answers
874 views

Are nucleic acids found in cell membranes?

I've found various results online and I was recently marked in on an important test as wrong when I made the assumption they were not found in the cell membrane. Does anyone know what the correct ...
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1answer
114 views

Membrane potential in gram negative bacteria

Does the membrane potential usually quoted for gram negative bacteria (e.g. E. coli) refer to the potential across both membranes? - If yes, then does the potential fall more over the inner or outer ...
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1answer
90 views

Do cell membranes have more phospholipids in one layer than in the other?

Assuming the cell membrane to have a spherical shape, geometry tells us that the area of the inner leaflet is smaller than the area of the outer due to the difference in radius between them. Does this ...
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1answer
429 views

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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2answers
474 views

Why does the 'Positive-inside Rule' exist?

Gunnar von Heijne's Positive-inside Rule seems to have been around for a couple of decades and underpins a lot of what we know about transmembrane topology. It is used to predict the topology of a ...
4
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1answer
71 views

Phospholipid movement in cell membranes

What causes phospholipids to flow so quickly in cell membranes? In Biology by Cambell et al. they state that a phospholipids can travel up to 2 micrometers per second. Is that a random movement or has ...
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1answer
1k views

What is the difference between rheobase and threshold?

Neuronal tissues can be excited by electrical stimulation. Two commonly encountered characteristics for electrically stimulating nerve cells is the threshold and the rheobase. My question is what the ...
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2answers
226 views

How to visualize the ECM?

Specifically, I'd like to look at changes in HA (hyaluronic acid) production. Most often you only see people staining the cell surface or removing cells from culture for fixation and then imaging. ...
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2answers
361 views

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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1answer
148 views

Understanding intra and extracelullar concentrations (membrane potential)

I have 4 question (not homework) What happens to the cells membrane potential if: a) Na+ outside rises by 40mM b) K+ inside rises by 10mM c) K+ outside rises by 10mM d) A- (impermeable ion) ...
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2answers
271 views

Why does K+ have more concentration inside of the cell compared to outside of the cell? Why is Na+ and Cl- the opposite? [closed]

Can someone tell me the fundamental reason why K+ has low concentration outside of the cell and more inside of the cell?