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

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Density of Receptors of a mammal

I know it's a very open question. It's for a paper. So as a reference I'm looking maybe for the average density of insulin receptors per cell of a human tissue. I want to compare it to the density of ...
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Does alcohol affect water potential across a tonoplast? If so, would it cause it to explode or implode?

This was a question I saw in a biology exam I recently sat. I know it affects the r-groups of the transport proteins, causing them to change shape and become leaky, but does it also affect water ...
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30 views

How many cell membranes are oxygen and carbon dioxide diffuse through in the lungs?

In the lungs, oxygen and carbon dioxide pass through cell membranes by diffusion. Which row is correct? The correct answer is D, but I think it should be B. I can only think about three layers as ...
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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 ...
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378 views

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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54 views

Photosynthesis and its subtopics [closed]

Which of the following statements about photosynthesis is true? a. Photosynthesis is an energy consuming process b. The light-dependent reactions produce the energy-rich compounds that are used up ...
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Doubt in a multiple choice question involving cell organelles

Find the odd one out and state the category of the rest. Chloroplast Mitochondria Nucleus Grana Now my answers are : 1st possibility : grana Category : presence of DNA in ...
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25 views

Effect of ethanol and detergent on cell membranes problem

I am currently writing my biology report for an experiment I did on how ethanol and detergent affect the cell membrane. For my ethanol experiment, all went as expected BUT for my detergent experiment, ...
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28 views

Effect of increasing Extracellular Na+ Concentration on resting voltage and likelihood of an action potential of occuring

If you increase the extracellular Na+ concentration how will this effect the resting voltage and likelihood that an action potential of will occur? Please explain using the Goldman–Hodgkin–Katz ...
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82 views

Why don't membrane proteins move?

I understand that based on their tertiary structure, intrinsic proteins have hydrophobic non-polar R-groups on their surface and that they 'interact with the hydrophobic core of the cell membrane to ...
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32 views

What are the secondary structure requirements for cell-penetrating peptides AKA protein transduction domains

Cell penetrating peptides. Cell penetrating peptides (CPPs) are a class of short amino acid sequences which are sufficient for crossing cell membranes and delivering themselves along with any ...
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22 views

Concentration gradients across membranes with different ions

I'm trying to gain an intuition for the dynamics of across neuronal membranes. The overarching idea here is they are controlled by ion concentration gradients across the membrane (which we can ...
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13 views

Amount of Na+ needed to be transfered in order to depolarize the membrane?

I found out that the number of $Na^+$ ions that is needed to be transfered across the membrane to make it depolarized is a small number. In what way its proved? (Goldman equation maybe?)
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53 views

Can an emulsion enter a cell?

I've been tempted on cooking.stackexchange to answer a question, and I did, out of my mind. (In retrospect, I shouldn't have done so, based on my lack of citable resources.) I've heard that a water ...
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12 views

Are receptors integral membrane proteins or peripheral membrane proteins?

In tegral membranes serve as transporters. Peripheral protiens serve as cell adhesion molecules, antigens and enzymes. So what about receptors? Which protiens carry out the duty of receptors?
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197 views

What would happen if a cell is poked by a fine needle?

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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69 views

What is membrane-partitioning free energy? Can it be simulated?

Firstly, is there a strict definition of the "membrane-partitioning free energy"? It is banded around in membrane biology, but I have never seen it strictly defined. The only non-scholarly site that ...
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1answer
843 views

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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36 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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20 views

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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564 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 advance,...
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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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289 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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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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77 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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45 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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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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52 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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172 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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170 views

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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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
175 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. http:/...
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41 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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786 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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284 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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204 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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339 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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95 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
90 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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43 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
46 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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382 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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4k 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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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
337 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
500 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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135 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 ...