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

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Photosynthesis and it's subtopics

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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18 views

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 : ...
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Wilting of plants at night?

I have seen that certain plants wilt at night as well! But its quite normal temperature and i tried to figure out the biological reason but in vain . I know that why they wilt during the day since I ...
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21 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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1answer
164 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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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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63 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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143 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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336 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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182 views

Are Gram negative bacteria classified as such because of their negative membrane potential?

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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509 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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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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132 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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21 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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48 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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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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41 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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659 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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85 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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5k views

How do inward rectifier potassium channels work in the heart?

Apparently in cardiomyocytes, there is an inward rectifying potassium channel that operates during phase 4 of the cardiomyocyte action potential. I have heard that despite this potassium channel ...
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34 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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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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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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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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399 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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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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203 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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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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125 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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74 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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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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41 views

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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808 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 ...
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1answer
50 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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301 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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4answers
153 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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688 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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40 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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219 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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179 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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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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1answer
85 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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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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42 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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1answer
3k 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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2answers
293 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 ...