Questions tagged [cell-membrane]

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

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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 attached ...
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Why don't all my cell membranes “smush” when I fall?

I've read the question about cell membranes breaking apart, which is close to what I'm asking, though I'm trying to probe a bit deeper. I understand that there are hydrophobic forces keeping the cell ...
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What's inside the perinuclear space?

The cell proper contains the cytoplasm in general and the cytosol in particular when referring to the fluid/gel without notable organelle. Once we move inside the nucleus there is the nucleoplasm and ...
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Do SARS-CoV-2 virus particles really travel through filopodia and “emerge from the tips”?

Watching the new University of California San Francisco video Coronavirus forces cells to produce tentacle-like structures that infect neighboring cells I saw The growths spread out, and ...
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What change would you expect in phospholipid orientation of the membrane if the enviornment were mostly heptane?

The external and internal environment of the cell is basically water, thus phospholipids organize themselves the way they do (bilayer). If the environment were to magically become mostly heptane, how ...
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What's the ratio of saturated to unsaturated fatty acids in human cell membrane?

It's well established that the fluidity of a cell is largely dependent upon the ratio of saturated to unsaturated fatty acids that exist within the membrane, but, what exactly are the values for this ...
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315 views

Why don't surfactants destroy or incorporate into cell membranes?

How do surfactants remain on the surface of pneumocytes without (1) acting as a detergent or (2) the phospholipids getting incorporated into the membranes of pneumocytes... I'm guessing the answer ...
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25 views

Can high energy photoelectrons damage cell membranes?

I've read that in addition to ionizing radiation causing damage to DNA through direct absorption, but DNA can also be damaged through photoelectrons with enough energy. The thing I was wondering is ...
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35 views

Why doesn't the concentration of one ion affect the concentration gradient of another ion across a plasma membrane?

In the initial stages, some ion channels across the plasma membrane open to allow for ions to flow down their concentration gradient into or out of the cell. I understand that each ion's overall ...
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37 views

Do carrier proteins constantly open and close or do they only work when a substance binds to them?

What causes carrier proteins to change shape ? Do they need energy to change shape? If that is true, how are they involved in Facilitated diffusion ? By changing shape, do we always mean opens from ...
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50 views

Pharmacokinetics and cell-membrane permeability of Adenosine triphosphate disodium hydrate

【My Question】 (1) Please tell me the pharmacokinetics of this ATP (or Adenosine triphosphate disodium hydrate) when it is administered orally or intravenously. In particular, Does this material has ...
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What is the end-point of material from an apoptotic cell, after phagocytosis?

Apoptosis occurs. The organelles and interior material form apoptotic bodies that are packed in vesicles. The cell membrane breaks apart (cell no longer exists) and apoptotic bodies enter the ...
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Osmosis/ Facilitated diffusion

Water can move across the (Semipermeable non polar lipid) membrane by simple diffusion (osmosis). But polar molecules cannot pass through the non polar lipid bilayer, they require carrier proteins to ...
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58 views

What regulates cyclic AMP?

After reading a textbook chapter on GPCRs I am still confused by what regulates cAMP. I took in my notes that cAMP is made by adenylyl cyclase and destroyed by cAMP phosphodiesterases (also another ...
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Lipid Diffusion

Epithelial cells in the small intestine absorb lipids through simple diffusion but how does diffusion of lipids occur in the first place if they are insoluble in water? I thought that substances need ...
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167 views

What is the biological relevance of RIPPLE phase in membranes?

I was reading about ripple phase in bilayer lipid membranes which is described here as a meta-stable state between lamellar tilted crystalline and lamellar fluid state. It is also known that ripple ...
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What attaches plant cells to the cell wall?

In animal cells integrins span the plasma membrane and attach the cell membrane to the extracellular matrix. I was wondering how are plant cells attached to the cell wall? Is it just the middle ...
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Do GPCRs have 7TMHs?

I've screened a non-redundant set of GPCRs acquired from UniProt. I found a handful of examples of record IDs that contain more than the 7 TMHs. For example Q89609 and P20905, both of which have been ...
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56 views

Ion channels affected by gravity

In the literature I have found that action potentials behave differently when gravity is changed (cannot access fully). Action potential properties are gravity dependent. http://link.springer.com/...
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51 views

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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When transmembrane proteins destined for the plasma membrane are in the ER membrane are they in their final folded form?

I am studying how transmembrane proteins are made and I have read that proteins that are destined for the plasma membrane are initially in the ER membrane and do not get translocated into the ER lumen ...
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What are the differences in ultrastructure of cilia and flagella?

Cilia and flagella are aimed for similar perpose, motion. And both of them show the (9+2) microtubule arrangement. They are nearly identical in structure. But to be more specific , where exactly does ...
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How are newly synthesised proteins targeted to the plasma membrane?

There does not seem to be a definitive answer to how proteins destined to be intrinsic plasma membrane proteins are directed there. Presumably, assuming starting at a cytosolic ribosome, the pathway ...
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What makes iodine an effective antiseptic?

I'm thinking about tincture of iodine, potassium iodide (Lugol's), and povidone-iodine (PVP-I) specifically, which, as is my understanding, work by solubilizing elemental iodine in an aqueous solution....
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How does the glycocalyx of cells attach together if they are negatively charged?

Context Thus, the entire outside surface of the cell has a loose carbohydrate coat called the glycocalyx. The carbohydrate moieties attached to the outer surface of the cell has several important ...
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52 views

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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What is the difference in the electrical excitability between a “large diameter soma” and a “large diameter axon”

There are two stereotyped statements that I have seen during my coursework regarding electric properties of neurons: Large diameter axons propagate action potentials more quickly than small diameter ...
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Reference request: Lipid composition in bacterial, yeast and human membranes

I would like to know about the lipid composition of different kinds of cellular membranes. I remember going through such a table once in a paper, but I am unable to find it anymore. What I am looking ...
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249 views

Why is ethanol osmotically active if it can enter through the plasma membrane easily?

This has been bugging me for a while, and I can't seem to find an answer to it, and I am sorry if I am asking a lot with this question(s). Firstly, I keep finding sources suggesting that ethanol is ...
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153 views

Why cells have a membrane potential?

What is the function of the membrane potential? Cells invest huge amounts of ATP to drive ion pumps to sustain this potential. Therefore it must have a very important function. I read somewhere that ...
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70 views

How to consider ions charges while calculating ions steady-state equilibrium concentration

i recently tried to find answer for following problem: "Assume that a membrane is permeable to Ca++ , K+ and Cl- but not to a large cation R+. The inside concentrations are [RCl] = 100mM and [...
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845 views

Is the signal peptide always cleaved during protein synthesis in the ER?

My university supervisor said that the signal sequence is always cleaved, however my text book differs. What I gather from my text book (though it isn't very clearly stated so i'm not sure) is that: ...
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How do (marine) cells not lose potassium?

Eukaryotic cells keep a sodium-potassium gradient across their external membrane. The concentration of potassium ions is about 5mM outside the cell. Although the potential gradient keeps most of these ...
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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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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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Differential Scanning Calorimetry for bacterial membranes

I would like to study the freezing and melting of bacterial membranes and would like to use Differential Scanning Calorimetry (DSC) to obtain the glass transition temperature of the membrane. However, ...
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Types of structures formed by various types of lipid molecules

Since Phosphatidylcholine (PC) and phosphatidylserine (PS) are roughly cylindrical in shape , they tend to form bilayers. Phosphatidylethanolamine (PE) on the other hand is conical in shape which ...
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What are the characteristics of a cancerous cell surface membrane?

A notable characteristic of cancer is that it thrives at a high glycolytic rate, and doesn't require much aerobic respiration. I am curious, how does the cell surface membrane composition change so ...
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Why do most negatively charged phospholipids concentrate in the inner leaftlet?

Due to the asymmetry of the lipid membrane, negatively charged phospholipids such as phosphatidylserine, phosphatidylinositol are concentrated in the inner leaflet, creating a different charge ...
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Through what mechanism does cholesterol act as a stabilizing agent and why does it depend on temperature?

As I understand it, at higher temperatures cholesterol has a tendency to make the membrane less fluid, and at lower temperatures it makes it more solid. My question is, what mechanisms causes this? At ...
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EM field in living organisms and tissue resonance frequency

I have two questions which I can't find enough information about, and I would be very grateful if someone could give me a lid to the answer: As far as I know, if we accelerate charged particle it ...
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33 views

Effect of opposing electric charges on cells

Is the affect on a cell between two negatively charged plates theoretically similar to between a positively and negatively charged plate? In other words, would it induce charges on the inside and ...
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22 views

Adding potassium outside of neuron: Hyper- or De- polarization?

At rest, the equilibrium potential for potassium given by the Nernst equation is ~ -80mV. Since the cell is mainly permeable to potassium, this is the reason for the cell membrane's rest potential to ...
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Why does insertion of transmembrane domains occur in the rough ER?

To elaborate on that question, why in the secretory pathway does the insertion of transmembrane domains into the membrane occur in the rough ER as the protein is translated and threaded across the ER ...
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Does the cell release the empty capsids?

The virus via the spike of the capsid connects to a receptor in a cell, then the DNA enters the cell wall. My question is what happens to the capsid - does it stay connected to the receptor or is ...
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same osmotic pressure of different solution

For example, There is a sugar solution with concentration $A_{1}$, how to determine the concentration of a NaCl solution which produce same osmotic pressure as the previous sugar solution toward ...
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Why inhbition of RTK will not help in a case of mutant EGF?

I was given the following as an example for a quiz question but i don't understand the answer. Any help will be most welcome: Question: Iressa is a Tyrosine Kinase Inhibitor. As a young oncologe, to ...
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151 views

Pelleting bacterial cells using centrifugation and getting proteins in the supernatant

Do significant amount of proteins from cells find their way in supernatant during pelleting? If the answer is yes then I see two ways in which protein can be in the supernatant . 1) Through lysis ...
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How does an increase in CO2 concentration affect Photosynthesis and Transpiration

I noticed a strange thing in my book. At one place it says that an increase in CO$_2$ concentration in the outside air decreases the rate of transpiration but at the other place it says that an ...
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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?)