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Questions tagged [cell-membrane]

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

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Confused about definition of bulk flow of water by osmosis

As a teacher of high school and introductory college chemistry, I used textbooks that defined osmosis as a flow of water (only) through a membrane that prevents other substances such as dissolved ...
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What does “PDPN+ cells” means?

Are they podoplanin positive cells (cells that tested positive for podoplanin)? "...though it has been shown that podoplanin (PDPN+) cells analogous to mouse FRCs are found in human secondary ...
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Why does tetracycline have such a broad spectrum of activity?

What are the structural and chemical characteristics that make tetracycline uniquely broad spectrum? I understand it acts on the A-site of the prokaryotic ribosome, but there exist many ribosome-...
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What is the difference between a signal peptide and a transit peptide?

From what I know, the two names are used interchangeably and I haven't found any resource which says otherwise either. Is there at all any difference, is there a transit peptide that is not a signal ...
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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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Could animal cell membrane be made of glycolipids instead of phospholipids?

I know that cell membrane contains lots of molecules that are not phospholipids, like cholesterol, glycoproteins and glycolipids. I was woundering what would happen if we just take all of the ...
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Cell wall constitution of Schizosaccharomyces pombe

where is located the 1,3-α-glucan in the cell wall of Schizosaccharomyces pombe? Is it in the inner or outer layer? Thanks
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Membrane potential and capacitance of the membrane

Cell membrane acts like a potent capacitor with charges bound to its both sides. It is often described that it's capacitance has one important significance: Movement of only few ions (1 per 100000) ...
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Why do soap molecules not break down your skin cells when you wash your hands?

Soap molecules are similar in structure to phospholipids and interact with the cell membrane. They can clearly cause damage to the cell membrane. If this is the case, why then, does soap not break ...
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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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T-Cell Motility: does motility require direction specific actin polymerization?

T-cells have been shown to migrate inside concentration gradients - both in the direction of the source or away. Even under shallow gradients, t-cells move. I argue that, to be able to move in a ...
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Tight Junctions in Cell Types

I took a quiz today on cell structure basics, which included cell junction types. I disagree with the "correct answer" according to the teacher. Here is the question: ...
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Glucose Carrier Proteins in Cell Membranes

I'm using Campbell's Biology textbook, and it states that certain carrier proteins transport glucose across the cell membrane much faster than would occur normally. It states that the "glucose ...
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116 views

Ambiguity about the relation between membrane potential and concentration gradient in neuron cells

I am stuck in an ambiguity about the equilibrium potentials of neuron cells. The following text is picked up from khanacademy website: In one part it is said that: We'll start out with K at a higher ...
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143 views

Osmosis in red blood cells and bacteria

This is a question from an exam in my biology course. Bacterial cells and human red blood cells were inserted into one solution. Upon testing one hour later the blood cells exploded, while the ...
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stabilization mechanism

I am trying to simulate a soma with sealed end in both side and injected current in the middle of the soma. I used Na K and Ca voltage gated channels to get a concentration inside soma. I got a result ...
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Why did protocell division coincide exactly with RNA replication?

I know that, in the RNA world, it has been suggested that the first protocell formed by a hollow liposome structure encapsulating an RNA molecule. However, from then on it becomes confusing: I've ...
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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, ...
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Phospholipid membrane fluidity if phospholipid had one type of fatty acid

How would membrane fluidity change if the phospholipid membrane had only one fatty acid?
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Does vesicles fragmantation (fusion) during endocytosis require energy?

In the process of endocytosis, does the stage of fragmanting of the vesicle membrane to the cell membrane requires energy? I know that the disconection of the Vsnare and t-snare from the membrane ...
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Why can only small molecules pass through the phospholipid bilayer of the cell membrane?

TO put simply: I am just wondering what mechanism or substance only enables small molecules to pass through the cell membrane. Is it cholesterol? My textbooks are not very clear.
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Glycoprotein binding with water to stabilise cell surface membrane

I am reading a book about the fluid mosaic model of the plasma membrane and it reads the following: Glycoproteins present on the outside of the plasma membrane can bind with water via hydrogen ...
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102 views

Do all transmembrane proteins contain channels or tunnels?

In my book, there is written something like this. The integral proteins pass into the lipid bilayer to different depths and establish hydrophobic bonds with lipid molecules. Some of the integral ...
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Transport in cell

Don’t the substances transported by the carrier protein against the concentration gradient diffuse through channel protein to again maintain the same concentration across the cell membrane? I mean , ...
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Why don't cells of aquatic animals burst?

We know that if we keep plant cells in water, they don't burst because of a cell wall. But the cells of aquatic animals lack cell walls but they still survive. Why?
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How does gram-negative bacteria use high molecular weight starch if the membrane is only permeable to small molecular weights?

So one of my question is: The outer membrane of a gram negative bacterium contains pores that allow only molecules with a molecular weight less than 1,000 to cross. What does this bacterium need in ...
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What is the purpose of co-transport?

My current understanding of co-transport is that, first, a substance is actively transported across a membrane, establishing a concentration gradient across said membrane. This same substance then ...
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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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237 views

Passive diffusion of non-polar molecules across plasma membrane

I understand that small, nonpolar molecules that can dissolve in the hydrophobic (nonpolar) part of the plasma membrane are able to cross it and passively diffuse into or out of the cell. But doesn'...
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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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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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Are all/most/any membranes comprised of lipids from the smooth ER?

I'm attending an introductory high school course to cell biology. Based on my understanding, lipids – the building blocks of membranes – are formed in the smooth ER. Are all/most/any membranes ...
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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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2answers
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Why are sugars like mannose expressed on the outside of eukaryotic cell membranes?

Bacteria are able to adhere to sugars (e.g. mannose) on the exterior of eukaryotic cells, leading to infection and disease. Why have eukaryotes not evolved so as to dispense with sugars on their cell ...
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How do membrane proteins find their target locations?

The question might be asked for any kind of "bound" proteins, but I'd like to restrict it to membrane proteins. Assuming membrane proteins (or their main parts) don't (or aren't) build in situ but at ...
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The membrane folds of dendritic cells

Dendritic cells have a larger surface area due to extended dendrites (membrane folding into itself). Do other mammalian cells (with functions other than immunological) present these membrane folds?
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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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177 views

Can the Na+/K+ pump backwards to generate ATP?

The standard physiological direction of the Na+/K+ pump is to export 3 Na+, import 2 K+, and hydrolyze one ATP to ADP. Can it be driven backwards, importing 3 Na+, exporting 2 K+, and generating ATP? ...
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265 views

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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Aquaporin and the exclusion of $H^+$ [closed]

As I read in my textbook, aquaporins exclude $H^+$ when absorbing water, but where does this $H^+$ come from? Additionally, is $H_3O^+$ a liquid that looks like regular water?
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How can carnitine enter the mitochondrial matrix without OCTN2?

Some people have defects on the gene SLC22A5, giving them problems with their OCTN2 transport protein (Organic cation transport). OCTN2 transports carnitine into the mitochondial matrix where it can ...
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385 views

Are cells electrically neutral or charged to setup the membrane potential across them?

While studying about membrane potential I usually come across the Na K pump . But I can't understand does it cause any generation of net charge in the cell If yes then how do charged cells stay ...
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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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How does cholesterol affect the fluidity of a plasma membrane?

I was previously taught that cholesterol affects the fluidity of a plasma membrane. At high temperatures, cholesterol decreases fluidity and at low temperatures cholesterol increases fluidity. The ...
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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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999 views

How does 'phosphorylation of glucose' maintain concentration gradient in membrane transport (facilitated diffusion)?

Our book explains how glucose from the blood plasma gets inside red blood cells via facilitated transport. It states here in the book that the glucose will be transported inside by a carrier protein....
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663 views

What are the differences between a liposome and simple cell membrane

I'm learning about chemical evolution and the transition from RNA to protocells to cells. I understand that the protocells have a phospholipid structure called a liposome. I recently saw a video ...
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107 views

Why doesn't the central vacuole of a plant cell fuse with the cell membrane?

As one can view the central vacuole as a kind of giant vesicle, the question arises why it doesn't fuse with the cell membrane - different than vesicles.
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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 ...