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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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At What Rate Do Ions Leak Out of a Plasma Membrane Segment That Has No Ion Channels?

In reading about the purpose of myelin during action potential propagation, I came across a point of confusion. From what I understand, one of the primary "benefits" of myelin is that it aids in ...
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What are the (evolutionary) advantages of secondary transport?

Secondary active transport uses electrochemical gradients as a source of energy for the uphill transport of substrates (coupled to downhill transport of the ion). However except for in a few cases (e....
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Spatially Encoded GPCRs?

I'm reading this paper, and I'm already lost in terms of what they mean by GPCR signaling is spatially encoded. How can signaling be spatially encoded?
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Can sperm cells penetrate the cell membrane of non-ovum cells?

Sperm cells have tiny bags of enzymes on their tip (the acrosome) which allow them to penetrate the ovum. My question is whether or not the process that allows sperm cells to penetrate the cell ...
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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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Why can small polar molecules (e.g. carbon dioxide) diffuse through the phospholipid bilayer of cell membrane? [duplicate]

Polar molecules cannot diffuse through the phospholipid bilayer because they get repelled by the hydrophilic fatty acid tails of the phospholipids. But why can small polar molecules diffuse through?
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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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What do the text annotations in an electron micrograph mean?

I saw a photograph taken from an electron microscope, with some text. I want to know what is the meaning of these numbers and letters? Thank you! Regards.
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What is the electric field strength of microalgae?

Question: What is the electric field strength of microalgae? Background: So I have been having some problems with fungi contaminating my chromera velia algae cell cultures. I haven't determined what ...
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Neuronal membrane resting potential for large cells

I'm reading Medical Physiology by Boron and Boulpaep (a really terrific book). In the chapter Electrophysiology of the Cell Membrane, section Membrane Potential Is Generated by Ion Gradients, Not ...
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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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Is the reason why lipid-soluble molecules can pass through membrane because [duplicate]

I have been studying about cell membranes and how water molecules are able to pass through it. (https://www.wiley.com/college/boyer/0470003790/animations/membrane_transport/membrane_transport.htm) It ...
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Why does carbon dioxide diffuse easier through the bilipid layer than oxygen?

When gas exchange occurs during respiration, the pressure of oxygen in alveoli is around 105 mmHg, whereas in the blood vessels in close contact with alveoli is 40 mmHg. For carbon dioxide the values ...
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176 views

Plasma Membrane Proteins and Cytoskeletal Attachment

Regarding membrane protein functions, which of the following statements is CORRECT? a. Membrane proteins are responsible for both cell to cell recognition and cell anchoring and are ...
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34 views

Glycerol - hydrophilic and hydrophobic properties?

Why does glycerol move across the lipid bilayer membrane using simple diffusion? To me, it seems like a relatively hydrophilic molecule, and I would expect it to have a difficult time moving across ...
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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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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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141 views

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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148 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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175 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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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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82 views

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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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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192 views

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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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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101 views

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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58 views

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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268 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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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 ...