Questions tagged [membrane-transport]

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Endocytic pathway: Macropinocytosis

So I'm trying to understand this phrase: Unlike other endocytic pathways, macropinocytosis is acutely induced by growth factors From the following paper The 4 endocytic pathways I know of are ...
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Which complexes physically pump protons in photosynthesis?

The cytochrome b6f complex is often drawn as pumping protons, but then someone told me that actually there is no pumping, rather the Q cycle. According to this view, what actually moves the protons ...
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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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Exocytosis of synaptic vesicles

I'm reading the following paper: http://jcs.biologists.org/content/123/6/819 The part I am really confused about is when they say: Exocytosis appears to use two alternative pathways: clathrin-...
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Lysosomal Storage Disease

In my biochemistry class today we did a problem detailing two lysosomal storage diseases. In the first scenario, a cell line for I-cell disease can synthesize lysosomal hydrolases that are perfectly ...
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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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Nerve/muscle fibre depolarizaitonand repolarization balance

if continously sodium is pumped in during depolarization and pottasium is pumped out during repolarization, eventually there will more sodium and less sodium inside. How the does the fibre/cell return ...
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Oil absorbed into human skin — where does it go?

For example, I apply petrolatum to my dry hands twice a day as in winter I am usually in a 20-30% RH environment. Within an hour, the petrolatum seems entirely absorbed. According to [1], ...
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Understanding the derivation of the Nernst equation

I am trying to understand how the Nernst equation can be derived and am mostly referring to the explanation given in the book Theoretical Neuroscience by Dayan and Abbott. Given we have a ...
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How does Ran GDP get from the cytoplasm back to the nucleus following nuclear import and export?

I understand that in Ran-dependent nuclear import Ran GTP binds importin in the nucleus, and after diffusing through the nuclear pore complex Ran GTP is hydrolyzed to Ran GDP and releases importin. ...
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How does CO2 gets diffused into the red blood cells?

Carbon dioxide diffuses out of the tissues and into the blood, where it is dissolved in the plasma. While some of the carbon dioxide remains dissolved in the plasma, most carbon dioxide diffuses into ...
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How does LDL leave the circulatory system and enter the interstitial fluid to deliver cholesterol to cells?

I have read that small molecules like oxygen and carbon dioxide diffuse through the capillaries, but larger structures can't fit through. This answer indicates that some proteins go through via ...
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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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Mobile carriers of Light reaction in higher plants

The hydrogen carrier PQ and the electron carrier PC are the mobile carriers in light reaction facilitating electron transfer from PS II to PS I during non-cyclic process. My question is - How do ...
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Exclusion Limit and permeability of outer membrane

According to this textbook: P aeruginosa, for example, which is extremely resistant to antibacterial agents, the outer membrane is 100 times less permeable than that of E coli.[pg.no 27] and then ...
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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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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 ...
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Why difference in degree of folding in a cell?

For a cell to maintain constant volume, input should be equal to output of substances. My question is, if the basolateral membrane, by less folding can attain the same rate of transport as of 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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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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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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Does osmosis require a protein channel?

Earlier today, I undertook an exam which featured a question regarding the stickiness of mucus in a person diagnosed with CF's. We had to explain why they had stickier mucus than a 'normal' person, ...
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Why does the mass increase in this question? [closed]

So, on 'http://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2016/june/AQA-BL3HP-QP-JUN16.PDF', question 1.b., they show a partially permeable bag of glucose solution, in a less concentrated ...
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Is co-transport within a cell active or passive transport?

ATP is used to actively transport H+ out of the cell against the concentration gradient. The H+ & sucrose cotransporter, for example, then uses this proton gradient for transport. H+ goes back ...
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COPI/COPII proteins and kinesins/dyneins

I am considering the transport of protein from ER to Golgi, and have read that this involves the COPII protein coat. I have also read that this is a form of anterograde transport, and elsewhere that ...
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Can Oxaloacetate cross the outer mitochondrial membrane?

I am aware of the Malate–Aspartate Shuttle, but something is not clear to me and different sources seem to contradict each other. Some show oxaloacetate (OAA) being reduced to malate in the ...
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Are Na+/K+ active pumps and K+/Na+ “Leak” channels same as given in the figure?

Na+/K+ channels maintain the resting potential with other sodium and potassium channels. Then what are these "Leak" channels? are they the same Na+/K+ pump in a special condition? If so, what is it? ...
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What are internal and external osmotic pressures when referring to a cell?

I've seen the term used but cannot find a clear answer: What are internal and external osmotic pressures when referring to a cell?
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Valve-like layers example in nature?

I am searching for an example in the nature, where a layer of something (skin, coat, film etc) can allow fluid to flow trough (not absorb) from one direction and prevent/repel from other direction. I ...
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Why do cell membranes let small non-polar molecules through but won't let small polar molecules through?

If the hydrophobic hydrocarbon chain of the phospholipid prevents the movement of polar molecules through the membrane. Why does the hydrophilic phosphate head of the phospholipid not prevent the ...
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Transport mechanism in absorption of monosaccharides in small intestine

In the cell membrane of the intestinal cells, there is a mobile carrier protein called Sodium Dependent Glucose Transporter(SGLT1).It transports glucose and galactose to inside the cell using energy....
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Difference between going against and going down a concentration gradient

The difference between facilitated diffusion and active transport is that facilitated distribution occurs down a concentration gradient and active transport occurs against a concentration gradient. I ...
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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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Do flowers transpire?

I have googled this out but no where found a satisfactory answer. The definition of transpiration states that it is the evaporative loss of water from the aerial surfaces of the plant but I am really ...
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Are there well studied examples of ERAD-mediated membrane insertion, especially from viruses?

Membrane insertion of transmembrane proteins typically requires highly hydrophobic alpha helixes at the N-terminus, N-terminal signal peptides, tail anchors, or a combination of the three. Byun, H., ...
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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?

Integral membranes proteins serve as transporters. Peripheral proteins serve as cell adhesion molecules, antigens and enzymes. So what about receptors? Which proteins carry out the duty of receptors?
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Why is the swelling of bread when placed in water not considered to be caused by osmosis? [closed]

Why is bread swelling up when placed in water not considered to be caused by osmosis? Is there a property of water that should make it leave the bread instead of enter?
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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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How do human cells respond to mechanical pressure such as heel contact during walking?

Basically, I'd like to do a full accounting (inventory, assets, liabilities) of a human cell under mechanical pressure. For example, if in steady-state, does the cell consume more or less energy ...
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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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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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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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Question about flux and changes in net flux of molecules across a membrane

I've been reading a book called Principles of Human Physiology by Stanfield 5th edition, and was reading a chapter on membrane transport when I came across a figure question which will be posted below....
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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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Active & passive transport question

If an element, ion or molecule is found in a cell is it possible to tell which method of transport was used? for example if a hydrogen or sodium ion was found in the cell could you tell if it got ...
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Can the Donnan effect be reversed so phospholipids follow ions? [closed]

I know that there are flipases and flopases that facilitate this sort of thing, but I'm curious about other possible influences. Can the Donnan effect be reversed so that phospholipids follow ions? ...