32 votes
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Why don't membrane proteins move?

Proteins can move around the membrane. Most proteins do move within the membrane. The membrane is a liquid crystal and has fluid behaviour. Specifically, this is due to the membrane being in a gel-...
James's user avatar
  • 11.3k
18 votes
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How do ion channels transport only specific ions?

I am restricting the answer to only $Na^+$ and $K^+$ channels, assuming similar mechanism for other channels. In these 2 channels, such high level of specificity is achieved because of two main ...
another 'Homo sapien''s user avatar
14 votes
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Why should phospholipid non-polar tails be "protected" in the membrane bilayer?

What should be the correct reason for bilayer arrangement? I'll answer your second question first, but there is an almost identical question on this site already: Why do cells have a bilayer? There ...
James's user avatar
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14 votes
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Why can't H3O+ ions pass through aquaporins?

This question has been directly addressed by the paper The Mechanism of Proton Exclusion in the Aquaporin-1 Water Channel. I think it's a pretty good one too! I paste the abstract below: Aquaporins ...
S Pr's user avatar
  • 6,202
11 votes
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Why don't the heads of phospholipid bilayers repel hydrophobic molecules?

Your question is rooted in a misundertsanding of the hydrophobic effect. Hydrophillic and hydrophobic molecules do not repel but, rather, attract one another through van der Waals interactions. The ...
canadianer's user avatar
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8 votes
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Why do soap molecules not break down your skin cells when you wash your hands?

The outer most layer of the mammalian epidermis (cornified layer or stratum corneum) is composed of 15-20 layers of dead cells called corneocytes, which are basically dead keratinocytes filled with ...
JasonBourne's user avatar
8 votes

Is plasma membrane permeable to sucrose

No, but yes. Sucrose is a large polar solute. Because it is polar, it cannot easily pass the hydrophobic core of the membrane. So, if the lipids of the plasma membrane are mostly impermeable to ...
James's user avatar
  • 11.3k
7 votes
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Difference between protein channels, protein carriers and protein pumps?

No, carriers are not the same as pumps. Carriers may or may not carry out active transport and pumps always use energy. Carriers, for example, can make use of the concentration gradient of a certain ...
AliceD's user avatar
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7 votes
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How do lipid-soluble substances diffuse through the cell membrane?

See this paragraph and image from The Cell: A Molecular Approach. 2nd edition.: During passive diffusion, a molecule simply dissolves in the phospholipid bilayer, diffuses across it, and then ...
another 'Homo sapien''s user avatar
7 votes

Why don't membrane proteins move?

No other answer has mentioned this so I created an account just to say this. Some membrane proteins do not move. This is because they are fixed in that position in the membrane due to the ...
Vampiric Scum's user avatar
7 votes
Accepted

Difference between going against and going down a concentration gradient

"Concentration" is "how much stuff is there someplace?" "Concentration gradient" is "how much is concentration changing from point A to point B?" Imagine a terrain where concentration is represented ...
Bryan Krause's user avatar
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7 votes
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Why does K+ move out of the cell?

The other answer is a bit misleading. "Another cause is the the intracellular K+ concentration" No, this is exactly the same cause, the differing concentrations is what causes the equilibrium ...
Bryan Krause's user avatar
  • 45.3k
6 votes

Why don't membrane proteins move?

There are two types of proteins that are present in a membrane, because you have not been specific about which type of protein you are talking about I will consider that you are talking about Integral ...
Harsimran kaur's user avatar
6 votes

Why do cell membranes have a lipid bilayer instead of a monolayer?

Why Bilayer and not a Monolayer Lipid monolayer vesicles are possible as you mentioned (for example micelles). However, you have to understand that the cellular interior i.e. the cytoplasm, is ...
WYSIWYG's user avatar
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6 votes

What is the transmembrane 'Positive-Inside Rule' nowadays? Has the definition changed over time?

I think you have misunderstood the "inside" part of the "positive-inside rule". Perhaps because "inside" is indeed an imprecise term (but now it is history and cannot be changed ;) ). In order to ...
UbuntingBiochemist's user avatar
6 votes
Accepted

How do membrane proteins find their target locations?

This is a great question. A comprehensive answer would be beyond the scope of an answer on a forum like this. I will summarize the best I can here, but if you are really interested in this you should ...
Hayden S's user avatar
  • 176
6 votes
Accepted

What do the text annotations in an electron micrograph mean?

The 1.40kX is the zoom (1400x), WD is the working distance (distance between the final lens and the object), ...
WYSIWYG's user avatar
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6 votes
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How does the DNA cross through bacterial cell wall during electroporation?

The bacterial cell wall is quite porous, and is not considered a permeability barrier for most small molecules. It mainly functions as structural support and to resist turgor pressures. The average ...
MikeyC's user avatar
  • 4,714
6 votes

Can some bacteria eat soap molecules in soapy water rather than get killed by it? How do they hang on to their surface lipids? Evolutionary advantage?

The traditional, 1000's of years old soaps (sodium or potassium salts of fatty acids, used at least as early as ancient Egypt) are perfectly eddible not only for bacteria, but for mammals as well. ...
fraxinus's user avatar
  • 277
5 votes

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

Short answer The distinction between Gram positive (Gram+) and negative bacteria (Gram-) has absolutely nothing to do with membrane potentials; it is all about the Gram staining procedure. ...
AliceD's user avatar
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5 votes
Accepted

What is the lipid membrane of SARS-CoV-2 made of?

I don't know if this questions has been studied in detail even for SARS, let alone SARS-CoV-2. As noted in a comment by reuns, the virus lipid envelope is most likely derived from that of the ...
Dolphin 613 Motorboat's user avatar
4 votes
Accepted

What does uniprot consider "unambiguous" evidence for the subcellular domain of a protein?

Following your question, we have updated the documentation for topological domains in UniProtKB: http://www.uniprot.org/help/topo_dom I hope you will find it more informative now. Please don't ...
Elisabeth.Gasteiger's user avatar
4 votes
Accepted

Why do ribosomes associate with rough endoplasmic reticulum but not other membranes?

Peptides that are destined to be either secreted or included in the cell membrane have a signal sequence that binds a protein called Signal Recognition Particle (SRP). The SRP will in turn bind to ...
kingfishersfire's user avatar
4 votes
Accepted

Problem with an analogy (Cell Membrane)

Osmosis is the diffusion of water. Pinocytosis is the endocytosis of liquid/water.
user30605's user avatar
4 votes
Accepted

What is the purpose of the outer mitochondrial membrane?

Structure origins Originally the mitochondrial outer membrane (MOM) was likely the result of a bacteria that could survive in a vesicle formed of the plasma membrane. This explains why the plasma ...
James's user avatar
  • 11.3k
4 votes
Accepted

Why are aminoglycoside antibiotics particularly effective for aerobic gram negative bacteria?

Anaerobiosis is incompatible with effective intracellular accumulation of aminoglycoside antibiotics such as streptomycin and gentamycin. After an initial binding step involving outer membrane ...
Alan Boyd's user avatar
  • 22.8k
4 votes

Why don't cells of aquatic animals burst?

Comparative physiology of body fluid regulation in vertebrates Cells are not passive components that always return to osmotic equilibrium. Through hormonal, cell signaling, and the number of pores ...
Tom V.'s user avatar
  • 321

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