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-...
- 11.3k
17
votes
Accepted
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 ...
- 14.1k
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 ...
- 11.3k
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 ...
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10
votes
Accepted
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 ...
- 17.6k
9
votes
Why do cell membranes have a lipid bilayer instead of a monolayer?
Why use membranes?
Compartmentalising the cell has lots of advantages and purposes. In Koshland's 2002 essay, compartmentalisation was described as one of the seven fundamental pillars of life. ...
- 11.3k
9
votes
Accepted
Can general soap kill bacteria?
Soap kills nearly all the bacteria it comes into contact with by dissolving the bacterial membrane. Some viruses with protein coats can resist soap, but many viruses have similar membranous coats (...
- 28.1k
9
votes
Accepted
At what point during an action potential are the sodium potassium pumps working?
The Sodium-Potassium Pumps are always at work. One can think of them as a continuous process that maintains the equilibrium potential for the individual ions. They always are grabbing internal sodium ...
- 712
9
votes
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How does membrane potential vary between intraceullar membranes and the cellular membrane?
Yes, various intracellular membranes do have potential differences, but as you can imagine they are more difficult to measure experimentally, so in general data on this is scarce.
Summary
...
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8
votes
Accepted
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 ...
- 96
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 ...
- 11.3k
7
votes
Accepted
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 ...
- 52.3k
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 ...
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 ...
- 42.5k
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 ...
- 42.5k
6
votes
At what point during an action potential are the sodium potassium pumps working?
Very good question. Most of your arguments, to the best of my knowledge are accurate. As to answer your questions, I'll provide a basic model of understanding. (Disclaimer:- I'm sorry if the ...
- 4,669
6
votes
Accepted
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 ...
- 14.1k
6
votes
Accepted
Membrane Permeability to Pyruvate
Pyruvate is negatively charged and quite polar, which makes it unfavourable to diffuse directly through any membrane. The outer mitochondrial membrane contains porins, which allow small molecules, ...
- 17.6k
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 ...
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 ...
- 35.2k
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 ...
- 126
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 ...
- 176
6
votes
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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), ...
- 35.2k
6
votes
Accepted
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 ...
- 4,641
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. ...
- 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.
...
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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 ...
- 3,052
Only top scored, non community-wiki answers of a minimum length are eligible