Covers selective permeability of membranes, diffusion, and facilitated diffusion (including channels and carrier proteins).
Log in AkashdeepKar2015 8 years agoPosted 8 years ago. Direct link to AkashdeepKar2015's post “Why no energy is spent on...” Why no energy is spent on switching the carrier proteins? • (31 votes) Sam 8 years agoPosted 8 years ago. Direct link to Sam's post “These carrier proteins ar...” These carrier proteins are gated trans-membrane proteins and do not require ATP (adenosine triphosphate) to function. The gate is activated due to the concentration gradient of its target molecule. The target molecule binds to the gated carrier protein and, in response, the carrier protein opens up - this allows the target molecule to enter. The carrier protein then changes shape and releases the target molecule into the cell. It waits in its closed position, once again, until it is activated by the binding of its target molecule (outside of the cell). Therefore, no energy is spent switching shapes. The shape change only occurs due to the binding of the carrier protein's target molecule, in accordance with a concentration gradient. (42 votes) Andrea Petersen 8 years agoPosted 8 years ago. Direct link to Andrea Petersen's post “What is the difference be...” What is the difference between simple diffusion and facilitated diffusion? • (8 votes) Sarah King 8 years agoPosted 8 years ago. Direct link to Sarah King's post “Simple diffusion is the m...” Simple diffusion is the movement of molecules through a cell membrane without using the channels formed by integral membrane protein. Facilitated diffusion is the movement of molecules through those channels. (14 votes) ujalakhalid01 8 years agoPosted 8 years ago. Direct link to ujalakhalid01's post “if particles moves from l...” if particles moves from low concentration to higher concentration can we call it the concentration gradient of that substance as the concentration changes? • (2 votes) Matt B 8 years agoPosted 8 years ago. Direct link to Matt B's post “Careful: it moves from HI...” Careful: it moves from HIGH to LOW, not the other way around. (20 votes) Mango a year agoPosted a year ago. Direct link to Mango's post “Can carrier proteins move...” Can carrier proteins move molecules from the inside to the outside? Also, is it possible to replace carrier proteins with channel proteins that are specific to the same molecules? Channel proteins is faster, and you can still precisely modulate how much goes in and out by gating. • (7 votes) sl;adkf sdfl;k a year agoPosted a year ago. Direct link to sl;adkf sdfl;k's post “Yes and it depends but ge...” Yes and it depends but generally yes (5 votes) Artemy 6 years agoPosted 6 years ago. Direct link to Artemy's post “I noticed that according ...” I noticed that according to the quiz (Practice: Passive transport) sodium, potassium, and calcium can't move through the channel proteins. In this article mentioned nerve and muscle cells in which channels can pass sodium, potassium, and calcium. Maybe it was about active transport, but this article about passive transport. It is strange, I had some troubles in the quiz because of it. Can somebody explain this stuff? • (4 votes) carlsagancosmos101 6 years agoPosted 6 years ago. Direct link to carlsagancosmos101's post “Yes , i also think that q...” Yes , i also think that question is wrong. There are channel proteins in the body for transport of those ions. (6 votes) ujalakhalid01 8 years agoPosted 8 years ago. Direct link to ujalakhalid01's post “the topic states above th...” the topic states above that "a concentration gradient itself is a form of stored (potential) energy" please explain this? • (4 votes) Matt B 8 years agoPosted 8 years ago. Direct link to Matt B's post “A concentration gradient ...” A concentration gradient will cause movement of molecules from high concentration to low concentration. Therefore, it is a driving force for the movement and thus can be considered as energy. (4 votes) ujalakhalid01 8 years agoPosted 8 years ago. Direct link to ujalakhalid01's post “What is faster, a simple ...” What is faster, a simple diffusion (of oxygen, for example), or a facilitated one (of water through aquaporines)? • (3 votes) Matt B 8 years agoPosted 8 years ago. Direct link to Matt B's post “I don't think there is a ...” I don't think there is a general rule (leaning toward facilitated but I have counter examples too). (5 votes) edgewaterah 6 years agoPosted 6 years ago. Direct link to edgewaterah's post “If a molecule wanted to d...” If a molecule wanted to diffuse across the plasma membrane, but wasn't able to make it all the way through, what would happen to it? Would it eventually work its way in, or would it get stuck in the membrane? • (4 votes) tyersome 6 years agoPosted 6 years ago. Direct link to tyersome's post “Interesting question, I d...” Interesting question, I don't know if anyone has looked into whether membranes might get "gummed up" by material getting stuck part way through. One interesting example I was able to find are the persistent organic pollutants known as PCBs (polychlorinated biphenyls) — these bioaccumulate and at least in some cases are known to disrupt membranes: Membranes are incredibly dynamic. Vesicles are constantly leaving and joining each membrane. In addition, membrane molecules (e.g. phospholipids) move between the two layers§ — for example the lipid composition of the inner and outer layer of the plasma membrane is quite different on most cells . This very tight control of membrane composition suggests to me that there are probably mechanisms for clearing out bad/contaminated sections of membrane. If this sort of thing interests you, you might want to consider going to grad school :-) §Note: This is done by enzymes called flippases and floppases, just in case you were wondering if biologists had a sense of humor! (3 votes) Thisbishjuju 7 years agoPosted 7 years ago. Direct link to Thisbishjuju's post “Which of these cells can ...” Which of these cells can help to move and transport blood • (2 votes) Ampersand 7 years agoPosted 7 years ago. Direct link to Ampersand's post “Blood is a cell, not a pa...” Blood is a cell, not a particle. That means that it could not be diffused. It actually gets transported by blood vessels, which are long chains of muscle cells. (5 votes) lawaschristine621 8 years agoPosted 8 years ago. Direct link to lawaschristine621's post “What is osmosis” What is osmosis • (3 votes) City Face 8 years agoPosted 8 years ago. Direct link to City Face's post “The movement of water acr...” The movement of water across a concentration gradient. (5 votes)Want to join the conversation?
That said, this is also the definition of a gradient: it changes as you move from high to low.
Using a real life example of gradient: lets say you are in a dark room and then you turn on one lightbulb. The light will have a gradient too because the closer to are to the lightbulb, the brighter it becomes (high concentration of light) and the further you move away, the less light there is (low concentration of light). The differences in light intensity is a gradient.
the big thing to keep in mind is that many of these gates are evolving randomly. So getting the most efficient solution while inevitable is not going to happen quickly so if it works it works. Also keep in mind that for larger molecules (think an enzyme or a long carbon chain) the channel would have to be very large meaning that a lot of things could flow out on accident due purely to the size of the pipe. So using a gate instead keeps internal pressure while also heavily regulating the release of the molecules.
Sodium : Voltage gated Channel Proteins in Neurons for propagation of nerve Impulse.
Potassium : There are Leaky Channels inside nerve cells ...refer Nerve trnsmission videos of Khan Academy itself.
Calcium : In smooth muscles of the Body...there are Voltage Gated Calcium Channels Present.
However, you cannot use passive diffusion to move things from low concentration to high concentration but you can do this with facilitated/active. Depending on the difference in concentration, the simple/passive diffusion will vary while facilitated diffusion can move against concentration gradients and if affected by other conditions too.
https://academic.oup.com/toxsci/article/80/1/54/1674897
