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    Can someone please explain the difference between a protein channel and carrier proteins.

    In my book it says that intrinsic proteins act as carriers to transport water soluble molecules.

    But for facilitated diffusion it says that proteins channels transport water soluble molecules across the phospholipid bilayer.

    So how do water-soluble molecules get transported - is it via a protein channel or a carrier protein?

    Any help will be greatly appreciated.
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    Yo Linked. I totally didn't get this either, but after a while I worked it out. Lemme get my notes.

    -gets notes-

    Okay,

    Firstly, extrinsic and intrinsic proteins are just types of protein. Intrinsic means it runs across the whole membrane. Extrinsic means it's just on one side of the membrane. That's all that means. The textbook has pictures of this. Now:

    Protein channels:
    • They are intrinsic proteins, so span across the whole membrane
    • They basically make a channel/pathway/hole for stuff to go through
    • The channel that the channel proteins make, is full of water. This means only water soluble substances can pass through.
    • Facilitated diffusion happens here. This is basically diffusion, from high to low concentration. Facilitated just means that it needs this protein to work, and the protein here is the channel protein that makes the hole in the membrane. (Don't say hole, use nicer words like channel/pathway)
    • Some channels are also gated and/or selective. Gated means it opens only when appropriately stimulated. Selective means it only lets certain substances through.


    Carrier proteins:
    • These can do both facilitated diffusion AND active transport
    • If you want an image of what it looks like, it picks up the molecule on one side of the membrane and then changes shape and deposits it on the other side.
    • The thing to remember here is the molecule that moves across the membrane actually binds with the protein, unlike channels where the protein just makes a hole for molecules to pass through.
    • For facilitated diffusion the molecules use their inbuilt kinetic energy means to bind with the channel protein, which moves it to the other side of the membrane. As this is diffusion it is moving from high concentration to low concentration.
    • For active transport ATP is used to move molecules from low concentration to high concentration.
    • In both situations, with carrier proteins, the molecule BINDS WITH THE PROTEIN.


    If I'm wrong, someone tell me. And ask if you got any questions
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    (Original post by Linked)
    Can someone please explain the difference between a protein channel and carrier proteins.

    In my book it says that intrinsic proteins act as carriers to transport water soluble molecules.

    But for facilitated diffusion it says that proteins channels transport water soluble molecules across the phospholipid bilayer.


    cazmasetro has given a very good summary of the characteristics of channel proteins and carrier proteins above, and it is very simple at it's crux: channel proteins are a 'tunnel' through the cell membrane, carrier proteins grab a molecule, move it to the other side of the membrane, and let it go. Super simple stuff.

    Carrier proteins are a little bit more complex in the mechanisms that they use, and they have a lot of different ways of working, but I don't think you need to worry about that, and the basic description is as I've already said.

    To clear up something I don't feel is very apparent in the above reply: 'facilitated diffusion' in carrier proteins just means that the process requires no energy: you don't need to expend any energy to move the molecule from one side of the membrane to another.

    You also don't need to memorise the list above; if you understand your basics of diffusion and active transport, and can use a bit of common sense, you can work out what channel proteins and carrier proteins do!

    So how do water-soluble molecules get transported - is it via a protein channel or a carrier protein?

    Any help will be greatly appreciated.
    It's both! Sometimes you use channels, sometimes you use carriers, depending on the situation.
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    (Original post by cazmasetro)
    Yo Linked. I totally didn't get this either, but after a while I worked it out. Lemme get my notes.

    -gets notes-

    Okay,

    Firstly, extrinsic and intrinsic proteins are just types of protein. Intrinsic means it runs across the whole membrane. Extrinsic means it's just on one side of the membrane. That's all that means. The textbook has pictures of this. Now:

    Protein channels:
    • They are intrinsic proteins, so span across the whole membrane
    • They basically make a channel/pathway/hole for stuff to go through
    • The channel that the channel proteins make, is full of water. This means only water soluble substances can pass through.
    • Facilitated diffusion happens here. This is basically diffusion, from high to low concentration. Facilitated just means that it needs this protein to work, and the protein here is the channel protein that makes the hole in the membrane. (Don't say hole, use nicer words like channel/pathway)
    • Some channels are also gated and/or selective. Gated means it opens only when appropriately stimulated. Selective means it only lets certain substances through.


    Carrier proteins:
    • These can do both facilitated diffusion AND active transport
    • If you want an image of what it looks like, it picks up the molecule on one side of the membrane and then changes shape and deposits it on the other side.
    • The thing to remember here is the molecule that moves across the membrane actually binds with the protein, unlike channels where the protein just makes a hole for molecules to pass through.
    • For facilitated diffusion the molecules use their inbuilt kinetic energy means to bind with the channel protein, which moves it to the other side of the membrane. As this is diffusion it is moving from high concentration to low concentration.
    • For active transport ATP is used to move molecules from low concentration to high concentration.
    • In both situations, with carrier proteins, the molecule BINDS WITH THE PROTEIN.


    If I'm wrong, someone tell me. And ask if you got any questions

    thank you very much for your help. You gave a brilliant explanation. Thank you once again.
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    (Original post by Hype en Ecosse)
    cazmasetro has given a very good summary of the characteristics of channel proteins and carrier proteins above, and it is very simple at it's crux: channel proteins are a 'tunnel' through the cell membrane, carrier proteins grab a molecule, move it to the other side of the membrane, and let it go. Super simple stuff.

    Carrier proteins are a little bit more complex in the mechanisms that they use, and they have a lot of different ways of working, but I don't think you need to worry about that, and the basic description is as I've already said.

    To clear up something I don't feel is very apparent in the above reply: 'facilitated diffusion' in carrier proteins just means that the process requires no energy: you don't need to expend any energy to move the molecule from one side of the membrane to another.

    You also don't need to memorise the list above; if you understand your basics of diffusion and active transport, and can use a bit of common sense, you can work out what channel proteins and carrier proteins do!



    It's both! Sometimes you use channels, sometimes you use carriers, depending on the situation.

    thank you to you too.
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    Cazmasetro did a great explanation. I'd also say that only water soluble molecules are allowed through the channel proteins because there are hydrophilic groups on the inside of the channel.
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    (Original post by awilson008)
    Cazmasetro did a great explanation. I'd also say that only water soluble molecules are allowed through the channel proteins because there are hydrophilic groups on the inside of the channel.
    thank you for your input too!
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    (Original post by Linked)
    thank you very much for your help. You gave a brilliant explanation. Thank you once again.
    No problem Doing this makes me remember it better too.

    (Original post by awilson008)
    Cazmasetro did a great explanation. I'd also say that only water soluble molecules are allowed through the channel proteins because there are hydrophilic groups on the inside of the channel.
    Oh cool I didn't know that
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    So useful. Thnx. Great for my revision for the exam next week.
 
 
 
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