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  1. #1
    elph is offline Newbie 510 points
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    Physiology Home Work

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    I received this problem on a home work assignment and I'm having a bit of a hard time figuring it out:

    Given an ion concentration gradient (high outside and low inside), if that ion were to enter the cell, what mechanisms are available (e.g. simple diffusion, active transport)? Explain your answer, including a description of any applicable membrane protein

    Anyone have any ideas, id really appreciate it. :)

  2. #2
    siim is offline Newbie 510 points
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    that must be active transport and this ion will be the Na or Ca,,,,,,,,,,but if any one asking a simple cell in example of container than u can say that by simple diffusion,,,,,,,,because the key word is concentration gradiant,,,,,,substance move from high to low concentration gradiant,,,,,,,,,,,
    Last edited by siim; 09-01-2012 at 07:51 AM. Reason: mistake

  3. #3
    sgk
    sgk is offline Newbie 510 points
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    Hi,
    I just did the chapter on ionic equilibrium. I am not able to understand the concept really well. Could anybody here please suggest the best book to get this cleared. .. I simply cant figure out:
    how does the inside of a cell be negative from the beginning? Whats the mechanism /principle because of which the interior of the cell becomes negative?

    secondly, we say K+, Mg+ are mainly intracellular and Na+, Cl- etc are extracellular.. so I am wondering again ..what is the reason for a particular ion to be more concentrated in a particular compartment?

    Thirdly, for any ion present in any compartment(ecf/icf) if there are two forces acting :concentration gradient and the elecrochemical gradient .. what would the cell try to equalise first and why?

    Are these doubts irrelevant or its that I am confused?

    Any help appreciated.
    Thanks!

  4. #4
    sgk
    sgk is offline Newbie 510 points
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    please do share the solution.
    thanks!

  5. #5
    QR93 is offline Newbie 510 points
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    I am not very good at this but I will see if I can explain what I understand about this. Though I may be completely wrong.

    Ions are non-lipid soluble. They may be on one side of the cell membrane but they can't pass through. Now as far as I am aware, they need some sort of transport mechanism to pass through (either passive or active).

    Now, if the ions need to move across a concentration gradient (from high to low), they they will move via ion channels (passive transport). I think of this passive transport like opening a gate or a door, and being like "'hey ions, do whatever you want - equalise yourselves across the inside and outside of the cell or whatever".- essentially just letting the ions move around freely. This would be movement by diffusion.

    However, if the ions are being pumped against their concentration gradient (from low to high), then they will require active transport (which will use ATP for energy). I think of this as the ions being "chucked or forced out".

    Hope this helps

    -------------------------------------------------------

    An example of a pump is below, and SGK hopefully this will answer some of your question:

    1. The Na+/K+ ATPase

    The cytosol of animal cells contains a concentration of potassium ions (K+) as much as 20 times higher than that in the extracellular fluid. Conversely, the extracellular fluid contains a concentration of sodium ions (Na+) as much as 10 times greater than that within the cell.

    These concentration gradients are established by the active transport of both ions. And, in fact, the same transporter, called the Na+/K+ ATPase, does both jobs. It uses the energy from the hydrolysis of ATP to

    actively transport 3 Na+ ions out of the cell
    for each 2 K+ ions pumped into the cell.
    This accomplishes several vital functions:
    It helps establish a net charge across the plasma membrane with the interior of the cell being negatively charged with respect to the exterior. This resting potential prepares nerve and muscle cells for the propagation of action potentials leading to nerve impulses and muscle contraction.
    The accumulation of sodium ions outside of the cell draws water out of the cell and thus enables it to maintain osmotic balance (otherwise it would swell and burst from the inward diffusion of water).
    The gradient of sodium ions is harnessed to provide the energy to run several types of indirect pumps.
    The crucial roles of the Na+/K+ ATPase are reflected in the fact that almost one-third of all the energy generated by the mitochondria in animal cells is used just to run this pump.

    Quote Originally Posted by sgk View Post
    Hi,
    I just did the chapter on ionic equilibrium. I am not able to understand the concept really well. Could anybody here please suggest the best book to get this cleared. .. I simply cant figure out:
    how does the inside of a cell be negative from the beginning? Whats the mechanism /principle because of which the interior of the cell becomes negative?

    secondly, we say K+, Mg+ are mainly intracellular and Na+, Cl- etc are extracellular.. so I am wondering again ..what is the reason for a particular ion to be more concentrated in a particular compartment?

    Thirdly, for any ion present in any compartment(ecf/icf) if there are two forces acting :concentration gradient and the elecrochemical gradient .. what would the cell try to equalise first and why?

    Are these doubts irrelevant or its that I am confused?

    Any help appreciated.
    Thanks!
    So SGK, as you can see "the reason for a particular ion to be more concentrated in a particular compartment? " is to allow for muscular contraction and action potentials, etc.
    And about whether the electrochemical or concentration gradient equilibrium I'd imagine they both happen simultaneously? I don't imagine one happening first. Though I'm not completely sure...



    Hope this helps
    Last edited by QR93; 03-03-2013 at 05:30 AM.

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