d********r
发帖数: 303 | 1 First I would start by posting a figure on this board.
what is the blue molecule?
and what is the yellow one?
Answer:
Membrane protein is very difficult to crystallize. Therefore, Mackinnon spent
lots of time to get monoclonical antibody against KcsA potassium channel. The
blue molecule is the the Fab fragment and the yellow molecule is the channel.
The amazing thing is only the fab fragment interact each other and mediate the
crystallization. Therefore, the hydrophobic residues on the channel d | d********r
发帖数: 303 | 2 The directinality of the channel is a good question.
I do not know. (though I can search for answer)
I say it is imporant becasue it verify the role of the helix term and the
cavity. Based on this principle, I will say the channel should have
directionality. That means, ion can only come out from the cell, not the
opposite, or the stabilization effect will not be there.
I bet ppl has done experiment on it. This is kind of classical
electriphysiology research.
I think dehydration is the the criti | s***e
发帖数: 911 | 3 我看了那个图象,通道不对称. cavity在靠近细胞内的一面. 所以我才问方向的
问题. 可如果这完全是单向的,那么最终细胞内K+浓度会减少到很低的水平. 必须
有反向的流动才能维持平衡.
另外,细胞内K+浓度比外面高了30倍.这是靠什么维持的呢?
【在 d********r 的大作中提到】
: The directinality of the channel is a good question.
: I do not know. (though I can search for answer)
: I say it is imporant becasue it verify the role of the helix term and the
: cavity. Based on this principle, I will say the channel should have
: directionality. That means, ion can only come out from the cell, not the
: opposite, or the stabilization effect will not be there.
: I bet ppl has done experiment on it. This is kind of classical
: electriphysiology research.
: I think dehydration is the the criti
| d********r
发帖数: 303 | 4 Cell has a Na/K pump. Basically it used ATP (energy) to pump out Na and pump
in K. Actually cell uses large amount of energy to establish such gradient.
Why need it?
For many reasons.
Example one:
neurons need this gradient for signal transduction.
Example two:
some cell in intestine need this gradient to transport in nutrients.
Generally the ion gradient across membrane is kind of stored energy that are
ready for use by many biological systme.
the ion channels do not generate this gradient. On
【在 s***e 的大作中提到】
: 我看了那个图象,通道不对称. cavity在靠近细胞内的一面. 所以我才问方向的
: 问题. 可如果这完全是单向的,那么最终细胞内K+浓度会减少到很低的水平. 必须
: 有反向的流动才能维持平衡.
: 另外,细胞内K+浓度比外面高了30倍.这是靠什么维持的呢?
| d********r
发帖数: 303 | 5 http://hebb.mit.edu/courses/8.515/lecture1/img027.jpg
Actually the study of ion channels is kind of biophysics. It is, as I know,
the first example of single molecule research. (see above figure)
basically, researchers use a patch clamp technique to clamp a small membrane
patch, containg very small or even singl number of channels. this kind of
reseach generate the bulk of information about membrane channel. (see below) | d********r
发帖数: 303 | 6
pump
gradient.
K*T*Log[100/4],
This is a very good question. i don't know how the pump look like, since no
structure about pump as I know has been solved. I have to say, it is very
likely it has some kind of channel like structure. remeber the potassium
channel? It has two configurations, one for high K and the other for low K. So
I can envision the pump should at least have two configurations.
Just suppose there is a potassium pump, it tries to do work against the
gradient, literally by pumpin
【在 s***e 的大作中提到】
: 我看了那个图象,通道不对称. cavity在靠近细胞内的一面. 所以我才问方向的
: 问题. 可如果这完全是单向的,那么最终细胞内K+浓度会减少到很低的水平. 必须
: 有反向的流动才能维持平衡.
: 另外,细胞内K+浓度比外面高了30倍.这是靠什么维持的呢?
| d********r
发帖数: 303 | 7 http://saturn.med.nyu.edu/~rice/density1.gif
This is the only figure I can find about the Na/K pump. It is a preliminary
low resolution structure. Kind of rough. |
|
