发信人: doggiebear (doggiebear), 信区: Biology
标 题: Re: SBIG: Channels
发信站: Unknown Space - 未名空间 (Thu Oct 16 22:43:26 2003) WWW-POST


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 the contrary, they consume
them. They use off this gradient to do some work. (see figure below)




【 在 space (排骨教主) 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?
:
:
:
: 【 在 doggiebear (doggiebear) 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 critical step for ion selection. The
selective
: : filter is small enough to for only dehydrated ion. Therefore, when an
hydrated
: : ion comes in, it is recognized by charged groups on the selective filter
and
: : tranfered from water molecules to the interation partners of the filter
and
: : start the transfering process.
: : 【 在 space (排骨教主) 的大作中提到: 】
: : : 我这几天脖子给拧了,没好好看文章. 今天在医院把K+ channel匆匆看了一下,很不
得
: : : 要领,和我缺乏生物知识有关系.首先我就没搞清楚K+ channel是不是双向的, 其次
: : : 我也没搞清楚hydration和dehydration在这里面的角色是什么, 最后我也不清楚
: : : 这channel尺寸(宽度和高度)怎么样. 我先看看你们的讨论学习学习吧.
: : from
: : charges
: : field
: : The
: : cavity.
: : energy
: : membrane
: : C-term
: : cavity.
: : axial
: : happens.
: : shows,
: : is
: : job,
:
:


--
I will vote a democrat even he is a dog.
Liberalism is something to be proud of!
※ 修改:·doggiebear 於 Oct 16 22:43:26 修改本文·[FROM: 208.180.]
※ 来源:．Unknown Space - 未名空间 mitbbs.com．[FROM: 208.180.]