?
Lv 5
? asked in 科學動物學 · 2 decades ago

<國一自然>水如何進入細胞?除了擴散作用?

據說擴散作用已被推翻是真的嗎? 新說法是什麼呢? 導管?~~~~~~~

2 Answers

Rating
  • 2 decades ago
    Favorite Answer

    細胞膜(無論動、植物、細菌、古細菌)均由磷脂雙層膜構成,雖不同生物所使用之磷脂並不相同,但皆具有相同特徵,即親水性部分與親脂性部分,在水中會形成雙層膜,相關圖片可由網路尋得(phospholipid bilayer)。水為一極性分子,單靠擴散作用是否能輕易通過細胞膜仍有相當爭議,可參閱此網址中的討論:http://www.sciscape.org/phpBB2/viewtopic.php?t=148...

    依現行細胞生物學的看法,細胞膜上有一群特殊的蛋白質,會形成可使水分此通過的小孔,稱為aquaporin,這一群蛋白現以發現數種,分別在不同的生理機制中發揮其作用例如一般細胞的水分調節,腎小管水分回收、眼睛內水分調節...

    此一類蛋白的發現者也獲得2003年的諾貝爾化學獎。

    又擴散作用並非被推翻,擴散作用為一物理現象,可由簡單實驗觀察得到。例如:在室內打開一瓶香水、水中滴入一滴墨水.....。水分子經由aquaporin進出細胞膜的主要驅動力仍為擴散作用,亦即受物質濃度差異的影響。

    Aquaporin:

    A water channel. Aquaporins form pores in the membranes of cells and selectively conduct water molecules through the membrane, while preventing the passage of ions (such as sodium and potassium) and other small molecules.

    Aquaporins are typically composed of identical subunit proteins. Water molecules traverse the narrowest portion of the water channel in single file. The presence of water channels increases the permeability of membranes to water by as much as ten-fold. Aquaporins prevent us from dying of dehydration by reabsorbing 99% of the water in the kidney.

    The existence of molecular water channels had been long suspected. However, their molecular identity remained unknown until the serendipitous discovery of aquaporin-1 in 1988. The protein known as AQP1 was first purified from red blood cell membranes.

    A number of different aquaporins have now been identified. They have been designated aquaporin-0, aquaporin-1, aquaporin-2, and so on while the corresponding aquaporin genes are symbolized AQP0, AQP1, and AQP-2. The results of mutations in the AQP genes differ. Mutation in AQP-0 causes cataracts. Mutations in AQP1 have been found in normal people. Mutations in the aquaporin-2 gene AQP2 cause an autosomal dominant form of nephrogenic diabetes insipidus.

    The 2003 Nobel Prize in Chemistry was shared by Peter Agre from Johns Hopkins University "for the discovery of water channels." The other half of the prize went to Roderick MacKinnon from Rockefeller University "for structural and mechanistic studies of ion channels."

    相關資料請於以下網站中閱讀。

    http://ntmf.mf.wau.nl/aquaporin/

    http://www.ks.uiuc.edu/Research/aquaporins/

    http://www.chemedu.ch.ntu.edu.tw/lecture/nobel2003...

    http://www.sciam.com.tw/news/newsshow.asp?FDocNo=3...

  • 2 decades ago

    我現在還是學到擴散作用ㄋㄟ...我國一...

    Source(s): 自己..
Still have questions? Get your answers by asking now.