細胞生物學(xué)期末試卷(2002年1月23日)-資料下載頁
2025-01-09 11:09本頁面
【正文】 二種解釋是熱動力學(xué)驅(qū)使磷脂的不對稱分布，因為 膜兩側(cè)的環(huán)境不同。另外在 ER 膜中有翻轉(zhuǎn)酶 (flippase),在新的磷脂合成之后 ,通過翻轉(zhuǎn)酶的作用也會造成磷脂的不對稱分布。 膜蛋白有整合蛋白和外周蛋白。用水泡性口炎病毒 (vesicular stomatitis virus,VSV)作為模式系統(tǒng)研究了細胞膜整合蛋白和外周蛋白的形成途徑 , 發(fā)現(xiàn)膜整合蛋白是通過內(nèi)膜系統(tǒng)經(jīng)小泡轉(zhuǎn)運到質(zhì)膜上的 , 而外周蛋白則是在游離核糖體上合成 ,并以可溶的形式釋放到胞質(zhì)溶膠中。然后再與細胞質(zhì)膜的胞質(zhì)溶膠面結(jié)合 ,成為外周蛋白。糖則是在內(nèi)質(zhì)網(wǎng)和高爾基體腔中通過對蛋白的修飾添加的。最后 在與質(zhì)膜融合時 ,通過外翻 ,糖的部分位于細胞質(zhì)膜的外側(cè)。這就是為何幾乎所有質(zhì)膜上的糖蛋白的糖都是朝向細胞外的原因。 脂錨定蛋白的形成有幾種可能的機制 : 糖脂錨定的膜蛋白是在粗面內(nèi)質(zhì)網(wǎng)上合成 ,然后在 ER 腔中被連接到 ER 膜的GPI 上，隨后通過小泡運輸 ,經(jīng)高爾基體出芽形成小泡 ,最后與質(zhì)膜融合 ,含糖的一面外翻朝向細胞外側(cè)。 脂肪酸錨定膜蛋白是水溶性的 ,在游離核糖體合成后釋放到胞質(zhì)溶膠中 ,然后與包埋在質(zhì)膜中的脂肪酸共價結(jié)合。連接的脂肪酸包括豆蔻酸 (myristic acid, 一種 14碳的飽和脂肪酸 )和棕櫚酸 (palmitic acid,一種 16 碳的飽和脂肪酸 )。 七、 1. 答：看起來，細胞核并不直接參與蛋白質(zhì)的合成，但是它卻控制著蛋白質(zhì)合成的兩 15 個關(guān)鍵元件，即 mRNA 的合成和核糖體的裝配?？刂浦兄颂求w的合成就等于控制中蛋白質(zhì)合成的裝配線，有利于控制生命的節(jié)奏。因此，為求得安定，必要的花費是值得的。 ①如果核糖體亞基的裝配在胞質(zhì)溶膠中，不僅極大地削弱了細胞核對蛋白質(zhì)合成的控制力，還會發(fā)生一些細胞核不良后果。②由于核糖體的空間構(gòu)型復(fù)雜，裝配過程長。如果 mRNA 同正在裝配中的未成熟的核糖體亞基結(jié)合的話，會導(dǎo)致蛋白質(zhì)合成的不正常。③由于組成核糖體的蛋白質(zhì)種類多，數(shù)量大，并且胞質(zhì)溶膠中代謝途徑多，會影響核糖體的裝配，從而影響其他的生化過程，最終影響細胞的正常聲明活動。 2.（ 5 分） Answer2: A. The problem is that vesicles having two different kinds of vSNAREs in their membrane could dock on either of two different membranes. B. The answer to this puzzle is presently not known, but we can predict that cells must have ways of turning the docking ability of SNAREs on and off. This may be achieved through other proteins that are, for example, copackaged in the ER with SNAREs into transport vesicles and facilitate the interactions of the correct vSNARE with the tSNARE in the cis Golgi work. 3 （ 10 分）。 Answer3. Membrane proteins are sorted to either the apical or basolateral domains by several different mechanisms. One mechanism for targeting proteins to the appropriate domain of the plasma membrane involves sorting in the transGolgi work. Except for the GPI anchor, which acts as an apical or basolateral targeting signal, no unique sequences have been identified that target proteins to the apical or basolateral domain. Another mechanism operates in bepatocytes where all newly made apical and basolateral proteins are first delivered together from the transGolgi work to the basolateral membrane. From there, both apical and basolateral proteins are endocytosed to the same vesicles. Within endosomes, there is then sorting and transport to the appropriate domain. The attachment of integral membrane proteins to the cytoskeleton serves as a retention signal and may assist in the apicaibasolateral sorting of some proteins. Hence, depending on cell type, at least three different mechanisms for apicalbasolateral sorting are possible. 16 4.(5 分 ) Answer4. Normally, cells divide only when they have grown to a certain size. This size control is clearly defective in the two mutant strains. In the case of gee cells, cell size increases without ever triggering cell division, suggesting that the mutant cellcycle control protein has lost its ability to monitor cell size. It might, for example, now permanently inhibit MPF. In wee cells, on the other hand, the mutant control protein triggers cell division prematurely, before cells have grown to the appropriate size. This could be a control protein, for example, that no longer inhibits MPF, so that MPF bees active prematurely. In fact, there is a yeast cellcycle control protein called Wee1, which is a kinase that phosphorylates MPF on a site that causes its inactivation。 yeast cells with a mutation in the wee1 gene have a short cell cycle and are small.
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