方向性 (分子生物学)
Multi tool use
五環糖分子的圖解，附有編號的碳原子。
方向性（英语：Directionality，亦称为定向性）在分子生物學中，是指一個核酸股的端對端化學方位。在核苷五碳糖命名碳原子的規則會形成有「3′端」及「5′端」。沿著核酸結構的相同位置，包括基因、轉錄因子及聚合酶等，都一般是以「上游」（接近5′端）或「下游」（接近3′端）來表示的。
這種命名方法的重要性是容易表示只會從5′至3′合成的核酸，而建立新股的聚合酶，必須以磷酸雙脂鍵附在新核苷的3′羥基。傳統上，脫氧核糖核酸（DNA）及核糖核酸（RNA）序列是由5′至3′表示的。
3′端
3′端的名稱是因一個股在五碳糖內第三個碳原子的羥基作終結而有的，並稱為「尾端」。這個3′羥基在合成新的核酸分子是必要的，因它被DNA黏合酶連接在不同核苷的5′磷酸鹽，形成一連串的核苷股。
透過使用缺少3′羥基的核苷（雙脫氧核糖核酸），來干擾DNA複製。這種技術稱為雙脫氧法或桑格法，來得出DNA核苷的序列。
3′端亦是翻譯前進行多聚腺苷酸化的位點，並在翻譯後立即將有50-250個腺苷的鏈附在mRNA上。這條鏈可以幫助確定mRNA在細胞內存在的時間，從而得知合成多少的蛋白質。
5′端
5′端的名稱是因一個股在五碳糖內第五個碳原子的磷酸根作終結而有的。如果是磷酸鹽附著在5′端時，DNA黏合酶就可以用磷酸二酯鍵將兩個核苷的5′磷酸鹽及3′羥基接合。如果沒有這個磷酸鹽，則不會有接合出現。透過磷酸酶移除磷酸鹽所產生的這個現象，可以阻止不必要的核酸接合。
5′端是轉譯前加帽的位點，加帽後稱為5′端帽，是對生產成熟的mRNA非常重要。加帽可以確保mRNA在進行轉譯的穩定性及提供對核酸外切酶降解的抵抗。它包含了一個甲基化後的核苷，並以罕見的5′至5′三磷酸鹽附在mRNA上。
參考
Lodish; 等. Molecular Cell Biology 5th edn. New York: W.H. Freeman and Company. 2004. ISBN 978-0-7167-4366-8.
参见
F,AS76hMOGw4X UgISP
Popular posts from this blog
Ramiro Burr's New Blog - to go back: www.ramiroburr.com From Latin rock to reggaeton, boleros to blues,Tex-Mex to Tejano, conjunto to corridos and beyond, Ramiro Burr has it covered. If you have a new CD release, a trivia question or are looking for tour info, post a message here or e-mail Ramiro directly at: musicreporter@gmail.com Top Tejano songwriter Luis Silva dead of heart attack at 64 By Ramiro Burr on October 23, 2008 8:40 AM | Permalink | Comments (12) | TrackBacks (0) UPDATE: Luis Silva Funeral Service details released Visitation 4-9 p.m. Saturday, Rosary service 6 p.m. Saturday at Porter Loring, 1101 McCullough Ave Funeral Service 10:30 a.m. Monday St. Anthony De Padua Catholic Church, Burial Service at Chapel Hills, 7735 Gibbs Sprawl Road. Porter Loring (210) 227-8221 Related New Flash: Irma Laura Lopez: long time record promoter killed in accident NewsFlash: 9:02 a.m. (New comments below) Luis Silva , one of the most well-known ...
1 I having trouble getting my ResourceDictionary.MergedDictionaries to load from app.xaml. My WPF app has a static class with a Main defined and startup object set to it. Within Main I created an instance of App and run it. The override OnStartup fires and the mainwindow.cs InitializeComponent gives the error "Message "Cannot find resource named 'MaterialDesignFloatingActionMiniAccentButton'. If I put the resources in the mainwindow.xaml everything is fine, but I wanted them to load at the app level so I they are not in each page. Any help appreciated. public partial class App protected override void OnStartup(StartupEventArgs e) base.OnStartup(e); var app = new MainWindow(); var context = new MainWindowViewModel(); app.DataContext = context; app.Show(); from the Main.. var app = new App(); app.Run(); app.xaml.. <Application x:Class="GS.Server.App" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:...
up vote 2 down vote favorite There is a clear pattern that show for two separate subsets (set of columns); If one value is missing in a column, values of other columns in the same subset are missing for any row. Here is a visualization of missing data My tries up until now, I used ycimpute library to learn from other values, and applied Iterforest. I noted, score of Logistic regression is so weak (0.6) and thought Iterforest might not learn enough or anyway, except from outer subset which might not be enough? for example the subset with 11 columns might learn from the other columns but not from within it's members, and the same goes for the subset with four columns. This bar plot show better quantity of missings So of course, dealing with missings is better than dropping rows because It would affect my prediction which does contain the same missings quantity relatively. Any better way to deal with these ? [EDIT] The nullity pattern is confirmed: machine-learning cor...
