• <nobr id="kydkt"></nobr>
      <span id="kydkt"><output id="kydkt"><b id="kydkt"></b></output></span>
    1. <acronym id="kydkt"></acronym>
      <samp id="kydkt"><output id="kydkt"><tbody id="kydkt"></tbody></output></samp>

      1. <optgroup id="kydkt"></optgroup>
      2. <optgroup id="kydkt"><li id="kydkt"></li></optgroup>
      3. 您的位置:三立在線 > SAT頻道頁 > 真題答案 > 2019SAT真題 > 2019年3月亞太SAT真題及答案-閱讀部分第五篇
        咨詢熱線:400-920-8185

        2019年3月亞太SAT真題及答案-閱讀部分第五篇

        2019-04-24 18:02 三立在線 admin

        分享到: 0

        摘要:2019年3月亞太SAT真題及答案-閱讀部分第五篇,雙篇文章. 具體真題截圖如下: 2019年3月亞太SAT真題及答案-閱讀部分第五篇答案: 43:C 44、C 45、B 46、D 47、B 48、B 49、C 50、A 51、D 52、D 第一篇文章說的是作者認為RNA可以幫助找到生命的起源。之前人們一直依賴DNA和Protein,但是現在RNA的出現會讓科學研究有重大的突破。DNA和Protein是互相依賴的,所

         2019年3月亞太SAT真題及答案-閱讀部分第五篇,雙篇文章.

        具體真題截圖如下:

        2019年3月亞太SAT真題及答案-閱讀部分第五篇
        2019年3月亞太SAT真題及答案-閱讀部分第五篇
        2019年3月亞太SAT真題及答案-閱讀部分第五篇
        2019年3月亞太SAT真題及答案-閱讀部分第五篇答案:
        43:C
        44、C
        45、B
        46、D
        47、B
        48、B
        49、C
        50、A
        51、D
        52、D

        第一篇文章說的是作者認為RNA可以幫助找到生命的起源。之前人們一直依賴DNA和Protein,但是現在RNA的出現會讓科學研究有重大的突破。DNA和Protein是互相依賴的,所以科學家很難知道到底哪個先出現。RNA可以幫助跳過這個難題,因為RNA可以起三個作用:第一,可以儲存信息;第二,可以復制配對;第三,可以起到催化作用。

        具體真題原文如下:

        Few events have electrified the origin-of-life community as much as the early 1980s discovery of RNA ribozymes-strands of RNA that not only carry genetic information,but also act as catalysts. Sidney Altman of Yale and Thomas Cech of the University of Colorado independently demonstrated that a particular segment of RNA can accelerate key biothemical reactions。This startling finding,which won Altman and Cech the Nobel Prize in 1989,inspired a new vision of life's origin.

        Modern life relies on two complexly interrelated molecules :RNA,which carries information,and proteins, which perform chemical functions。This interdependence leads to a kind of chicken-and-egg dilemma: Proteins make and maintain DNA, but DNA carries the instructions to make proteins.Which came first?RNA,it turns out,has the potential to do both jobs.

         

        The RNA world theory quickly emerged following the discovery of ribozymes .IT champions the central role of genetic material in the dual tasks of catalyst and information transfer.Over the years, “RNA World” has come to mean different things to different people, but three precepts are common to all versions of the theory: (1) Once upon a time, RNA rather than DNA stored genetic information;(2)ancient RNA replication followed the same rules as modern DNA replication by matching pairs of bases: A-U (the pyrimidine uracil, whose DNA equivalent is thymine) and C-G;and(3)ancient RNA played the same catelytic roles as modern protein enzymes.In this scenario,the first life-form was simply a self-replicating strand of RNA,perhaps enclosed in a protective lipid membrane.According to most versions og this hypothesis, modern metabolism emerged later, as a means to make RNA replication more efficient

        第二篇文章說的是作者反對RNA的重要性。主要基于兩點:第一,RNA沒有足夠的時間進化;第二,RNA可能不會在那么早存在。作者提到一個科學家做的實驗,提到起催化劑其實是酶的作用。

        具體真題原文如下:

        "The RNA world hypothesis is extremely unlikely," said Carter. "It would take forever."

        Moreover, there's no proof that such ribozymes even existed billions of years ago. To buttress the RNA World hypothesis, scientists use 21st century technology to create ribozymes that serve as catalysts. "But most of those synthetic ribozymes," Carter said, "bear little resemblance to anything anyone has ever isolated from a living system."

        Carter, who has been an expert in ancient biochemistry for four decades, took a different approach. His experiments are deeply embedded in consensus biology.

        Our genetic code is translated by two super-families of modern-day enzymes. Carter's research team created and superimposed digital three-dimensional versions of the two super-families to see how their structures aligned. Carter found that all the enzymes have virtually identical cores that can be extracted to produce "molecular fossils" he calls Urzymes -- Ur meaning earliest or original. The other parts, he said, are variations that were introduced later, as evolution unfolded.

        These two Urzymes are as close as scientists have gotten to the actual ancient enzymes that would have populated Earth billions of years ago.

        "Once we identified the core part of the enzyme, we cloned it and expressed it," Carter said. "Then we wanted to see if we could stabilize it and determine if it had any biochemical activity." They could and it did.

        Both Urzymes are very good at accelerating the two reactions necessary to translate the genetic code.

        "Our results suggest that there were very active protein enzymes very early in the generation of life, before there were organisms," Carter said. "And those enzymes were very much like the Urzymes we've made."

        The finding also suggests that Urzymes evolved from even simpler ancestors -- tiny proteins called peptides. And over time those peptides co-evolved with RNA to give rise to more complex life forms.

        In this "Peptide-RNA World" scenario, RNA would have contained the instructions for life while peptides would have accelerated key chemical reactions to carry out those instructions.

        "To think that these two Urzymes might have launched protein synthesis before there was life on Earth is totally electrifying," Carter said. "I can't imagine a much more exciting result to be working on, if one is interested in the origin of life."

         

        The study leaves open the question of exactly how those primitive systems managed to replicate themselves -- something neither the RNA World hypothesis nor the Peptide-RNA World theory can yet explain. Carter, though, is extending his research to include polymerases -- enzymes that actually assemble the RNA molecule. Finding an Urzyme that serves that purpose would help answer that question.

        2019年3月亞太SAT真題閱讀5篇真題自此分享完畢,點擊查看前四篇真題:

        2019年3月亞太SAT真題及答案-閱讀部分第四篇

        2019年3月亞太SAT真題及答案-閱讀部分第三篇

        2019年3月亞太SAT真題及答案-閱讀部分第二篇

        2019年3月亞太SAT真題及答案-閱讀部分第一篇

         

        需要下載2019年3月亞太真題完整版的同學,請根據需要點擊以下兩個按鈕免費索取!

        相關字搜索:   

        Copyright ?2004-2018 www.d8335.com All Rights Resserved 三立在線版權所有

        課程咨詢電話:400-920-8185 郵箱:tech@sanlischool.com

        課程咨詢請掃描以上二維碼

        關于我們 網站地圖

        京ICP備14009560號-3

        京公網安備 11010802021370號













        男人天堂网av在线视频