题目

某三十九肽中共有丙氨酸残基4个，现去掉其中的丙氨酸残基得到4条长短不等的多肽（如图），这些多肽中肽键总数为 ( )A. 31 B. 32C. 34 D. 35 答案：【答案】A【解析】在三十九肽中，第8、18、27、39个氨基酸是丙氨酸，在除去第8、18、27号氨基酸的丙氨酸时每去掉1个丙氨酸要水解2个肽键，去掉第39号丙氨酸只水解一个肽键即可，因此该39肽去掉其中的丙氨酸得到4条长短不等的多肽共需水解肽键数是3×2+1=7个，原来肽键数为39-1=38个，因此这些多肽中Most people want to know how things are made. They honestly admit, however, that they hard­ly know a thing when it comes to understanding how a piece of music is made. Where a composer (作曲家) begins, how he manages to keep going - in fact, how and where he learns his trade -all are covered in complete darkness. The composer, in short, is a man of mystery (神秘). One of the first things the common man wants to know about is the part inspiration (灵感) plays in a composer' s work. He finds it difficult to believe that composers are not much interested in that question. Writing music is as natural for the composer as eating or sleeping for all. Music is something that the composer happens to have been born for. The composer, therefore, does not say to himself: "Do I feel inspired?" He says to himself: "Do I feel like working today?" And if he feels like working, he does. It is more or less like saying to himself: "Do I feel sleepy?" If you feel sleepy, you go to sleep. If you don't feel sleepy, you stay up. If the composer doesn’t' feel like working, he doesn’t work. It’s as simple as that. 1. What would be the best tide for the text? A. Composer: a man of mystery          B. Practice makes good music C. Relation between sleeping and music      D. Music: product of nature 2. The words "covered in complete darkness" underlined in Paragraph I most probably mean A. difficult to be made      B. without any light      C. black in color    D. not known 3. Most people seem to think that a composer _______ . A. finds it difficult to write music         B. considers it important to have a good rest C. should like to talk about inspiration   D. never asks himself very simple questions 4. The author will most probably agree that composers _______ A. are born with a gift for music                 B. are people full of mystery C. work late at night for their music            D. know a lot about eating and sleeping