问题 单项选择题 A1型题

组成人体蛋白质多肽链的基本单位是()

A.L-α-氨基酸

B.D-α-氨基酸

C.L-β-氨基酸

D.D-β-氨基酸

E.L-α-氨基酸和D-β-氨基酸

答案

参考答案:A

解析:本试题考核"肽链的基本组成单位是氨基酸"及"组成人体蛋白质氨基酸的类型"。毫无疑问,组成多肽链或蛋白质的基本单位是氨基酸。依"氨基"在碳链骨架上的位置不同,有α-氨基酸(氨基在α-碳原子上),β-氨基酸(氨基在β-碳原子上)等;按构型有L-型和D-型之分。在化学合成反应中,只要控制反应条件等,可以获得各种氨基酸,但在自然界,天然存在的氨基酸种类有限,存在人体中的则更有限,是L-α-氨基酸。

问答题 简答题
单项选择题

For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never ending flood of words. In (1) a job or advancing in one, the ability to read and comprehend (2) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (3) readers. Most of us develop poor reading (4) at an early age, and never get over them. The main deficiency (5) in the actual stuff of language itself—words. Taken individually, words have (6) meaning until they are strung together into phrases, sentences and paragraphs. (7) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (8) words or passages. Regression, the tendency to look back over (9) you have just read, is a common bad habit in reading. Another habit which (10) down the speed of reading is vocalization—sounding each word either orally or mentally as (11) reads.

To overcome these bad habits, some reading clinics use a device called an (12) , which moves a bar(or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (13) the reader finds comfortable, in order to "stretch" him. The accelerator forces the reader to read fast, (14) word by word reading, regression and subvocalization practically impossible. At first (15) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (16) your comprehension will improve. Many people have found (17) reading skill drastically improved after some training. (18) Charlie Au, a business manager, for instance. His reading rate was a reasonably good 172words a minute (19) the training; now it is an excellent 1,378 words a minute. He is delighted that how he can (20) a lot more reading material in a short period of time.

第(9)空应选择()

A.what

B.which

C.that

D.if