问题 选择题

下列说法错误的是(  )

A.分子式为C3H6Cl2的有机物有四种

B.医疗上用硫酸钡作“钡餐”,是由于硫酸钡难溶于水

C.用氢氟酸雕刻玻璃,是由于氢氟酸能与二氧化硅反应

D.相同物质的量的2-甲基丁烷和2,2-二甲基丙烷中共用电子对数目相同

答案

A.分子式为C3H6Cl2的有机物有CHCl2CH2CH3、CH2ClCHClCH3、CH3CCl2CH3、CH2ClCH2CH2Cl四种同分异构体,故A正确;

B.硫酸钡难溶于水,难溶于酸,不被X射线透过,如能溶于酸,则也不能用作钡餐,故B错误;

C.二氧化硅与氢氟酸反应生成四氟化硅,可用作雕刻,故C正确;

D.-甲基丁烷和2,2-二甲基丙烷互为同分异构体,分子中C-C、C-H数目相等,则等物质的量时共用电子对数目相同,故D正确.

故选B.

单项选择题
单项选择题

In a science-fiction movie called "Species", a mysterious signal from outer space turns out to describe the genome of an unknown organism. When the inevitable mad scientist synthesizes the DNA described by the instructions, the creature he breeds from it turns out to resemble Natasha Henstridge, an athletic actress. Unfortunately, the alien harbors within her delicate form the destructive powers of a Panzer division, and it all ends badly for the rash geneticist and his laboratory.

Glen Evans, chief executive of Egea Biosciences in San Diego, California, acknowledges regretfully that despite seeking his expert opinion--in return for which he was presented with the poster of the striking Mr Henstridge that hangs on his office wall--the producers of "Species" did not hew very closely to his suggestions about the feasibility of their script ideas. Still, they had come to the right man. Dr Evans believes that his firm will soon be able to create, if not an alien succubus, at least a tiny biological machine made of artificial proteins that could mimic the behavior of a living cell.

Making such proteins will require the ability to synthesize long stretches of DNA. Existing technology for synthesizing DNA can manage to make genes that encode a few dozen amino acids, but this is too short to produce any interesting proteins. Egea’s technology, by contrast, would allow biologists to manufacture genes wholesale. The firm’s scientists can make genes long enough to encode 6,000 amino acids. They aim to synthesize a gene for 30,000 amino acids within two years.

Using a library of the roughly 1,500 possible "motifs" or folds that a protein can adopt, Egea’s scientists employ computers to design new proteins that are likely to have desirable shapes and properties. To synthesize the DNA that encodes these proteins, Egea uses a machine it has dubbed the "genewriter". Dr Evans likens this device to a word-processor for DNA, on which you can type in the sequence of letters defining a piece of DNA and get that molecule out.

As Egea extends the length of DNA it can synthesize, Dr Evans envisages encoding not just proteins, but entire biochemical pathways, which are teams of proteins that conduct metabolic processes. A collection of such molecules could conceivably function as a miniature machine that would operate in the body and attack disease, just as the body’s own defensive cells do. Perhaps Dr Evans and his colleagues ought to get in touch with their friends in Hollywood.

Elen Evans’ technology of new protein design may prove useful()

A. in athletic training programs

B. in film making spectacles

C. in medical treatments

D. in software programming