万物简史 第593期:生命的物质(19)

The shape of a DNA¹ molecule², as everyone knows, is rather like a spiral staircase or twisted rope ladder: the famous double helix. The uprights of this structure are made of a type of sugar called deoxyribose, and the whole of the helix is a nucleic acid — hence the name "deoxyribonucleic acid." The rungs (or steps) are formed by two bases joining across the space between, and they can combine in only two ways: guanine is always paired with cytosine and thiamine always with adenine. The order in which these letters appear as you move up or down the ladder constitutes the DNA code; logging it has been the job of the Human Genome Project.

正如人人所知道的那样，DNA分子的形状像一个螺旋状楼梯或扭曲的绳梯：著名的双螺旋结构。这种结构的支柱是一种被称为脱氧核糖的糖组成的，整个双螺旋是一个核酸——因此取名为“脱氧核糖核酸”。横档（或梯级）由两个碱基跨越中间的空间相连而成。它们只以两种方式配对，腺嘌呤总是与胸腺嘧啶配对，鸟嘌呤总是与胞嘧啶配对。当你在梯子上上下下走动时，这些字母所排列的顺序就组成了DNA的密码；记录这些密码一直是“人类基因组工程”所要做的工作。

Now the particular brilliance³ of DNA lies in its manner of replication. When it is time to produce a new DNA molecule, the two strands⁵ part down the middle, like the zipper⁶ on a jacket, and each half goes off to form a new partnership⁷. Because each nucleotide along a strand⁴ pairs up with a specific other nucleotide, each strand serves as a template for the creation of a new matching strand. If you possessed⁸ just one strand of your own DNA, you could easily enough reconstruct the matching side by working out the necessary partnerships⁹: if the topmost rung on one strand was made of guanine, then you would know that the topmost rung on the matching strand must be cytosine. Work your way down the ladder through all the nucleotide pairings, and eventually you would have the code for a new molecule. That is just what happens in nature, except that nature does it really quickly — in only a matter of seconds, which is quite a feat¹⁰.

且说DNA的绝妙之处在于它的复制方式。当需要产生一个新的DNA分子时，两条单链从中间裂开，就像夹克上的拉链一样，每条单链的一半脱离而去，形成新的组合。由于一条单链上的每一个核苷酸与另一个特定的核苷酸匹配在一起，每条单链成为创造一条与之匹配的新链的模板。如果你只有你自己DNA的一条单链，通过必要的组合，你就很容易重建另一条与之匹配的单链。如果一条单链的第一级是由鸟嘌呤构成的，你就会知道与之配对的另一条单链的第一级一定是胞嘧啶。要是你沿着所有核苷酸配对组成的阶梯往下走，最后你将获得一个新的分子的密码。这就是大自然中所发生的事，只不过这一切是以极快的速度，完成的——仅仅几秒钟时间，快得令人不可思议。

1 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

2 molecule   

n.分子，克分子

参考例句：

• A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈̬f婘̬ 妈̬成的。
• This gives us the structural formula of the molecule.这种方式给出了分子的结构式。

3 brilliance   

n.光辉，辉煌，壮丽，（卓越的）才华，才智

参考例句：

• I was totally amazed by the brilliance of her paintings.她的绘画才能令我惊歎不已。
• The gorgeous costume added to the brilliance of the dance.华丽的服装使舞蹈更加光彩夺目。

4 strand   

vt.使（船）搁浅，使（某人）困于（某地）

参考例句：

• She tucked a loose strand of hair behind her ears.她把一缕散发夹到了耳后。
• The climbers had been stranded by a storm.登山者被暴风雨困住了。

5 strands   

n.（线、绳、金属线、毛发等的）股( strand的名词复数 )；缕；海洋、湖或河的)岸；（观点、计划、故事等的）部份v.使滞留，使搁浅( strand的第三人称单数 )

参考例句：

• Twist a length of rope from strands of hemp. 用几股麻搓成了一段绳子。 来自《简明英汉词典》
• She laced strands into a braid. 她把几股线编织成一根穗带。 来自《简明英汉词典》

6 zipper   

n.拉链；v.拉上拉链

参考例句：

• The zipper is red.这条拉链是红色的。
• The zipper is a wonderful invention.拉链是个了不起的发明。

7 partnership   

n.合作关系，伙伴关系

参考例句：

• The company has gone into partnership with Swiss Bank Corporation.这家公司已经和瑞士银行公司建立合作关系。
• Martin has taken him into general partnership in his company.马丁已让他成为公司的普通合伙人。

8 possessed   

adj.疯狂的；拥有的，占有的

参考例句：

• He flew out of the room like a man possessed.他像着了魔似地猛然冲出房门。
• He behaved like someone possessed.他行为举止像是魔怔了。

9 partnerships   

n.伙伴关系( partnership的名词复数 )；合伙人身份；合作关系

参考例句：

• Partnerships suffer another major disadvantage: decision-making is shared. 合伙企业的另一主要缺点是决定要由大家来作。 来自英汉非文学 - 政府文件
• It involved selling off limited partnerships. 它涉及到售出有限的合伙权。 来自辞典例句

10 feat   

n.功绩；武艺，技艺；adj.灵巧的，漂亮的，合适的

参考例句：

• Man's first landing on the moon was a feat of great daring.人类首次登月是一个勇敢的壮举。
• He received a medal for his heroic feat.他因其英雄业绩而获得一枚勋章。