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扭曲的DNA

The twisting tale of DNA - Judith Hauck

壁虎和草蜢 蠕虫和西瓜
Geckos and grasshoppers, worms and watermelons,
大象和大肠杆菌
elephants and Escherichia Coli,
人和蘑菇 在形式和功能上完全不同
man and mushroom. All so different in form and function,
但是令人惊讶的是决定他们的组成和功能的因素却是相同的!
but amazingly the same in how their form and function are determined.
首先 所有的这些有机体都是由单个或多个细胞组成的!
First, all these organisms are made of one or more cells,
而且地球上任何生物的任何细胞
and every cell of every living thing on earth
都包含它所携带的所有信息!
contains all the information it takes
使其能制造并复制组成其身体的各个组成部分!
to create and duplicate and make variations of itself.
这些信息都储存在一条非常长但很简单
That information is stored in a very long but quite simple
被称为DNA的双分子链上
double molecule called DNA,
或称为脱氧核糖核酸
or Deoxyribonucleic Acid.
每个生命体的DNA都是由四个被称为核苷酸的小分子组成的链
And the DNA of every living organism is made of chains of four smaller molecules
人和蘑菇之间的差异是由
called nucleotides. What dictates the difference between a man and a mushroom
长长的DNA链条中核苷酸的序列所决定的
is the sequence of these nucleotides in the long DNA chain.
四种不同的核苷酸片段 被称为碱基
The four differing nucleotide parts, called bases,
它们由少量的碳 氧 氢 氮和磷原子构成
are made of a few carbon, oxygen, hydrogen, nitrogen and phosphorus atoms,
它的分子结构看上去是这样的
and the molecules look like this.
这四种碱基中的每一个都被连接到同一个糖类分子上
And each of these four bases is attached to an identical backbone molecule,
这种分子被称为脱氧核糖-这就是DNA里的D-还有一个磷酸基团
a sugar called deoxyribose – the ‘D’ in DNA – and a phosphate group.
我们来简化一下这些核苷酸 这样来表示
Let’s simplify these nucleotides and show them like this.
于是 由共同的五碳糖分子所串连起来的核苷酸单链看起来就像这样
So, a single sequence of nucleotides joined by their common sugars would look like this.
两条这样的单链互相结合 就形成了DNA分子 就像这样
And the DNA molecule where such sequences are stored looks like this.
但是 这样一个简单的分子 是如何来决定成千上万种不同生物的性状的呢
But how does a simple molecule dictate the form and function of millions of different living things?
你可以把DNA想象成一个储存着庞大信息的图书馆
You can think of DNA as a great library of information,
这个图书馆里储存的信息只有一个用途
information that is used to do one thing and one thing only:
那就是控制不同蛋白质分子的合成
direct the building of different protein molecules.
正是这些蛋白质构成了细胞 并且维持了它们的正常运作 变化和增殖
And it’s the proteins that build the cells and keep them functioning
这时大家喜闻乐见的词“基因”就闪亮登场了
and changing and reproducing. Here’s where the familiar word ‘gene’ comes in.
如果你的DNA是一座储存着信息的图书馆 那么基因就是其中的一本本书
If your DNA is a library of information, a gene is a book in that library.
基因是DNA分子中的一个个小片段
A gene is a segment of the DNA molecule.
打个比方 假如你的身体需要一种蛋白质 比如胰岛素
Let’s say your body needs a particular protein, like insulin.
为了得到它 你身体里的某一些细胞会发出信号蛋白质分子
To get it, some of your cells send a protein signal through the bloodstream
它们在血液里穿梭 直到抵达分泌胰岛素的胰腺
to the cells in your pancreas, where insulin is made.
信号蛋白指示胰腺细胞核里的其他蛋白质
That signal protein tells other proteins in the cell’s nuclei
去打开DNA中控制胰岛素合成的那一部分双链 也就是控制胰岛素合成的基因
to open up a part of the DNA double helix, the insulin gene,
然后开始合成胰岛素
and start making insulin proteins.
一旦合成了足够多的胰岛素
As soon as enough insulin has been produced,
另外一个信号蛋白分子就会指示胰腺细胞停止合成
another signal protein comes to the pancreas’ cells that tells them to stop making insulin.
就像去DNA图书馆查阅关于胰岛素的书
It’s like looking up a book in the DNA library about insulin,
看完了就把它合上放回去
and then putting it back when you’re done.
你身体的那些性状 无论是看得见的还是看不见的 在DNA中都有其对应的基因
There are genes in DNA for visible and invisible things that make up your body,
有控制眼睛颜色的 色素蛋白 还有控制肤色的
like genes for eye color, protein pigments, for skin color,
控制发色的 控制骨骼发育的
for hair color, for stopping and starting bone growth,
控制血型的 控制你长多少根手指、多少只胳膊和腿的
for your blood type, for how many fingers or arms and legs you have,
还有控制合成那些决定你寿命的蛋白质的
for proteins that influence how long you live.
通常你的DNA中大概有25000到40000个基因
Your DNA probably contains between 25 thousand and 40 thousand genes,
而在一条蠕虫 或是一株植物 甚至是一只果蝇的DNA中
while the DNA of a worm or a plant or a fruit fly
通常只有12000到20000个基因
contains about 12 thousand to 20 thousand genes.
这些基因中有一些和你的核苷酸序列大相径庭
Some of those genes have quite different sequences of nucleotides than yours,
而有一些又和你的大同小异
and some are similar to yours.
尽管这样的情况不常见
Though it happens infrequently,
我们自身的核苷酸序列可能会在环境遭到破坏时
our own nucleotide sequences can change
或者是自发地发生改变
as the result of spontaneous or environmental damage
这些改变会导致核苷酸的缺失和移位
which might remove or shift a nucleotide position.
从而会改变它们关联的基因 以及这些基因所控制合成的蛋白质
This changes the gene involved, and can then change the protein.
这些改变 被称为突变
Most of these changes, called mutations,
大部分的突变实际上对生物的机体或后代没有多大的影响
have very little effect on the organism or its descendants.
有一些会造成轻微的损伤
some are mildly damaging,
有一些甚至会使机体更加适应环境
and a few can make the organism better-suited to its environment.
千百年来 正是这些发生在DNA中的微小变化
It is these tiny changes in DNA gene sequences, happening over millions of years,
才创造了纷繁多姿的生命世界——从壁虎到草蜢 从蠕虫到西瓜 从大象到大肠杆菌 从人类到蘑菇
that create the differences among living organisms, from geckos to grasshoppers.worms to watermelons, elephants to Escherichia Coli, and man to mushroom.

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