elephants and Escherichia Coli,

大象和大腸桿菌，

man and mushroom. All so different in form and function,

人和蘑菇。 全部都具有不同外型和功能，

but amazingly the same in how their form and function are determined.

但卻神奇地藉由 相同方法決定外型與功能。

First, all these organisms are made of one or more cells,

首先，這些生物都 具有一個以上的細胞，

and every cell of every living thing on earth

而地球上每個生物的每一個細胞

contains all the information it takes

都帶有能讓自己創造、複製

to create and duplicate and make variations of itself.

和改變外型的訊息。

That information is stored in a very long but quite simple

這些訊息存在 一條很長卻很簡單的雙分子，

double molecule called DNA,

稱為 DNA，

or Deoxyribonucleic Acid.

或去氧核糖核酸。

And the DNA of every living organism is made of chains of four smaller molecules

不同生物的 DNA 皆是由四種小分子組成

called nucleotides. What dictates the difference between a man and a mushroom

它們被稱為核苷酸。 而就是 DNA 上不同的核苷酸組成

is the sequence of these nucleotides in the long DNA chain.

決定了人與蘑菇的不同。

The four differing nucleotide parts, called bases,

四個核苷酸不同之處稱為鹼基，

are made of a few carbon, oxygen, hydrogen, nitrogen and phosphorus atoms,

它們由幾個碳、氧、氫、氮和磷原子組成，

and the molecules look like this.

完整分子長得像這樣。 （譯注：這是兩個配成對的核苷酸）

And each of these four bases is attached to an identical backbone molecule,

而這四種鹼基都接在相同的分子上，

a sugar called deoxyribose - the "D" in DNA - and a phosphate group.

這被稱為去氧核糖， 也是 DNA 中 D 所代表的糖和磷酸根。

Let's simplify these nucleotides and show them like this.

我們把核苷酸簡化成這種圖示。

So, a single sequence of nucleotides joined by their common sugars would look like this.

在同一股上的核苷酸以 同樣一種去氧核糖連結成長鏈。

And the DNA molecule where such sequences are stored looks like this.

而保存核苷酸序列資訊 的 DNA 分子則長成這樣。

But how does a simple molecule dictate the form and function of millions of different living things?

但單一分子如何決定 不同生物的形式與功能？

You can think of DNA as a great library of information,

你可以把 DNA 想成 儲存資訊的大圖書館，

information that is used to do one thing and one thing only:

每條資訊都只和一件事相關：

direct the building of different protein molecules.

那就是製造特定的蛋白質分子。

And it's the proteins that build the cells and keep them functioning

蛋白質可以建構細胞 並讓細胞執行功能、改變與增生。

and changing and reproducing. Here's where the familiar word 'gene' comes in.

這就是「基因」這個熟悉名詞的來源。

If your DNA is a library of information, a gene is a book in that library.

如果 DNA 是圖書館，基因就是裡面的書。

A gene is a segment of the DNA molecule.

基因就是一小片段的 DNA。

Let's say your body needs a particular protein, like insulin.

假設你的身體需要胰島素這種蛋白質。

To get it, some of your cells send a protein signal through the bloodstream

為此，部份細胞會將蛋白質訊號釋放到血液

to the cells in your pancreas, where insulin is made.

藉此傳達到胰臟細胞， 也就是負責製造胰島素的地方。

That signal protein tells other proteins in the cell's nuclei

這個訊號蛋白質會 告訴細胞核內的其他蛋白質

to open up a part of the DNA double helix, the insulin gene,

打開 DNA 上胰島素基因的雙股螺旋

and start making insulin proteins.

並開始合成胰島素蛋白質。

As soon as enough insulin has been produced,

當足夠的胰島素製造完成，

another signal protein comes to the pancreas' cells that tells them to stop making insulin.

另一個訊號蛋白質會 告訴胰臟細胞停止製造。

It's like looking up a book in the DNA library about insulin,

這就在 DNA 圖書館裡 像看一本關於胰島素的書，

and then putting it back when you're done.

看完之後在放回去。

There are genes in DNA for visible and invisible things that make up your body,

你身體可見與不可見的部份 都由基因決定，

like genes for eye color, protein pigments, for skin color,

像是眼睛的顏色及色素蛋白、 膚色、髪色、

for hair color, for stopping and starting bone growth,

何時開始或停止骨頭生長，

for your blood type, for how many fingers or arms and legs you have,

血型，以及手指、手和腳的數目，

for proteins that influence how long you live.

或是影響壽命的蛋白質。

Your DNA probably contains between 25 thousand and 40 thousand genes,

你的 DNA 大約包含 2.5 到 4 萬個基因，

while the DNA of a worm or a plant or a fruit fly

而蠕蟲、植物或是果蠅的 DNA

contains about 12 thousand to 20 thousand genes.

大約包含 1.2 到 2 萬個基因。

Some of those genes have quite different sequences of nucleotides than yours,

它們有些基因中的序列和你截然不同，

and some are similar to yours.

有些卻很相似。

Though it happens infrequently,

雖然不太常發生，

our own nucleotide sequences can change

但我們自身的核苷酸序列，

as the result of spontaneous or environmental damage

常會因為自發性 或環境的傷害

which might remove or shift a nucleotide position.

造成缺失或順序轉換。

This changes the gene involved, and can then change the protein.

這些基因上的改變會影響到蛋白質。

Most of these changes, called mutations,

大部份這些被稱作「突變」的變異，

have very little effect on the organism or its descendants.

對個體及其後代沒有太大影響。

some are mildly damaging,

有些則會造成傷害，

and a few can make the organism better-suited to its environment.

而又有些可以讓個體更適應所在環境。

It is these tiny changes in DNA gene sequences, happening over millions of years,

而就是數百萬年來 累積在 DNA 序列上的變異，

that create the differences among living organisms, from geckos to grasshoppers.

造成了不同種的生物 ──從壁虎到蚱蜢，

worms to watermelons, elephants to Escherichia Coli, and man to mushroom.

蠕蟲到西瓜，大象到大腸桿菌，以及人到蘑菇。