Biotechnology and genetic modification
IGCSE Biology Topic 21 7:59 English narration · English + 中文 subtitles burned in
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Steel tanks, warm and gently stirred.
一排排钢罐，温热，被缓缓搅拌。
Inside tanks like these, billions of living microbes are working for us — making penicillin, a protein food called mycoprotein, and the insulin that keeps millions of people alive.
在这样的罐子里，几十亿个活的微生物在为我们工作—— 生产青霉素、一种叫真菌蛋白的蛋白质食物，还有让数百万人活下去的胰岛素。
And here is the other half of the story: D N A itself, cut into pieces, sorted by size, and seen as glowing bands.
而这是故事的另一半：DNA本身被剪成片段，按大小分开，显示成一条条发亮的带。
Living things, and their genes, put to work — that is biotechnology.
让生物和它们的基因为我们工作——这就是生物技术。
Millions of people with diabetes need insulin every single day.
全世界有数百万糖尿病人每天都需要胰岛素。
For a long time the only supply came from the pancreas of pigs and cattle.
很长一段时间里，唯一的来源是猪和牛的胰腺。
It was slow to collect, expensive, and never quite human.
提取很慢，很贵，而且并不完全是人的胰岛素。
Today the same medicine is grown in a tank.
今天，同样的药物是在罐子里培养出来的。
Give a bacterium one human gene, and it makes real human insulin.
给细菌一个人类基因，它就能制造真正的人胰岛素。
Start with the organism itself.
先从生物本身开始。
A bacterium is one small cell with no nucleus.
细菌是一个小小的细胞，没有细胞核。
Its main D N A is a single circle, floating free.
它的主要DNA是一个单独的环，自由地漂着。
Now look at the two green rings. Those are plasmids — tiny extra loops of D N A.
现在看这两个绿色的环， 它们就是质粒——额外的小小DNA环。
A plasmid can be taken out, cut open, and put back.
质粒可以取出来、剪开，再放回去。
Remember that ring.
记住这个环。
So why bacteria?
那么为什么用细菌？
Four reasons, and the exam asks for them directly.
有四个理由，考试会直接考。
First, they have a high rate of reproduction — one cell becomes millions overnight.
第一，它们繁殖非常快—— 一个细胞一夜之间变成几百万个。
Second, they make complex molecules, including human proteins.
第二，它们能制造复杂的分子，包括人的蛋白质。
Two more for the supplement paper.
补充部分还有两点。
Third, there are few ethical concerns.
第三，几乎没有伦理上的顾虑。
And fourth, they contain plasmids, which are easy to cut and move.
第四，它们含有质粒，很容易剪开和搬动。
Now yeast — a fungus, and the oldest tool in biotechnology.
再看酵母——一种真菌，也是生物技术中最古老的工具。
With no oxygen, yeast carries out anaerobic respiration: it breaks glucose down into ethanol and carbon dioxide.
在没有氧气时， 酵母进行无氧呼吸：把葡萄糖分解成乙醇和二氧化碳。
Follow the top path. The ethanol is burned as a biofuel. Follow the lower path.
看上面那条路径， 乙醇被当作生物燃料燃烧。
In bread making, the carbon dioxide makes bubbles that are trapped in the dough, so the bread rises.
看下面那条路径，做面包时二氧化碳形成气泡， 被困在面团里，面包就发起来了。
Sometimes we do not need the whole living cell — the enzyme alone is enough.
有时候我们并不需要整个活细胞，单独用酶就够了。
Pectinase breaks down plant cell walls, so the fruit gives more juice, and clearer juice.
果胶酶分解植物细胞壁， 于是水果出汁更多，果汁也更澄清。
Biological washing powders contain proteases and lipases; they digest protein and fat stains at a lower temperature, which saves energy.
生物洗衣粉里含有蛋白酶和脂肪酶， 它们在较低的温度下就能消化蛋白质和油脂污渍，这样能节省能源。
For the supplement paper, lactase breaks lactose down, giving lactose-free milk.
补充部分：乳糖酶把乳糖分解掉，做出无乳糖牛奶。
To grow microbes on a large scale you need a fermenter: a big tank for growing bacteria or fungi to make a useful product.
要大规模培养微生物，就需要发酵罐：一个用来培养细菌或真菌、 制造有用产物的大罐子。
Three products to remember. Insulin, the hormone. Penicillin, an antibiotic from a fungus.
要记住三种产物：胰岛素，一种激素； 青霉素，一种由真菌产生的抗生素；还有真菌蛋白，一种蛋白质食物。
And mycoprotein, a protein food. Look at the fittings: a water jacket, a stirrer, air bubbling in, a p H probe, nutrients in, and waste out.
看看罐子上的装置：水套、搅拌轴、通入的空气、一个pH探头， 营养物质进入，废物排出。
Five conditions, and each needs its reason.
有五个条件，每一个都要说出理由。
Temperature is held at the best value by the water jacket: too hot and the enzymes are denatured, too cold and growth is slow.
温度由水套保持在最合适的数值： 太热酶会变性，太冷生长又太慢。
The p H is kept steady, because enzymes only work in a narrow range.
pH要保持稳定，因为酶只在很窄的范围内才好用。
Oxygen is bubbled through so the microbes respire aerobically.
氧气被通入，好让微生物进行有氧呼吸。
Nutrients are fed in, because they need food to grow.
营养物质不断加入， 因为它们需要食物才能生长。
And waste products are removed, because they are toxic.
废物要排出，因为它们有毒。
Before we move a gene, be clear what one is.
在搬动一个基因之前，先弄清楚基因是什么。
Inside a nucleus are chromosomes.
细胞核里有染色体。
A chromosome is a long molecule of D N A.
一条染色体是一个很长的DNA分子。
And a gene is simply a length of that D N A — the short yellow section here.
而基因就是这段DNA上的一小段—— 这里黄色的那一小节。
One gene carries the instructions for one protein.
一个基因携带制造一种蛋白质的指令。
Genetic modification means changing the genetic material of an organism by removing, changing or inserting individual genes.
基因改造是指通过去除、改变或插入个别基因，来改变一个生物的遗传物质。
Those three words — removing, changing, inserting — are the definition, so learn them.
去除、改变、插入——这三个词就是定义本身，一定要背下来。
And notice what it does not say. You do not build a new organism.
也要注意它没有说什么：你并不是造出一个全新的生物。
You move one gene, and everything else stays as it was.
你只是搬动一个基因，其余一切都保持原样。
Now the method, and it starts with cutting.
现在讲方法，第一步是剪。
The insulin gene is cut out of a human chromosome using restriction enzymes.
用限制酶把胰岛素基因从人的染色体上剪下来。
These enzymes do not cut straight across. They leave a short single strand hanging at each end, and these are called sticky ends.
这些酶并不是齐齐地剪断，它们在两端各留下一小段单链，这就叫做黏性末端。
Then the plasmid is cut open with the same restriction enzyme, so its sticky ends match the gene.
接着，质粒要用同一种限制酶剪开，这样它的黏性末端才能和基因配上。
That one word, same, is worth a mark.
“同一种”这三个字就是一个得分点。
Here is the rest of the route in one picture.
这一张图就是流程的其余部分。
On the left, the human gene in yellow, and the plasmid cut open with restriction enzymes.
左边是黄色的人类基因， 还有用限制酶剪开的质粒。
In the middle, D N A ligase joins the gene into the plasmid.
中间，DNA连接酶把基因接进质粒里。
Ligase is the glue — it never cuts, it only seals.
连接酶就是胶水——它从不剪切，只负责封口。
The plasmid now carries a human gene, so we call it a recombinant plasmid.
现在质粒带上了一个人类基因， 我们就叫它重组质粒。
On the right, it goes into a bacterium, which multiplies and expresses the gene, making human insulin.
右边，它进入细菌，细菌不断繁殖并表达这个基因， 制造出人胰岛素。
A real exam question, and it comes up almost every year.
一道真题，几乎每年都会考。
Four steps in making human insulin, in the wrong order.
制造人胰岛素的四个步骤被打乱了顺序。
Insulin is removed from the culture.
从培养液中取出胰岛素。
An enzyme cuts the insulin gene from a chromosome.
用一种酶把胰岛素基因从染色体上剪下来。
The gene is put into the plasmid.
把这个基因放进质粒里。
Bacteria carrying the gene reproduce fast.
带有这个基因的细菌快速繁殖。
Pause and try it.
先暂停，自己试一试。
For each step, ask what must exist before it.
对每一步都问一句：在它之前必须先有什么？
Cutting the gene out must be first: with no gene, nothing can be inserted.
剪下基因一定是第一步： 没有基因就没有东西可以插进去。
Putting it into the plasmid comes next.
把它放进质粒是第二步。
Then the bacteria reproduce, because you need millions.
然后细菌繁殖，因为你需要几百万个。
And removing the insulin must be last — until they make it, it does not exist.
取出胰岛素一定是最后一步—— 细菌造出来之前，它根本不存在。
So the order is: cut, insert, multiply, collect.
所以顺序是：剪、插、增殖、收集。
On the longer paper the same idea is worth six marks, and here is a full-mark answer.
在长卷上，同样的内容值六分，这里就是一份满分答案。
Cut the insulin gene out with a restriction enzyme, leaving sticky ends.
用限制酶把胰岛素基因剪下来，留下黏性末端。
Cut a plasmid with the same enzyme, so the ends match.
用同一种酶剪开质粒，让末端能配上。
Join them with D N A ligase to make a recombinant plasmid.
用DNA连接酶把它们接起来，做成重组质粒。
Put it into a bacterium and grow them in a fermenter.
把它放进细菌，在发酵罐里培养。
And read the note: the insulin is identical to human insulin, so there are fewer allergic reactions.
再看那段说明：这种胰岛素和人的胰岛素完全相同，所以过敏反应更少。
What else do we modify?
我们还改造什么？
Learn these four.
记住这四个例子。
Human genes go into bacteria to make human proteins, such as insulin.
把人的基因放进细菌里， 让它们制造人的蛋白质，比如胰岛素。
Genes go into crops to give resistance to herbicides, so a farmer can spray weeds without killing the crop.
把基因放进作物里，使它们抗除草剂， 这样农民打除草剂时不会伤到作物。
Genes go into crops to resist insect pests, so less pesticide is needed.
把基因放进作物里，使它们抗虫害， 这样就少用农药。
And genes go into crops to improve their nutritional value — rice with more vitamin A.
把基因放进作物里，改善营养价值——比如含更多维生素A的水稻。
Now read the bottom line.
再读最下面那一行。
Modified crops can give higher yields and better nutrition, but people worry about health, about genes reaching wild species, and about the cost of the seed.
转基因作物能提高产量、改善营养， 但也有人担心健康，担心基因扩散到野生物种，还担心种子太贵。
Give both sides.
两面都要写。
Three marks students lose.
三个学生常丢的分。
First: the same restriction enzyme must cut both the gene and the plasmid — that is what makes the sticky ends match, and the examiner wants the word same.
第一：同一种限制酶必须同时剪基因和质粒—— 正是这一点让黏性末端能配上，评卷人要的就是“同一种”。
Second: restriction enzymes cut, ligase joins. Never write that ligase cuts.
第二：限制酶负责剪，连接酶负责连，千万别写成连接酶剪切。
Third: for a fermenter, name the condition and give the reason — temperature and p H for the enzymes, oxygen to respire, nutrients to grow, waste removed because it is toxic.
第三：说到发酵罐，要写出条件再写出理由——温度和pH是为了酶， 氧气是为了呼吸，营养是为了生长，废物要排出因为它有毒。
Four lines to take away.
四句话带走。
Bacteria: fast, complex molecules, plasmids.
细菌：繁殖快，能造复杂分子，带有质粒。
Yeast: ethanol for fuel, carbon dioxide for bread.
酵母：乙醇做燃料，二氧化碳让面包发起来。
Fermenters: insulin and penicillin, with the conditions controlled.
发酵罐：生产胰岛素和青霉素，条件受到控制。
And genetic modification: cut with restriction enzymes, join with ligase.
基因改造：用限制酶剪，用连接酶连。