人体奥妙之细胞的暗战（2012）

And at its heart, it carries a tiny string of DNA,
它的终极武器
its ultimate weapon.
这是进化和设计的杰作
It’s a masterpiece of evolution and design.
科学家直到现在还未确定
And yet scientists still can’t decide
它是否是生物
if it’s actually alive or dead.
对于大型动物 例如我们人类
At the level of large animals like ourselves,
生物和非生物的区别
the difference between living things and non-living things
十分明显
is very obvious.
而对于更小的物体 如细胞
Come down a level, though, to cells,
界限开始变得模糊
and it becomes a bit more ambiguous.
我们仍可以立即判断出人体自身细胞
For our own cells, of course, you can still tell immediately
是否活着
that they are alive.
但更进一步 到了病毒的层面
Come down another level, though, to the virus,
就不好说了 它看上去不像活的
and it’s no longer obviously alive. They don’t look alive.
然而它们的行为又像有生命力
Yet they behave perhaps as if they are.
它们的行为很有目的性
They behave with a sense of purpose.
严格来说 病毒并非活着的
A virus isn’t strictly alive,
它无法自食其力地繁殖
it can’t make more of itself on its own.
而只能靠
It only can replicate
劫持细胞部件进行自我复♥制♥
if it uses parts that it hijacks from a cell.
然而细胞仍然拥有强大的防御系统
But the cell still has a formidable array of defences
来阻止这群杀戮机器
to keep these killing machines at bay.
细胞接收到的所有物质
Every delivery that the cell receives
都会被送到一个叫核内体的分拣站
is taken to a sorting station, called an endosome.
核内体对传入物质进行加工
Endosomes process incoming supplies
并决定将它们运往细胞的哪个部位
and decide where inside the cell they will be delivered.
此过程的第一步就是将它们分解
The first step of the process is to break them down.
病毒大军即将被侵蚀
The virus army is about to be digested.
分拣站内壁
The walls of the sorting stations
配有专用的蛋白质泵
are fitted with specialised protein pumps.
泵吸入特殊原子
The pumps draw in special atoms,
使核内体的内部呈酸性
turning the inside of the endosome into an acid bath.
酸将大分子营养物分解为小分子
The acid breaks down large nutrients into smaller molecules
从而便于细胞对其的运输和利用
that are easier for the cell to transport and use.
当酸侵蚀掉病毒的衣壳
And as the acid eats away at the virus’s outer shell,
病毒开始被分解
it begins to break apart.
这本应是腺病毒的末日
This should spell disaster for the adenovirus.
但是 酸正是病毒逃离计划的一部分
But the acid is part of its escape plan.
病毒纤维首先被分解开
The virus fibres are the first to break away.
但它们的瓦解释放出一种隐藏于内部
But their disintegration releases a special protein
的特殊蛋白质
hidden inside the virus
会将自己粘附于分拣站内壁
that targets the wall of the sorting station,
将壁膜撕开 释放病毒
tearing the membrane apart and setting the virus free.
但并不是所有病毒都能逃脱
But not every virus escapes.
许多病毒依然被抗体紧紧粘附
Many still carry antibodies locked to their surface.
其最初作用是提醒免疫系统入侵者来袭
Their primary job was to alert the immune system to intruders,
而现在却确保病毒衣壳无法分解
but their firm grip now ties the shell together.
使纤维无法脱离
The fibres cannot break free,
因此逃离蛋白质也就无法释放
and the escape protein stays trapped inside the shell.
无数病毒在逃离前被酸侵蚀
Countless viruses are eaten away before they can escape.
但仍有足够病毒被释放
But enough are released.
如今已没有任何防线阻挡这些病毒
Now there is nothing between these viruses
攻入它们的最终目的地 细胞核
and the nucleus of the cell – their ultimate goal.
虽然病毒离目标只有五微米
Yet although they are just five micrometres from their target
但是距成功还有十万八千里
most might as well be a million miles away.
对于九♥成♥的病毒而言 入侵到此为止
For 90% of the army, the invasion will end here,
它们将无助地在细胞内游荡
floating helplessly beneath the surface.
虽然它们身处
Although they are surrounded
细胞内部繁忙活动的范围里
by the constant bustle of cellular activity,
这些无自动力的入侵者无法自行移♥动♥
the inert invaders have no way of moving themselves.
它们也无法利用
And they have no way of utilising the energy generated
细胞内游动的发电厂 线粒体
by the cells’ floating power stations,
所产生的能量
the mitochondria.
在每个线粒体中
Inside each mitochondrion,
我们摄入的食物和吸入的空气
the food we eat and the air we breathe
推动了上千的涡轮
drives thousands of turbines
为数十亿个小电池充电
that continually recharge billions of tiny batteries.
更非同寻常的是
But what is even more extraordinary
科学家们认为
is that scientists believe that
线粒体曾经就是个单细胞
mitochondria were once simple cells themselves.
然后被另一个细胞吞噬
Then one was swallowed by another cell,
引发了进化史上最伟大的飞跃
firing one of the greatest leaps in evolution –
复杂生命的出现
complex life.
想要复杂生命 就必须有依据DNA指令
To be complex at all, you must have all this machinery,
造出的所有蛋白质装置
all these proteins encoded by genes.
而想让它们正常工作
And to support all of that
就需要大量的能量
requires a tremendous amount of energy.
所有复杂生物都共同拥有一位原始祖先
All complex life share a single common ancestor,
而它在生命出现在地球起的这四十亿年中
and that ancestor arose just once in four billion years
仅出现了一次
of life on Earth.
在头二十至三十亿年间
For two to three billion years,
细菌是唯一的生物
it was bacteria and nothing else,
直到这个复杂细胞的出现
and then this complex cell arose.
一个单细胞进入了另一个单细胞
One simple cell got inside another simple cell,
这种事件本身极为罕见
it’s a very rare event in itself.
于此时起
And once this happened,
它改变了生物获得能源的途径
it transforms the energetic possibilities of life.
没有那能源 绝不可能进化出
Without that energy, evolution could never have produced
我们现在所看到的多样化生物
the astonishing diversity of life that we see around us.
没有那能源 就不会出现动植物
Without that energy, we wouldn’t see plants and animals,
或是人类自己
we wouldn’t see ourselves.
世界将会是一片不毛之地
The world would be an almost sterile desert.
每个细胞内都有
Throughout each cell,
数以百计的线粒体
hundreds of mitochondria feed energy to
为维持人类这种复杂生物的
power the network of protein that
蛋白质网络提供能量
make us the complex creatures that we are.
病毒已进化成为高效性的典范
The virus has evolved into a model of efficiency.
但其简单的结构使它一旦脱离复杂生物
But the simplicity of its design makes it useless
便一无是处
without the machinery of complex life.
细胞膜之下 大量的马达蛋白
But just beneath the surface, large numbers of motor proteins,
即分子搬运工
molecular haulage workers,
正等着运输核内体加工好的营养物
await nutrients processed for delivery by the endosomes.
在这场历时数亿年的军备竞赛中
And in this billion-year arms race,
病毒已进化出能依附于
the virus has evolved the precise mechanism
马达蛋白的精确结构
to attach to the cell’s motor proteins.
现在它可以利用线粒体产生的能量了
Now it can use the energy of the mitochondria.
病毒向细胞核迈进
The virus is on its way.
它劫持了细胞自身的运输系统
It has hijacked the cell’s own transport system,
被带往细胞核 以及它的终极目标
and is being carried towards the nucleus and its ultimate prize,
劫持复♥制♥DNA所需的机械从而控制细胞
the DNA machines it needs to take control of the cell.
这双微小的机动腿
These microscopic motorised legs
是自然界的奇迹
are a wonder of the natural world.
将其正常速度放慢三十倍
Slowed down to one-thirtieth of their normal speed,
它们的运动就会清晰可见
their movement is clearly visible.
但若以每秒超过一百步的实速播放
But at their actual speed, over 100 steps a second,
它们只会是模糊一闪
they would appear a blur.
不过只有速度还不够
But speed isn’t everything.
细胞内结构密集
Cells are densely packed,
运输轨道充满障碍物
and their internal highways are littered with obstacles.
这些马达蛋白只能单向移♥动♥
And these motor proteins can only move in one direction.
这个病毒看似已无去路
For this virus, it seems to be the end of the road.
但最近 科学家们发现
But scientists have recently discovered
病毒会锁定另一个马达蛋白
the virus locks on to a second motor protein.
而这个蛋白专门朝反方向移♥动♥
And this one is built to move in the opposite direction.
两个马达蛋白齐心协力
Together, the two motor proteins can navigate
几乎可以跨越任何障碍物
around almost any obstacles.
侵略者再次获益
And once again, the invader benefits.
病毒再次向目标迈进
The virus is on the move again.
身后带领了一个数以百计的军队
And it leads an army of hundreds.
首个腺病毒袭击细胞
It’s been almost an hour
已过去将近一个小时了