Documentary, BBC - Our Secret Universe: The Hidden Life of the Cell
#OurSecretUniverse #Documentary #HiddenLifeoftheCell
#OurSecretUniverse #Documentary #HiddenLifeoftheCell
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00:00It takes 120 trillion cells to make a human.
00:07They are the fundamental units of life.
00:11Making up our brain, muscles, organs, every part of us.
00:21In the last decade, scientists have been able to witness what once seemed impossible.
00:26The world inside a human cell.
00:35When I was a student, the idea that we could burrow deep inside a living cell was unthinkable.
00:43Recent advances have made it so scientists can see inside cells like never before.
00:49We can see the parts of single cells and how they work together.
00:53The more we learn about the universe, the simpler it seems.
00:58But the cell isn't like that.
01:00The more we find out, the more complicated things get.
01:05But these beautiful worlds are also on the front line of the longest war in history.
01:10This is a battle that goes back into the depths of time.
01:14To a time when the earth was dominated by single cells and viruses.
01:19Every day, our cells confront these ancient virus enemies.
01:23Tiny, ruthless machines that kill to reproduce.
01:26There is this whole mechanism inside cells that are taking out viruses that previously we just didn't know was there.
01:32It is a four-billion-year-old struggle that has changed the course of our evolution.
01:39This battle of these viruses against yourselves, this amazing epic science fiction movie.
01:47It's going on inside your body all the time.
01:50And you don't even know it.
01:51Cells are the basic building blocks of living tissue.
02:19And the smallest units of what makes us human.
02:28And yet, beneath the surface of every one, lies a world stranger than any in science fiction.
02:38A world in which a billion microscopic machines all play their part.
02:48Working in concert through every second of our life.
02:51Every one of us is made of 120 trillion cells.
02:57And every one of those cells is different.
02:59But they contain the same instructions.
03:01Cells are a bit like babies.
03:03When they're born, they all look the same.
03:04But they change very quickly.
03:06In different countries, they learn to speak different languages.
03:09And our bodies like that.
03:10Some cells speak heart, and some cells speak liver.
03:14The workers of this incredible world are proteins.
03:21Chains of complex chemicals.
03:23That can lock together to transform into spectacular machines.
03:28Others work to create incredible structures.
03:33Like the internal skeleton that holds the cell together.
03:37These great trusses are constantly adjusting to stresses and strains.
03:42Building and rebuilding to give the cell its shape and strength.
03:47Then there are the motor proteins, haulage workers, that use the cell's skeleton as highways to deliver food, chemicals, and the essential building materials of life to wherever they are needed.
04:07They are just one of the astonishing micromachines that keep this bustling community healthy.
04:12Scientists are asked all the time, how do things in a cell know how to grow?
04:16How do things in a cell know how to get where they're supposed to go to do their job?
04:19And for sure, cells are very chaotic, and things are bumping into each other, and most of that's just random.
04:25But enough things get where they're supposed to go that the entire system works.
04:32And powering all this activity are the cell's power stations.
04:39Inside these free-floating structures called mitochondria, turbines spin at over a thousand times per minute.
04:46Recharging billions of tiny chemical batteries.
04:49Recharging billions of tiny chemical batteries.
05:01Everything we do, every heartbeat, every movement, every thought, is powered by the batteries charged by these cellular power stations.
05:12And everything in this world works to a master plan.
05:31And the plan is protected deep in the heart of every cell.
05:37The nucleus is the vault containing the instruction manual for life.
05:46DNA.
05:52DNA is a chain of chemicals organized into genes.
05:59Each gene holds the instructions to build a specific protein.
06:02The double helix contains over 20,000 instructions that tell our cells what to make and when.
06:11How to organize not just our cells, but our entire bodies.
06:17The double helix has become the icon of the 21st century.
06:24And it's pretty amazing stuff.
06:26There's six feet of DNA in every cell of the body.
06:29And if all those bits were set out in a straight line, they'd reach to the moon and back thousands of times.
06:34But this crucial chain of chemicals would be useless without an army of microscopic machines that endlessly travel its length, repairing it and transcribing it.
06:55Turning the DNA into instructions that the cell can understand.
07:04Once a gene has been copied, the instructions are carried outside the nucleus.
07:14Here, mobile factories read them and turn them into proteins.
07:24Up to two million different kinds.
07:32Each with its own specific shape and purpose.
07:36And little goes to waste in the cell.
07:48Used and faulty proteins are tagged for recycling.
07:55Then chewed apart by powerful roving shredders called proteasomes.
08:01Reducing them to tiny building blocks for new proteins.
08:04But each cell is also part of a wider neighborhood of cells.
08:12All continually communicating with each other.
08:15Fragments of shredded proteins are constantly transported to the surface.
08:23Here, they are presented for inspection.
08:29To be monitored by the guardians of our body's immune system.
08:32Our white blood cells.
08:33These roving soldiers check the protein fragments for signs of damage or infection.
08:48And for the moment, everything is in order.
08:49And for the moment, everything is in order.
08:51And for the moment, everything is in order.
08:55And for the moment, everything is in order.
08:56And for the moment, everything is in order.
09:02And there.
09:22Every single human cell contains this world of breathtaking complexity, organized by the
09:31nuclear machines at its heart, ceaselessly working from instructions written down in
09:37our DNA.
09:51Our cells are under constant attack, and this cell is about to face an ancient enemy.
10:00In an encounter that starts with an event so commonplace, you seldom even notice it.
10:14Every day our bodies are constantly bombarded by these invisible critters, bacteria and
10:19viruses, but we have our skin.
10:21It's our first line of defense that keeps them out.
10:24But we have Achilles' heels.
10:26We have openings to the outside world.
10:28Our mouths, our noses touch things.
10:30We rub our lips.
10:31We rub our eyes or wipe our nose.
10:34They can get in.
10:35And once they're in, they're in.
10:37Inhaled from a sneeze, an alien army is being carried into our body.
10:56A million invaders, hell-bent on destruction.
11:16This is one of our most common enemies.
11:19The adenovirus.
11:23It's a masterpiece of design.
11:28And each one has a single aim.
11:41To breach a cell's defenses and reach the nucleus.
11:49Once inside, any one of these viruses can take control of the cell.
11:56And reproduce 10,000 times over.
12:02The result could be anything.
12:04From the common cold, to pneumonia, even death.
12:15But our bodies are prepared.
12:29As the viruses approach the cell, they are met by a cloud of resistance.
12:38Antibodies, Y-shaped proteins that identify alien intruders.
12:44We patrol the space between our cells.
12:49Looking for viruses.
12:54Recognizing the invader, they lock to the viruses' armor plating.
12:59Shackling them together.
13:01Making the viruses easy meat for the white blood cells that feed on alien invaders like these.
13:07Antibodies and white blood cells form the front line of our immune system.
13:13The immune system is certainly amazing.
13:16And it actually evolved to see invading microbes and get rid of them.
13:20But that's just one part of your body's defenses.
13:23Our DNA encodes all these other features that help us to fight against virus at every single step.
13:30Despite the body's early immune response, hundreds of thousands of viruses make it through to our cell.
13:47But at the surface, they face their next obstacle.
13:54The cell's membrane, or skin.
14:11The surface of the cell is an amazingly complicated place.
14:16There are hundreds, maybe thousands, of receptor proteins sticking out of the cell.
14:21And they all have a unique function to play.
14:23Some of them would be just transporting information from outside the cell into the cell.
14:28Other receptors can bring whole cargoes in.
14:35The surface of each cell is a living barrier.
14:38Teeming with security proteins that constantly monitor molecules as they enter and leave.
14:43Small molecules like water and oxygen can simply seep through the membrane.
15:04Larger molecules like sugar are allowed entry through specialised pumps.
15:11But the largest deliveries require a special key before they are allowed into the cell.
15:19These protein keys are recognised by teams of mobile sentries that continually roam the surface.
15:29This sophisticated system is designed to keep harmful molecules out of the cell.
15:35But over billions of years of evolution, the adenovirus has evolved its very own key.
15:42Etched into the end of these projecting fibres.
15:51Antibodies still cling to some of these fibres, blocking many of the counterfeit keys.
15:56Antibodies, but not all.
15:59One by one, sentries all over the cell's surface are fooled.
16:10And the virus army quietly slips inside.
16:16In this ancient battle for the cell, it's round two to the virus.
16:26So, how far back does it go, this cat-and-mouse game, this battle between cells and viruses?
16:37Every indication suggests it goes right back to the origins of life on Earth.
16:42Wherever life started, very early on there was a divergence.
16:46Two different strategies that life followed.
16:48One of them was to become more complex, to become cells, to become ultimately organisms like ourselves.
16:54The other way was to remain simple, to become viruses, and to exploit those cells to their own ends, to replicate themselves.
17:02Beneath the surface, the cell prepares to receive the deadly invaders.
17:15Fooled into thinking that the virus is an important nutrient, special proteins slot together to form a spherical mould.
17:24They pinch out a bubble of cellular membrane, wrapping the virus inside.
17:35Finally, a separate protein pinches the bubble free, delivering the virus into the cell's interior.
17:46Unwittingly, the cell has just taken a large step towards its own downfall.
17:55Every single member of this invading virus army has the weaponry to ultimately destroy this cell.
18:12Its protein shell is a multi-layered cloak of deception, which is still more surprises in store.
18:19And at its heart, it carries a tiny string of DNA.
18:26Its ultimate weapon.
18:28It's a masterpiece of evolution and design.
18:31And yet scientists still can't decide if it's actually alive or dead.
18:38The level of large animals like ourselves, the difference between living things and non-living things is very obvious.
18:44Come down a level, though, to cells, and it becomes a bit more ambiguous.
18:49For our own cells, of course, you can still tell immediately that they're alive.
18:54Come down another level, though, to the virus, and it's no longer obviously alive.
18:59They don't look alive.
19:00Yet they behave perhaps as if they are.
19:03They behave with a sense of purpose.
19:06A virus isn't strictly alive.
19:10It can't make more of itself on its own.
19:13It only can replicate if it uses parts that it hijacks from a cell.
19:21But the cell still has a formidable array of defences to keep these killing machines at bay.
19:27Every delivery that the cell receives is taken to a sorting station called an endosome.
19:41Endosomes process incoming supplies and decide where inside the cell they will be delivered.
19:50The first step of the process is to break them down.
19:57The virus army is about to be digested.
20:03The walls of the sorting stations are fitted with specialised protein pumps.
20:12The pumps draw in special atoms, turning the inside of the endosome into an acid bath.
20:18The acid breaks down large nutrients into smaller molecules that are easier for the cell to transport and use.
20:36And as the acid eats away at the virus's outer shell, it begins to break apart.
20:41This should spell disaster for the adenovirus.
20:48But the acid is part of its escape plan.
20:53The virus fibres are the first to break away.
20:58But their disintegration releases a special protein hidden inside the virus that targets the wall of the sorting station.
21:14Tearing the membrane apart and setting the virus free.
21:19But not every virus escapes.
21:29Many still carry antibodies locked to their surface.
21:34Their primary job was to alert the immune system to intruders, but their firm grip now ties the shell together.
21:40The fibres cannot break free and the escape protein stays trapped inside the shell.
21:53Countless viruses are eaten away before they can escape.
21:56But enough are released.
22:07Now there is nothing between these viruses and the nucleus of the cell.
22:12Their ultimate goal.
22:16Yet although they are just five micrometres from their target,
22:19most might as well be a million miles away.
22:36For 90% of the army, the invasion will end here, floating helplessly beneath the surface.
22:43Although they are surrounded by the constant bustle of cellular activity, the inert invaders have no way of moving themselves.
23:04And they have no way of utilising the energy generated by the cells floating power stations.
23:10The mitochondria.
23:34Inside each mitochondrion, the food we eat and the air we breathe,
23:38drives thousands of turbines that continually recharge billions of tiny batteries.
23:45But what is even more extraordinary is that scientists believe that mitochondria were once simple cells themselves.
23:53Then one was swallowed by another cell, firing one of the greatest leaps in evolution.
24:00Complex life.
24:01To be complex at all, you must have all this machinery, all these proteins, encoded by genes, and to support all of that requires a tremendous amount of energy.
24:13All complex life share a single common ancestor, and that ancestor arose just once in four billion years of life on Earth.
24:22For two to three billion years, it was bacteria and nothing else, and then this complex cell arose.
24:29One simple cell got inside another simple cell.
24:32It's a very rare event in itself, and once it happened, it transforms the energetic possibilities of life.
24:37Without that energy, evolution could never have produced the astonishing diversity of life that we see around us.
24:46Without that energy, we wouldn't see plants and animals, we wouldn't see ourselves.
24:51The world would be an almost sterile desert.
24:54What is it?
25:08Throughout each cell, hundreds of mitochondria feed energy to power the network of proteins that make us the complex creatures that we are.
25:17The virus has evolved into a model of efficiency, but the simplicity of its design makes it useless without the machinery of complex life.
25:32But just beneath the surface, large numbers of motor proteins, molecular haulage workers, await nutrients processed for delivery by the endosomes.
25:46And in this billion-year arms race, the virus has evolved the precise mechanism to attach to the cell's motor proteins.
26:11Now, it can use the energy of the mitochondria.
26:27The virus is on its way.
26:33It has hijacked the cell's own transport system, and is being carried towards the nucleus, and its ultimate prize, the DNA machines it needs to take control of the cell.
26:50These microscopic motorized legs are a wonder of the natural world.
27:05Slowed down to 1 30th of their normal speed, their movement is clearly visible.
27:10But at their actual speed, over 100 steps a second, they would appear a blur.
27:15But speed isn't everything.
27:32Cells are densely packed, and their internal highways are littered with obstacles.
27:38And these motor proteins can only move in one direction.
27:45For this virus, it seems to be the end of the road.
28:08But scientists have recently discovered the virus locks on to a second motor protein.
28:22And this one is built to move in the opposite direction.
28:36Together, the two motor proteins can navigate around almost any obstacles.
28:57And once again, the invader benefits.
29:04The virus is on the move again.
29:25And it leads an army of hundreds.
29:33Plus red and yellow.
29:34Sold to be 970-1980.
29:35It's been almost an hour since the Adenovirus first attacked,
29:36so it's been taxed to be 100.
29:37To be less than 100.
29:38...
29:40It's been almost an hour since the Adenovirus first attacked…
29:41…
29:42…
29:54…
29:59…
30:02first attacked the cell the nucleus is just one more hour away until recently
30:12scientists thought that once the viral army was on the march nothing could stop
30:17it but then they found that the cell has its own internal immune system there is
30:25this whole mechanism inside cells that are taking out viruses that previously
30:30we just didn't know was there and I remember the day on which we published the paper about it
30:34I woke up to hear it being announced on the national radio and then went into a
30:39shop to pick up the newspapers to discover it was on the front page
31:00dotted along the cells highway system a special protein searches for anything carrying antibodies
31:25from the surface the clever thing about this protein is it uses systems that the cell already
31:31has in place once it's stuck to the antibody it sends signals to a cellular machine called the
31:37proteasome and the proteasome plays a role of recycling proteins in the cell so it gets brought
31:42along to the virus and it destroys the virus breaking down all its parts into tiny fragments
31:48once attached the defense protein initiates a chain reaction attracting specialized tagging proteins
31:56together they mark the virus for destruction
32:01then it's only a matter of time before the recyclers arrive
32:18they rip the virus to shreds
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33:01Somewhere inside your body, this battle is raging right now.
33:15The discovery of Trin21 provides potentially new ways of making therapeutics to fight viruses.
33:21And one way this could work is if we could find ways for encouraging the immune system to make more Trin21.
33:26So as soon as that virus enters into the cell, the Trin21 is ready to recognise the antibodies and destroy the virus.
33:43By working together, the defence proteins and recycling shredders can destroy an army of viruses in just a few hours.
33:56But it only takes a single virus to take control of an entire cell.
34:03Spreading infection throughout the body.
34:08With no antibodies attached, this virus has evaded the cell's shredders.
34:11But it only takes a single virus to take control of an entire cell.
34:15Spreading infection throughout the body.
34:20With no antibodies attached, this virus has evaded the cell's shredders.
34:27The virus has evaded the cell's shredders.
34:39Nothing now stands between it and its target.
34:43The virus is now just one thousandth of a millimetre from the nucleus.
35:01But if it is to achieve its ultimate goal, it first has to get inside.
35:14Compared to the cell, the virus is tiny.
35:16But really they're just different versions of the same machine.
35:19And its only job is to copy itself.
35:22But the virus needs to take advantage of our cell mechanism for its own selfish ends.
35:27At the heart of every cell lies the nucleus.
35:34And it is a world all of its own.
35:36Its surface is made of the same molecules as the cell membrane.
35:46But entry into this world is governed by completely different gateways.
35:52Across the surface, protein arms search for molecules to draw inside nuclear pores.
36:05Through these gateways, billions of chemical messages and instructions pass between the DNA and the cell.
36:12But only if they are recognised by the protein arms.
36:25But once again, the viral shell carries a counterfeit pass.
36:29The arms lock on, but the virus is too large to be ferried inside.
36:37Thinking that they have hit an obstruction, the motor proteins shunt the virus into reverse.
36:54Immediately if they haveops.
36:55People are just going to makescenes.
36:56There are cysts that they are so small to find into where they are.
36:57I am frightened of a 벌써.
36:58I am permission to enter into the new power, but they are not so cool.
36:59I'm sorry, there's something that diyesting came out of that possible.
37:00Then they have invaded the happy parts, not merely of levail.
37:02tears they Economics rules for hours.
37:14Haaaahhhh!!!
37:16Pulled in 2 directions.
37:19There is aoonsvory Souks.
37:20The virus is ripped apart.
37:32But what looks like a catastrophe for the virus is, in fact, its masterstroke.
37:50Now, the single strand of DNA it held inside is carried through the pore and into the cell's control centre.
38:20Inside the human cell nucleus, there are about 23,000 genes.
38:31They code for thousands and thousands of biochemical pathways.
38:35The virus has just got 40, but with those 40, it can do remarkable things.
38:41It's so tiny, just a piece of DNA, a couple of proteins to make its shell,
38:47and yet it can take over and wreak havoc in a huge human cell.
38:53It's brilliant.
39:06The adenovirus has proven itself a master of deception,
39:11continually exploiting the cell's processes to further its own deadly aims.
39:17But its greatest trick is yet to come.
39:27The cell's DNA machines have no way of telling the difference between its own DNA and the DNA of the virus.
39:37Blindly, they set about converting its deadly code into thousands of instructions for the cell to act upon.
39:43Blueprints for the cell's own destruction.
39:56It should remove whoever they're adhering to, just once는데요 and this is turned on.
39:58The cell's DNA onto the sample with an actual shuttle tree.
40:01The cell's DNA and a огром расскacking toolbs will create a STRGTH-AAA rule.
40:06Something you can use, transfer Carrschaften K来virova theyмуse non-40's or Aí Хroянful Qu 700's ball one-60's.
40:10The cell's DNA is turned into the cell's DNA is still ka Sabmahmmis.
40:11The cell's DNA in the cell's DNA.
40:14The cell's DNA and a Justice tab marked the server wasylum where it was nove olvides.
40:16The cell's DNA is a because of the cell's DNA has helped.
40:18The cell has to become dead.
40:19But the cell's DNAket system has been performed social transformation.
40:21But the machines that turn the blueprints into proteins lie outside the nucleus.
40:37Out in the main body of the cell, the instructions are met by a squadron of mobile protein factories
40:43called ribosomes.
40:47The ribosomes precisely follow the instruction and start to construct viral proteins.
40:53Each is carefully folded into a specific shape with a unique job to do.
40:59These large cellular machines, ribosomes, are absolutely fundamental to life and very
41:03similar forms of them are found in every type of living cell on the planet.
41:07They read the genetic information and they decode it, bringing in the building blocks
41:11that make up proteins and sticking them together to make these functional molecules that are
41:15going to work inside the living cell.
41:28Only these functional molecules are the kit of parts needed to build an enemy army.
41:37But the army will not be built out here.
41:55The raw material for the new army is drawn back inside the nucleus, ready for construction.
42:17construction.
42:33With its mission reaching its climax, the virus turns its attention to the cell's DNA, halting
42:39any process it doesn't need.
42:44The virus has taken complete control.
42:55And yet the cell still has a small window of opportunity.
43:02While all normal activity stops, it has just enough time to send a message to the outside world.
43:09This parcel contains fragments of the viral army.
43:30The parcel merges with the cell membrane, and the enemy fragments are pushed to the surface.
43:42Flags warning of the invasion that has taken place.
43:46If patrolling white blood cells spot the distress signal, they will destroy the cell along with the entire alien army inside.
43:59If not, the infection will spread from cell to cell to cell.
44:16After just one day of occupation, the virus has complete control over the cell.
44:22With routine maintenance halted, the cell has started to decay.
44:28And all activity is now focused on building the brand new viral army inside the nucleus.
44:45The new army self-assembles.
44:47How do viruses know how to invade our cells, how to break and enter the nucleus itself?
44:56We know that viruses and cells co-evolved together over long periods of time, but it's more than that.
45:02We're actually surprisingly closely related.
45:06It turns out that the viruses that attack us are actually made from bits and pieces of our own cells.
45:12As our cells were evolving, as the nucleus itself was first coming to be, so these viruses were cobbled together from bits and pieces.
45:20And they can attack our nucleus because they're made of the same stuff.
45:25Already built into its surface are the binding sites for the cell's motorised legs.
45:36Fibres snap into place, arming each virus with the keys to enter other cells.
45:42But these shells are harmless without its instructions.
46:03The final component is loaded.
46:06Identical copies of the virus's deadly DNA.
46:16Carried by powerful motors, long strands of DNA are fed into every single virus.
46:22All this is the result of one single virus getting through our cells' defences.
46:48It's been two days since the virus entered the body.
46:58And the nucleus, once the centre of cellular organisation, now harbours an army of 10,000 deadly viruses.
47:06But before it can begin its conquest, it has to overcome two barriers.
47:24The army is trapped inside the tough nuclear membrane held at the centre of the cell itself.
47:31And then there is the skin of the cell itself.
47:36The protein factories outside the nucleus are instructed to build viral saboteurs.
47:44The first are released into the decaying cell and target its cytoskeleton.
48:05The effects are cataclysmic.
48:07Without support, the cell starts to collapse.
48:16Now, the virus turns its attention to the nuclear membrane.
48:26A second protein is released.
48:35Called the adenovirus death protein.
48:41It burrows into the membrane.
48:44It burrows into the membrane.
48:46And weakens it.
48:48The nucleus can no longer contain the bulging army.
49:04Beyond the nucleus.
49:05The cell is a wasteland.
49:06Beyond the nucleus.
49:07The cell is a wasteland.
49:08Beyond the nucleus.
49:09Beyond the nucleus.
49:10The cell is a wasteland.
49:27Unrecognizable from the harmonious buzzing community of just 48 hours ago.
49:55The cell is now completely helpless to stop the virus army from flooding into surrounding tissue.
50:02Attacking neighbouring cells.
50:08And spreading infection throughout the body.
50:13The battle for this cell is over.
50:24But the war has only just begun.
50:40While the virus has been busy inside the cell.
50:58Our antibodies have adapted.
51:00And now come back in force carrying new receptors.
51:03Tailor made to lock on to the escaping army.
51:10Yet even in these numbers.
51:12They cannot stop every virus.
51:17But they are not alone.
51:20The cell's dying message to the outside world was not in vain.
51:24Giant white blood cells.
51:25Giant white blood cells flock to the stricken cell.
51:27To devour the escaping hordes.
51:30They too are learning how to tackle this particular invader.
51:35Once the virus has been detected by the immune system.
51:38There's a heightened level of security inside your body.
51:40And one of the results of this.
51:42Is that the cells that make antibodies.
51:44And make the right antibody for that virus.
51:46Will make lots of copies of themselves.
51:48And then they will start pumping out.
51:50Up to 5,000 antibodies per second.
51:52To flood your bloodstream.
51:53The spaces between your cells.
51:55So as viruses emerge from dying cells.
51:57They can get tagged by antibodies.
51:58And then destroyed by white blood cells.
52:01And then destroyed by antibodies.
52:02Taking no chances.
52:03White blood cells engulf nearby cells.
52:06That may have been infected.
52:12Meanwhile.
52:13Surrounding healthy cells.
52:15Make the ultimate sacrifice.
52:17Destroying themselves.
52:20To stop the spread of the virus.
52:22It is only at this stage.
52:27That we become aware.
52:28Of the battle taking place inside us.
52:30Increasing blood flow.
52:32Brings more white blood cells.
52:33To the battle ground.
52:34Causing our nasal tissue.
52:36To become inflamed.
52:37What we feel.
52:39As a blocked nose.
52:40Is in fact.
52:41The clearest sign.
52:42Of a viral onslaught.
52:44Once you've had an infection.
52:47One cell.
52:48That makes the right antibody.
52:49For that infection.
52:50Will be kept inside your bone marrow.
52:51For the rest of your life.
52:53That if you ever get.
52:54Another infection.
52:55With the same virus.
52:56The immune system.
52:57Already knows how to respond.
52:58It knows what antibody to make.
52:59And it can respond very quickly.
53:00And stop you getting sick.
53:06Working together.
53:07The body's immune system.
53:08Finally prevents.
53:09The viral infection.
53:10From spreading.
53:11It's one more battle.
53:14In an unending war.
53:16The struggle.
53:17Between viruses.
53:18And ourselves.
53:19Is evolution.
53:20But it's co-evolution.
53:21Both sides.
53:22Have to change.
53:23It's a bit like an arms race.
53:24One party.
53:25Gets better weapons.
53:26The other party.
53:27Has to match them.
53:28Even though the individual cells.
53:29Are fighting this epic battle.
53:30Against the viruses.
53:31Remember you have trillions of cells.
53:32And so even if one cell loses.
53:33It's war.
53:34Most of the time.
53:35The organism wins.
53:36And we get better.
53:37The war is over.
53:38For now.
53:39The war is over.
53:40For now.
53:41the war is over.
54:04The war is over.
54:08now.
54:18Although many cells have been lost, there are many more healthy cells waiting to replace
54:23them.
54:31And at the heart of each one lies an identical copy of our DNA.
54:41Inherited from our parents and their parents over countless generations, our DNA connects
54:47us to a family tree that stretches back over three billion years to the very first cell.
54:56A cell that existed long before humans, long before mammals, long before the dinosaurs.
55:04It's a lineage that connects us to every living creature and plant on Earth.
55:09We are all descended from a single prehistoric ancestor.
55:12A cell containing the single strand of DNA that started it all.
55:22The virus is as old as we are.
55:25It has evolved alongside us, forcing us to adapt, to change or die in a deadly game of cat and
55:31mouse.
55:37This eternal arms race has driven our evolution and made us both stronger.
55:46We wouldn't be what we are today were it not for this battle with our ancient enemy.
55:56The story of the cell is a story of innovation and change.
55:59And because viruses continuously force cells to change, they actually aid their adaptation
56:06to different environments.
56:07And for that reason, they've also helped shape us, they've made us who we are.
56:21Every minute of every day, this battle with the virus rages within seven billion of us.
56:28That we are rarely aware of it, we fight each other, change each other, improve each other.
56:49Uncovering the truth about our ancestors here on BBC HD this week, a groundbreaking prehistoric
56:55autopsy gets underway tomorrow at nine.
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