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  • Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to

  • check out their Computational Biology course.

  • {♫Intro♫}

  • Hot springs and hydrothermal vents might not be the first places you'd look to find ways

  • to fight a pandemic.

  • But they've given us some of the most important tools we have for identifying, tracking, and

  • understanding pathogens.

  • In fact, without them, the entire field of molecular biology would be stuck in the 1960s,

  • and not in the fun way.

  • See, that's when researchers discovered a microbe in Yellowstone that allowed them

  • to actually replicate DNA at will.

  • This processknown as Polymerase Chain Reaction, or PCR for shortwas really a game changer

  • for genetics.

  • And we here at SciShow do not use that phrase lightly.

  • The pathway to developing PCR began way back in the middle of the twentieth century.

  • Scientists had just really seen DNA for the first time, but already, they were searching

  • for ways to read these genetic blueprints. FST01

  • Problem was, sequencing DNAand its simpler cousin, RNArequired a lot of genetic material,

  • because it relied on cutting longer strings into smaller ones with enzymes that sliced

  • at certain sequences, and then back-calculating what the whole string looked like from those

  • pieces.

  • And, simply put, it wasn't easy to obtain that volume of genetic materialespecially

  • for anything not microbial in nature.

  • So they knew being able to make copies of DNA would open the door to all kinds of research.

  • And the potential to do that traces back to 1957—just a few years after the structure

  • of DNA was first describedwhen researchers identified the first DNA polymerase.

  • These enzymes build strands of DNA from nucleotides, the essential building blocks of nucleic acids.

  • They take a single strand of DNA as a template, and string together a complementary strand.

  • And all organisms have the blueprints for at least one of these enzymes written into

  • their genetic code. That's how they make copies of their genome when their cells divide.

  • Researchers soon discovered that they could isolate these enzymes from bacteria like E.

  • coli, which meant, hypothetically, they could use them to replicate any DNA they wanted.

  • Except, there was a small catch.

  • Before the polymerase can start copying DNA, the tightly wound, paired strands of DNA found

  • in organisms like us have to be separated into single strands.

  • That way, short sequences of single-stranded DNA called primers can bind to the open strand

  • and tell the polymerase where to start and stop copying.

  • In nature, this unwinding requires yet another enzyme, plus a several other proteinstoo

  • complicated to recreate in a tube.

  • Luckily, DNA strands can be separated another way.

  • Above 90°C, the bonds holding the strands together break apart.

  • So you can heat up DNA to get single strands, then cool things down a bit to let the primers

  • bind and so DNA polymerase can make its copies.

  • After each heating and cooling cycle, you essentially double the amount of DNA.

  • Today, each of these cycles takes about five minutes, so within a few hours, you can go

  • from a very small number of copies to millions of copies of a given DNA sequence.

  • But in the '60s, the whole process took much longer than that.

  • See, heat also permanently inactivates the DNA polymerases from E. coli.

  • So, in early DNA replication efforts, fresh polymerase had to be added each time a copy

  • of DNA was mademaking the process very slow and very expensive.

  • That's where extreme microbes come into play.

  • P05 In 1966, scientists discovered a microbe living

  • in the 70-plus degree waters of hot springs in Yellowstone National Park.

  • They named it Thermus aquaticus, after its ability to thrive in the hot spring's high

  • temperatures.

  • And in 1976, researchers isolated one of its DNA polymerases.

  • They called it Taq polymeraseor, just Taq, for short.

  • And, like the microbe itself, it could withstand the high temperatures needed for separating

  • DNA strands.

  • So you could throw it in with your sample, some primers, and nucleic acids, and then

  • let a machine heat and cool everything over and over again to produce millions of copies

  • of DNA.

  • And that, in a nutshell, is Polymerase Chain Reaction.

  • Ever since researchers developed these methods in the mid eighties, PCR has allowed scientists

  • to turn teeny amounts of DNA into much larger ones in a matter of hours.

  • For geneticists, it was like going from carbon-copy paper to a Xerox machine!

  • It meant they could figure out whose cells are on the end of a hair at a crime scene.

  • Or, spot the genes of a virus hiding in someone's blood.

  • In short, Taq polymerase revolutionized genetics. And it's still widely used for PCR today.

  • But newer enzymes are coming into play, too.

  • See, Taq sometimes makes mistakes. It grabs the wrong nucleotide and attaches it instead.

  • This is a problem for applications that need a high level of accuracylike, if you're

  • trying to detect the small mutations that can happen to a virus over time.

  • Doing that can help experts understand how the pathogen is moving about and changing.

  • Luckily, researchers discovered Pyrococcus

  • abyssi—a deep sea microbe that lives in even more extreme conditions.

  • Its enzymes are more resilient than Taq, but more importantly, they also proofread themselves

  • while making copieswhich is why they're forty to fifty times more accurate.

  • They're now among the several specialized polymerases available to geneticists.

  • And researchers keep going back to extreme environments because their microbes have all

  • sorts of unique and useful molecular tricks up their sleeves.

  • So who knows what else we'll discover by studying these remarkably resourceful organisms.

  • PCR didn't just provide new tools for studying viral outbreaks, of course. Suddenly, scientists

  • could use genetic information to study all sorts of evolutionary and biological questions.

  • And you can learn all about that with the Computational Biology course from Brilliant.

  • Brilliant offers dozens of interactive and engaging STEM courses to take your science,

  • math, and engineering skills to the next level. And with their Computational Biology course,

  • you can really dig deep into all the amazing things researchers can learn from sequencing

  • genetic molecules.

  • Plus, if you're one of the first two hundred people to sign up for an annual Premium subscription

  • at Brilliant.org/SciShow, you'll get twenty percent off! So if you're interested,

  • check it out!

  • {♫Outro♫}

Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to

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    林宜悉 發佈於 2021 年 01 月 14 日
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