Name: TED-ED】DNAが傷つくとどうなる？- モニカ・メネシーニ (【TED-Ed】What happens when your DNA is damaged? - Monica Menesini)
Uploaded: 2021-01-14T05:47:33.000Z
Duration: 4 min 59 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

gets damaged tens of thousands  of times per day.

Multiply that by your body's hundred trillion or so cells,

and you've got a quintillion  DNA errors everyday.

And because DNA provides the blueprint for the proteins  your cells need to function,

damage causes serious problems, such as cancer.

Sometimes nucleotides,  DNA's building blocks, get damaged,

other times nucleotides get matched up incorrectly,causing mutations,

and nicks in one or both strands can interfere with DNA replication,

or even cause sections of DNA to get mixed up.

Fortunately, your cells have ways of fixing most of these problems most of the time.

These repair pathways  all rely on specialized enzymes.

Different ones respond  to different types of damage.

the enzyme DNA polymerase is supposed to bring in the right partner

to pair with every base on each template strand.

Adenine with thymine, and guanine with cytosine.

But about once every hundred thousand additions,

The enzyme catches  most of these right away,

and cuts off a few nucleotides and replaces them with the correct ones.

a second set of proteins  comes behind it to check.

they cut out the incorrect nucleotide and replace it.

Together, these two systems reduce the number of base mismatch errors to about one in one billion.

But DNA can get damaged after replication, too.

Lots of different molecules can cause chemical changes to nucleotides.

Some of these come  from environmental exposure,

But others are molecules that are found in cells naturally,like hydrogen peroxide.

Certain chemical changes are so common that they have specific enzymes assigned to reverse the damage.

But the cell also has more general repair pathways.

it can usually be fixed by a process called base excision repair.

and other enzymes come in to trim around the site and replace the nucleotides.

UV light can cause damage  that's a little harder to fix.

Sometimes, it causes two adjacent nucleotides to stick together,

Damage like this requires  a more complex process

A team of proteins removes a long strand of 24 or so nucleotides,

Very high frequency radiation, like gamma rays and x-rays,

They can actually sever one or both strands of the DNA backbone.

Double strand breaks are the most dangerous.

The two most common pathways for repairing double strand breaks

are called homologous recombination and non-homologous end joining.

Homologous recombination uses an undamaged section of similar DNA as a template.

Enzymes interlace the damaged and undamgaed strands,

get them to exchange sequences of nucleotides,

to end up with two complete double-stranded segments.

Non-homologous end joining, on the other hand, doesn't rely on a template.

Instead, a series of proteins trims off a few nucleotides

and then fuses the broken ends  back together.

It can cause genes to get mixed up, or moved around.

But it's useful when sister DNA isn't available.

Of course, changes to DNA  aren't always bad.

Beneficial mutations  can allow a species to evolve.

But most of the time,  we want DNA to stay the same.

Defects in DNA repair are associated with premature aging and many kinds of cancer.

So if you're looking for  a fountain of youth,

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TED-ED】DNAが傷つくとどうなる？- モニカ・メネシーニ (【TED-Ed】What happens when your DNA is damaged? - Monica Menesini)

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