Name: 宇宙はどのようにして私たちのDNAを形成してきたのか (How Space Might Have Shaped Our DNA)
Uploaded: 2021-01-14T10:28:13.000Z
Duration: 3 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：

The DNA double helix is one of the more iconic images in all of science.

Slapping a twisty piece of DNA on something is guaranteed

The DNA inside our cells is almost exclusively right-handed.

This doesn't mean it never has to fight over the single

Instead, it means the double helix twists from lower left to upper right

whether you're holding it upside down or right side up.

Now, just to be clear, our DNA can temporarily form left-handed helices

But those lefty molecules look pretty bizarre,

and while they might crop up in cells in specific situations,

the majority of the time our genetic code is stored in a right-handed twist.

And that's the kind of helix our cells are adapted to decode

if our genetic information were left-handed, our cells wouldn't be able to use it!

This biological preference for right-handed DNA is very strict.

In fact, it holds across all forms of life… which is kind of odd.

Why does DNA have to twist the same way in every living organism?

The leading hypothesis to explain why DNA always twists to the right

has to do with the shape of its building blocks, or nucleotides.

And nucleotides are chiral, a word used to describe things

that are mirror images of each other, like your left and right hand.

No matter how much you flip or twist a pair of chiral molecules,

The double helix twists toward the right.

But when we talk about left- or right-handed when talking about a nucleotide,

it just means one of those two mirror-image forms.

Our cells only have the left-handed form of these DNA nucleotides,

The mirror images of our nucleotides would theoretically

why do all living cells only use left-handed nucleotides?

The short answer is that there may just have been more of them around

4 billion years ago when life first evolved.

But the longer, more interesting answer might come from space.

Specifically, from the high-energy radiation known as cosmic rays.

When cosmic rays shower down on Earth's atmosphere,

they cause gas molecules in the atmosphere

to break down into atomic particles like electrons.

In the breakdown process, the cosmic rays put a bit of a spin on the electrons.

Which, once again, means they can go left or right.

But a funny quirk about electrons from degraded atoms

is that they are more likely to spin towards the left than the right.

In fact, while rightward spinning electrons can be generated in a lab,

And physicists have yet to come up with a good reason why.

Regardless, about fifty years ago, scientists tried to reconcile

this electron asymmetry with the lack of left-handed DNA helices in nature.

They proposed that these lefty electrons could

preferentially destroy chiral molecules of a single handedness,

like the right-handed nucleotides that form left-handed DNA helices.

Then, in 2015, scientists demonstrated that that's physically possible -- maybe.

They shot a beam of left- or right-handed electrons at a gas

0.03% more right-handed gas molecules than lefty ones.

But researchers believe it's possible that over billions of years,

or that this reaction could be amplified somehow through other means.

Regardless, if left-handed DNA nucleotides are even that tiny bit

they'd still be an evolutionary advantage for right-handed helices.

Of course, this experiment only demonstrates the general chemical idea

that electrons might interact differently with different-handed molecules.

It didn't actually show anything to do with DNA directly.

But it is a first step toward understanding why our cells

have such an ingrained bias against southpaw DNA.

Thanks for watching this episode of SciShow,

and thanks to all the awesome patrons who support what we do.

If you'd like to help out, as well as join an awesome community

of people and maybe earn some sweet perks, check out patreon.com/scishow.

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宇宙はどのようにして私たちのDNAを形成してきたのか (How Space Might Have Shaped Our DNA)

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