How we think complex cells evolved - Adam Jacobson

Kako mislimo, da so se razvile kompleksne celice - Adam Jacobson

Translator: Nika Kotnik Reviewer: Matej Divjak

What if you could absorb another organism

Kaj če bi lahko absorbirali drug organizem

and take on its abilities?

in prejeli njegove sposobnosti?

Imagine you swallowed a small bird and suddenly gained the ability to fly.

Predstavljajte si, da bi pogoltnili malega ptiča in dobili sposobnost letenja.

Or if you engulfed a cobra

Ali če bi požrli kobro

and were then able to spit poisonous venom from your teeth.

in bi bili potem sposobni pljuvati strup iz svojih zob.

Throughout the history of life,

Skozi zgodovino življenja,

specifically during the evolution of complex eukaryotic cells,

še posebej med evolucijo kompleksnih evkariontskih celic,

things like this happened all the time.

so se take stvari dogajale ves čas.

One organism absorbed another,

En organizem je absorbiral drugega

and they united to become a new organism with the combined abilities of both.

in združila sta se v nov organizem z združenimi sposobnostmi obeh.

We think that around 2 billion years ago,

Mislimo, da so bili pred 2 milijardama let

the only living organisms on Earth were prokaryotes,

edini živi organizmi na Zemlji prokarionti,

single-celled organisms lacking membrane-bound organelles.

enocelični organizmi, ki niso imeli organelov z membrano.

Let's look closely at just three of them.

Pobliže si poglejmo samo tri.

One was a big, simple blob-like cell

En je bil velika, preprosta, mehurčkasta celica

with the ability to absorb things by wrapping its cell membrane around them.

s sposobnostjo absorpcije snovi tako, da jo je ovila s svojo celično membrano.

Another was a bacterial cell

Druga je bila bakterijska celica,

that converted solar energy into sugar molecules through photosynthesis.

ki je pretvorila sončno energijo v molekule sladkorja s fotosintezo.

A third used oxygen gas to break down materials like sugar

Tretja je uporabljala kisik za razgradnjo molekul, kot je bil sladkor,

and release its energy into a form useful for life activities.

in sprostila energijo v obliki, uporabni za življenjske aktivnosti.

The blob cells would occasionally absorb the little photosynthetic bacteria.

Mehurčkasta celica je občasno absorbirala foto-sintetično bakterijo.

These bacteria then lived inside the blob and divided like they always had,

Te bakterije so nato živele znotraj mehurčka in se delile kot vedno,

but their existence became linked.

a njihov obstoj je postal povezan.

If you stumbled upon this living arrangement,

Če bi naleteli na to življenjsko ureditev,

you might just think that the whole thing was one organism,

bi morda pomislili, da gre za en organizem,

that the green photosynthetic bacteria were just a part of the blob

da so zelene fotosintetske bakterije samo del mehurčka,

that performed one of its life functions,

ki izvaja eno izmed življenjskih funkcij,

just like your heart is a part of you

tako kot je tvoje srce tisti del tebe, ki izvaja funkcijo črpanja krvi.

that performs the function of pumping your blood.

This process of cells living together is called endosymbiosis,

Ta proces skupnega življenja celic se imenuje endosimbioza,

one organism living inside another.

en organizem živi znotraj drugega.

But the endosymbiosis didn't stop there.

A endosimbioza se ni ustavila tu.

What would happen if the other bacteria moved in, too?

Kaj bi se zgodilo, če bi se noter premaknile še druge bakterije?

Now the cells of this species started becoming highly complex.

Sedaj so celice te vrste postajale zelo zapletene.

They were big and full of intricate structures

Bile so velike in polne zapletenih struktur,

that we call chloroplasts and mitochondria.

ki jim pravimo kloroplasti in mitohondriji.

These structures work together to harness sunlight,

Te strukture delujejo skupaj, da ujamejo sončno svetlobo,

make sugar,

naredijo sladkor in razgradijo ta sladkor s pomočjo kisika,

and break down that sugar using the oxygen

that right around this time started to appear in the Earth's atmosphere.

ki se je ravno v tem času pojavil v Zemljini atmosferi.

Organisms absorbing other organisms

To, da organizmi absorbirajo druge organizme,

was one way species adapted to the changing environmental conditions

je en način prilagoditve vrst na spreminjajoče se okoljske pogoje,

of their surroundings.

v prostoru, ki jih obdaja.

This little story highlights what biologists call the endosymbiotic theory,

Ta kratka zgodba vam prikaže nekaj, čemur biologi pravijo endosimbiotska teorija,

the current best explanation of how complex cells evolved.

trenutno najboljšo razlago evolucije kompleksnih celic.

There's a lot of evidence that supports this theory,

Veliko dokazov je, ki potrjujejo to teorijo,

but let's look at three main pieces.

a poglejmo tri glavne.

First, the chloroplasts and mitochondria in our cells multiply the very same way

Prvič, kloroplasti in mitohondriji se delijo na isti način

as those ancient bacteria,

kot tiste starodavne bakterije,

which are still around, by the way.

ki so še zmeraj tu, mimogrede.

In fact, if you destroy these structures in a cell, no new ones will appear.

V bistvu, če uničiš te strukture v celici, se ne bodo pojavile nove.

The cell can't make them.

Celica jih ne more narediti.

They can only make more of themselves.

Samo same se lahko pomnožijo.

Second piece of evidence.

Drugi dokaz.

Chloroplasts and mitochondria both contain their own DNA and ribosomes.

Kloroplasti in mitohondriji imajo oboji svojo DNK in ribosome.

Their DNA has a circular structure

Njihova DNK je krožna

that is strikingly similar to the DNA of the ancient bacteria,

in je neverjetno podobna DNK starodavnih bakterij

and it also contains many similar genes.

in prav tako vsebuje mnogo podobnih genov.

The ribosomes, or protein assembly machines of chloroplasts and mitochondria,

Ribosomi, oziroma naprave za nastanek proteinov v kloroplastih in mitohondrijih,

also have the same structure as ribosomes of ancient bacteria,

imajo enako strukturo kot ribosomi starodavnih bakterij,

but are different from the ribosomes

a so drugačni od ribosomov, ki so v drugih evkariontskih celicah.

hanging around the rest of eukaryotic cell.

Lastly, think about the membranes involved in the engulfing process.

Nazadnje, pomislite na membrane, vpletene v proces požiranja.

Chloroplasts and mitochondria both have two membranes surrounding them,

Kloroplasti in mitohondriji imajo oboji dve membrani, ki jih obdajata,

an inner and outer membrane.

notranjo in zunanjo membrano.

Their inner membrane contains some particular lipids and proteins

Notranjo membrano sestavljajo lipidi in proteini,

that are not present in the outer membrane.

ki niso prisotni v zunanji membrani.

Why is that significant?

Zakaj je to pomembno?

Because their outer membrane used to belong to the blob cell.

Ker je njihova zunanja membrana včasih pripadala mehurčkasti celici.

When they were engulfed in the endosymbiosis process,

Ko so bili zajeti v procesu endosimbioze,

they got wrapped up in that membrane and kept their own as their inner one.

so bili oviti v to membrano in obdržali svojo kot notranjo membrano.

Surely enough, those same lipids

Ti isti lipidi in proteini se nahajajo na membranah starodavnih bakterij.

and proteins are found on the membranes of the ancient bacteria.

Biologists now use this theory

Biologi sedaj uporabljajo to teorijo,

to explain the origin of the vast variety of eukaryotic organisms.

da pojasnijo izvor velike raznolikosti evkariontskih organizmov.

Take the green algae that grow on the walls of swimming pools.

Poglejte naprimer zelene alge, ki rastejo na stenah bazenov.

A larger eukaryotic cell with spinning tail structures, or flagella,

Velika evkariontska celica z vrtečimi se repki oziroma bički

at some point absorbed algae like these to form what we now call euglena.

je na neki točki absorbirala alge, kot so te, da so se oblikovale evglene.

Euglena can perform photosynthesis,

Evglena lahko izvaja fotosintezo,

break down sugar using oxygen,

razgradi sladkor s pomočjo kisika

and swim around pond water.

in plava v jezerski vodi.

And as the theory would predict,

Kot predvideva teorija,

the chloroplasts in these euglena have three membranes

imajo kloroplasti v tej evgleni tri membrane,

since they had two before being engulfed.

saj so imeli dve, preden so bili zajeti.

The absorbing process of endosymbiotic theory

Postopek absorpcije v endosimbiotski teoriji

allowed organisms to combine powerful abilities

omogoča organizmom, da združijo močne sposobnosti,

to become better adapted to life on Earth.

da se bolje prilagodijo življenju na zemlji.

The results were species capable of much more

Rezultat so bile vrste, sposobne veliko več

than when they were separate organisms,

kot takrat, ko so bile ločeni organizmi

and this was an evolutionary leap

in to je bil evolucijski preskok,

that lead to the microorganisms, plants,

ki je vodil k mikroorganizmom, rastlinam

and animals we observe on the planet today.

in živalim, ki jih opazujemo na planetu sedaj.