How we think complex cells evolved - Adam Jacobson

Hvordan vi tror komplekse celler opstod - Adam Jacobson

Translator: Melanie Weilguny Reviewer: Anders Finn Jørgensen

What if you could absorb another organism

Tænk hvis du kunne absorbere en anden organisme

and take on its abilities?

og overtage dens egenskaber.

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

Forestil dig, at du slugte en lille fugl og pludselig fik evnen til at flyve.

Or if you engulfed a cobra

Eller hvis du spiste en kobra,

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

og derefter kunne sprøjte gift fra dine tænder.

Throughout the history of life,

Gennem livets historie,

specifically during the evolution of complex eukaryotic cells,

specielt under udviklingen af komplekse eukaryote celler,

things like this happened all the time.

skete sådan nogle ting hele tiden.

One organism absorbed another,

En organisme absorberede en anden,

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

og de blev forenet til en ny organisme med en kombination af begges egenskaber.

We think that around 2 billion years ago,

For omkring 2 milliarder år siden

the only living organisms on Earth were prokaryotes,

var de eneste levende organismer på Jorden prokaryoter,

single-celled organisms lacking membrane-bound organelles.

encellede organismer uden membranbundne organeller.

Let's look closely at just three of them.

Lad os se nærmere på tre af dem.

One was a big, simple blob-like cell

En af dem var en stor og simpel klumpet celle,

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

som havde evnen til at absorbere ting ved at svøbe sin cellemembran omkring dem.

Another was a bacterial cell

En anden var en bakteriecelle,

that converted solar energy into sugar molecules through photosynthesis.

som omdannede solenergi til sukkermolekyler gennem fotosyntese.

A third used oxygen gas to break down materials like sugar

En tredje brugte ilt til at nedbryde materialer som sukker

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

og omdanne energien til en form, velegnet til livsaktiviteter.

The blob cells would occasionally absorb the little photosynthetic bacteria.

Den klumpede celle ville til tider absorbere den lille fotosyntetiserende bakterie.

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

Bakterierne levede derefter inde i klumpen og delte sig, som de altid havde gjort,

but their existence became linked.

men deres eksistens blev forbundet.

If you stumbled upon this living arrangement,

Hvis du løb ind i dette levende bofællesskab,

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

ville du sikkert tro, at det var en enkelt organisme,

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

at den grønne fotosyntetiserende bakterie bare var en del af klumpen,

that performed one of its life functions,

der udførte en af dens livsfunktioner,

just like your heart is a part of you

ligesom at dit hjerte er en del af dig,

that performs the function of pumping your blood.

der udfører den funktion at pumpe blodet rundt i kroppen.

This process of cells living together is called endosymbiosis,

Denne proces af levende celler, der bor sammen, kaldes endosymbiose,

one organism living inside another.

en organisme der bor inde i en anden.

But the endosymbiosis didn't stop there.

Men endosymbiosen stoppede ikke bare der.

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

Hvad ville der ske, hvis den anden bakterie også flyttede ind?

Now the cells of this species started becoming highly complex.

Nu begyndte denne celletype at blive meget kompleks.

They were big and full of intricate structures

De var store og fyldt med komplicerede strukturer,

that we call chloroplasts and mitochondria.

som vi kalder grønkorn og mitokondrier.

These structures work together to harness sunlight,

Disse strukturer arbejder sammen om at udnytte sollyset,

make sugar,

lave sukker,

and break down that sugar using the oxygen

og nedbryde sukkeret ved hjælp af ilten,

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

der omkring dette tidspunkt begyndte at dukke op i Jordens atmosfære.

Organisms absorbing other organisms

Organismer der absorberer andre organismer,

was one way species adapted to the changing environmental conditions

var en måde hvorpå, arterne tilpassede sig det skiftende miljø

of their surroundings.

i deres omgivelser.

This little story highlights what biologists call the endosymbiotic theory,

Denne fortælling fremhæver, hvad biologer kalder for den endosymbiostiske teori,

the current best explanation of how complex cells evolved.

den nuværende bedste forklaring på, hvordan komplekse celler opstod.

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

Der er mange beviser, der understøtter teorien,

but let's look at three main pieces.

med lad os kigge på de tre største.

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

For det første formerer grønkorn og mitokondrier i vores celler sig på samme måde,

as those ancient bacteria,

som de gamle bakterier,

which are still around, by the way.

som forresten stadig eksisterer.

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

Ødelægger du disse strukturer i en celle, vil ingen nye opstå.

The cell can't make them.

Cellen kan ikke lave dem.

They can only make more of themselves.

De kan kun lave flere af sig selv.

Second piece of evidence.

Bevis nummer to.

Chloroplasts and mitochondria both contain their own DNA and ribosomes.

Grønkorn og mitokondrier indeholder begge deres eget DNA og ribosomer.

Their DNA has a circular structure

Deres DNA har en rund struktur,

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

som påfaldende meget ligner de gamle bakteriers DNA,

and it also contains many similar genes.

og det rummer også mange lignende gener.

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

Ribosomerne, eller proteinmaskinerne, i grønkorn og mitokondria

also have the same structure as ribosomes of ancient bacteria,

har også samme struktur som ribosomerne i de gamle bakterier,

but are different from the ribosomes

men er forskellig fra ribosomerne

hanging around the rest of eukaryotic cell.

i resten af den eukaryote celle.

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

Endeligt, tænk på de involverede membraner i absorptionsprocessen.

Chloroplasts and mitochondria both have two membranes surrounding them,

Grønkorn og mitokondrier er begge omgivet af to membraner,

an inner and outer membrane.

en indre og en ydre membran.

Their inner membrane contains some particular lipids and proteins

Den indre membran indeholder nogle særlige fedtstoffer og proteiner,

that are not present in the outer membrane.

som ikke er tilstede i den ydre membran.

Why is that significant?

Hvorfor er det væsentligt?

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

Fordi deres ydre membran engang tilhørte den klumpede celle.

When they were engulfed in the endosymbiosis process,

Da de blev opslugt under den endosymbiotiske proces,

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

blev de pakket ind i membranen og bevarede deres egen indenunder.

Surely enough, those same lipids

Som forventet, er fedtstofferne

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

og proteinerne de samme som dem, fundet i de gamle bakterier.

Biologists now use this theory

Biologerne bruger denne teori

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

til at forklare den store mangfoldighed af eukaryote organismer.

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

Tag for eksempel grønalgen der gror på svømmepølens vægge.

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

En større eukaryot celle med roterende halestrukturer, eller flageller,

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

har engang absorberet alger som denne og dannet, hvad vi nu kalder for euglena.

Euglena can perform photosynthesis,

Euglena kan lave fotosyntese,

break down sugar using oxygen,

nedbryde sukker ved hjælp af ilt

and swim around pond water.

og svømme rundt i søer og damme.

And as the theory would predict,

Og som teorien forudsiger,

the chloroplasts in these euglena have three membranes

har grønkornene i euglena tre membraner,

since they had two before being engulfed.

da de havde to, inden de blev omslugt.

The absorbing process of endosymbiotic theory

Absorptionsprocessen i den endosymbiotiske teori

allowed organisms to combine powerful abilities

tillod organismer at forene kraftfulde egenskaber

to become better adapted to life on Earth.

for at tilpasse sig bedre til livet på Jorden.

The results were species capable of much more

Resultatet var arter, der var i stand til meget mere,

than when they were separate organisms,

end da de var separate organismer,

and this was an evolutionary leap

og dette var et evolutionært skridt,

that lead to the microorganisms, plants,

der førte til de mikroorganismer, planter,

and animals we observe on the planet today.

og dyr, vi kan observere på planeten i dag.