Cell membranes are way more complicated than you think - Nazzy Pakpour

Stanične membrane puno su kompliciranije nego što misliš - Nazzy Pakpour

Prevoditelj: Irma Komljenović Recezent: Ivan Stamenković

Cell membranes are structures of contradictions.

Stanične su membrane kontradiktorne strukture.

These oily films are hundreds of times thinner than a strand of spider silk,

Ova uljaste opne stotinjak su puta tanje od niti paukove svile,

yet strong enough to protect the delicate contents of life:

no dovoljno su jake da štite delikatni sastav života:

the cell's watery cytoplasm, genetic material, organelles,

vodenastu citoplazmu stanice, nasljedne upute, organele,

and all the molecules it needs to survive.

i sve molekule potrebne za opstanak.

How does the membrane work, and where does that strength come from?

Kako funkcionira membrana i otkud dobiva svu tu snagu?

First of all, it's tempting to think of a cell membrane

Možda je primamljivo zamišljati staničnu membranu

like the tight skin of a balloon,

kao zategnutu površinu balona,

but it's actually something much more complex.

no ona je nešto puno kompliciranije.

In reality, it's constantly in flux,

Ustvari je u neprestanom pokretu,

shifting components back and forth to help the cell take in food,

mičući svoje sastavnice naprijed i nazad kako bi unijela hranu u stanicu,

remove waste,

izbacila otpad,

let specific molecules in and out,

propustila određene molekule,

communicate with other cells,

komunicirala s drugim stanicama,

gather information about the environment,

prikupljala informacije o okolini,

and repair itself.

i popravila samu sebe.

The cell membrane gets this resilience, flexibility, and functionality

Stanična membrana svoju elastičnost, savitljivost i funkcionalnost dobiva

by combining a variety of floating components

spajanjem raznih plutajućih sastavnica

in what biologists call a fluid mosaic.

u tzv. tekući mozaik.

The primary component of the fluid mosaic

Primarna sastavnica tekućeg mozaika

is a simple molecule called a phospholipid.

jednostavna je molekula fosfolipid.

A phospholipid has a polar, electrically-charged head,

Fosfolipid ima polarnu, električki nabijenu glavu

which attracts water,

koja privlači vodu,

and a non-polar tail, which repels it.

i nepolaran rep koji ju odbija.

They pair up tail-to-tail in a two layer sheet

Slože se, rep do repa, u dva sloja

just five to ten nanometers thick that extends all around the cell.

debela od pet do deset nanometara koji okružuju stanicu.

The heads point in towards the cytoplasm

Glave su okrenute prema citoplazmi

and out towards the watery fluid external to the cell

i vani prema vodenastoj tekućini izvan stanice

with the lipid tails sandwiched in between.

s lipidnim repovima umetnutim između njih.

This bilayer, which at body temperature has the consistency of vegetable oil,

U ovom dvosloju, koji je na tjelesnoj temperaturi sličan gustoći biljnog ulja,

is studded with other types of molecules,

nalaze se i druge vrste molekula,

including proteins,

poput bjelančevina,

carbohydrates,

ugljikohidrata,

and cholesterol.

i kolesterola.

Cholesterol keeps the membrane at the right fluidity.

Kolesterol održava elastičnost membrane,

It also helps regulate communication between cells.

ali i regulira komunikaciju među stanicama.

Sometimes, cells talk to each other

Nekad stanice pričaju jedna s drugom

by releasing and capturing chemicals and proteins.

otpuštanjem i hvatanjem kemikalija i bjelančevina.

The release of proteins is easy,

Otpuštanje bjelančevina je lagano,

but the capture of them is more complicated.

no hvatanje je kompliciranije.

That happens through a process called endocytosis

Ono se događa procesom endocitoze

in which sections of the membrane engulf substances

u kojem izdanci membrane okružuju tvari

and transport them into the cell as vesicles.

i uvode ih u stanicu u mjehuriću.

Once the contents have been released,

Kad je sadržaj ispušten,

the vesicles are recycled and returned to the cell membrane.

mjehurić se reciklira i vraća do stanične membrane.

The most complex components of the fluid mosaic are proteins.

Najkompliciraniji dijelovi tekućeg mozaika su bjelančevine.

One of their key jobs is to make sure

Njihov je važan posao pobrinuti se

that the right molecules get in and out of the cell.

da u stanicu ulaze i izlaze ispravne stanice.

Non-polar molecules, like oxygen,

Nepolarne molekule, poput kisika,

carbon dioxide,

ugljikovog dioksida,

and certain vitamins

i nekih vitamina

can cross the phospholipid bilayer easily.

lako mogu proći kroz fosfolipidni dvosloj.

But polar and charged molecules can't make it through the fatty inner layer.

Polarne i nabijene molekule ne mogu proći kroz masni unutrašnji sloj.

Transmembrane proteins stretch across the bilayer to create channels

Transmembranske bjelančevine prolaze cijelim dvoslojem stvarajući kanale

that allow specific molecules through, like sodium and potassium ions.

kroz koje određene molekule, poput iona natrija i kalija, mogu proći.

Peripheral proteins floating in the inner face of the bilayer

Periferne bjelančevine vezane na unutrašnjem sloju dvosloja

help anchor the membrane to the cell's interior scaffolding.

pomažu učvrstiti membranu za unutrašnjost stanice.

Other proteins in cell membranes can help fuse two different bilayers.

Druge bjelančevine u staničnim membranama mogu spajati dva različita dvosloja.

That can work to our benefit, like when a sperm fertilizes an egg,

To može biti korisno, npr. kad spermij oplodi jajnu stanicu,

but also harm us, as it does when a virus enters a cell.

no može nam i naštetiti, kao kad virus uđe u stanicu.

And some proteins move within the fluid mosaic,

Neke se bjelančevine kreću unutar tekućeg mozaika,

coming together to form complexes that carry out specific jobs.

spajajući se u cjeline koje obavljaju određene poslove.

For instance, one complex might activate cells in our immune system,

Npr. jedna bi cjelina mogla aktivirati stanice u našem imunološkom sustavu,

then move apart when the job is done.

a onda se razići kad posao završi.

Cell membranes are also the site of an ongoing war

Na staničnim se membranama odvija rat

between us and all the things that want to infect us.

između nas i tvari koje nas žele zaraziti.

In fact, some of the most toxic substances we know of

Neke od najtoksičnijih tvari za koje znamo

are membrane-breaching proteins made by infectious bacteria.

bjelančevine su koje su napravile bakterije s mogućnosti prolaska kroz membranu.

These pore-forming toxins poke giant holes in our cell membranes,

Ti toksini koji prave pore stvaraju ogromne rupe u našim membranama,

causing a cell's contents to leak out.

zbog kojih sadržaj stanice iscuri u okoliš.

Scientists are working on developing ways to defend against them,

Znanstvenici traže način obrane protiv njih,

like using a nano-sponge that saves our cells

koristeći nano-spužve koje spašavaju našu stanicu

by soaking up the membrane-damaging toxins.

upijajući toksine koji oštećuju membranu.

The fluid mosaic is what makes all the functions of life possible.

Tekući mozaik omogućava sve životne funkcije.

Without a cell membrane, there could be no cells,

Bez stanične membrane ne bi bilo stanica,

and without cells, there would be no bacteria,

a bez stanica ne bi bilo bakterija,

no parasites,

parazita,

no fungi,

gljiva,

no animals,

životinja,

and no us.

ni nas.