Life #01 | The Most Important Moment in the History of Life on Earth ! !

Welcome to the brand new episode of Imagicnation ! A blog where we will reveal the answers to some of the most interesting & curious questions related to science... 

Hey friends…let’s have a change in taste today. Unlike other days, today I will be discussing not on any health-related topic but may be something you will love more than that. Actually, I’m gonna tell you about an event so rare but vital that it happened only once in nearly 4 billion years of life on Earth…to which what I would probably call the most important moment in history of life. I mean, if that had never happened…perhaps there would be no Eukaryotes on Earth.

Fig. Diversity of life forms on Earth

 (Credits)  

Complex life looks quite different on the outside. But, whether it’s a plant, a bacterium or a frog, at the most basic level, Earth’s all complex life eukaryotes are built from essentially the same stuff. And because eukaryotes share so many similar things, it’s likely that we all have a common ancestor.  Did you ever know that you and that mango tree you used to climb, are cousins, just a few billion years removed?? But, for most of the history of life on Earth there was no anything as “Eukaryotes”. Earth was habitat to only two domains of basic life, the Bacteria and the Archaea. Also known as “Prokaryotes” these single celled organisms dominated the Earth billion years back, but in all of life’s history they have never got big or complicated like the eukaryotes did. And the reason is simply because they could not aggregate the energy produced. I don’t know whether you know or not, but the energy we produce is stored in the form of ATP (Adenosine Triphosphate). 

Fig. Diagrammatic representation of ATP

(Credits) 

It’s like a token that gives us one play in the cellular arcade. We may use a token in a protein that cuts DNA…or maybe one that breaks down our food into simple particles. And when we run out of these tokens…game over !! But, prokaryotes can only manufacture those energy tokens or ATPs on their outer surface, and expanding their surface area to create more energy ATP would exponentially increase their volume which then requires more energy to sustain. Let’s suppose a bacterium wanted to increase its radius by 25 times. Then it would have 625 times as much membrane to make those energy tokens with! All right ! But you’d also need to manufacture 625 times more proteins and membranes for those new ATP factories. In the meantime, the volume of your cell has increased 15000 times and you have got to fill that with protein machinery too, so you’re going to need 15000 genomes to keep up with demand. And, that was a catch-22 that prokaryotes could never overcome...on their own!!!  

So, what exactly happened ?? 

Then, something unimaginable happened. An event so rare that it happened only once in entire life’s history. One day, an Archaean cell bumped with a Bacterium and engulfed it up. And for some unknown reason, it didn’t digest it. We don’t exactly know why, but for the first time one organism was living in symbiosis NOT with another organism but INSIDE the other organism, which we call today as ENDOSYMBIOSIS. 

Fig. Endosymbiosis

(Credits) 

And every living thing we can see today with the naked eye is descended from that synthesis. By cooperating with its new host, this bacterium was able to avoid 99% of its genome, switch off most of its own machinery and concentrate on one main task, i.e, making ATP. Thus, this way, the first mitochondrium was born and its power level was over 9000 !!!

Fig. Prokaryotic cell v/s Eukaryotic cell

(Credits) 

That first eukaryote was extremely wealthy ! Huge amount of ATP than it knew what to do with ! It was free to grow and specialize, and experiment with new great abilities. Later, some of them swallowed up a second bacterium that could perform photosynthesis, and they eventually became plants ! And long before back, eukaryotes morphed into everything from octopus to pine trees, to dinosaurs and penguins… and even us. Our single cell can use about 10 million ATPs every second. All together we burn through our body weight in these ATP tokens every day. Considering we only have 60 grams of ATP tokens in our entire body, at any one period of time there’s a lot of recycling going on. And all that happens in the numerous mitochondria present in our cells. To recycle all these ATP tokens we need in a day, it takes an tremendous number of mitochondria, hundreds or thousands per cell…or maybe a quadrillion in our entire body. If we stretched their folded membranes out altogether, our body would carry four football fields worth of ATP-making real estate. We know that the mighty mitochondria started this way because they still contain their own genome, a circle of DNA like that of a prokaryote’s, and we can trace one third of our genes to either bacteria or archaea. Hence, simply speaking, “Eukaryotes are a genetic mashup”. In a world filled with bacteria and archaea bumping into each other every minute of every day for the past couple of billion years, this eukaryotic origin story has happened only once. You and the mango tree’s common ancestor tells us so.

!

 (Credits) 

And finally...

We all are thankful to that single moment when two branches from two divergent trunks on the tree of life joined back into one, freeing life from its energetic constraints and giving nature the freedom to build endless forms immensely beautiful…

---

 That's all for today guys...

Hope you liked that ! 

And if u did, please feel free to drop your comments your too !!