The top portion of the campus entrance gate showing IISER Pune logo

This Soup Had Prebiotic Croutons

Posted on
Share this article
In Which I Talk (Really, Really Quickly) About Life By Bruhad Dave It’s the stuff of existential nightmares. Why is this stuff happening in my life? What is happening in my life? What exactly is life in the first place? That last one is among the first questions that a basic biology textbook would ask too. Turns out that quite a few biologists think about such questions professionally, although in less personal terms. Origins-of-life (OoL) research has been variously described as ‘the most fundamental question facing biology’, ‘just another internet rabbit hole and no clarifying Wonderland at the other side’, and also ‘what? just…what?’ It would seem that all these are rational responses to what OoL research aims to uncover: how did chemistry transition into biology? How did a bunch of atoms come together to form something as complex as a cell, let alone evolve into something as complex as a human being? Physicists have thought about this question too, because life seems contrary to the laws of thermodynamics at the first glance; scientists such as Schrodinger — who wrote a booklet titled ‘What is Life?’ — have wondered about the precise nature of life. What is life? How Did It Come About?  Defining life is important in order to be able to puzzle out how it arose. There are a few characteristics that most scientists agree an entity should have for it to be called alive. It should be highly organised, be able to maintain its internal environment despite the flux on the outside, it should react to being poked (or more generally, to stimuli), it should be capable of growth, and it should be able to create more of itself via some form of reproduction. Metabolism, which is essentially the chemistry that lets living things harvest energy from a source, is also sometimes added as the sixth defining characteristic of life. Good, now we can talk about where life actually came from. The most obvious and perhaps the least rigorous answer is that life did not arise out of any messy, ancient chemistry. Instead, it was designed to be the way it is. A comparably iffy theory called panspermia proposes that microbes hitched a ride on meteors and plunged to earth in a firework show. Since this hypothesis has not yet led to demonstrable proof, it, runs up against a problem: It just informs us of a possible way by which life landed on earth, not how it actually came about, instead shunting that particular liability to the stars. The theory that life is eternal sidesteps the question altogether. What’s left is the primordial soup. The warm little pond, as Darwin put it. The chemical origins of life. The Chemical Origins of Life: RNA, Proteins, or Lipids?  Life, as science tells us, is fundamentally based on chemistry, and interactions between chemical entities. However, the reason why biochemistry is unique is that life depends on a specific set of ‘complex chemicals’, such as DNA, RNA and proteins. These are three examples of biomolecules, and these are at the core of some of the more specific questions that OoL researchers ask. Which came first, the nucleic acids or the protein? There is a school of thought that would tell you that the answer is ‘neither’. It suggests instead that lipids (the biomolecules which form fats and oils) came first. All our cells have cell membranes, sacs which demarcate inside from outside, and these cell membranes are made of lipids. It is safe to assume that lipids turned up at some point before proto-cells were formed. But the argument is that the first objects that approached anything like a cell were simply bubbles made of lipids inside a water body, aka vesicles. This is not as weird as it might sound and you can make some at home if you add a bit of oil to water and stir. But there is no mention of metabolism, nor how such metabolic machinery would’ve gotten into such a vesicle. A lot of people, long before discussions related to vesicles or metabolism, had already been talking about an RNA World, a world where RNA had somehow formed and become both the informational molecule as well as the machinery of metabolism and replication. Again, not as out there as it might sound. RNA is ridiculously versatile and we know of RNA-enzymes (most enzymes are made of proteins). There are also subscribers to the pre-RNA World, a world where RNA-like molecules were the main players. The backbone of nucleic acids (RNA and DNA) is made of a long chain of sugar molecules (this is a sugar called ribose, not table sugar, mind you) linked together by phosphate bonds. Pre-RNA world proponents suggest that compounds such as threose (another kind of sugar), peptides (the units proteins are made of) or glycol (also made of a bunch of carbons, hydrogens and oxygens) might have formed the backbone of pre-RNA nucleic acids. At the same time, the information carrying bits which form the rungs of the nucleic acid ladder — those strings of letters you see which biologists point at and call DNA sequences, for instance — might have been distinct from the ones we call the canonical bases today. Both the pre-RNA World theory and the RNA World theory agree on one thing though, that polymerisation of what we know today to be biologically important molecules had to occur. But of course, there had to have been these individual molecules on terra antiqua for them to line up in orderly chains in the first place. Were these organic molecule around at the time? Oparin and Haldane both thought about this question, and they both arrived at the following conclusion: Given some sort of energy source, simple inorganic compounds could spontaneously give rise to organic ones. Famously, Miller and Urey decided that the said energy source might have been lightning. They put a bunch of stuff including methane and ammonia gas inside a flask and shocked it. It sounds iffy but their reaction setup was exceedingly scientific and nothing blew up. Instead, their reaction mixture was later found to contain amino acids among other things that are relevant to life’s biochemistry. Where Did Life Originate?  The primordial soup was still the prime candidate as the concoction where the first inklings of life came into existence. Whether this soup was inside or by hot springs or around deep sea vents was another matter completely. You can easily find supporters for either location. Deep sea vents might seem like an altogether hostile place for life to exist, let alone for it to arise. We’re talking temperatures that may be anywhere between 60 and 460 degrees Celcius, way down in the abyssal deep. But life not only exist there, it thrives there. These vents are more biodiverse than their surrounding patch of sea floor, because organisms called chemoautotrophs (a big word for things that break down inorganic chemicals in order to produce energy for themselves) just love these underwater geysers. Their metabolisms also provide clues to how early life may have gone about things. So, boiling water several kilometres under the sea? Not a ridiculous idea. What about hot springs? Well, evidence — including fossilised rocks called stromatolites — exists, which suggests that hot springs might have been popular locales for the emergence of early cells too. The debate rages on, but the bigger question remains. How did life manage to pop up? We could attempt to try and synthesise it inside a lab, and many people try to do just that. The issue with that might be that even though some lab manages it using biochemical pathway X, it might not be the same path that life as we know it actually took, but rather a really good alternative. It’s frustrating, and not only because biologists do not have access to time machines (hurry up, physicists!). As complex as life is, our ancestors may be forgiven for coming up with the concept of creation. It seems difficult to imagine those little cells, the simplest units of life, were made as if by chance, and also how mind numbingly slow (and geologic history does operate at that pace) that process must have been. Even scientists, in what I like to think of as moments of clarity rather than weakness, have been known to conclude, after chipping away at the problem until it is irreducible, that at this most minuscule of stages, bookended by biochemistry, some miracle occurred. At this smallest of scales, it becomes clear that such assumptions of the miraculous are well founded rather than separate from science. After all, so many of the most fascinating scientific certainties were once firmly in the realm of the wondrous. This then, is an ideal attitude, insurance that the bones of this “miracle” will be made to shine through (perhaps even by radioisotope or fluorescent tagging). But make no mistake, OoL researchers are not likely to resort to some kind of ‘divine foot in the door’, as Richard Lewontin put it. We’ll get there eventually, and when somebody asks in frustration, ‘What is life?!’, we will be able to provide a full and detailed answer. That will do nothing whatsoever to alleviate the angst of said frustrated person, but it will represent the fact that we, in the biggest circle of life there may be, used our brains, ‘the most complex and orderly arrangement of matter in the universe’ according to Asimov, to tease apart the answer to life, and perhaps by extension, the universe and everything. It will be a cosmic joke indeed if it somehow turns out to be 42.