Ever wondered or thought of figuring out the answer of the world famous unsolved riddle “Which came first, chicken or the egg? If taken a literal interpretation of the Bible, it would put the chicken before the egg. To quote Genesis: “And God blessed them, saying, be fruitful, and multiply, and fill the water in the seas, and let fowl multiply in the earth.” There is no creation, so neither the egg nor the chicken came first.
But, astoundingly, scientists like James Watson and Francis Crick worked out the first ever 3D structure of the DNA. The structure was a double helix with two long chains of four basic chemicals which acted as the basic alphabets for the language of life. This structure and its stability permitted information storage for all of life’s needs. Each of this chain specified the content of its partner. This arrangement suggested a mechanism for reproduction. The two strands of the DNA double helix parted company. As they did so, new DNA building blocks, called nucleotides. Two double helices now existed in place of one, each a replica of the original.
This double helix structure initiated an avalanche of discoveries about how living cells function and reproduce. They also triggered speculations about life’s origins. There are various definitions of life because it is one of the least understood subjects. The simplest and accurate definition would be “Life is a self-sustained chemical system capable of undergoing evolution”.
Genes are a sequence of DNA, Richard Dawkins elaborated on this in his book The Selfish Gene: “At some point a remarkable molecule was formed by accident. We will call it the Replicator. It may not have been the biggest or most complex but it could make copies of itself, which is uncommon for a molecule.” DNA fits as a perfect candidate for this molecule. But there were a lot of complications, as DNA replication cannot proceed without the help of a number of proteins, proteins are members of a family of large molecules that are chemically different from DNA. just like DNA proteins are constructed by linking smaller units called amino acids, together it forms a long chain. Cells use twenty such different blocks in combination to do a variety of tasks. Enzymes a subclass of proteins act in speeding up chemical processes that would otherwise take place too slowly for life to exist. DNA holds the recipe for proteins. Yet that information cannot be retrieved or copied without the help of some proteins in the first place.
So which molecules appeared first? Is it the proteins (the chicken) or DNA (the egg)? A possible solution appeared when we introduced RNA. this class of molecule is like DNA, assembled by the same building blocks played a versatile role inside a cell. Certain RNA carries information from the DNA to construct proteins. RNA takes many forms during the process it can also form a double helix that resembles the DNA. In 2006 the Nobel prizes in both chemistry and medicine were awarded for discoveries concerning the role of RNA in editing and censoring DNA instructions.
A simple solution for the chicken-and-egg riddle fell into place. Life began with the appearance of the first RNA molecule. Nobel Laureate Walter Gilbert of Harvard University quoted “One can mull over an RNA world, containing only RNA molecules that serve to catalyze the synthesis of themselves. And The first step of evolution proceeds then by RNA molecules performing the catalytic activities necessary to assemble themselves from a nucleotide soup.” In this vision, the first self-replicating RNA that emerged from non-living matter carried out the functions now executed by RNA, DNA and proteins. Various other clues also supported the idea that RNA appeared much before proteins and DNA in the evolution of life.
So to conclude it was RNA all this time, and where did RNA come into existence? Was it really randomness that led to the formation of the first RNA molecule? Or are we descendants of a really old alien species whose RNA somehow travelled through the depths of space, preserved in time, took a piggyback ride to earth millions of years ago on a frozen comet?
Keep thinking! Maybe you, our next scientist in the origin-of-life field can crack it.
For Kritika happiness is chocolates, loads of Netflix, journal scribblings and of course music. A child at heart she is currently grappling with adulting. On any given day you'll find her on the lookout to learn new things and the perfect cup of coffee. Drop in a line at [email protected] if you liked her stories or have exciting ideas to share!
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