Stated Clearly presents What is the RNA world hypothesis? If you
were to go back in time a 120 million years, you'd find yourself
in a dinosaur world. 500 million years ago was a world of trilobites and other
strange sea creatures. 3.4 billion years ago was the world of the first living
cells and if you were to go back further still scientists suspect that chains of a
chemical called RNA, or something similar to RNA, kick-started this entire
beautiful mess that we call life! RNA is thought to have given rise to life for several reasons: Chains of RNA are found abundantly in all
living cells today, RNA is a closed chemical cousin to DNA, and with very
little help from researchers, chains of RNA can replicate evolve and interact with
their environments. While many details have yet to be worked out, the RNA world
hypothesis is the simple idea that somewhere on early planet, perhaps in a
tide pool or hot spring, the Earth's chemistry was producing random chains of RNA. Once formed they begin replicating, evolving, and competing with each other for survival. As these chains evolved and diversified, some eventually began
cooperating to produce the genetic code a wide array of complex proteins, and
even living cells which, from the perspective of RNA, can actually be
thought of as houses or survival machines for RNA to live inside. To
understand how RNA chains can interact with their environments, replicate, and
evolve; we first need to understand the simple process of base pairing. chains of RNA are made of nucleotides -
small molecules that come in four different types labeled A, C, U, and G.
The backbone atoms of a nucleotide, shown here is a yellow bar, can form strong
chemical bonds with the backbone atoms of any other RNA nucleotide. This means
that different chains can have completely different sequences from left
to right. The parts we call the bases of nucleotides - the colored section labeled
A, C, U, or G - are attracted to other bases sort of like a magnet but they're
selective about who they will stick to. G selectively pairs with C, A selectively
pairs with U. When basis find their matches and stick together, we call it
"base pairing". Researchers have found that with a little bit of assistance,
base pairing allows chains of RNA to replicate and evolve. Here's how it works: When a long chain of
RNA is suspended in cool water with high concentrations of free nucleotides, the
chain can act as a template for its own replication. Nucleotides automatically
base pair with their partners on the existing chain. If their backbone atoms
form chemical bonds with each other (and, by the way this is the part that currently requires assistance from researchers, we're not yet sure how this
would have happened in the wild) a complimentary RNA strand is born - one
with the exact inverse sequence of the original! If the water is then heated,
paired basis lose their grip allowing both chains to act as templates when the
cycle repeats. The great thing about this process is that every other RNA chain
produced as a copy of the original, but sometimes mutations slip in. This means
that as these chains compete for survival and reproduction, true evolution - descent with
modification acted upon by selection - can operate on chains of RNA. As amazing as
replication is, base pairing also gives RNA chains a second special ability. When placed in water cool enough for base pairing but without enough free nucleotides
for replication, chains will fold up and base pair with themselves! The end result is a complex shape with
certain sticky basis pointing outward because they weren't able to find
partners. These sticky, outward-facing bases can
cause unique chemical reactions by interacting with other molecules in
their environment. A folded chain of RNA capable of guiding a specific chemical
reaction is what we call a ribozyme. Some ribozymes break certain molecules apart others joined certain molecules together.
A ribozyme's specific function is determined by its specific shape, and its
shape is determined by its sequence. If a mutation changes a ribozyme sequence the, shape can be modified and so can its function. When ribozymes were first
discovered, scientists wondered how difficult it would be for random chains
of RNA to evolve legitimate survival functions. Imagine, for example, a ribozyme that could build nucleotides out of molecules it finds in its environment.
Across multiple generations, natural selection could promote and refine this
ribozyme because the chain would tend to have access to more free nucleotides than its rivals, allowing it to replicate more often. To explore this idea researchers at Simon Fraser University
produced a large group of random RNA chains and examined them to see if any
happened to be able to make nucleotides. Surprisingly, some actually could, but
they weren't very efficient. Researchers selected out the successful chains and
then use a lab technique called PCR to quickly replicate them with slight
random mutations. After just 10 rounds of PCR followed by selection, highly
efficient nucleotide building ribozymes evolved. These are molecules with the
life-like ability to actively participate in their own survival! These ribozymes,
and many others produce through similar experiments, are beginning to blur the
line between living things and simple chemistry! So to sum things up, the RNA
world hypothesis is the simple idea that the first things to replicate and evolve
on our planet, may have been chains of RNA or something similar to them. While the basic idea of the RNA world
does seem to give us a promising pathway to the origin of life, it's still very
much a work in progress. As mentioned, one of several unsolved problems is: how did
nature get backbone binding to function without the special enzymes or lab
techniques we use today? While many researchers continue to focus on RNA,
others are investigating alternative molecules: chemical systems that might
replicate and evolve without assistance and could have given rise to RNA.
Continual breakthroughs are being found in both avenues of research. I'm Jon Perry, and that's the RNA world hypothesis Stated Clearly. This video is funded by the Center for
Chemical Evolution, the National Science Foundation, and NASA! Though we do receive grants from time to time, Stated Clearly is made possible with financial
contributions from viewers like you. To support us, visit our website at statedclearly.com and click "contribute" I'm happy to announce that you can now alsosupport us at patreon.com/statedclearly So long for now stay curious!
Sooooooo cells are like Mechs for RNA to fight in cool
How does a rna ribosime replicate? If it’s all self bound (creating nucleotides) then it’ll never be in the form needed to allow it to replicate
Seems like a logical regression from Dawkins’selfish gene model.
That's really cool. I might have gotten into chemistry if I had known about this hypothesis in college.
Fun fact: you can't PCR RNA directly. PCR only works on DNA. To be able to replicate RNA, there are three steps: (1) reverse transcribe the RNA into DNA, (2) PCR the DNA, and (3) transcribe the DNA back into RNA. There's probably some purification that happens as well and then the actual selection process where the various RNA molecules are exposed to whatever they are studying to see which RNA do best. That's all one round - the video said 10 rounds were needed to get to where they wanted. I'm surprised it didn't take more.
What's the origin story of RNA? How did it come to be?
Life is just emergent self-referential systems shaped by competition with other systems through survival, replication, and random anomalies. This pattern can be seen at every level, from the behaviour of crowds, linguistics, musical theory, all the way down to viruses, single-cell organisms, and genetics. This digital age is really just the first step towards understanding these innate emergent properties of our universe.
This was really cool to watch till his voice almost put me to sleep. He’s got a soothing voice
https://en.wikipedia.org/wiki/RNA
https://en.wikipedia.org/wiki/Ribozyme
https://en.wikipedia.org/wiki/Simon_Fraser_University