Okay. So, in this topic, we're going to talk about RNA and the origins of life. This video will mainly focus on the properties of RNA that suggest that it potentially came before other things like DNA and protein. The reason that we think RNA came before DNA and protein is because it has unique properties that suggest it predated them. So, what are these properties? Well, one of them, and we talked about some of these before, is that RNA can fold into complex three-dimensional structures. We can't just have these linear strings of RNA in order to be able to form the complex structures or chemical reactions that were needed for life to form. But, RNA has the ability to form into 3D structures, suggesting that it could form these structures that have functions, allowing for the formation of life. One of these functions is through RNA molecules called ribozymes, which are complex 3D RNA molecules that actually have abilities to catalyze chemical reactions. When these structures form, they are really complex today, but you can imagine, in the origins of life, early Earth, these RNA molecule three-dimensional structures were simple, and they helped speed up small chemical reactions, which are necessary for life. This is one of the properties that allows us to think that RNA likely formed before DNA, because DNA doesn't have these properties. Another final property we want to talk about is that the shape of RNA, the shape of these three-dimensional structures, can change when bound to small molecules or other RNAs. The fact that these three-dimensional structures are not entirely rigid allows for RNA to respond to signals in the environment through conformational changes of its structure. The fact that RNA can fold into these structures, catalyze chemical reactions, and respond to its environment, independent of life, suggests that these were the foundations that led to the creation or formation of life on Earth. So, just to get an idea, this is actually a ribozyme, an RNA molecule that can catalyze chemical reactions. And you can see that it's complex, it's 3D, but it also has the ability to respond to different small molecules or something that comes in and binds, and then can change its structure. These are really important properties of RNA that suggest that it predated DNA and protein. So let's move on.
RNA and the Origins of Life - Online Tutor, Practice Problems & Exam Prep
Properties of RNA
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Life Requirements
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So if RNA is going to be, you know, if we're going to say, RNA was the molecule responsible for the origination of life, it has to meet certain requirements. So, the first requirement it has to meet is it has to be able to store information. Because things like heredity are responsible for the ability to pass on genetic information to our offspring in order to continue life. So, RNA has to have the ability to do this. And today, obviously, it doesn't do this for the most part because it is so complex today. But you can imagine in the beginnings, it did have the ability to do this because it forms these polynucleotide chains that store information, can be replicated, but also have the ability in certain ribozymes to guide its own formation and replication. DNA doesn’t have these properties, but RNA does. Now, the second requirement for life is that life requires the ability to speed up, or otherwise known as catalyze, chemical reactions. Sustaining reactions really occur too slowly to have happened by chance. So, RNA has the ability to catalyze and speed up these reactions. And today, we see this. We have ribozymes or things like rRNA and ribosomes, which are really responsible for speeding up chemical reactions. And, as RNAs were thought to be present before proteins, we can see things like ribosomes as a remnant of evolution because RNA was likely driving that process. It still drives it today. So if we look at RNA as a storage molecule, we've seen these before. We have these single-stranded RNA molecules that have bases, and the order of these bases determines its structure, its function, and that's really important for being an origin of life molecule. So, let's move on.
Evolution of RNA
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So now, let's talk about the evolution of the RNA world. There were likely three phases in the history of life. The first one is going to be called the pre-RNA world. This world had an RNA-like molecule before RNA was actually created, and it had the ability to catalyze reactions. There was probably some kind of polymerase-like structure, much simpler than RNA. But, eventually, over time, it became and transitioned into RNA, and probably catalyzed the formation of the first RNA molecules. It is believed that this world may have even arisen before the first cell. These are just chemical reactions that occurred before there were even cells present on Earth. But eventually, RNA became the dominant force.
When the RNA world was really in full swing, chemical reactions likely occurred in compartments to separate them. Sometimes, chemical reactions need to be separated from other molecules to occur. During this time, the first cell likely had a sort of small or very simple membrane bilayer, and inside of it, the only thing inside of it likely was catalytic RNAs that could do chemical reactions. You have chemical reactions on the outside and then chemical reactions inside this membrane bilayer. You can barely consider this a cell, but it was. It had a membrane bilayer and sort of things going on inside, but this is very early. Because the RNA molecules existed inside the membrane bilayer, they could evolve separately from the chemical reactions going on outside the environment. This separation is really important and likely led to the development of more complex cells.
At this time, RNA molecules had to be able to self-replicate themselves because they were separated from the environment. The only way they could continue is to replicate their own cells. But eventually, this transition to DNA occurred. Today, we know that DNA is more stable than RNA and acts as a better sort of store of genetic information because it is more stable. The problem is, deoxyribose is more complicated to make than the ribose found in RNA. But today, we don't really care about that, or it doesn't really matter, because we have all these complex proteins that can handle the formation of deoxyribose. Eventually, it became the permanent information storage molecule. So, those are the three phases of this evolution process that began with the pre-RNA world, led to the RNA world, and then led to what we know now, which is what we are living in currently: the DNA world. So let's move on.
Choose all of the following properties that indicates RNA pre-dated both DNA and proteins.
a) RNA has the ability to catalyze chemical reactions
b) RNA is extremely stable
c) RNA can fold into complex 3D shapes
d) RNA can store information
e) RNA is more complicated to make than DNA
Problem Transcript
Ribozymes have catalytic functions because of why?