RNA and the Origins of Life: Study with Video Lessons, Practice Problems & Examples

RNA is believed to have preceded DNA and proteins in the origins of life due to its unique properties. It can fold into complex three-dimensional structures, catalyze chemical reactions as ribozymes, and respond to environmental signals. RNA also serves as a genetic information storage molecule, capable of self-replication. The evolution of life likely progressed through three phases: the pre-RNA world, the RNA world, and the current DNA world, with RNA playing a crucial role in early cellular processes and the eventual transition to more stable DNA for genetic information storage.

Properties of RNA

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.

Life Requirements

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

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

Okay. So, this says, choose all of the following properties that indicate RNA predates DNA and proteins. So, let's go through these together and ask sort of yes or no questions. Is this a property of RNA that allowed it to predate DNA proteins? So, the first says that RNA has the ability to catalyze chemical reactions. So, does RNA have the ability to do this? Yes, it does. So, 'a' is one of the reasons that we think that RNA predated DNA because it does have the ability to catalyze these reactions. 'B' says the RNA is extremely stable. Well, is RNA stable? I mean, it is semi-stable, but not as stable as DNA and not as stable as proteins. So, this is not a property. So, 'b' is not one of the answers. 'C' says, RNA can fold into complex 3D shapes. Well, does this happen? Right. Yes. It does happen. And, it is one of the reasons that we believe that RNA predated DNA and proteins. 'D' says RNA can store information. Well, we know RNA stores information through mRNAs or microRNAs or different types of RNAs that we have today. So, 'd' is true. RNA does have the ability to store information, and that is a requirement for life. And, therefore, it is one of the reasons we think it predated DNA. And, finally, 'e', RNA is more complicated to make than DNA. Well, this is not true. Deoxyribose is more complicated to make than ribose, making DNA more complicated than RNA. So 'e' is not the answer. So the answers for this practice problem are 'a', 'c', and 'd'. So let's move on.

Ribozymes have catalytic functions because of why?

• A. They bind to proteins, which allow them to exert their effect on other molecules
• B. They are translated into proteins
• C. They can fold into 3D conformations that act similarly to proteins
• D. None of the above

Here’s what students ask on this topic:

What properties of RNA suggest it came before DNA and proteins in the origins of life?

RNA is believed to have preceded DNA and proteins due to its unique properties. Firstly, RNA can fold into complex three-dimensional structures, allowing it to perform various functions necessary for life. Secondly, RNA molecules called ribozymes can catalyze chemical reactions, a property not found in DNA. Lastly, RNA can respond to environmental signals through conformational changes in its structure. These properties suggest that RNA could have facilitated the chemical reactions and information storage needed for the formation of life before the evolution of DNA and proteins.

How does RNA store genetic information and replicate itself?

RNA stores genetic information in the sequence of its nucleotide bases (adenine, uracil, cytosine, and guanine). These sequences can be replicated through complementary base pairing, where each base pairs with its complement (A with U, and C with G). Certain RNA molecules, known as ribozymes, can catalyze their own replication by guiding the formation of new RNA strands. This self-replicating ability was crucial in the early stages of life, allowing RNA to pass on genetic information before the evolution of more stable DNA.

What is the RNA world hypothesis?

The RNA world hypothesis suggests that early life forms relied on RNA for both genetic information storage and catalysis of chemical reactions. According to this hypothesis, life evolved through three phases: the pre-RNA world, where simpler RNA-like molecules existed; the RNA world, where RNA became the dominant molecule for catalysis and information storage; and the current DNA world, where DNA took over as the primary genetic material due to its greater stability. RNA's unique properties, such as its ability to form complex structures and catalyze reactions, support this hypothesis.

What are ribozymes and why are they important in the context of the origins of life?

Ribozymes are RNA molecules that can catalyze chemical reactions, similar to protein enzymes. They are important in the context of the origins of life because they demonstrate that RNA can perform essential biochemical functions without the need for proteins. This catalytic ability supports the idea that RNA could have been the first molecule to facilitate the chemical reactions necessary for life. Ribozymes provide evidence that RNA could have played a dual role in early life forms, both as a genetic material and as a catalyst for metabolic processes.

What are the three phases in the evolution of life according to the RNA world hypothesis?

According to the RNA world hypothesis, the evolution of life progressed through three phases: the pre-RNA world, the RNA world, and the DNA world. In the pre-RNA world, simpler RNA-like molecules existed and catalyzed reactions. The RNA world followed, where RNA became the dominant molecule for catalysis and genetic information storage. Finally, the DNA world emerged, where DNA took over as the primary genetic material due to its greater stability, while RNA continued to play roles in protein synthesis and regulation. These phases highlight the transition from simple to more complex molecules in the evolution of life.