In this video, we're gonna be talking about something pretty interesting, how life first began on Earth. And so, ABO Genesis is the natural process of the origin of life on Earth. And it describes how life first formed from nonliving simple molecules. And the theory suggests that life originated in the oceans of Earth about 3,800,000,000 years ago, and this is billion with a b. So we're talking about an incredibly long time ago. And the theory suggests that life arose from non biological And these prebiotics were in high abundance on early Earth and include molecules such as hydrogen gas, water, ammonia, carbon dioxide, and methane. And so the question is, how did these prebiotics or these non biological molecules convert into the very first biomolecules? And so there are a few different theories. The atmospheric conversion theory suggests that the sun and lightning converted the prebiotics into the first simple biomolecules. And the hydrothermal vents theory suggests that the first biomolecules were formed in areas where the sunlight and lightning could not penetrate and that the vents on the ocean floors were the ones to provide the energy to convert the prebiotics into the first biomolecule monomers. And so let's take a look at our example to clear this up. And in this example of the biomolecule monomer formation, on the left over here, what we have are the prebiotic materials or the non biological materials. And so the first theory suggests that solar radiation and lightning provided the energy to spark the prebiotics to convert into the 1st biomolecule monomers. And, the second theory, theory 2, suggests that again, the first biomolecule monomers formed in areas where the sunlight and lightning could not penetrate and that, hydrothermal vents provided the energy to convert the first prebiotic materials into the first biomolecule monomers. And so these are 2 competing theories that both have a lot of supporting experimental evidence. And, over here we have a biomolecule monomer and the example that's being shown is an amino acid. And so we may never know which of these two theories is correct, but we do know that biomolecule monomers were formed. And so the next video, what we're gonna talk about is how did the first biomolecule polymers form. And so I'll see you guys in that video.
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concept
Biomolecule Polymer & Membrane Formation
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So now that we know how the first biomolecule monomers likely formed, we can now focus our attention on the polymers. So question, how did these more complex biomolecule polymers begin to form if living cells were not around yet to produce them? And so the answer to that is that the 1st biomolecule polymers likely polymerized or linked together, by proper alignment using the charged mineral surfaces of objects monomers that are negatively charged, and we also have this positively charged clay surface. And so there's an attraction between oppositely charged components. And notice in the next image, we have these bio these negatively charged biomolecule monomers that are aligned on the positively charged clay surface. And if there's proper alignment between neighboring biomolecule monomers and the conditions are right, then covalent bonds can form and link the biomolecule monomers together to create a biomolecule polymer. And there's lots of experimental evidence out there that shows that RNA and other polymers can polymerize in this fashion. So it's likely that the very first polymers formed in this way. So now that we've got biomolecule polymers formed, the next step is to get these biomolecule polymers to interact with one another, and that's where membranes and protocells come into play. So membrane formation was important because it enclosed biomolecule monomers and polymers and prevented them from diffusing away from each other, which increased the likelihood of those molecules to interact. And so membranes formed via what's known as the hydrophobic effect. And we'll talk more about the hydrophobic effect later effect later on in our course. But for now, I want you to know that membranes formed via the hydrophobic effect and that the formation of membranes was an important step for a biogenesis. So in our next example, what we're gonna see is that we have these phospholipids. And the phospholipids, we'll talk more about in our, later in our course. But in an aqueous solution, these phospholipids clump together and they accumulate. And in the way that they accumulate, you can see that they create a phospholipid membrane. And notice that, previous to the formation of the lipid membrane, we have these biomolecule monomers and polymers that are just floating around in solution, and they're likely diffusing away from each other. However, after the formation of the membrane, we have our biomolecule monomers and polymers enclosed within the membrane, which increases the likelihood of their interaction. And so this pool of molecules that are enclosed in a lipid membrane is known as a protocell. And a protocell is not a cell yet. It's actually the precursor to a cell and it has the ability to acquire characteristics over a long period of time and develop into a cell. So in the next video, what we're gonna do is talk about how these protocells link to the double origin theory of life. So I'll see you guys in that video.
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The Double Origin Theory of Life
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So the double origin theory states 2 different things. The first is that life has 2 origins, a coding system as well as an enzyme catalysis system. And the second thing that the double origin theory states is that these two systems developed in completely separate protocells and so they developed in separate protocells. And then later, these 2 separate protocells would have combined together. So let's take a look at our example down below and notice that we have 2 separate protocells And again, the double origin theory states that a coding system developed in one protocell whereas an enzyme catalysis system developed in the other protocell. And then these 2 separate protocells with different systems would have merged together to generate a single protocell with both systems, and then this protocell would have had plenty of time to acquire characteristics and to develop into the first life or the first cells. And so the next thing I wanna tell you guys is that RNA, not DNA, is believed to have been the 1st coding material and we can see that down here where RNA is shown as the coding system. And that's simply because during the origin of life, it would have been better to have a single molecule that can do more things, and RNA can do more things than DNA. RNA has both encoding and catalytic abilities whereas DNA only has encoding abilities. And so you might be thinking that this contradicts the double origin theory, because we have RNA and a single protocell that has a coding and catalysis system, But there's no contradiction, and that's because of this word here, enzyme. So, yes, RNA has a catalysis system, but it doesn't have an enzyme catalysis system. And recall that enzymes are proteins, and proteins and enzymes are way better catalysts than RNA. And so this protocell here with an enzyme catalysis system can do things that this coding RNA system cannot do. So there's no contradiction. So, DNA is believed to have shown up later down the line, and so the very first cells would have had an RNA coding system, an enzyme catalysis system and DNA. And so to summarize coding system, which developed in one protocell, and the a coding system, which developed in 1 protocell, and the second origin is an enzyme catalysis system, which developed in a separate protocell. And so that concludes our lesson on aveogenesis and I'll see you guys in the practice problems.
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Problem
Problem
Which of the following is not a popular theory for how biomolecule monomers first originated on Earth?
A
Previously assembled biomolecules likely arrived on Earth via an asteroid.
B
The sun and lightning energized the conversion of prebiotics to biomolecules.
C
Hydrothermal vents on ocean floors energized the conversion of prebiotics to biomolecules.
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Problem
Problem
Which theory relates to abiogenesis?
A
Endosymbiotic theory
B
Double Origin Theory
C
Cell Theory
D
Big Bang Theory
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Problem
Problem
What molecule was likely the first genetic/coding material? Why?