Abiogenesis - Online Tutor, Practice Problems & Exam Prep

Abiogenesis describes the natural process of life originating from nonliving molecules around 3.8 billion years ago, likely in Earth's oceans. Theories suggest that prebiotic materials, like hydrogen and methane, formed biomolecule monomers through atmospheric conversion or hydrothermal vents. These monomers polymerized on charged mineral surfaces, leading to the creation of protocells, which enclosed biomolecules via the hydrophobic effect. The double origin theory posits that separate protocells developed distinct coding and enzyme systems, merging later to form the first cells, with RNA as the initial coding material before DNA emerged.

Formation of Life

In this video, we're going to be talking about something pretty interesting: how life first began on Earth. ABO Genesis is the natural process of the origin of life on Earth. It describes how life first formed from nonliving simple molecules. 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. The theory suggests that life arose from non-biological elements, and these prebiotics were in high abundance on early Earth and include molecules such as hydrogen gas, water, ammonia, carbon dioxide, and methane. The question is, how did these prebiotics or these non-biological molecules convert into the very first biomolecules?

There are a few different theories. The atmospheric conversion theory suggests that the sun and lightning converted the prebiotics into the first simple biomolecules. 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. Let's take a look at our example to clear this up. 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.

The first theory suggests that solar radiation and lightning provided the energy to spark the prebiotics to convert into the first biomolecule monomers. The second theory, again, suggests that 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. These are two competing theories that both have a lot of supporting experimental evidence. Over here, we have a biomolecule monomer, and the example that's being shown is an amino acid. We may never know which of these two theories is correct, but we do know that biomolecule monomers were formed.

In the next video, we're going to talk about how the first biomolecule polymers formed. So I'll see you guys in that video.

Biomolecule Polymer & Membrane Formation

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? The answer to that is that the first 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. There's an attraction between oppositely charged components. Notice in the next image, we have these negatively charged biomolecule monomers that are aligned on the positively charged clay surface. 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. There's lots of experimental evidence out there that shows that RNA and other polymers can polymerize in this fashion. 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.

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. Membranes formed via what's known as the hydrophobic effect. We'll talk more about the hydrophobic 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 abiogenesis.

In our next example, we're going to see that we have these phospholipids. And the phospholipids, we'll talk more about later in our course. But in an aqueous solution, these phospholipids clump together and accumulate. In the way that they accumulate, you can see that they create a phospholipid membrane. Notice that, previous to the formation of the lipid membrane, we have these biomolecule monomers and polymers just floating around in solution, 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. This pool of molecules that are enclosed in a lipid membrane is known as a protocell. 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.

In the next video, we're going to talk about how these protocells link to the double origin theory of life. So I'll see you guys in that video.

The Double Origin Theory of Life

So the double origin theory states two different things. The first is that life has two origins, a coding system as well as an enzyme catalysis system. The second thing that the double origin theory states is that these two systems developed in completely separate protocells. These separate protocells later combined. Let's take a look at our example below and notice that we have two separate protocells. The double origin theory states that a coding system developed in one protocell whereas an enzyme catalysis system developed in the other protocell. These two separate protocells with different systems would have merged together to generate a single protocell with both systems. This protocell would have had plenty of time to acquire characteristics and to develop into the first life or the first cells.

The next thing I want to tell you is that RNA, not DNA, is believed to have been the first coding material, as shown down here where RNA is depicted as the coding system. This is because during the origin of life, it would have been more advantageous to have a single molecule that can do more things, and RNA can do more than DNA. RNA has both encoding and catalytic abilities, whereas DNA only has encoding abilities. You might think this contradicts the double origin theory because we have RNA in a single protocell that has both a coding and catalysis system. However, there is no contradiction because of the presence of the word "enzyme". Yes, RNA has a catalysis system, but it does not have an enzyme catalysis system. Recall that enzymes are proteins, and proteins and enzymes are far superior catalysts compared to RNA. Therefore, this protocell with an enzyme catalysis system can perform functions that the coding RNA system cannot.

DNA is believed to have appeared later in the timeline. So, the very first cells would have had an RNA coding system, an enzyme catalysis system, and eventually DNA. In summary, the double origin theory posits a coding system, which developed in one protocell, and an enzyme catalysis system, which developed in a separate protocell.

That concludes our lesson on abiogenesis, and I'll see you guys in the practice problems.

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.

Which theory relates to abiogenesis?

• A. Endosymbiotic theory
• B. Double Origin Theory
• C. Cell Theory
• D. Big Bang Theory

What molecule was likely the first genetic/coding material? Why?

• A. Protein
• B. RNA
• C. DNA
• D. Carbohydrates

Here’s what students ask on this topic:

What is abiogenesis and how does it explain the origin of life on Earth?

Abiogenesis is the natural process by which life arose from nonliving matter on Earth, approximately 3.8 billion years ago. It explains the origin of life by suggesting that simple molecules like hydrogen gas, water, ammonia, carbon dioxide, and methane, which were abundant on early Earth, underwent chemical reactions to form the first biomolecule monomers. These monomers then polymerized on charged mineral surfaces, leading to the creation of more complex biomolecule polymers. Eventually, these polymers were enclosed within lipid membranes, forming protocells. Over time, these protocells acquired characteristics that led to the development of the first living cells.

What are the main theories explaining the formation of the first biomolecule monomers?

There are two main theories explaining the formation of the first biomolecule monomers: the atmospheric conversion theory and the hydrothermal vents theory. The atmospheric conversion theory suggests that solar radiation and lightning provided the energy needed to convert prebiotic molecules into biomolecule monomers. In contrast, the hydrothermal vents theory posits that the energy for this conversion came from hydrothermal vents on the ocean floor, where sunlight and lightning could not penetrate. Both theories have substantial experimental support, but it remains unclear which one is correct.

How did the first biomolecule polymers form in the absence of living cells?

The first biomolecule polymers likely formed through a process involving charged mineral surfaces. Negatively charged biomolecule monomers aligned on positively charged clay surfaces, and if the conditions were right, covalent bonds formed between neighboring monomers, creating polymers. This process did not require living cells and has been supported by experimental evidence showing that RNA and other polymers can polymerize in this manner. The formation of these polymers was a crucial step in the development of early life.

What is the double origin theory in the context of abiogenesis?

The double origin theory in abiogenesis posits that life originated from two separate systems: a coding system and an enzyme catalysis system. These systems developed in separate protocells. The coding system, likely based on RNA, emerged in one protocell, while the enzyme catalysis system, involving proteins, developed in another. Eventually, these two protocells merged, combining their systems to form a single protocell with both coding and catalytic capabilities. This combined protocell then evolved into the first living cells, with RNA initially serving as the coding material before DNA appeared.

Why is RNA believed to have been the first coding material instead of DNA?

RNA is believed to have been the first coding material because it has both encoding and catalytic abilities, unlike DNA, which only has encoding capabilities. During the origin of life, having a single molecule that could perform multiple functions would have been advantageous. RNA can act as a catalyst in biochemical reactions and store genetic information, making it a more versatile molecule for early life forms. DNA is thought to have appeared later, providing a more stable means of storing genetic information as life became more complex.