Prokaryote Metabolism and Ecology - Online Tutor, Practice Problems & Exam Prep

Prokaryotic metabolism is diverse, with organisms classified as autotrophs or heterotrophs based on their carbon source. Energy sources include light (phototrophs), organic molecules (chemoorganotrophs), and inorganic molecules (chemolithotrophs). Prokaryotes play crucial roles in the nitrogen cycle through nitrogen fixation, converting atmospheric nitrogen into usable forms. They also contribute to the carbon cycle as decomposers and produce oxygen via photosynthesis. Understanding these metabolic pathways highlights the essential functions of prokaryotes in ecosystems and their interdependence with other organisms.

Prokaryote Metabolism

Hi. In this video, we'll be taking a look at prokaryotic metabolism, as well as how prokaryotes factor into the ecosystem. Now, you might recall that prokaryotes have a diverse array of metabolic options. And just to review all the different terms that can apply to metabolism, let's take a look at these terms here. Now to be clear, these first two terms, heterotroph and autotroph. Right? These two terms essentially, specify where the carbon source comes from for the organism. Right? Autotrophs will make their own carbon compounds. Right? They're going to oxidize, like we learned about the Calvin cycle, for example, and they're going to use inorganic carbon, right, like CO2, CH4, these are both gases. They're going to take carbon from those gases and they're going to synthesize carbon compounds to use as fuel for various metabolic pathways. Heterotrophs, on the other hand, use carbon compounds that are synthesized by other organisms to fuel their metabolic processes. So essentially, heterotrophs all depend on autotrophs to build the carbon compounds that they're going to end up using. So again, autotroph and heterotroph simply refer to where the carbon source is coming from for these organisms. Now these next three terms, phototroph, chemoorganotroph, and chemolithotroph, these terms refer to the energy source that the organism is going to use in order to perform its metabolic functions. So, essentially, what we have here is carbon source and energy source. And we're actually going to have to combine these terms to give the full name to the metabolic pathways of a particular organism. But before I get ahead of myself there, let's talk about what each of these terms means. So phototrophs, use light energy and they're going to produce ATP via photophosphorylation, which is a process we've already talked about, back when we were discussing, photosynthesis. Now chemoorganotrophs are going to oxidize organic molecules for energy, and some are going to produce ATP via oxidative phosphorylation, which is again another process that we talked about during our discussion of cellular respiration. Lastly, chemolithotrophs oxidize inorganic molecules for energy. And, again, ATP is going to be produced by oxidative phosphorylation there. So, essentially, the difference between chemoorganotrophs and chemolithotrophs, whether or not they're using organic or inorganic molecules, and phototrophs, they are using light, not molecules, as their energy source. So you can have photoautotrophs, but you can also have photoheterotrophs. Likewise, you can have chemoorganoautotrophs or chemoorganoheterotrophs. So, essentially, you know, will pick heterotroph or autotroph, and then, one of the three below, mush them together and there you have your type of metabolism. So there are many different combinations. Right? And the basic breakdown is where are you getting your carbon from, where are you getting your energy from? Right? Those are the distinguishing factors. And, you can see that in this little diagram, many different organisms are heterotrophs. Many different organisms are autotrophs, and they actually feed into each other. You know, autotrophs provide the carbon compounds that heterotrophs are going to need to use. Heterotrophs are going to provide the inorganic materials that autotrophs will need to use like carbon dioxide. Hopefully, this is all familiar territory as these are ideas that we have discussed previously. For example, when we talked about photosynthesis. Now, the other distinctions that you need to be aware of in terms of metabolic pathways and prokaryotes involve the use of oxygen. So, some prokaryotes, eukaryotes, but we're really just worried about prokaryotes here, but some prokaryotes must use oxygen as part of cellular respiration. Right? They are obligated to use oxygen, so we call them obligate aerobes. Right? They have to use oxygen. So, this little test tube right here is supposed to represent our obligate aerobes. And the reason for that is notice that all of our cells are gathered right at the surface here, right near the air-liquid interface. So right near where the oxygen is. So they're going to be able to use that oxygen in their metabolic pathways. On the other hand, some organisms are obligate anaerobes. Oxygen is actually toxic to these species. They don't use oxygen for cellular respiration. And here is our example of those obligate anaerobes. And you can see that they are growing at the bottom of our test tube, right? As far away from the oxygen as they can get. Right? They want to be as far from that oxygen as possible because it is toxic to them. Now, we also will see organisms which we'll call facultative anaerobes, and basically these organisms can perform cellular respiration with or without oxygen. That's what we have going on here. These cells in these in this test tube all the way on the right here are facultative anaerobes. And you can see that they're pretty evenly distributed throughout the entirety of the test tube. Right? And that's because they can grow near the oxygen, they can grow far away from the oxygen, it doesn't matter. They have options when it comes to cellular respiration. They're not obligated to do anything. Lastly, some organisms will actually not perform cellular respiration at all. Right? They're not going to do electron transport. They're not going to do oxidative phosphorylation to generate ATP. Instead, they're going to rely on glycolysis. Right? Glycolytic pathways. Simply rely on the breakdown of carbon molecules and you might recall that these get that get used up in glycolysis. And this is going to allow for continued ATP production. Now you might recall that there are two types of fermentation we talked about. We talked about alcohol fermentation, which is obviously the most important type of fermentation, of course. I mean, just, duh. But then, we also, talked about lactic acid fermentation, which is actually the type of fermentation that we do in our bodies. So sorry, hate to break it to you, but you can't get drunk from making your cells do a lot of fermentation. Now looking at these different types of metabolic options, hopefully, you can see that prokaryotes really cover a very diverse range of metabolic pathways. They do a lot of different things. And that kinda gets back to the point that I've been trying to make that these are super important organisms. And actually, we're going to turn the page right now and just talk about, you know, just how important these organisms are to the ecosystem. In fact, the biosphere, life on earth, truly depends on prokaryotes to continue functioning properly, both at the level of individual organisms, but really, more importantly, for the biosphere as a whole to function properly, we need these prokaryotes. So let's flip the page and find out how that works.

Prokaryote Ecology

There are many cycles of energy flow and nutrient flow or, you know, the flow of matter through the biosphere. Bacteria and archaea play very important roles in all of these processes. The most notable one, the one that really could not happen without them, is the nitrogen cycle. Specifically, prokaryotes are responsible for what's called nitrogen fixation, where they take atmospheric nitrogen. Right? N2, that gas that most of the air we breathe is made up of. Right? Like over 70% is N2. And they convert it to a usable form of nitrogen, as in a form that other organisms can actually utilize and must utilize. And this is ammonium or nitrogen dioxide. So, essentially, the entire nitrogen cycle depends on prokaryotes to perform nitrogen fixation. This makes bacteria and archaea the drivers of the nitrogen cycle on this planet. Now, here we have a little image of the nitrogen cycle. You don't need to worry about all the specifics of the nitrogen cycle. That's something we'll cover in ecology. The main thing that I want you to appreciate and understand is this bottleneck that essentially occurs here. These processes all rely on bacteria. We need that bacteria to generate usable nitrogen that will feed back into plants, animals, and other organisms, and is essential for much of life as we know it. So, it's a super important process that is completely and eloquently performed by these prokaryotes.

Now that's not the only way that prokaryotes influence the biosphere on a cycle level. For example, there's also what's termed the carbon cycle, how carbon flows through the biosphere. And remember that bacteria, or prokaryotes in general, are very important decomposers. They break down organic matter, so they help cycle carbon through the biosphere as well. Additionally, photosynthetic bacteria like cyanobacteria produce oxygen and they actually are responsible for having generated a lot of the atmospheric oxygen on Earth. We're talking ancient history, billions of years ago. These organisms were responsible for all of this oxygen in the atmosphere. Huge impact on the biosphere. Unbelievable impact on the biosphere. As I mentioned previously, bacteria and archaea also play an important role in the internal environments of humans and ruminants, like cows. Actually, a lot of other organisms too. I'm specifically mentioning ruminants because of the methanogens previously mentioned that help them digest their food. Also, it's become a very hot topic in medicine as of late, exploring the relationship between humans and the bacteria that help us function. Not only the bacteria that live inside us but also the bacteria that live on us. Specifically, the hottest topic is how the bacteria in our gut help us live, and the implications are way beyond what you'd expect. There are even studies that have shown some connection between the animal brain and these bacteria. Like literally, these bacteria can influence the brains of animals and their thinking. Really cool stuff. And also, you wouldn't be able to live without these bacteria. That should also be said. The bacteria that live inside you allow you to stay alive. And the last fact about how important bacteria are because I can just go on and on. I love prokaryotes. I think they're amazing. There are more cells living inside of you, more of these bacteria inside of you, than there are cells that make up your entire body. Okay. Drop the mic. I'm done. That's all I've got for this video. Go bacteria.

Here’s what students ask on this topic:

What are the differences between autotrophs and heterotrophs in prokaryotic metabolism?

Autotrophs and heterotrophs differ in their carbon sources. Autotrophs synthesize their own carbon compounds using inorganic carbon sources like CO₂ or CH₄. They often use processes like the Calvin cycle to convert these gases into usable carbon compounds. Heterotrophs, on the other hand, rely on carbon compounds produced by other organisms. Essentially, heterotrophs depend on autotrophs to create the carbon compounds they need for their metabolic processes. This distinction is crucial for understanding the flow of carbon in ecosystems, as autotrophs provide the foundational carbon compounds that heterotrophs utilize.

How do phototrophs, chemoorganotrophs, and chemolithotrophs differ in their energy sources?

Phototrophs, chemoorganotrophs, and chemolithotrophs differ in their energy sources. Phototrophs use light energy to produce ATP via photophosphorylation. Chemoorganotrophs oxidize organic molecules to generate energy, often producing ATP through oxidative phosphorylation. Chemolithotrophs, on the other hand, oxidize inorganic molecules for energy, also producing ATP via oxidative phosphorylation. The key distinction lies in the type of energy source: light for phototrophs, organic molecules for chemoorganotrophs, and inorganic molecules for chemolithotrophs.

What roles do prokaryotes play in the nitrogen cycle?

Prokaryotes play a crucial role in the nitrogen cycle, primarily through nitrogen fixation. They convert atmospheric nitrogen (N₂) into forms usable by other organisms, such as ammonium (NH₄⁺) and nitrogen dioxide (NO₂). This process is essential because most organisms cannot utilize atmospheric nitrogen directly. By performing nitrogen fixation, prokaryotes make nitrogen available to plants, animals, and other organisms, thereby driving the entire nitrogen cycle and supporting life on Earth.

What is the significance of prokaryotes in the carbon cycle?

Prokaryotes are significant in the carbon cycle due to their role as decomposers. They break down organic matter, releasing carbon back into the environment, which can then be used by other organisms. Additionally, photosynthetic bacteria like cyanobacteria contribute to the carbon cycle by producing oxygen and fixing carbon dioxide through photosynthesis. This dual role in decomposition and photosynthesis highlights the essential function of prokaryotes in maintaining the balance of carbon in ecosystems.

How do prokaryotes contribute to human health and the ecosystem?

Prokaryotes contribute to human health by aiding in digestion and supporting the immune system. The gut microbiome, composed of various bacteria, helps break down food, produce essential vitamins, and protect against pathogens. In ecosystems, prokaryotes are vital for nutrient cycling, such as nitrogen fixation and decomposition, which support plant growth and maintain soil health. Their roles in both human health and ecological processes underscore their importance in sustaining life on Earth.