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Introduction to metabolism: Anabolism and catabolism

Metabolism refers to the set of chemical reactions that occur within living organisms to maintain life. Anabolism is the process of building up larger, more complex molecules from smaller ones. This process requires energy. Catabolism is the process of breaking down larger molecules into smaller ones. This process releases energy that can be used by the organism. Created by Sal Khan.

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  • piceratops tree style avatar for user Klemen Kersic
    How can you get energy form breaking bonds ? I thought that breaking bonds was an endothermal reaction .. thus requiring energy to be done ?
    (28 votes)
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    • blobby green style avatar for user mkiwan
      Catabolism indeed consumes energy as you mentioned, but the output energy is higher, so there is a NET release of energy. If we take cellular respiration as an example, which is catabolic, we are actually breaking down Glucose into H2O and CO2 and (most importantly) energy. It's simply a combustion of Glucose (oxidation by O2), which is a favourable reaction, hence releases energy
      (20 votes)
  • male robot donald style avatar for user En David
    Which one requires more energy; catabolism or anabolism, and why?
    (17 votes)
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    • aqualine ultimate style avatar for user Mike Zhuang
      Hello Enido, great question. Catabolism and anabolism are complex processes which may not be easily generalized. For example, in our everyday lives we may choose to drink a can of soda or eat an apple. Though they may contain the same amount of sugar (carbohydrates), which one do you think takes longer or requires more energy to break down? Similarly, depending on the molecule your body is making, a little energy can be expended or a lot. A simple molecule such as ATP may take little energy, whereas complex proteins may take a lot more.

      If you are thinking about the processes as a a whole, remember that your body cannot maintain itself if you are losing more energy than you are gaining. Catabolism is often the process which results in a net gain of energy (ATP) whereas anabolism requires ATP to create new molecules. Therefore, the body likely expends more energy for anabolism. Even though Catabolism is a process which generates net ATP molecules, it still requires a little bit of investment of energy.
      (26 votes)
  • sneak peak yellow style avatar for user <_TAXI_>
    I learnt that if there is more trees in an area it reduce the Carbon Dioxide in the air. So if we want to go to a planet such as Mars (Which is full of Carbon dioxide) Could we possibly use trees and plants to somehow terraform Mars?
    (7 votes)
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    • blobby purple style avatar for user Arpit M.
      There is multiple reasons why it wouldn't work. Some basics is that the increased amount of UV radiation from the sun would wilt a tree. Adding to that, the sunlight in Mars isn't nearly enough for the plants. Also the martian soil is inhospitable for plants. Now (this one I had to do a little bit more research) you might know that plants take in oxygen at night. Even if the plants produce oxygen at morning the oxygen would diffuse into the atmosphere leaving very few molecules for the tree at night (I think). Another problem with the atmosphere is that it would need to have a lot more nitrogen. Although this idea could maybe work if there is more technological advances, for now it is just a dream.

      P.S. I liked researching about this.
      (22 votes)
  • orange juice squid orange style avatar for user Madelyn Youngren
    Because of the methods of photosynthesis, could we possibly use sun to breath in carbon dioxide but make it useful for us?
    (10 votes)
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    • female robot grace style avatar for user tyersome
      That is theoretically possible.

      However, we would need to figure out how to either incorporate single celled photosynthetic organisms into our skin or add chloroplasts to our skin and then add genes to our genome to support the chloroplasts. Either way we would run the risk of side-effects – e.g. becoming allergic to our own skin! I'm also not sure how useful this would be since it takes a lot of plants (or algae) to make enough food and oxygen for one person ...
      (14 votes)
  • duskpin ultimate style avatar for user C4LOwenZ
    If ATP is so valuable, can we use the marvels of modern science to manufactore it put it in pills and sell it as a medical supplement to those who need it, i.e. those with Leigh Syndrome, so the ATP loss in their bodies can be compensated?
    (5 votes)
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  • blobby green style avatar for user davevaibhav1988
    while metabolism works how much energy is used by body?
    (7 votes)
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  • blobby green style avatar for user Aradhya Madhura
    How important is metabolism? and what is the difference from anabolism and catabolism FROM metabolism??
    (6 votes)
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    • blobby green style avatar for user drishti pareek
      metabolism is a characteristic of living things.
      sum total of all the reactions going on in our body is called metabolism.
      catabolism and anabolism are two types of metabolic processes.
      catabolism is breakdown of any complex substance into simpler once. Eg - digestion
      whereas anabolism is formation of something complex by joining many simpler substances. Eg - photosynthesis
      (8 votes)
  • leafers seed style avatar for user Nur Aunseri
    how can i understand all the explanations clearly as everything i heard in school are mostly different than what were presented here
    (6 votes)
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  • starky ultimate style avatar for user Penguindle
    According to this video we're famous... haha get it??
    Joke aside, does plants breaking down carbon dioxide also count as catabolism?
    (5 votes)
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  • hopper cool style avatar for user Aum Shah
    Why would you want to break down proteins only to build them back up?
    (3 votes)
    Default Khan Academy avatar avatar for user

Video transcript

- [Voiceover] What I want to do in this video is talk about the processes that make all life as we know it, life as we know it, and at it's essence, we can call this metabolism. Metabolism. And this is the taking energy in different forms, breaking it down into its more fundamental components, and then building it up in ways that we would find useful, useful for energy, useful for structure, so that we can actually live our lives, we can grow, we can reproduce, we can respond to our surroundings. So as I just said, metabolism, and we're gonna go into a bunch of examples of this. Metabolism at it's heart is really two different processes. There's the breaking down of the substances for energy or for structure to getting back to the building blocks, and we call that catabolism. Catabolism. So this is the breaking down of things and then once we've broken down things, we're ready to rebuild them in ways that we would find useful, and we call this anabolism. Anabolism or anabolism. Anabolism, just like that. And one way to think about it is imagine that someone had built something with Legos and you want to build something with Legos. Well you could go to those Legos and you'd want to break it down, but not break it down too much. You wouldn't melt the plastic. You would break it down into the individual Lego pieces and then you would build it back up into whatever shape that you actually cared about. And you might not actually have to even break it down all the way to the basic Lego pieces. There might be structures in that first Lego castle that was constructed that you might find useful. So let's just think about how all of this gets started. And what's exciting is that all of this got started, or gets started, from stars, from fusion reactions in stars. And this right over here is a picture of a star, and a star that we are very familiar with. This is the sun. But you may or may not realize that the sun is only one of probably several stars that have been involved in life as we know it. The sun is our most direct source of energy for most of life as we know it. There are some bacteria and things that are able to live off of vents at the bottom of the ocean because of the heat created, but the sun is our primary source of energy. But when I say that other stars might have been involved, including dead stars that existed billions of years ago, it's because the heavier elements that we're composed of, or that are around us in the environment, the carbon, the oxygen, we could just keep going, pretty much everything other than hydrogen, it was constructed in fusion reactions from hydrogen inside of stars. So we really are made up of the remnants of stars. And so here we are, we're on Earth. Earth is all this condensed matter from four and a half billion years ago. Probably some nearby supernova got all of this dust that was constructed in a previous star to coalesce in that way, and you have radiation. You have energy from the sun. And once again, that energy's coming from fusion reactions, and it's what fusing lighter elements into heavier elements, so the sun is also constructing more heavy elements, but that energy, that energy makes its way to the Earth. And you have organisms, like plants, that are able to use that energy to construct the material, the food, we could say, that is eventually going to get around to us. And so this process you may or may not be familiar with it, this is photosynthesis. And we're going to go into a lot more detail. Synthesis. And as the word implies, photo, it's photosynthesis, it's making things out of light, and one thing I like to ask people when they are first exposed to photosynthesis, is like okay, we can see this grass growing or we can see this wheat growing, or we can see a tree growing, but where is that material coming from? And the most common answer is like, "Oh, somehow it's coming from the ground," and there are some nutrients that are coming from the ground but it's really all about fixing carbon, and you're going to hear about this a lot especially as we talk about the carbon cycle. But you have carbon dioxide primarily in the air, so you have carbon, you have, I'll just write it this way. So you have carbon dioxide in the air and what photosynthesis allows these plants to do is take the carbon in that carbon dioxide and form bonds with it, turn it from its gas form into solid forms, into glucose molecules, and then use that glucose to build up cellulose and to build out other forms of starch and whatever else it might be. So it's taking these molecules in the air... I'll just draw them as these little... It's taking these molecules that are in the air, and it's using the energy of the sun to fix them, to actually form bonds between the carbons and with other things. As we said, we're mostly carbon and hydrogen and we have some oxygen in there, but we're able to form these structures. Now from there other living organisms, and this is a huge oversimplification, it could involve bacteria, it could involve all sorts of things. And just a reminder, you know, that photosynthesis, it isn't just light and it isn't just the carbon dioxide. It also involves the water and we talk about that. So you also have water involved. You also have the water involved. So you have the carbon dioxide, so CO2, light from the sun, and water. These things are able to grow and nutrients from the Earth. And then from that, you're able to construct things like, well, you can directly go to these plants that are taking energy from the sun and construct things like bread or you have other animals that will eat things like the grass, and then break them down in their own way and they will be assisted by bacteria and then rebuild themselves up into a cow, into milk. And so what this cow is doing, it's metabolizing this grass. It's able to break it down, it's able to catabolize the various molecules in the grass and break them down into building blocks that can then used to build up the cow, to build up milk, and whatever else. And you might be saying, "What are these types of molecules "that we keep breaking down "and then building back up?" Well, you have carbohydrates. Carbohydrates, and you're going to see most of the molecules that I'm about to talk about. Frankly, all of them on the back of nutritional package because it tells you what's inside of it. What is your body going to metabolize when it eats that whatever's inside of the package? So carbohydrates, these are either simple sugars like glucose or fructose, or it could be polymers of these sugars, polysaccharides. It could be starches made up of many, many elements of the... Or many, many multiples of these simple sugars. We could be talking about lipids. Lipids. So fatty acids, we could be talking about cholesterols. These are essential structures, and they're also essential for, well, various metabolic pathways inside of, well, all of life, or it could be proteins. It could be proteins made up of amino acids. Sometimes people say the reason why you want the proteins is because it's made up of these amino acids. So you could break down these proteins and get the amino acids and then build it up into new proteins. Proteins and amino acids. And all of these things, they are found in things like in the foods, in the foods we eat, which we will then consume, we will then metabolize. We will first catabolize them and break them down and then we will use those building blocks to build it back up. And at the end of the day, these provide the structures that make our bodies what they are. They allows us to interact with our environment and they provide energy, and that energy, at the end of the day, the true molecular currency for that energy is a molecule called ATP. That's a molecule of ATP right over there. Adenosine triphosphate. And the key for ATP, why it is the molecular currency for energy, are the three phosphate groups. So it has these three phosphate groups and we have a whole video on it, or a whole series of videos on it really, but the main key is that there's a lot of energy, especially beween I guess on the last phosphate group. And this energy and that bond as the phosphate group breaks off it can release it to provide all sorts of life mechanisms including being able to metabolize things. So ATP right over here, this is the currency of energy in life as we know it. And it's actually an interesting molecule because it's essentially, it's a piece of... If you were to just take this section of it right over here, it really is, it looks like a piece of RNA. It looks like you're taking a... You have ribose, you have the adenine, you have a phosphate group, and it can actually be used to construct things like RNA and even DNA beyond just being the molecular currency of energy. So it's fun to see how these pieces all fit together, how they can be broken up, and you see these patterns over and over again in biological systems, and these biological systems are really just made up of breaking down and building back up carbohydrates, lipids, fatty acids, cholesterols, other things, and proteins/amino acids. So this whole thing, you know, look around you, look at your day, look at the things you're consuming and you'll see this pattern over and over and over again and it's all a little mind-blowing, because at the end of the day, the energy is coming from the fusion reaction in stars and all of the heavy elements around you or even the not so heavy elements, all of the carbon, the oxygen, all of the really non-hydrogen elements, they've been made inside of fusion reactions in stars that might have existed billions and billions and billions of years ago, so hopefully that makes you feel a little bit more connected to the universe.