01.03 Introduction to Metabolism

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  1. Overview
    1. Metabolism is about breakdown vs build-up & simple vs. complex molecules
    2. Cellular needs
      1. Our bodies need complex molecules (proteins, carbohydrates, lipids and nucleic acids) for life to happen
      2. We eat complex molecules (carbohydrates, fat & protein in food)
    3. Energy
      1. Energy is released when complex, “high energy”, & unstable molecules are broken down
      2. Energy is required as new complex molecules are made
  2. Three examples of cellular processes needed for life
    1. Molecular machines that convert DNA to RNA to protein
    2. Repair systems that prevent DNA damage
    3. Detox systems that help us excrete toxic molecules like ammonia
  3. Break Down = Catabolism
    1. Carbs & fat are “high energy” molecules
      1. Carbs & fat are burned with the oxygen we breathe to make carbon dioxide & water & lots of energy
      2. Through this process (aka cellular respiration) ATP is made
      3. If energy isn’t needed, the breakdown product of carbs & fat (acetylCoA) is used to create new fats that are stored in fat cells
    2. Proteins are broken down into amino acids which can then be used to build new proteins or can be converted into glucose or acetylCoA
    3. Vitamins and essential amino acids & essential fats are complex molecules we need to eat because our bodies don’t make them.
    4. Nucleic acids are in the food we eat, but our bodies do not reuse them
  4. Build Up = Anabolism (think anabolic steroids)
    1. Combining simple building blocks into complex molecules takes energy
      1. Example: Fatty acids from acetyl CoA
      2. How ATP & NADPH are used
    2. Vitamins are co-factors
    3. Hormones are regulators


Hey there. What we’re going to talk about today is metabolism. And this video is just going to be an overview, like the big, broad perspective of what metabolism is about. Two of the most important words about metabolism here are going to be catabolism and anabolism. Metabolism is amazing–we’re seeing just a small part of it here. It’s so incredibly complicated. It’s thousands of reactions, many of which are related to each other in some way or another. And it’s super cool. What we’re going to do here is just take a very big perspective and just try to simplify what the basic ideas are and what’s going on.

What I have here, I’m going to create, is a picture in two areas: We want to be thinking about complex molecules and we want to be thinking about energy…ADP and phosphate, and NAD. Those are both energy molecules. And what happens in the break down part of metabolism…this is what we call the catabolic side over here, put. So catabolism is what’s going to be happening on this side. These molecules–these complex molecules–are going to get broken down into simple products down here. Meanwhile, the molecules that are in their low energy form…low energy here…those guys are going to get converted into their high energy form. If we think about ATP–you’re probably pretty familiar with ATP being a high energy molecule. If I were to draw a little graph of what that’s like high energy means that on an energy diagram, it would be up high here. This is where the ATP would be, and then down here would be the ADP plus P. And so going from here to here, that amount of energy, that’s the amount of energy that ATP has, it is this amount. This would be energy over here on that Y axis. Now you may not be as familiar with NAD so there’s NAD, and NADP.

There’s actually a lot more NADP and NADPH than the plain old NAD. Maybe you recall NADH from the electron transport chain…this other guy–NADPH–is really important for what’s called reductive biosynthesis. That’s what NADPH is about. Basically, the idea is that a bunch of little H’s are going to get put on things to build molecules up, but that’s not what this slide is about. This slide is really about catabolism. So the breakdown. Let’s go back to this again, summarizing: Complex molecules go to simple molecules, and then the low energy molecules become high energy molecules. Let’s stay focused on this catabolism side for a moment here. Here are some examples of catabolism: proteins that we eat, starch that we eat, fat, that we eat…those things are going to get broken down into simpler molecules. Proteins down to amino acids. Those things could get broken down further. We can talk about that in a little bit. Starch can get broken down to glucose. Glucose, going through glycolysis, can get converted to pyruvate, which then can get converted to acetylCoA. That’s a small molecule.

Let’s take a look at what a acetylCoA looks like. I’m just going to draw it this way. If you go to the Kreb’s cycle video, you’re going to see a little bit more information about what a acetylCoA is, but there’s basically a carbon sitting right here and another carbon over here. And so I call this guy a two “carbon chunk”, and it’s a lot more than just those two carbons. But these are the two that are really important about acetylCoA. When we were seeing, in the previous slide, about going from a complex molecule, like starch, like in the carbs that we eat, breaking it down, breaking those carbs down to just these little two carbon chunks. That’s the idea of going from complex to something simple. Here we have fat. Fat gets broken down into fatty acids, and then fatty acids can get broken down into acetylCoA. AcetylCoA is so incredibly important. It’s pretty cool stuff.

Glucose and fatty acids both go through combustion reactions. So they react with oxygen to make CO2 and water. And then of course we were talking about creating energy. So simple molecules, the two most important ones are probably the acetylCoA and CO2. Those are examples of simple molecules. So that was that side. We looked at the breakdown side. Now let’s talk about the buildup side. So to go from simple products back up here to the complex molecules. That is what we call anabolism. It helps me to think about anabolic steroids. Maybe that’s a phrase that you’ve heard of before: there are some body builders that will take anabolic steroids to get big. That’s that idea of building up over on this side. Things like acetylCoA and CO2, those can be simple products that get built up into new complex molecules. And one of the key things to think about here is that you’re eating complex molecules…how come we’re not just using those? Why do we have to build new ones? Well, good question. And I think I’ll help answer that on the next slide. Basically, we don’t eat exactly what we need, so we have to do more building up in order to get what we need. Energetically, it takes energy in order to convert these simple products up to the complex molecules.

What’s going to happen now is you’re going to go back to having your high energy molecules, they are going to get converted into the low energy molecule. As I was saying with the NADPH and reductive biosynthesis. Biosynthesis means building the biological molecules. It’s going to use these H’s on the NADPH. They’re going to get used probably the most obvious example of that is going to be in fatty acid synthesis. There will be a video on that, that you can check out.

Here are three examples of complex molecules that our bodies need to make. If we think about DNA and RNA and all the things that have to happen in order to go through the central dogma, the DNA needs to get read and get converted into RNA. The RNA needs to get read and get converted into protein. That all requires tons of enzymes…polymerases and helicases and all sorts of things. And those are not the things that you’re eating. That’s an example of what your body needs to build in order to get this process to happen. Another example would be a repair of damaged DNA. We have so many things that damage our DNA every day, but the cool thing is our bodies have amazing repair systems like multi-level repair system, so that if there is some kind of mutation or damage to the DNA, if we’re healthy, we have ways to repair it and get things right back to how they supposed to be. That requires enzymes. That’s a good one. And then another one is we have toxins. So these aren’t toxins that are when there’s toxins in the environment, obviously. But even just eating amino acids. We have proteins and there’s amino groups in those amino acids and those amino groups can get converted into ammonia. That’s just totally normal. But too much ammonia buildup is a bad thing, and so that’s part of the detoxification process is converting that over to urea. And that is what we pee out and that is just totally a normal process, but we need enzymes to do that kind of thing.

And now I want to give you some examples of anabolism. These are at that molecular level…so amino acids can get converted into proteins, many of which are gonna be enzymes. Glycerol–if you think back on maybe what a triglyceride looks like–these are all fatty acid chains out the side here…three fatty acid chains. This has the glycerol backbone. You can have two of those can come together. There’s three carbons here. One, two, three. Those three carbons can combine with another glycerol molecule to make six carbons and ta da, you’ve got glucose. That’s an example of going from something smaller to something bigger. And then the glucose can go on to become glycogen–that’s the storage form of glucose and it’s a really big molecule. So again, going from small to something big. This process can also happen with some amino acids…they can get converted into glucose. And then I’ve already mentioned, that acetylCoA has this relationship with fatty acids. They get broken down into acetylCoA. And acetylCoA can get used to make fatty acids. That’s one of the ways in which glucose can get converted into fat is because you could make some acetylCoA from the glucose and then make fatty acids. Then the fatty acids can go on to do different things. They can become cell membranes; they can become signaling molecules; and they also can fill fat cells. So that’s how, if we end up with too much acetylCoA, we end up with too much fat in our body.

Lastly, here we’ve got nucleic acids…nucleic acids are pretty beautiful, cool structures. Interestingly, we do not recycle the ones that we eat (not much). Nucleic acids are in the cells in the food that we eat, and yet our bodies don’t recycle them to the extent we would amino acids. Certain amino acids are going to get combined with CO2, so this is an example of a small molecule. Another small molecule is formic acid. So CO2, formic acid, and certain amino acids are used to build a nucleic acids. Your body does that on a regular basis.

Before we wrap up here, I do want to mention what the word ‘essential’ means. I’ve been talking about foods that we eat that can be broken down to small molecules and give us energy. Well, there’s also going to be a group of molecules that we can’t break down. We don’t use them in the broken down form. We use them as they are. So they are what we call essential. So essential amino acids, like what I have here is lysine and then, uh, fatty acids. So this is, I can’t remember which one, this is probably EPA. I think it’s probably maybe got 20 carbons in it. Um, these things are, um, so this is an Omega three fatty acid, and these things are essential. So our body does not make this.

We cannot take small building blocks and build something like this up. We have to eat it. And that’s why it’s called essential. And then of course, vitamins, that’s another example of something that’s essential. What I have here is vitamin A–vitamin A is what helps us take light signals and turn them into a neural signals in our brains. We need to have vitamins in order to do those kinds of things. So as complex as metabolism is, what we can do is really break it down to three parts here: 1) Complex molecules are broken down into simple molecules. 2) Simple molecules are building blocks for the complex molecules that our bodies specifically need. 3) Energy is going to be released during that breakdown part, and energy will then be used in order to build up those complex molecules that our bodies need. That’s the basic three ideas of metabolism. We love you guys! Go out and be your best self today and as always happy nursing!