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Current time:0:00Total duration:7:42

Why we need metabolism?

Video transcript

when I think about metabolism I think about a pawn shop and what do I mean by this well let's say you have a few objects an old cell phone you know maybe your grandfather's pocket watch maybe some precious metals and even a diamond or two now all of these objects have value but try going down to your local Starbucks and using any one of them to purchase a cup of coffee it doesn't work because in everyday interactions these objects are not a useable form of currency in order to purchase things you need cash now this is where the idea the pawnshop comes in the purpose of a pawnshop is to convert items into a useable form of currency now if you understand the basic principle of a pawnshop that it's there to convert value into a usable currency then you also understand the purpose of metabolism and let me show you that so metabolism is kind of like the pawnshop of the body we take macro nutrients like protein and carbohydrates and fats which have vast stores of energy but our body can't directly use that energy in order to use it it has to be converted into usable energy in the form of ATP just like at a pawn shop you had all these items it had value but the value wasn't usable you had to first convert them into cash let's go into some of the details about how metabolism works how do you transfer the energy between these different macronutrients let's start with carbohydrates in the major carbohydrate that you want to remember is glucose glucose can be broken down into pyruvate or it can be stored in a more efficient manner in the form of glycogen pyruvate is then broken down into a single Kawai now in order to see how the different macronutrients can be converted between one another let's move on to protein now protein is composed of numerous amino acids and when protein is metabolized is broken down into these individual amino acids these amino acids can then subsequently be converted to pyruvate or Co Co notice how in many of these reactions the arrows point both directions so and that demonstrates the reaction can go either direction so a protein can be converted can be broken down into its amino acids that are then turned into pyruvate and then it can be converted to glucose and stored as glycogen and this reaction can also go the other direction glycogen can be broken down into glucose and then through pyruvate it can become amino acids and then store this protein so let's see how this works for fats the basic form of fat is a triglyceride in triglycerides are broken down into glycerol and fatty acids it's these glycerol and fatty acids that can then be converted into other metabolic intermediates so just like with proteins fats can also be broken down into glycerol and glycerol can be converted to pyruvate and then that pyruvate can either eventually become a protein or grow up and become a carbohydrate so just like in a pond shop where you can trade different items for items in metabolism you can kind of trade in the different macronutrients for one another but they don't all have the same value and by value I mean energy so glucose is not as efficient at storing energy and chemical bonds as triglycerides and because of this when the body needs to store energy it takes the glucose it has and it converts it into triglycerides because that's a more efficient manner of storage but what happens when the body needs to utilize the energy stored here in triglycerides or in glucose or in protein well to answer that question we have to go through another series of reactions known as cellular respiration where did you so I'm gonna remove these metabolism lines here for a second and I'm going to use another color to describe the reactions of cellular respiration and how we produce usable energy in the form of ATP so let's start with glucose just like before glucose is converted to pyruvate and this is the same reaction that I mentioned before and metabolism but I want to note one additional part of this reaction and it's that the this reaction where you break glucose down into pyruvate the process known as glycolysis you produce a couple molecules and these molecules are ATP and NADH so you can already see that we're starting to produce some energy but it's really not that much the next step is to convert that pyruvate into a CoA and notice here that I only put I put a one directional arrow and that's because pyruvate can only be converted to a co co a acetyl co i can't go backwards I put acetyl co a here in red because it's a very important intermediate in the process of producing energy and it's important because it's our entry molecule into the TCA cycle TCA stands for tri carboxylic acid and this cycle is also known by a couple other names such as the krebs cycle or the citric acid cycle but it's a series of reactions and there's only one reaction that I want you to remember and that's the conversion of oxaloacetate to citrate and I want you to remember it because it's the first reaction in this TCA cycle and in this reaction we take excel o acetate and it's combined with the coa to produce citrate now this cycle includes a few more reactions but the particulars of these reactions are less important and as the cycle progresses it produces a few byproducts and these byproducts are co2 and nadh and fadh2 now note that this that in glycolysis we also produce an NADH in this NADH will also come into play down here so nadh and fadh2 are known as high energy electron carriers and they're important because they can be thought of as the fuel that runs the electron transport chain and the electron transport chain is just a stair-step of reactions it produces a whole bunch of ATP and in the process you have oxygen converted to water so we use the energy that is contained in these high energy electron carriers to produce ATP so let's go through a quick review here remember we started with the pod shop with the idea that different items of value are convertible but they're not necessarily and not necessarily usable unless they're converted to a usable form of currency like cash now this is the same idea in metabolism where our different macro nutrients can be converted between one another in order to store energy in different forms but if we want to use that energy we have to go through the process of cellular respiration to produce ATP which can be thought of as the energy currency of the body