Source: Video and Images Created by Amanda Soderlind
In this lesson today we are going to describe what metabolism is, the role it has in your body, and the two types of metabolic pathways. So first of all, to define metabolism. Metabolism describes the chemical reactions that occur in cells. So there are various types of chemical reactions that occur in cells all of the time.
And these chemical reactions are necessary in order for cells to be able to function properly and in order for us to be able to survive. Some of these reactions that happen in cells use ATP, and some produce ATP. So ATP is an energy storage molecule. It stands for Adenosine Triphosphate.
So it's a molecule that takes place in these reactions and is either produced or used by these reactions. So let's take a look at the structure of ATP. So first of all, ATP is a nucleotide. And it's made up of a ribose sugar, an adenine-- remember that's one of our nitrogen bases, adenine. And it's made up of three phosphate groups.
If you'll think back to previous lessons we had on nucleotides, you'll remember most nucleotides only have one phosphate group. But ATP is different because it has a total of three phosphate groups. And energy, the reason that ATP is an energy storage molecule is because energy is stored in this bond between the second and third phosphate.
So what happens in a reaction is that enzymes will be able to break that bond. And this third phosphate here will be transferred to another molecule, therefore providing stored energy. So this is how ATP is different from other nucleotides that we've looked at because it has energy stored in this extra phosphate that it has, so stored energy.
So when that bond is broken, energy can be released. And enzymes, as I mentioned, which are usually proteins, will take part in speeding up metabolic reactions in cells. So enzymes can make these reactions happen millions of times faster than they would otherwise. And enzymes are also responsible for helping to break that bond between the second and third phosphate in ATP.
So let's take a look at this diagram that we have listed over here. So there's kind of a cycle that ATP will go through when it's used or produced in chemical reactions. So we're going to label this as ATP. And if you'll remember, I mentioned a little bit earlier that ATP stands for adenosine triphosphate.
So the prefix tri- means three. And we remember that from our diagram over here. We have three phosphate groups. OK, so when ATP takes part in a reaction and energy is used, one of those phosphates is removed and added on to another molecule. So we're actually getting rid of one of our phosphate groups from ATP.
So what we end up with then is something called ADP. And the D stands for Di, so adenine diphosphate, which tells us that it now only has two phosphate groups. So one of these phosphates has been eliminated, put on with another molecule as energy storage. And now our ATP is changed into ADP with only two phosphate groups.
Then maybe that's ADP will take part in a reaction where energy is released. And if energy is released, the ADP can pick up another phosphate, and now it will become ATP again. So it can go through this cycle where it gains or loses phosphates and can either be an ATP if it has three phosphates or an ADP if it has two.
So we're going to take a look at the two types of metabolic pathways. I'll get this on here so hopefully you can read it all. OK, here we go. So there are two types of metabolic pathways depending on what is happening with the molecules in each of these.
So in one type of metabolic pathway, small molecules are actually turned into larger molecules. They're combined and turned into larger molecules. So I'm going to label this here as anabolism, small molecules being turned into larger molecules.
In this type of metabolic pathway, it assembles complex carbohydrates, proteins, and other molecules. So this is the way in which complex carbohydrates are built or proteins are built. So smaller molecules are being combined together to build a larger molecule.
And because we have all of these bonds-- we have several bonds between all of the smaller molecules holding them together to form this larger molecule-- there are a lot of energy stored in these bonds because there are so many bonds. So there's large amounts of energy stored.
So an example would be when monosaccharides are built into polysaccharides. So we're starting with those simple building blocks of simple sugars, monosaccharides. And we're putting a whole bunch of them together being held by bonds and turning them into something called a polysaccharide.
So just a little visual example here is we're starting with small molecules, and we're building them together into this larger molecule here. Our other type of metabolic pathway then is catabolism. Hope you can read that OK.
So this is basically just the opposite. Large molecules are being broken down into smaller molecules. So rather than assembling, it's disassembling. It's dissembling complex carbs, proteins, and other molecules, breaking them down into smaller molecules.
And in this case, compounds released are used by cells. So these cells are taking these large molecules, breaking it down into something smaller. And then it's able to use those smaller molecules for whatever reason it needs. So an example is, we're taking complex carbohydrates that you eat, and those are getting broken down into glucose, which your cells can then use for cellular respiration to make ATP.
And here's just a visual example then of what this would look like. We're starting with a large molecule, and we're breaking it down into a smaller molecule that cells can then use. So these are the two types of metabolic pathways. And this lesson has been an overview on metabolism as well as the two metabolic pathways and the role that it has in your body.