 Okay, now is the fun stuff. So we've established the different cells that make up the epidermis. We know that cells, different kinds of cells working together for a common function make up a tissue. We are comfortable with the kind of tissue this is. And now we're going to zoom in to the single cell, the melanocyte. And you can see how I feel about the melanocyte. And I want to remind you that the melanocyte is this awesome looking, very unique looking cell at the bottom in the most deep layer of the epidermis. That's where the melanocyte hangs out. Hangs out along with those basal cells, which are giving rise to everybody else. Melanocytes don't have that same function. They have a different function in which is what? To produce melanin. So we're going to look at how that happens. The melanocyte. Okay. First of all, anytime you answer the question, how did that happen inside a cell? You are likely looking at something we call a cellular mechanism. So a cellular mechanism is the process or the various events that take place to get you from point A to point B in a cell. The melanocyte doesn't just go, okay, I'm going to go to the oven and combine some ingredients and put them in the oven, cook them for a little while and out is going to pop melanin. That's not how the melanocyte works. And in fact, there's a really complicated series of chemical reactions that ultimately lead to melanin. I'm going to show you how I normally draw out the process, how I draw out cellular mechanisms. And then I'm going to show you the chemicals involved in this cellular mechanism. Let's give it a name before we go any further. This process that we're going to look at, this example of a cellular mechanism is called melanogenesis. And that makes sense. Amino melanin, genesis birth of. How do we make melanin from the beginning? My strategy when I do cellular mechanisms is usually to break it down to what's the most important, what are the most important ingredients? Melanogenesis starts with an amino acid, tyrosine. Take you back, take you back to this list. And we're looking at macromolecules and amino acid is a macromolecule, it's a big molecule with many different pieces. It's one part of building a protein and that one part is going to enter the process of melanogenesis. The next thing that I'm going to tell you is where are we going to end up? Well, the fact is that there are two forms of melanin that we're going to look at. And I want to have both of them on here. We have pheomelanin and we have you melanin. So we start out with tyrosine and then here's how I usually do cellular mechanisms. Are you ready? We start out with tyrosine. We have a series of chemical reactions that result in the production of melanin. Either pheomelanin or humelanin. The other thing that I want to throw at you or have you cozy with is this stuff doesn't happen for free. The process of taking tyrosine amino acids and building melanin usually requires some sort of energy input and usually requires a helper. And the helper in this case is an enzyme. There's probably lots of them. But I want to introduce you to, number one, the idea that in these cellular mechanisms, we need help. They don't just, these chemical reactions usually just won't happen on their own. And enzymes do that help. And enzymes often are easy to identify because of the name that they have. The enzyme that we're dealing with here is called tyrosinase. And the key part of this or your cute little brain is the ACE. ACE often is a ending, not always, but it's often an ending that we see on enzymes. An enzyme is a protein usually that does, that catalyzes a chemical reaction. So let's put some pieces together here or let's restate what this visual is explaining. First of all, we have tyrosine and amino acid that enters this process, this cellular mechanism. We have a series of chemical reactions that take place that are catalyzed by the enzyme tyrosinase. And we end up, there are two pathways we can follow. And we end up with one of, or we end up with two possible forms of melanin. We have phthalomelanin and we have eumelanin. In Rigslandia, that's usually the extent of our details with cellular mechanisms. But I'm always, even though I'm like, okay guys, that's all we need to know. We're good as long as you have this process and you're cool with like that swirly-wirly. In my world, when I see this swirly-wirly, I go, oh phew, there's a whole bunch of chemical reactions that are happening there that we don't have to memorize or know all the stages of. But you could know all the stages of them. We could lay it out piece by piece. Check it out. Do you agree? We start out with tyrosine and this is what tyrosine looks like. Who do you see right here? I can't remember my enzyme. I made it blue. Look, tyrosinase is, and I know this is really tiny, isn't it? Does that help? There. That helps a little bit. I wonder if you could see it before. We start with the tyrosine. Tyrosinase does some magic. This is why I go, awesome, it's magic because now we have dopa and it looks like that. I'm only showing you so that you go like, oh, there's a molecule. Tyrosinase turned tyrosine into dopa. That's a great name for a molecule. Look, tyrosinase is back at it again. Has more to say tyrosinase does as it turns, okay, look, it turns the dopa into dopa quinone. Again, I'm only showing you this to say there is a series of things that happen that you could know. We could have to memorize all those intermediate bits of this process, which is called melanogenesis. We're not going to, but look, here's where we have two pathways that we are going to travel. We can go, we can turn dopa quinone and you know, there's an enzyme that is likely involved in that process. We can turn dopa quinone into dopa crone and then dopa crone tata mayors and then 5-6 dehydroxy indole to carboxylic acid, of course, or 5-6 dihydroxyindole, either way, we end up with eumelanin at the end. We could go through this whole process, starting with tyrosine. If we go this route through the process, we end up with eumelanin. If we go this route and we turn the dopa quinone into cysteine, oh no, it looks like cysteine is another amino acid that comes in to join this mix and then we get cysteine aldopa and cysteine aldopa, 2-5 and 5-S, okay, nobody knows what I'm saying, but ultimately we get pheomelanin, starting with the same thing, ending with either pheomelanin or eumelanin. Do you agree that this is a nice way, right here, I'm saying the same thing and we got to the final outcome of producing either pheomelanin and eumelanin. Everybody's different. I am definitely in the camp of, I like the tortoly wets, I like to know that we know how something happens, that's really interesting and cool to me. I don't want to memorize that, I don't want to have to name it or draw it or memorize all the stages and parts of it. We could, if that was important for something that we were learning, it's a nicer way to do it with the outcome being these two different kinds of melanin. Now melanin, why, like what, why do we need melanin and what is it going to do? Well, it plays a role, it has lots of functions and so we'll look at that and in particular it is what causes your skin color.