Chemistry Basics in Human Physiology

All right. So in your book, the first couple of sections, you know, because there's no text in the book, it's kind of divided into those two-page spreads. Well, the first few of those in Chapter 2 are really a review of what I consider to be high school chemistry. So we're not going to go over that stuff in class. You're not going to be directly tested on that material, but you need to review it, particularly if you have had kind of a weak chemistry background. Because you're going to use that chemistry as we talk about physiology, but I'm not going to ask you specific chemistry questions, if that kind of makes sense. So do use the resources in the book to review, particularly if it's been a while or if you didn't do so well in chemistry. But we're going to kind of pick up at where we start talking about the human being, so elements in the body. So like everything in the universe, You know, the human being is made of elements, and most of those are in this top box right here. So what are we made of? Well, mostly oxygen, carbon, hydrogen, and nitrogen. So the hydrogen and oxygen together, that's going to make up water, and we all know that we're, you know, about 60% to 80% water, depending. So that's where a lot of that goes. Most of the carbon and nitrogen are found in proteins in the body. that create the connective tissue or the structure or substance of the body. But even though these other elements are in the body in much smaller amounts, in many ways these like sodium, potassium, calcium, iron are some of the most important things because they actually make it so we can do stuff. We're going to see throughout the course that calcium plays a major role. in all the fancy things that we do. So things like muscle contraction, nerve conduction, you know, the way the brain works. We're going to see that calcium is critical for a lot of those functions. So the bulk elements are these four, but then these others that we're going to see throughout the course play a major role in how things actually happen. So just a quick review of what an enzyme is, because we're going to talk a lot about enzymes in certain aspects of the course. An enzyme is simply a molecule that assists a chemical reaction. So as a little chemistry review, in order to go from, you know, reactants are what you start with. So you know, you take chemical A and chemical B and you mix them together. So those are your reactants. And what you get out if there's a chemical reaction that occurs is products. So you mix reactants to create products. Well for most reactions... In order to get those reactants to change or do anything, you usually have to put energy in. And then once you put that energy in, then this reaction can proceed forward. So we call that energy that we have to put in the activation energy. So like in chemistry, a lot of times, when you've mixed two chemicals, you'll have to heat them up. You know, you have to put them on the hot plate. Well, what you're doing there is you're adding that activation energy. Another form of this is, let's say you have to shake something. Again, you're adding energy to that equation. Well, what an enzyme does is it drastically reduces the amount of energy that's required to go from reactants to products. And when we talk about proteins, which is probably going to be at the beginning of next time, we're going to see that many proteins in the body act as enzymes. In other words, they make some chemical reaction happen. So, for example, the blood clotting protein is called fibrin, and there's an enzyme that's called thrombin that turns fibrinogen, which is a reactant, into the product fibrin that then creates a blood clot. So we're going to see lots of examples of these enzymes that make things happen. So as a chemistry refresher, what's really going on is that enzyme is reducing the activation energy that's required. So the reaction can proceed faster and at a lower temperature or at a lower energy. Alright. Well, we all know that we're mostly water, but why does that matter? There's a reason why water and life on Earth kind of go together. And a couple of those we'll talk about specifically. So one is solubility. Solubility is the property of a substance that allows it to dissolve stuff. And water... ...is an excellent solvent. All kinds of things that are found on planet Earth dissolve very readily in water. You know, the one... that we know or that comes to mind first is salt. You know, the oceans are salt water. And what we've got there is we've got water that has sodium chloride dissolved in it. So because of water's chemical properties, it can dissolve all kinds of different things. So all of that diversity of solutes is sort of how life on Earth works. There are so many different things dissolved in water that those things can interact and create you know, biology and life. So solubility. Another is reactivity. A lot of times we think of water as kind of passive. You know, it's the place where stuff happens, but it doesn't really participate in what happens. And we're going to see a number of examples in this course of how water does participate in the chemistry of life. So for example, when we Hydrolysis is we can take a molecule that looks like this, you know, that has two parts, an A and a B. We can add a water molecule to it, and we can break that larger molecule apart into two pieces. So, you know, we add the H and the O, and we get an A, H, and a B, H2, or a VO. So we can split using water. We can also put things back together. This is called a dehydration reaction. So we can take an AH and a VOH. We can pull the water out and then we get a molecule called AB. So we can put two pieces, two molecule pieces together into a larger molecule in dehydration or split them apart in hydrolysis. And you'll see that water is playing a role here. It's not just sitting around. It's being incorporated into these new molecules or it's being created from these old molecules. So one of the principal reactions that fuels our body occurs in the mitochondria, and that's where we take carbon compounds like glucose, and we turn them into carbon dioxide, water, and then a great deal of cellular energy called ATP. So here again, you can see that water isn't just a solvent here, it's actually participating in the chemistry. So, you know, when we break down sugar to create energy, we not only... create CO2, we actually create some water too out of that sugar. So we'll see much, you'll see a lot more of this in the next semester when you talk about nutrition, nutrients, and energetics. But for now, we're talking about water. All right, so one of the reasons that water has these fascinating properties is because it's polar. In other words, it has a side that has a positive charge and it has a side that has a negative charge. And of all the chemicals out there, you know, in the world, you can divide them all according to are they polar or nonpolar. In other words, do they have a plus and minus end like a magnet, or are they balanced and they don't have a plus or minus end? So because water is polar, it allows these structures called hydration spheres to occur. Okay, so here's our water molecule. Giant oxygen atom right here. here, tiny little hydrogen atom over here. Oxygen is greedy and it holds on to the electrons in this molecule more often and more vigorously than the hydrogen ions do. So that means that the oxygen side of this molecule ends up getting a small negative charge and the hydrogen ends get a small positive charge. So we know that negatives and positives are attracted to the opposite, right? Well, if we take a sodium chloride crystal, so this is salt like you'd find in the ground or, you know, in Utah at the salt flats. If we take that and we put it in water, what we see happens is the sodium and the chloride dissociate. In other words, they split away from each other. So we're going to say that the chloride is in green here and the sodium is in purple. Well, when they split, they get a charge because the chloride ion... has a negative charge and the sodium has a positive charge. So here's where that polar aspect of water starts to matter. Because water has a negative end and a positive end, it can balance out the electrical charge in these different ions. So like if we look at the sodium here, sodium has a positive charge, right? Well, we see that the negative end of the oxygen molecule is all... pointing towards the sodium. Here, the water molecules are all spun around. Because the chloride has a negative, they attract the hydrogen, the positive hydrogen end. So what this all means is water kind of wraps itself around charged atoms or molecules, which are ions. Ions are charged molecules. And by wrapping themselves around like this, they essentially keep the original molecules apart. You know, the sodium and chloride, well, they'd like to join together because they have an opposite charge. But because the water is in the way all the time, it effectively keeps the sodium and chloride dissolved. In other words, in solution, not as a solid, which is what we started with with salt. We see the same thing occur with much larger molecules like glucose, which we're going to talk about in a minute. Glucose is a sugar molecule, and it too is polar. So the water molecules wrap around it in much the same way that they wrap around these ions to produce the same effect. We can take a solid. you know, sugar cube, and we can dissolve it in water because those water molecules wrap around the sugar atoms or sugar molecules that actually keep them in solution. So it's, why is water a good solvent? It's because it's highly polar, so it can dissolve things very easily. Now the other big category of liquid substances is polar. Sorry, it's non-polar. Water's polar. but the other is nonpolar. So what are these? These are fats and oils. You know the classic oil and water doesn't mix? Well the reason that that's true is because oil is nonpolar, water is polar, and those two things they can't dissolve each other. So they end up separating. Like in our picture here you know we've got the fats and oils are just kind of sitting here on the top and that's because they don't have positives and negatives inside for the water to wrap around. They're all neutral molecules, so the water can't really do anything with them. But if you look down here, we do have some large molecules that water is wrapped around. And these are proteins, which, like I said, we're going to talk more about next time. But proteins usually have positive and negative charges, too. So we end up with that same polar effect. So polar molecules can dissolve polar molecules. Non-polar molecules dissolve non-polar molecules. The opposite is not true. Polar and non-polar don't dissolve anything, so you have to stay in your class. So the non-polar biologic molecules we're going to talk about are the lipids. So lipids are the fats and oils that we either take in as part of our diet or that the body makes as part of its processes. All right, so polar and non-polar. The last two important properties of water, the first is water has a high heat capacity. And here's what I mean by that. It takes a lot of energy to change water's temperature. You know, if you're going to heat water up by one degree, you have to put a lot of energy in. And here again, the reason for that is that polarity again. Because water has a plus and minus end, water has a tendency to stick to itself. And because it sticks to itself. It means it's hard to heat up, so you have to put a lot of energy in to get a temperature increase. And what that means is, it means that as we do various things, you know, say you go from resting to exercise, and the amount of heat you're producing suddenly goes up. Well, it takes a lot of heat to actually elevate your temperature, because water is quite thermally stable. In other words, it's hard to heat water up, it's hard to cool water down. So it sort of stays at a fixed temperature, which is good for our cells. Another caveat to that is when water does evaporate, it ends up taking a lot of heat away with it. So, you know, we, unlike many mammals, have sweat glands, and that puts water on our skin. That water evaporates, and when it does, it takes an enormous amount of heat away with it. So it helps to cool us down. That same thing takes place in your lungs as well as kind of a central cooling. You'll notice that when you get very hot, you'll breathe deeper. Again, you're evaporating water to lower your temperature. All right. So high heat capacity. And then finally, lubrication. Because water kind of sticks to itself, if you put a small amount of water between two surfaces, they can flow past each other very easily. In other words, very slippery. And we're going to see a number of different instances where water is used as a lubricant in the body. So like in the joints, in the sac that surrounds the heart, in the membranes that surround the heart. In all those places, water is used as a lubricant. So just some examples of stuff that's dissolved in water, in bodily fluids. Here's the obvious one, sodium chloride, that's table salt. But then we also have potassium chloride. We have calcium, plays a major role in the body. So does phosphate. This is bicarbonate, magnesium. So we're going to see lots of examples of these. minerals and other molecules at work in the body. So you can't really do a brief synopsis of chemistry and how it matters to the human without talking about pH. So pH is the measure of acidity in a solution. And it can be a little counterintuitive, which is why it'll probably get reviewed multiple times as you go through the course. Water always exists both as H2O, which we all know, but then also as OH and H. The reason for this is this oxygen atom is very greedy for that electron. And when it holds on to that electron very tightly, one of the hydrogens falls off of this molecule. So in normal neutral water, there is a sort of balance between water in this form as H2O and water in this form as an H plus and an OH minus. So when those two are in equilibrium, then we call that a pH of 7. So that's neutral. Normal distilled water with nothing else in it is going to be at 7. Now, an acid is any substance that releases a hydrogen ion. So we're going to talk... quite a bit about hydrogen ions in this course, both in this semester and next semester. So it's good of you to start thinking about, you know, what is a hydrogen ion? Well, it's, number one, it's the thing that makes an acid an acid. So what is an acid? An acid is a solution that has a lot of hydrogen ions in it. And how does that matter? Well, when you get a lot of these hydrogen ions, they get very reactive. You know, you've all seen in chemistry, How an acid can destroy a thing. Well what's happening there is those hydrogen ions, they're not happy. You know, they have a small positive charge. They would really like to have another electron. So when you get a lot of those hydrogen ions, they're electron hunters, so to speak. So they're going to go out and they're going to try to grab electrons anywhere they can. That makes it very reactive. So an acid is any substance like here's hydrochloric acid, so here's a Here's a chloride, here's a hydrogen. When we put those in water, we get a hydrogen ion and a chloride ion. So this is an acid because we have added a hydrogen ion to the solution. You'll also hear these called protons. A proton and a hydrogen ion are really the same thing. A proton is one of the nuclear particles. There's protons and neutrons. Well for hydrogen, A single proton and a single electron, that's a normal hydrogen atom. So when we have an H+, well that's the proton without the electron. So we just call it a proton. So for example, we'll talk about a proton pump later on in the course. So an acid is any substance that adds a hydrogen ion, adds a proton. A base is just the opposite. A base is any substance that grabs a hydrogen ion or contributes an OH-. Because if we take an OH-and we add it to an H+, we get water back. So it's sort of like pushing this reaction backwards. All right. So the pH scale actually goes backwards from what you'd think. And that's because it's a tricky math, but it's a logarithmic scale. So the more hydrogen ions you have, the lower the pH gets. So... A pH of 4, let's say, is much, much more acidic than a pH of 7. And then as we go above 7, now we're talking about basic. In other words, instead of having a preponderance of hydrogen ions, now we're getting a preponderance of these OH-minuses instead. So we have bases are very reactive, you know, like household ammonia, oven cleaner. You know, you... You've smelled that smell. You've seen what those things can do. That's a base at work. So bases are always trying to grab hydrogen ions, and acids are always trying to grab electrons. So we'll see. We see that in the body, the pH range is kept very narrowly around 7.4. So if 7 is neutral, 7.4, that means that we're just a little bit basic. And we'll see that the body has a tendency to create acid, so we maintain our pH a little on the basic side, sort of for safety's sake. One of the ways that our body... maintains that pH in that normal range is using what are called buffers. So a buffer is any chemical that resists change in pH. Now, we could talk for the rest of the hour about exactly what a buffer is and how it works, but for our working pragmatic definition for this course, a buffer is a molecule that helps to maintain a solution at a particular pH. Now, Next semester you're going to talk about a number of specific buffers that the body uses. But one that is very common is right here, which is sodium bicarbonate. And essentially what happens is this reaction is reversible. So it can either go this way, CO2 and water can go to bicarbonate and a hydrogen ion, or it can go backwards. And because it's reversible, it means that when extra acid is around, this system goes this way, when there's extra base around or not enough acid around, it has a tendency to go this way. So essentially, it's kind of this give and take between two different forms of the same molecule here that either increases pH or decreases pH as necessary. But, short version, buffers prevent changes in pH. All right. All right, let's do a quick question here to engage everybody. Alright, so I'm going to end that and send you a question. Alright, so enzymes are proteins that increase the rate of chemical reactions by doing which of those things? So tick tick tick. Alright, jump in there. Alright, well most of you did get the correct answer. That's B. So enzymes work by decreasing the activation energy. Lower activation energy means... that that reaction is going to proceed faster and more often. So what an enzyme does is speed up a reaction or allow a reaction to occur at conditions where it might not otherwise occur. And like I said, we're going to see a lot of enzymes in this course. All right. So the presence of water in our bodies allows which of those things to be true? Alright, last two people. There we go. Well, clearly this one was easy. So the answer there is E. All of these are correct. Okay, so we talked about cooling the body with sweat. Water's high heat capacity means it takes a lot of energy away from it when it evaporates. That also maintains our body temperature fairly stable because it takes a lot of energy to change it. That solubility and polarity of water. water creates an environment for chemical reactions. And then of course water keeps tissues moist and helps to reduce friction as well. Okay, so that's water. Water obviously is a major player in everything. So much so that we kind of forget to talk about it. Next up is carbohydrates. So everything in your body is water, carbohydrates, lipids, or protein. minerals. So there aren't very many things there. So our first The biological compound is carbohydrates. So these are molecules that are made only of carbon, hydrogen, and oxygen. And because of how those three elements interact, they tend to be in the same ratio all the time. So it's a one-two-one ratio. In other words, for every carbon atom and oxygen atom, there are two hydrogen atoms. So the car-and they're the equal numbers of carbon and oxygen. So we'll see an example here that we'll make a little bit. clearer. So carbohydrates are the body's preferred source of fuel. Now the reason for that is because carbohydrates are easy for us to metabolize. So all of the cells of the body can use carbohydrates to create energy to keep themselves alive, to do cell division, to do all the things that our body does, fire nerves off, move muscles, all those things. Now the brain can only use glucose. So the neurons in the brain are so specialized for what they do that they can only run on one fuel. And that one fuel they can run on is glucose, which is a carbohydrate. It's a simple sugar. So when you think carbohydrates, think fuel because that's mostly what it is. Most of the carbohydrate metabolism in our body is about creating energy, creating adenosine triphosphate, ATP. in the mitochondria. Now carbohydrates do have some other functions. They play a role in certain kinds of proteins and cell structures, but we're going to look at that later on when we talk about the cell. So for now, we're just going to look at the fuel sources. So carbohydrates come in really three varieties, monosaccharides, disaccharides, and polysaccharides. Okay, mono means one. Saccharide means sweet or sugar. So this is a one sugar, monosaccharide. And there's three of those, glucose, fructose, and galactose. But we're only going to look at glucose. Alright, glucose is kind of an interesting molecule because it has six carbons and they form a ring. Now hopefully some of you remember from chemistry that ring-shaped molecules tend to be very stable. Now a molecule that's very stable means that there's a lot of energy in there. So glucose is a relatively high energy molecule because it exists in this 6 carbon ring. Now the way that the body uses this glucose is it actually breaks it up. So it takes this 6 carbon ring and it splits it into two, three carbon chains and then those carbon chains go into the mitochondria and create huge amounts of ATP. which you're going to pick up more on in A&P 2. So for now, let's just look at the glucose. Ring-shaped molecule, and you can see that for every carbon, there's an oxygen, right? And then for every carbon and oxygen, there's two hydrogens. So there's that 1 to 2 to 1 ratio of carbon, hydrogen, and oxygen. All right. So you'll be hearing a lot about glucose as we go through the course, and it's... The body actually uses all kinds of molecules for fuel, but glucose is one of the most studied of those molecules. So we use it as kind of a reference point as we look at metabolism. Alright, so that's glucose. A monosaccharide. Why mono? Because it's just one piece. You know, there's not, it's just one unit. Disaccharides are where you take two monosaccharides. And you stick them together. So now we have a di. Di is two. Saccharide is sweet. So it's two sweets or two sugars. And here again, there are a number of these disaccharides. Here is sucrose, for example, which is table sugar. And the body can split these back into monosaccharides. So if we go this direction, this bond right here is broken and we get two. glucose and a fructose, or it can push it in the other direction. So monosaccharides, disaccharides, and then the last form of carbohydrate is the polysaccharide. These are great big long chains of simple sugars. Now, anytime you have a lot of a substance dissolved in water, it starts to have an effect. You know, many of you have heard about osmosis. Well, the more stuff that's dissolved in a fluid, the more water... is being pulled towards that fluid all the time. So given that physics problem or chemistry problem, the body also wants to store glucose. Glucose is the only fuel the brain can use. It's the preferred fuel source for all the cells in the body. So we want to keep our fuel tank full, so to speak. We want to store up glucose for those times when we're not actively eating or digesting. So it creates this problem. You know, we want to have a lot of glucose, but if we have a lot of glucose around, we're going to have water being pulled towards it all the time because of osmosis. So the trick that the body does is to take many glucose molecules, so I'm just going to make circles here, and it joins them all together. So rather than storing glucose as glucose, we store glucose in a... in a branched form. So it looks a little bit like this. So each one of those rings here is a glucose molecule, and they've all been attached together. They're sort of all stuck together in this big branching chain. So this large branching chain of glucose molecules, we call this glycogen. So glycogen is made and stored in the liver, as well as the skeletal muscle. And it provides a way for the body to store glucose, you know, for use by the brain or use for fuel, without having to deal with, you know, a bazillion individual glucose molecules. So a starch is an example of a polysaccharide. Now this is one that mammals make. Plants make a variety of different starches. So like in rice, in potatoes, in many vegetables. Again, you have these complex chains of simple sugars that are carbohydrates, and we call those starches. So another name for a polysaccharide is a starch. You also find that in wheat, trees, you know, all kinds of things. All right. Okay, so polysaccharides and glucose. All right, let's do a little question here. Polysaccharides, what are polysaccharides? I have to send it to you, so hold on a minute. There we go. Alright, 3, 2, 1, last person didn't quite get in there. Alright, so the answer here is, and almost all of you got that, D. So a polysaccharide is a long chain of monosaccharides. A monosaccharide is a simple sugar. So the simple sugars are like glucose, fructose, galactose. There aren't very many of those. When sucrose and glucose combine, you're going to get a, it sort of doesn't make sense, because glucose combines with fructose to make sucrose. So it's not that one. Polysaccharides are certainly not the smallest carbohydrates. Smallest carbohydrates are your monosaccharides, your simple sugars, glucose, fructose, galactose. Carbon, hydrogen, phosphate, no. If there's phosphate in there, it's not a carbohydrate. So carbohydrates have only... carbon, oxygen, and hydrogen in them. And we talked about how plants make polysaccharides quite well. All right, so first we talked about water, then we talked about carbohydrates, next lipids, because we're in our carbohydrates, lipids, proteins. The whole body is made up of water, carbohydrates, lipids, and proteins. Okay, so lipids also contain carbon, hydrogen, and oxygen. but in differing ratios. You know, for the carbohydrate it's 1, 2, 1. You know, for every carbon there's an oxygen and two hydrogens. Well, for lipids, we look at the carbon-hydrogen ratio. So lipids are mostly carbon and hydrogen with very little amount of oxygen. Carbohydrates have the same amount of oxygen as they have carbon, so that's the big difference. And then lipids, unlike carbohydrates, can also contain other compounds, so phosphorus, nitrogen, sulfur. One of the principal characteristics of lipids is that they are not as high in lipid content as they are in oxygen. These lipids are non-polar, which means that they are what we call hydrophobic. In other words, they don't dissolve in water. So those three words mean the same thing. Non-polar, hydrophobic, is insoluble in water. And then polar is soluble in water, so we call that hydrophilic. Phobic is afraid of, philic is likes. So hydrophobic, these lipids. are afraid of water. In other words, they separate themselves from water. Because of that, lipids present a very interesting challenge for the body because we're mostly water. Our blood is mostly water. What goes circulating around our body is mostly water. So how do we move lipids around if lipids don't dissolve in water, but water is what's moving around? And the body has developed some tricks for that. One of them is to package lipids inside of something that will dissolve in water, like protein, which we'll talk more about later. So the body uses lipids for energy reserves. You know, we all know that a post-tissue is mostly triglyceride, which is a kind of lipid. It allows us to store excess energy. Lipids insulate, pad, and lubricate different areas. When we get into the cadaver lab, you'll see that there's fat in all different kinds of places and that's because fat is nice and slippery. Fat is very flexible. Fat can take a beating, you know, like it's good padding. And then also it's a good insulator. In other words, it helps keep our body heat in. You know, just like the blubber on whales, it works on us too. The lipids help to keep us warm. The body also uses lipids as hormones. because unlike proteins and carbohydrates, lipids can pass right through cell membranes. They don't need any kind of transporter. They don't need any assistance because the cell membrane is made of lipids, so the lipids can pass through those lipids. So many hormones use that characteristic. All right. And then lipids also are important structural components of cells. So for example, the cell membrane and the nucleus membrane, the nuclear membrane, are both made of lipids called phospholipids, which we'll talk more about later. So one of the simplest lipids is called a fatty acid. And what you can see here is really we have just a long chain of carbon atoms. Carbon, carbon, carbon, carbon. carbon, with hydrogen filling up the rest of the binding sites. And then it's only at the end that we have a couple of oxygens. So these long chains of carbon and hydrogen with an oxygen at the end, that's a fatty acid. Why an acid? Because when we take this and dissolve it in water, this hydrogen falls off. And you know that any substance that donates a hydrogen, that a hydrogen falls off of, that's an acid. So this is called an acid because of that. fat because this hydrogen ion gets donated. You've all heard about saturated and unsaturated fats, you know, at the grocery store. Well, here's what that means. It's actually a chemistry word. A saturated fat has no double bonds. So they're all single carbon-carbon bonds. An unsaturated fat has at least one, but can have many, many more than one, at least one double bond. So here, we see no double bonds here, we see one, two, three, four, or more. Now, the research seems to suggest that these unsaturated fats are actually healthier for you than the saturated ones. Now, in part, that may be because this double bond right here provides some protection against oxidation, so they have some antioxidant properties. It's also probably easier for the body to process these fats because of this double bond and the change in the shape that it makes. So the only exception to that are the trans fats, which is an unsaturated fat that has a different shape than that. All right, so saturated fats tend to be found in animals, unsaturated fats in plants. So your plant oils like peanut oil, sunflower, soybean. Those are going to be primarily unsaturated. All right. So an important class of molecule in the lipid family are the glycerides. Now, they get their name because... They have a glycerol backbone. So this molecule right here is a glycerol and we can take that glycerol and we can add fatty acids to it. So we can attach fatty acids to this glycerol backbone. We can attach one and we'll get a monoglyceride. We can attach two fatty acids and we'll get a di or two glyceride. Or we can attach three fatty acids because there's three carbons here to work with. And then we can get a triglyceride. The triglyceride is the single most common lipid in the body. And the reason for that is it's what makes up adipose tissue or fat tissue. So the triglycerides are, here's an example of one right here, three fatty acids on a glycerol backbone. Now, the triglycerides are energy storage molecules. You know, why do we make triglycerides? Well, some of it's to keep us warm and to keep some padding, but the traditional or typical fat stores are really energy stores. At times when there isn't as much food around, you know, think ancient human beings, they would have utilized their triglyceride stores to make it through the winter, let's say, or to make it until the harvest. So triglycerides are the most common lipid found in the body. All right. A couple of others, the eicosanoids are, you know, you can see that this molecule looks pretty complicated, right? Spend absolutely no time memorizing any of these chemical formulas, okay? Don't, that's not important. What's important is, like, for example, I do want you to know that a triglyceride is three fatty acids and a glycerol backbone, but you won't have to, like, draw it for me or anything like that. Think words, not chemical formulas. These eicosanoids are also fancy lipids that end up, they work as chemical messengers between cells. Very similar to these compounds called the steroids. Now, yes, these are the very same steroids you hear about in professional sports and things like that. Steroids are a class of hormones that all share this common ring. orientation right here, you can see that there's sort of four and a half rings that are all joined together. Well, this starts as cholesterol, and it's modified into the other steroid hormones like estrogen, like testosterone, like cortisol. So, cholesterol is important. It's not just a bad thing. Cholesterol is important for the cell membrane. And then cholesterol also is important because it's the precursor to these important steroid hormones like estrogen and testosterone. So these also are lipids, so nonpolar, and they're easy to identify because they have this complicated connected ring design here. So you can see that all these compounds are related because they all share that same structure. All right. And then our last molecule for the day is going to be the phospholipid. And we're going to talk at length about these when we start our cell check, which I believe is going to be next time. But phospholipids are what make up the cell membrane. And they're fascinating compounds because they have a head and two tails. The head likes to be around water, so it's hydrophilic. and the two tails not having any oxygen in there, you know, they look like fatty acids, right? The two tails are very hydrophobic. So we end up with a hydrophilic end and a hydrophobic end. And what happens is we get these ball shapes that form. You know, all the heads point out, all the tails point in, and we get these little balls of lipid. Now what we'll see next time is if you take... two of these and you put the tails together in the center and the heads outward, that's how you end up with a cell membrane or a lipid bilayer. So we're going to pick this process up when we get to the cells and we'll see how phospholipids create the cell membrane. But for now, we are out of time for the day. So I will see you out on Wednesday.

Because you're going to use that chemistry as we talk about physiology, but I'm not going to ask you specific chemistry questions, if that kind of makes sense. So do use the resources in the book to review, particularly if it's been a while or if you didn't do so well in chemistry. But we're going to kind of pick up at where we start talking about the human being, so elements in the body.

So like everything in the universe, You know, the human being is made of elements, and most of those are in this top box right here. So what are we made of? Well, mostly oxygen, carbon, hydrogen, and nitrogen.

So the hydrogen and oxygen together, that's going to make up water, and we all know that we're, you know, about 60% to 80% water, depending. So that's where a lot of that goes. Most of the carbon and nitrogen are found in proteins in the body. that create the connective tissue or the structure or substance of the body. But even though these other elements are in the body in much smaller amounts, in many ways these like sodium, potassium, calcium, iron are some of the most important things because they actually make it so we can do stuff.

We're going to see throughout the course that calcium plays a major role. in all the fancy things that we do. So things like muscle contraction, nerve conduction, you know, the way the brain works.

We're going to see that calcium is critical for a lot of those functions. So the bulk elements are these four, but then these others that we're going to see throughout the course play a major role in how things actually happen. So just a quick review of what an enzyme is, because we're going to talk a lot about enzymes in certain aspects of the course. An enzyme is simply a molecule that assists a chemical reaction. So as a little chemistry review, in order to go from, you know, reactants are what you start with.

So you know, you take chemical A and chemical B and you mix them together. So those are your reactants. And what you get out if there's a chemical reaction that occurs is products.

So you mix reactants to create products. Well for most reactions... In order to get those reactants to change or do anything, you usually have to put energy in. And then once you put that energy in, then this reaction can proceed forward. So we call that energy that we have to put in the activation energy.

So like in chemistry, a lot of times, when you've mixed two chemicals, you'll have to heat them up. You know, you have to put them on the hot plate. Well, what you're doing there is you're adding that activation energy.

Another form of this is, let's say you have to shake something. Again, you're adding energy to that equation. Well, what an enzyme does is it drastically reduces the amount of energy that's required to go from reactants to products. And when we talk about proteins, which is probably going to be at the beginning of next time, we're going to see that many proteins in the body act as enzymes.

In other words, they make some chemical reaction happen. So, for example, the blood clotting protein is called fibrin, and there's an enzyme that's called thrombin that turns fibrinogen, which is a reactant, into the product fibrin that then creates a blood clot. So we're going to see lots of examples of these enzymes that make things happen. So as a chemistry refresher, what's really going on is that enzyme is reducing the activation energy that's required. So the reaction can proceed faster and at a lower temperature or at a lower energy.

Alright. Well, we all know that we're mostly water, but why does that matter? There's a reason why water and life on Earth kind of go together.

And a couple of those we'll talk about specifically. So one is solubility. Solubility is the property of a substance that allows it to dissolve stuff. And water... ...is an excellent solvent.

All kinds of things that are found on planet Earth dissolve very readily in water. You know, the one... that we know or that comes to mind first is salt.

You know, the oceans are salt water. And what we've got there is we've got water that has sodium chloride dissolved in it. So because of water's chemical properties, it can dissolve all kinds of different things. So all of that diversity of solutes is sort of how life on Earth works.

There are so many different things dissolved in water that those things can interact and create you know, biology and life. So solubility. Another is reactivity.

A lot of times we think of water as kind of passive. You know, it's the place where stuff happens, but it doesn't really participate in what happens. And we're going to see a number of examples in this course of how water does participate in the chemistry of life. So for example, when we Hydrolysis is we can take a molecule that looks like this, you know, that has two parts, an A and a B.

We can add a water molecule to it, and we can break that larger molecule apart into two pieces. So, you know, we add the H and the O, and we get an A, H, and a B, H2, or a VO. So we can split using water. We can also put things back together. This is called a dehydration reaction.

So we can take an AH and a VOH. We can pull the water out and then we get a molecule called AB. So we can put two pieces, two molecule pieces together into a larger molecule in dehydration or split them apart in hydrolysis. And you'll see that water is playing a role here.

It's not just sitting around. It's being incorporated into these new molecules or it's being created from these old molecules. So one of the principal reactions that fuels our body occurs in the mitochondria, and that's where we take carbon compounds like glucose, and we turn them into carbon dioxide, water, and then a great deal of cellular energy called ATP. So here again, you can see that water isn't just a solvent here, it's actually participating in the chemistry.

So, you know, when we break down sugar to create energy, we not only... create CO2, we actually create some water too out of that sugar. So we'll see much, you'll see a lot more of this in the next semester when you talk about nutrition, nutrients, and energetics.

But for now, we're talking about water. All right, so one of the reasons that water has these fascinating properties is because it's polar. In other words, it has a side that has a positive charge and it has a side that has a negative charge. And of all the chemicals out there, you know, in the world, you can divide them all according to are they polar or nonpolar. In other words, do they have a plus and minus end like a magnet, or are they balanced and they don't have a plus or minus end?

So because water is polar, it allows these structures called hydration spheres to occur. Okay, so here's our water molecule. Giant oxygen atom right here. here, tiny little hydrogen atom over here. Oxygen is greedy and it holds on to the electrons in this molecule more often and more vigorously than the hydrogen ions do.

So that means that the oxygen side of this molecule ends up getting a small negative charge and the hydrogen ends get a small positive charge. So we know that negatives and positives are attracted to the opposite, right? Well, if we take a sodium chloride crystal, so this is salt like you'd find in the ground or, you know, in Utah at the salt flats.

If we take that and we put it in water, what we see happens is the sodium and the chloride dissociate. In other words, they split away from each other. So we're going to say that the chloride is in green here and the sodium is in purple. Well, when they split, they get a charge because the chloride ion... has a negative charge and the sodium has a positive charge.

So here's where that polar aspect of water starts to matter. Because water has a negative end and a positive end, it can balance out the electrical charge in these different ions. So like if we look at the sodium here, sodium has a positive charge, right? Well, we see that the negative end of the oxygen molecule is all...

pointing towards the sodium. Here, the water molecules are all spun around. Because the chloride has a negative, they attract the hydrogen, the positive hydrogen end.

So what this all means is water kind of wraps itself around charged atoms or molecules, which are ions. Ions are charged molecules. And by wrapping themselves around like this, they essentially keep the original molecules apart.

You know, the sodium and chloride, well, they'd like to join together because they have an opposite charge. But because the water is in the way all the time, it effectively keeps the sodium and chloride dissolved. In other words, in solution, not as a solid, which is what we started with with salt.

We see the same thing occur with much larger molecules like glucose, which we're going to talk about in a minute. Glucose is a sugar molecule, and it too is polar. So the water molecules wrap around it in much the same way that they wrap around these ions to produce the same effect.

We can take a solid. you know, sugar cube, and we can dissolve it in water because those water molecules wrap around the sugar atoms or sugar molecules that actually keep them in solution. So it's, why is water a good solvent? It's because it's highly polar, so it can dissolve things very easily.

Now the other big category of liquid substances is polar. Sorry, it's non-polar. Water's polar.

but the other is nonpolar. So what are these? These are fats and oils.

You know the classic oil and water doesn't mix? Well the reason that that's true is because oil is nonpolar, water is polar, and those two things they can't dissolve each other. So they end up separating.

Like in our picture here you know we've got the fats and oils are just kind of sitting here on the top and that's because they don't have positives and negatives inside for the water to wrap around. They're all neutral molecules, so the water can't really do anything with them. But if you look down here, we do have some large molecules that water is wrapped around.

And these are proteins, which, like I said, we're going to talk more about next time. But proteins usually have positive and negative charges, too. So we end up with that same polar effect. So polar molecules can dissolve polar molecules.

Non-polar molecules dissolve non-polar molecules. The opposite is not true. Polar and non-polar don't dissolve anything, so you have to stay in your class.

So the non-polar biologic molecules we're going to talk about are the lipids. So lipids are the fats and oils that we either take in as part of our diet or that the body makes as part of its processes. All right, so polar and non-polar. The last two important properties of water, the first is water has a high heat capacity. And here's what I mean by that.

It takes a lot of energy to change water's temperature. You know, if you're going to heat water up by one degree, you have to put a lot of energy in. And here again, the reason for that is that polarity again. Because water has a plus and minus end, water has a tendency to stick to itself. And because it sticks to itself.

It means it's hard to heat up, so you have to put a lot of energy in to get a temperature increase. And what that means is, it means that as we do various things, you know, say you go from resting to exercise, and the amount of heat you're producing suddenly goes up. Well, it takes a lot of heat to actually elevate your temperature, because water is quite thermally stable. In other words, it's hard to heat water up, it's hard to cool water down. So it sort of stays at a fixed temperature, which is good for our cells.

Another caveat to that is when water does evaporate, it ends up taking a lot of heat away with it. So, you know, we, unlike many mammals, have sweat glands, and that puts water on our skin. That water evaporates, and when it does, it takes an enormous amount of heat away with it.

So it helps to cool us down. That same thing takes place in your lungs as well as kind of a central cooling. You'll notice that when you get very hot, you'll breathe deeper. Again, you're evaporating water to lower your temperature.

All right. So high heat capacity. And then finally, lubrication. Because water kind of sticks to itself, if you put a small amount of water between two surfaces, they can flow past each other very easily. In other words, very slippery.

And we're going to see a number of different instances where water is used as a lubricant in the body. So like in the joints, in the sac that surrounds the heart, in the membranes that surround the heart. In all those places, water is used as a lubricant.

So just some examples of stuff that's dissolved in water, in bodily fluids. Here's the obvious one, sodium chloride, that's table salt. But then we also have potassium chloride.

We have calcium, plays a major role in the body. So does phosphate. This is bicarbonate, magnesium. So we're going to see lots of examples of these.

minerals and other molecules at work in the body. So you can't really do a brief synopsis of chemistry and how it matters to the human without talking about pH. So pH is the measure of acidity in a solution. And it can be a little counterintuitive, which is why it'll probably get reviewed multiple times as you go through the course.

Water always exists both as H2O, which we all know, but then also as OH and H. The reason for this is this oxygen atom is very greedy for that electron. And when it holds on to that electron very tightly, one of the hydrogens falls off of this molecule. So in normal neutral water, there is a sort of balance between water in this form as H2O and water in this form as an H plus and an OH minus.

So when those two are in equilibrium, then we call that a pH of 7. So that's neutral. Normal distilled water with nothing else in it is going to be at 7. Now, an acid is any substance that releases a hydrogen ion. So we're going to talk...

quite a bit about hydrogen ions in this course, both in this semester and next semester. So it's good of you to start thinking about, you know, what is a hydrogen ion? Well, it's, number one, it's the thing that makes an acid an acid.

So what is an acid? An acid is a solution that has a lot of hydrogen ions in it. And how does that matter?

Well, when you get a lot of these hydrogen ions, they get very reactive. You know, you've all seen in chemistry, How an acid can destroy a thing. Well what's happening there is those hydrogen ions, they're not happy.

You know, they have a small positive charge. They would really like to have another electron. So when you get a lot of those hydrogen ions, they're electron hunters, so to speak.

So they're going to go out and they're going to try to grab electrons anywhere they can. That makes it very reactive. So an acid is any substance like here's hydrochloric acid, so here's a Here's a chloride, here's a hydrogen. When we put those in water, we get a hydrogen ion and a chloride ion. So this is an acid because we have added a hydrogen ion to the solution.

You'll also hear these called protons. A proton and a hydrogen ion are really the same thing. A proton is one of the nuclear particles. There's protons and neutrons. Well for hydrogen, A single proton and a single electron, that's a normal hydrogen atom.

So when we have an H+, well that's the proton without the electron. So we just call it a proton. So for example, we'll talk about a proton pump later on in the course.

So an acid is any substance that adds a hydrogen ion, adds a proton. A base is just the opposite. A base is any substance that grabs a hydrogen ion or contributes an OH-. Because if we take an OH-and we add it to an H+, we get water back. So it's sort of like pushing this reaction backwards.

All right. So the pH scale actually goes backwards from what you'd think. And that's because it's a tricky math, but it's a logarithmic scale. So the more hydrogen ions you have, the lower the pH gets.

So... A pH of 4, let's say, is much, much more acidic than a pH of 7. And then as we go above 7, now we're talking about basic. In other words, instead of having a preponderance of hydrogen ions, now we're getting a preponderance of these OH-minuses instead.

So we have bases are very reactive, you know, like household ammonia, oven cleaner. You know, you... You've smelled that smell.

You've seen what those things can do. That's a base at work. So bases are always trying to grab hydrogen ions, and acids are always trying to grab electrons.

So we'll see. We see that in the body, the pH range is kept very narrowly around 7.4. So if 7 is neutral, 7.4, that means that we're just a little bit basic.

And we'll see that the body has a tendency to create acid, so we maintain our pH a little on the basic side, sort of for safety's sake. One of the ways that our body... maintains that pH in that normal range is using what are called buffers. So a buffer is any chemical that resists change in pH. Now, we could talk for the rest of the hour about exactly what a buffer is and how it works, but for our working pragmatic definition for this course, a buffer is a molecule that helps to maintain a solution at a particular pH. Now, Next semester you're going to talk about a number of specific buffers that the body uses. But one that is very common is right here, which is sodium bicarbonate.

And essentially what happens is this reaction is reversible. So it can either go this way, CO2 and water can go to bicarbonate and a hydrogen ion, or it can go backwards. And because it's reversible, it means that when extra acid is around, this system goes this way, when there's extra base around or not enough acid around, it has a tendency to go this way. So essentially, it's kind of this give and take between two different forms of the same molecule here that either increases pH or decreases pH as necessary.

But, short version, buffers prevent changes in pH. All right. All right, let's do a quick question here to engage everybody. Alright, so I'm going to end that and send you a question.

Alright, so enzymes are proteins that increase the rate of chemical reactions by doing which of those things? So tick tick tick. Alright, jump in there.

Alright, well most of you did get the correct answer. That's B. So enzymes work by decreasing the activation energy. Lower activation energy means...

that that reaction is going to proceed faster and more often. So what an enzyme does is speed up a reaction or allow a reaction to occur at conditions where it might not otherwise occur. And like I said, we're going to see a lot of enzymes in this course.

All right. So the presence of water in our bodies allows which of those things to be true? Alright, last two people.

There we go. Well, clearly this one was easy. So the answer there is E. All of these are correct.

Okay, so we talked about cooling the body with sweat. Water's high heat capacity means it takes a lot of energy away from it when it evaporates. That also maintains our body temperature fairly stable because it takes a lot of energy to change it. That solubility and polarity of water.

water creates an environment for chemical reactions. And then of course water keeps tissues moist and helps to reduce friction as well. Okay, so that's water. Water obviously is a major player in everything. So much so that we kind of forget to talk about it.

Next up is carbohydrates. So everything in your body is water, carbohydrates, lipids, or protein. minerals.

So there aren't very many things there. So our first The biological compound is carbohydrates. So these are molecules that are made only of carbon, hydrogen, and oxygen. And because of how those three elements interact, they tend to be in the same ratio all the time.

So it's a one-two-one ratio. In other words, for every carbon atom and oxygen atom, there are two hydrogen atoms. So the car-and they're the equal numbers of carbon and oxygen. So we'll see an example here that we'll make a little bit.

clearer. So carbohydrates are the body's preferred source of fuel. Now the reason for that is because carbohydrates are easy for us to metabolize.

So all of the cells of the body can use carbohydrates to create energy to keep themselves alive, to do cell division, to do all the things that our body does, fire nerves off, move muscles, all those things. Now the brain can only use glucose. So the neurons in the brain are so specialized for what they do that they can only run on one fuel.

And that one fuel they can run on is glucose, which is a carbohydrate. It's a simple sugar. So when you think carbohydrates, think fuel because that's mostly what it is.

Most of the carbohydrate metabolism in our body is about creating energy, creating adenosine triphosphate, ATP. in the mitochondria. Now carbohydrates do have some other functions. They play a role in certain kinds of proteins and cell structures, but we're going to look at that later on when we talk about the cell.

So for now, we're just going to look at the fuel sources. So carbohydrates come in really three varieties, monosaccharides, disaccharides, and polysaccharides. Okay, mono means one. Saccharide means sweet or sugar.

So this is a one sugar, monosaccharide. And there's three of those, glucose, fructose, and galactose. But we're only going to look at glucose.

Alright, glucose is kind of an interesting molecule because it has six carbons and they form a ring. Now hopefully some of you remember from chemistry that ring-shaped molecules tend to be very stable. Now a molecule that's very stable means that there's a lot of energy in there. So glucose is a relatively high energy molecule because it exists in this 6 carbon ring.

Now the way that the body uses this glucose is it actually breaks it up. So it takes this 6 carbon ring and it splits it into two, three carbon chains and then those carbon chains go into the mitochondria and create huge amounts of ATP. which you're going to pick up more on in A&P 2. So for now, let's just look at the glucose. Ring-shaped molecule, and you can see that for every carbon, there's an oxygen, right?

And then for every carbon and oxygen, there's two hydrogens. So there's that 1 to 2 to 1 ratio of carbon, hydrogen, and oxygen. All right.

So you'll be hearing a lot about glucose as we go through the course, and it's... The body actually uses all kinds of molecules for fuel, but glucose is one of the most studied of those molecules. So we use it as kind of a reference point as we look at metabolism. Alright, so that's glucose. A monosaccharide.

Why mono? Because it's just one piece. You know, there's not, it's just one unit. Disaccharides are where you take two monosaccharides. And you stick them together.

So now we have a di. Di is two. Saccharide is sweet.

So it's two sweets or two sugars. And here again, there are a number of these disaccharides. Here is sucrose, for example, which is table sugar. And the body can split these back into monosaccharides.

So if we go this direction, this bond right here is broken and we get two. glucose and a fructose, or it can push it in the other direction. So monosaccharides, disaccharides, and then the last form of carbohydrate is the polysaccharide. These are great big long chains of simple sugars.

Now, anytime you have a lot of a substance dissolved in water, it starts to have an effect. You know, many of you have heard about osmosis. Well, the more stuff that's dissolved in a fluid, the more water...

is being pulled towards that fluid all the time. So given that physics problem or chemistry problem, the body also wants to store glucose. Glucose is the only fuel the brain can use.

It's the preferred fuel source for all the cells in the body. So we want to keep our fuel tank full, so to speak. We want to store up glucose for those times when we're not actively eating or digesting. So it creates this problem.

You know, we want to have a lot of glucose, but if we have a lot of glucose around, we're going to have water being pulled towards it all the time because of osmosis. So the trick that the body does is to take many glucose molecules, so I'm just going to make circles here, and it joins them all together. So rather than storing glucose as glucose, we store glucose in a... in a branched form. So it looks a little bit like this.

So each one of those rings here is a glucose molecule, and they've all been attached together. They're sort of all stuck together in this big branching chain. So this large branching chain of glucose molecules, we call this glycogen.

So glycogen is made and stored in the liver, as well as the skeletal muscle. And it provides a way for the body to store glucose, you know, for use by the brain or use for fuel, without having to deal with, you know, a bazillion individual glucose molecules. So a starch is an example of a polysaccharide.

Now this is one that mammals make. Plants make a variety of different starches. So like in rice, in potatoes, in many vegetables.

Again, you have these complex chains of simple sugars that are carbohydrates, and we call those starches. So another name for a polysaccharide is a starch. You also find that in wheat, trees, you know, all kinds of things.

All right. Okay, so polysaccharides and glucose. All right, let's do a little question here.

Polysaccharides, what are polysaccharides? I have to send it to you, so hold on a minute. There we go.

Alright, 3, 2, 1, last person didn't quite get in there. Alright, so the answer here is, and almost all of you got that, D. So a polysaccharide is a long chain of monosaccharides.

A monosaccharide is a simple sugar. So the simple sugars are like glucose, fructose, galactose. There aren't very many of those. When sucrose and glucose combine, you're going to get a, it sort of doesn't make sense, because glucose combines with fructose to make sucrose.

So it's not that one. Polysaccharides are certainly not the smallest carbohydrates. Smallest carbohydrates are your monosaccharides, your simple sugars, glucose, fructose, galactose. Carbon, hydrogen, phosphate, no.

If there's phosphate in there, it's not a carbohydrate. So carbohydrates have only... carbon, oxygen, and hydrogen in them.

And we talked about how plants make polysaccharides quite well. All right, so first we talked about water, then we talked about carbohydrates, next lipids, because we're in our carbohydrates, lipids, proteins. The whole body is made up of water, carbohydrates, lipids, and proteins. Okay, so lipids also contain carbon, hydrogen, and oxygen. but in differing ratios.

You know, for the carbohydrate it's 1, 2, 1. You know, for every carbon there's an oxygen and two hydrogens. Well, for lipids, we look at the carbon-hydrogen ratio. So lipids are mostly carbon and hydrogen with very little amount of oxygen. Carbohydrates have the same amount of oxygen as they have carbon, so that's the big difference. And then lipids, unlike carbohydrates, can also contain other compounds, so phosphorus, nitrogen, sulfur.

One of the principal characteristics of lipids is that they are not as high in lipid content as they are in oxygen. These lipids are non-polar, which means that they are what we call hydrophobic. In other words, they don't dissolve in water.

So those three words mean the same thing. Non-polar, hydrophobic, is insoluble in water. And then polar is soluble in water, so we call that hydrophilic.

Phobic is afraid of, philic is likes. So hydrophobic, these lipids. are afraid of water.

In other words, they separate themselves from water. Because of that, lipids present a very interesting challenge for the body because we're mostly water. Our blood is mostly water. What goes circulating around our body is mostly water.

So how do we move lipids around if lipids don't dissolve in water, but water is what's moving around? And the body has developed some tricks for that. One of them is to package lipids inside of something that will dissolve in water, like protein, which we'll talk more about later.

So the body uses lipids for energy reserves. You know, we all know that a post-tissue is mostly triglyceride, which is a kind of lipid. It allows us to store excess energy. Lipids insulate, pad, and lubricate different areas.

When we get into the cadaver lab, you'll see that there's fat in all different kinds of places and that's because fat is nice and slippery. Fat is very flexible. Fat can take a beating, you know, like it's good padding. And then also it's a good insulator.

In other words, it helps keep our body heat in. You know, just like the blubber on whales, it works on us too. The lipids help to keep us warm.

The body also uses lipids as hormones. because unlike proteins and carbohydrates, lipids can pass right through cell membranes. They don't need any kind of transporter.

They don't need any assistance because the cell membrane is made of lipids, so the lipids can pass through those lipids. So many hormones use that characteristic. All right.

And then lipids also are important structural components of cells. So for example, the cell membrane and the nucleus membrane, the nuclear membrane, are both made of lipids called phospholipids, which we'll talk more about later. So one of the simplest lipids is called a fatty acid.

And what you can see here is really we have just a long chain of carbon atoms. Carbon, carbon, carbon, carbon. carbon, with hydrogen filling up the rest of the binding sites. And then it's only at the end that we have a couple of oxygens.

So these long chains of carbon and hydrogen with an oxygen at the end, that's a fatty acid. Why an acid? Because when we take this and dissolve it in water, this hydrogen falls off.

And you know that any substance that donates a hydrogen, that a hydrogen falls off of, that's an acid. So this is called an acid because of that. fat because this hydrogen ion gets donated. You've all heard about saturated and unsaturated fats, you know, at the grocery store. Well, here's what that means.

It's actually a chemistry word. A saturated fat has no double bonds. So they're all single carbon-carbon bonds. An unsaturated fat has at least one, but can have many, many more than one, at least one double bond. So here, we see no double bonds here, we see one, two, three, four, or more.

Now, the research seems to suggest that these unsaturated fats are actually healthier for you than the saturated ones. Now, in part, that may be because this double bond right here provides some protection against oxidation, so they have some antioxidant properties. It's also probably easier for the body to process these fats because of this double bond and the change in the shape that it makes.

So the only exception to that are the trans fats, which is an unsaturated fat that has a different shape than that. All right, so saturated fats tend to be found in animals, unsaturated fats in plants. So your plant oils like peanut oil, sunflower, soybean. Those are going to be primarily unsaturated.

All right. So an important class of molecule in the lipid family are the glycerides. Now, they get their name because...

They have a glycerol backbone. So this molecule right here is a glycerol and we can take that glycerol and we can add fatty acids to it. So we can attach fatty acids to this glycerol backbone.

We can attach one and we'll get a monoglyceride. We can attach two fatty acids and we'll get a di or two glyceride. Or we can attach three fatty acids because there's three carbons here to work with.

And then we can get a triglyceride. The triglyceride is the single most common lipid in the body. And the reason for that is it's what makes up adipose tissue or fat tissue. So the triglycerides are, here's an example of one right here, three fatty acids on a glycerol backbone.

Now, the triglycerides are energy storage molecules. You know, why do we make triglycerides? Well, some of it's to keep us warm and to keep some padding, but the traditional or typical fat stores are really energy stores. At times when there isn't as much food around, you know, think ancient human beings, they would have utilized their triglyceride stores to make it through the winter, let's say, or to make it until the harvest. So triglycerides are the most common lipid found in the body.

All right. A couple of others, the eicosanoids are, you know, you can see that this molecule looks pretty complicated, right? Spend absolutely no time memorizing any of these chemical formulas, okay? Don't, that's not important.

What's important is, like, for example, I do want you to know that a triglyceride is three fatty acids and a glycerol backbone, but you won't have to, like, draw it for me or anything like that. Think words, not chemical formulas. These eicosanoids are also fancy lipids that end up, they work as chemical messengers between cells. Very similar to these compounds called the steroids.

Now, yes, these are the very same steroids you hear about in professional sports and things like that. Steroids are a class of hormones that all share this common ring. orientation right here, you can see that there's sort of four and a half rings that are all joined together. Well, this starts as cholesterol, and it's modified into the other steroid hormones like estrogen, like testosterone, like cortisol.

So, cholesterol is important. It's not just a bad thing. Cholesterol is important for the cell membrane. And then cholesterol also is important because it's the precursor to these important steroid hormones like estrogen and testosterone.

So these also are lipids, so nonpolar, and they're easy to identify because they have this complicated connected ring design here. So you can see that all these compounds are related because they all share that same structure. All right. And then our last molecule for the day is going to be the phospholipid. And we're going to talk at length about these when we start our cell check, which I believe is going to be next time.

But phospholipids are what make up the cell membrane. And they're fascinating compounds because they have a head and two tails. The head likes to be around water, so it's hydrophilic.

and the two tails not having any oxygen in there, you know, they look like fatty acids, right? The two tails are very hydrophobic. So we end up with a hydrophilic end and a hydrophobic end. And what happens is we get these ball shapes that form. You know, all the heads point out, all the tails point in, and we get these little balls of lipid.

Now what we'll see next time is if you take... two of these and you put the tails together in the center and the heads outward, that's how you end up with a cell membrane or a lipid bilayer. So we're going to pick this process up when we get to the cells and we'll see how phospholipids create the cell membrane. But for now, we are out of time for the day.

So I will see you out on Wednesday.

Transcript for:Chemistry Basics in Human Physiology

Transcript for:
Chemistry Basics in Human Physiology