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Biological molecules - You are what you eat

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- Hello, and welcome, to the kitchen. I wanted to invite you here today because last week we started off in my bathroom, and I kinda feel bad about that, and also because as I'm making lunch today, I wanted to sort of use it as a lab. During this time in my kitchen, I'm going to talk to you about three different things. One, the three most important molecules on the Earth. Two, possibly the grossest sandwich I'm ever going to eat. And three, an obscure scientist who taught us everything that we know about urine. (upbeat music) So far we've talked about carbon and we've talked about water. And now we're gonna talk about the molecules that make up every living thing and every living thing in every living thing. I don't care if you're a bacterium or if you're a blue whale or if you're Lady Gaga or if you're a mite living on the Queen of England's eyelashes. They're called biological molecules. These aren't just building blocks. These are the molecules necessary for every living thing on Earth to survive. They are essential sources of energy, they are the means of storing that energy, they are also the instructions that all organisms use to be born, to grow and to ultimately pass those same instructions on the the future generation. They are the ingredients for life. And we call them, the Carbohydrates, the Lipids, the Proteins, and the Nucleic Acids. And today we're just gonna be talking about the first three. It's no coincidence that we classify them in the same way that we classify food. Because, they're food. And for this classification we have to thank a little known English physician, who hundreds of years ago dedicated his life to the study of human pee. (upbeat music) Wow, my goodness, I'm back in the den so that must mean that it's time for the most awkwardly named segment here on crash course, Biolography. His name was William Prout. And in the early 1800's he became fascinated with human digestion, especially our urine. And that's because he thought that the best way to understand the human body was through chemistry. And the best way to understand the body's chemistry was to understand what it does to food. By day, he was a practicing physician but every morning before breakfast he did research in his home laboratory in London. And there he did many great things like being the first to discover that our stomachs contained Hydrochloric Acid and writing a breakthrough book about Kidney Stones called, An Inquiry Into the Nature and Treatment of Gravel, Calculus and Other Diseases Connected with a Deranged Operation of the Urinary Organs. And he was, of course, the first person to discover the chemical composition of pure urea, the main component of urine. For the record, here it is. And in the presence of water, urea gives off Ammonia. Which is why your pee smells. Through his years of studying urine, Prout came to the conclusion that all foods stuff fell into three categories. The Saccharinous, carbohydrates. The Oleaginous, the fats and the Albuminous, the proteins. He went so far as to say that in order to be healthy you needed to eat all three of these things. Not just, sheep, kidneys and gin which is probably what most of London was living on at the time. But like many great minds, Prout was overlooked in his own lifetime, because while he was study actual science everybody else was walking around believing that the color of your urine was determined by your personality. This guy looks like a total jerk to me. And if you could tell that much by color, I wonder what you could tell by taste. Now he didn't understand that there were biological molecules. He didn't understand what these things were. But he did understand that there were three ingredients necessary for life. And it turns out that all organisms either need to synthesis or ingest those ingredients in order to live. We're gonna start off with the most basic of these ingredients for life and that is the carbohydrate. You've no doubt heard of them, you may in fact be avoiding them like the plague. But the fact is that nothing, and no one can avoid carbohydrates because they are the source of all energy that we have available to us. Carbohydrates are made up of sugars. And the simplest of them are called Monosaccharides. Mono, for one, saccharides for the actual root of the word sugar. The star of the show here is Glucose because it's truly fundamental. By which I mean, like number one of the global food chain because it comes from the sun. All biological energy is originally captured from the sun by plants as glucose through photosynthesis. And every cell that needs energy uses glucose to get that energy through a process called Respiration. In addition to glucose, there are other monosaccharides like Fructose, which has the same molecular formula C-6-H-12-O-6 but arranged differently. These subtle chemical differences do matter. Fructose for example, is significantly sweeter that glucose. It's also processed by our bodies in different ways. And then there are, Disaccharides. Which like the name says, are just two monosaccharides put together. And the most famous of these is Sucrose. Which is simply a glucose molecule and a fructose molecule joined by a covalent bond. Mono and disaccharides are pretty much just little niblets of energy that are really easy for our bodies to process. But when these carbohydrates start to form into longer and longer chains their functions and their roles change as well. Instead of being sources for instant energy they become store houses of energy or structural compounds. These are Polysaccharides. Instead of being just two, or three monosaccharides put together, polysaccharides can contain thousands of simple sugar units. And because they're so big and burley, they're great for building with. In plants, cellulose is the most common structural compound, it's just bunch of glucose molecules bound together and it is the most common organic compound on the planet. Unfortunately, it's very difficult to digest. Cows can do it but humans certainly cannot. Which is why you don't enjoy eating grass. Polysaccharides are also really good for storing energy and not just structurally, but just as an energy store. And that's where we get bread. Now really interesting thing here, bread made up of starch, the most simple of which is called Amylose. Amylose and cellulose looked almost exactly identical. But one is grass and the other is bread. Like, chemistry! Plants store glucose in the form of starch and it comes in lots and lots of different forms. From roots and tuberose, to the sweet flesh of fruits, to the starchy seeds of the wheat plant that end up being milled into flour. Ground up grain is the main ingredient in the bread of course and most the calories, or the energy content comes from carbohydrates. When I eat this, and I'm gonna eat the hell out of it I'm gonna be eating all of the chemical energy that this wheat plant got from the sun in order to feed it's next generation of seeds that we then stole for our own use, all for me. Now we have human beings can't grow fruits or tubers so we have to store our energy in a couple of different ways. The way that we tend to store carbohydrate energy is in glycogen which is very similar to amylose or starch but has more branches and is more complicated. It's basically made up of the glucose that we have left over after we eat and it sits in our muscles really ready to use and it's also stored in our livers. It's generally a pretty short-term store, if we don't eat for like a day pretty much all of our glycogen gets depleted. But over in the longer term, the way that we store our energy is through fat. All of our mom's worst energy, the fat which turns out to be actually really important. And are the most familiar sort of a very important biological molecule, the lipid. Lipids are smaller and simpler than complex carbohydrates and they're grouped together because they share an inability to dissolve in water. This is because their chemical bonds are mostly non-polar. As since water, as we learnt in the previous episode despises non-polar molecules, the two do not mix. It's like oil and water. In fact, it's exactly like oil and water. And if you've ever read a nutrition label or seen this thing called a television, you're probably pretty conversant in the way that we classify fats. But then you know, 99% of us have no idea what those classifications actually mean. Fats are made up mainly of two chemical ingredients, glycerol, which is a kind of a alcohol and fatty acids, which are long, carbon hydrogen chains that end in a carboxyl group. When you get three fatty acid molecules together and connect them to a glycerol, that's a triglyceride. These feature prominently in things like butter, and peanut butter and oils and white parts of meat. These triglycerides can either be saturated or unsaturated and I know that when we put the word fat and saturated into the same sentence it sounds like an evening at KFC. But here we're talking about being saturated with hydrogen. As you hopefully remember from our first lesson, carbon is very nimble in how it uses it's four electrons, it can form single, or double or even sometimes triple bonds. This means that if a carbon atom and a fatty acid are connected by single bonds all of the carbon atoms end up connected to at least two hydrogen atoms, and one of them picks the third. So the fatty acid is saturated with hydrogen. But when some of the carbon atoms are connected to each other with double bonds, all those carbon's electrons are spoken for and so they're not able to pick up those hydrogen atoms. This means that they're not saturated with hydrogen and they are unsaturated fatty acids. To demonstrate, may I direct your attention to this jar of peanut butter. Here you can kind of see both kinds of fat the liquid stuff you see at the top here, that is the unsaturated fat, which we generally think of as oils. The pasty stuff done here also contains lots of unsaturated fat but also contains saturated fat. Which doesn't have any double bonds so it can pack more tightly and form solids at room temperature. And there are also other fat classifications you've heard of. Trans fats, which everyone tells you never to eat. They're right, don't eat them. They don't exist in nature and are basically unsaturated fatty acids that instead of kinking, go straight across and so they're extra, super bad for you. Don't eat them. Omega three fats are fatty acids that are unsaturated at the three position, which is like right there, then that's the only difference. But the reason why these are important is because we can't synthesis them ourselves, they're essential fatty acids, meaning that we need to eat them in order to get them. All this is starting to make me pretty hungry. But before we get to more food stuff there are some unappetizing sort of lipids that we also need to talk about. So remember that triglycerides are three fatty acids connected to a glycerol. Swap one of those fatty acids out for a phosphate group and you have a phospholipid. And these make up cell membrane walls. Since that phosphate group gives that end a polarity it's attracted to water. And the other end is non-polar and it avoids water. So if you were to scatter a bunch of phospholipids into some water, they would automatically arrange themselves like this, with the hydrophobic ends facing each other and the hydrophilic ends sticking out to face the water. Every cell in your body uses this natural structure to form its cell wall in order to keep the bad stuff out and the good stuff in. Another class of lipids is the steroids. Steroids have a backbone of four interconnected carbon rings which can be used to form hundreds of variations. The most fundamental of them is cholesterol, which binds with phospholipids to help form cell walls. But these can also be activated to turn into different lipid hormones. And so now we approach the most complicated, powerful, polymorphously awesome chemicals in our body, the protein. And by complicated, I mean that they are probably the most complicated chemical compound on the planet. In fact, they're so amazing that we're gonna do a separate episode on them and how they are created by DNA. But right now, in you there are tens of thousands of proteins doing everything they can to keep you alive. There are enzymes regulating chemical processes, helping you digest food. There are antibodies connecting themselves to invaders like bacterium and viruses so that your immune system can get 'em! There are protein endorphins that like mess around with your brain and make you like feel emotions. So they're everywhere, they do everything! And proteins do all of this stuff using just 20 different ingredients and these are the amino acids. Just like fatty acids, amino acids have a carboxyl group at one end and on the other end they have an amino group, Amino acid. Now hey I don't know if you noticed this but this is the first time that nitrogen has shown up in our food. This is super important because despite the fact that nitrogen is like everywhere, it's like 80% of the air, we can't just pull it out of the air and put it into our bodies. We have to get nitrogen from food and so we have to eat foods that are high in protein, like this egg which, by its very virtue, because it is, all the white part is protein, it contains a goodly amount of nitrogen. Now on the middle of the amino and the acid group is a carbon and it shares one of its electrons with a group of hydrogen and the other electron is free to be shared with R. Which is just to kind of fill in the blank. We call it the R group. It can also be called a side chain and there are 20 different kinds of side chains. Whatever fits in the blank will determine the shape and the function of that amino acid. So if we put this in there we get Valine, which is an amino acid that does a lot of stuff like protecting and building muscle tissue. And if we put this in there you get Tryptophan which may be best known for it's role in helping you regulate mood and energy level. Amino acids form long chains called polypeptides. Proteins are formed when these polypeptides not only connect, but elaborate into frankly really elegant structures. They fold, they coil, they twist. If they were sculptures I would go to the museum every day just to look at them. And I'd walk straight passed the nudes without even looking. But protein synthesis is only possible if you have all of the amino acids necessary and there are nine of them that we can't make ourselves. Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. By eating foods that are high in protein, we can digest them down into their base particles and then use these essential amino acids and building up our own proteins. Some foods, especially ones that contain animal protein have all of the essential amino acids, including this egg. And that concludes this triple decker sandwich of biological awesomeness, which is all we need to be happy, healthy people. And I'm sure because of that it's going to be delicious. Nope!
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