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Biological molecules - You are what you eat

Video transcript
Hank: 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. (energetic 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. (bell rings) 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 ultimately, pass those same instructions onto to their future generation. They are the ingredients for life and we call them (bell rings) the Carbohydrates, (bell rings) the Lipids, (bell rings) the proteins (bell rings) 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. (lively piano music) Ooohh, my goodness, I'm back and that must mean that it's time for the most awkwardly named segment here on Crash Course, the Biolo-graphy. 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 food stuffs 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, you know, 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 studying 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 organism either need to synthesize or ingest those ingredients in order to live. We're gonna start out with the most basic of these ingredients for life (bell rings) and that is the Carbohydrate. You've now, have 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. (bell rings) Carbohydrates are made up of sugars (bell rings) and the simplest of them are called Monosaccharides. Mono for one, saccharides for the actual root of the word sugar. (bell rings) The star of the show here is Glucose because it's truly fundamental, by which I mean, like number one on the global food chain because it comes from the sun. (bell rings) 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, (bell rings) like Fructose, which has the same molecular formula C6H12O6 but arranged differently. (bell rings) This subtle chemical differences do matter. Fructose for example, is significantly sweeter than Glucose. It's also processed by our bodies in different ways and then there are (bell rings) Diasaccharides, which like the names says, are just two Monosaccharides put together. (bell rings) And the most famous of this is Sucrose, which is simply, a Glucose molecule and a Fructose molecule joined by a covalent bond. Mono and Diasaccharides are pretty much little nibblets of energy that are really easy for our bodies to process but when these carbohydrates start to form into longer and longer chains, their function and their roles change as well. Instead of being sources for instant energy they become storehouses of energy or structural compounds. (bell rings) 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 burly, they're great for building with. (bell rings) And plant Cellulose is the most common structural compound. It's just a 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 look almost exactly identical but one is grass and the other is bread like chemistry. (bell rings) Plants store Glucose in the form of starch and it comes in lots and lots of different forms from roots and tubers, 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 of 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 its next generation of seeds that we then store for our own use. All for me. Now, we as human beings can't grow fruits or tubers so we have to store our energy in a couple of different ways. (bell rings) 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 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 liver. 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. However, the longer term way that we store our energy is through fat. All of our mums' worst enemy is the fat, which turn out to be actually really important and are the most familiar sort of a very important biological molecule, the lipid. (bell rings) 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 (bell rings) and since water, as we learned in 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 the television, you're probably pretty conversant in the way that we classify fats but then you know, 99% of us have no idea of what those classifications actually mean. Fats are made up mainly of two chemical ingredients, Glycerol, which is a kind of 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 the Glycerol, (bell rings) that's a Tryglyceride. These feature prominently, in things like butter and peanut butter and oils and the white parts of meat. These Tryglycerides 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. (bell rings) As you hopefully remember from our first lesson, carbon is very nimble in how it uses its four electrons. It can form single or double or even sometimes triple bonds. This means that if the carbon, atoms and the fatty acid are connected to each other with single bonds, all of the carbon atoms, end up connected to at least two hydrogen atoms and one of them picks up a third. (bell rings) 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 carbons, 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 (bell rings) 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 down here also contains lots of unsaturated fat but also contains saturated fat, which doesn't have any double bonds so it could pack more tightly and form solids at room temperature. There are also other fat classifications that 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, goes straight across and so, they're extra super bad for you. Don't eat them. Omega 3 fats or 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 synthesize 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 the Tryglycerides are three fatty acids connected to Glycerol. Swap one of those fatty acids out for a Phosphate Group (bell rings) and you have a Phospholipid. These make up cell membrane walls. Since that Phosphate Group gives that end a polarity, it's attracted to water. The other end is non-polar and it avoids water. So, if you were to scatter a bunch of Phospholipids in bits of 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. (bell rings) Another kinds of Lipids is the Steroids. Steroids have a backbone of four interconnected carbon rings, which can be used to form hundreds of variation. (bell rings) The most fundamental of them is Cholesterol, which binds with Phospholipids to help form cell walls. (bell rings) But this 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, (bell rings) the protein. And by complicated, I mean that they are probably, the most complicated chemical compounds on the planet. (bell rings) 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. (bell rings) They are enzymes regulating chemical processes, helping you digest food. (bell rings) They're antibodies connecting themselves to invaders. like bacterium and viruses so that your immune system can get them. (bell rings) They're protein endorphins that like mess around with your brain and make you feel emotions. They're everywhere. They do everything. Proteins do all of the stuff, using just 20 different ingredients and these are the amino acids. (bell rings) 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, ah, 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, 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 all the white part is protein, it contains a goodly amount of nitrogen. Now, in the middle of the amino and the acid group is a carbon. And it shares one of its electrons with the good ole hydrogen and the other electron is free to be shared with R, which is just a 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 that blank will determine the shape and the function of that amino acid. So, if you put this and there, you get Valine. It's an amino acid that does a lot of stuff like protecting and building muscle tissue and if you put this in there, you get Tryptophan, which may be best known for its role in helping you regulate mood and energy levels. (bell rings) Amino acids form long chains called Polypeptides. Proteins are formed when these Polypeptides not only connect, but elaborate in 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 pass the nudes without even looking. (bell rings) The 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 in 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.