hello, and welcome to the kitchen. i wantedto invite you here today because last week we started off in my bathroom and kinda feelbad about that. and also because as i'm making lunch today i wanted to sortof use it as a lab. during this time in my kitchen i'm going to talk to you about threedifferent things: 1) the three most important molecules on theearth
crash diets of models, 2) possibly the grossest sandwich i'm evergoing to eat 3) an obscure scientist who taught us almosteverything we know about urine. so far we've talked about carbon and we'vetalked about water, and now we're going to talk about the molecules that make up everyliving thing
and every living thing in every living thing.i don't care if you're a bacterium or a blue whale or if you're lady gaga, of ifyou're a mite living on the queen of england's eyelashes. they're called biological molecules. thesearen't just building blocks, these are the molecules necessary for every living thingon earth to survive. they are essential sources of energy. they are the means of storing thatenergy. they are also the instructions that all organisms use to be born and grow andto ultimately pass those same instructions on to their future generations. they are the ingredients for life. and we call them: the carbohydrates, the lipids,the proteins, and the nucleic acids.
today we're going to be talking about thefirst three. it's no coincidence that we classify them in the same way that we classifyfood, because they're food. [hank so smart!] and for this classification, we have to thanka little-known english physician who hundreds of years ago dedicated his life to the studyof human pee. oh, my goodness... i'm back in the- that must mean that it's time for the mostawkwardly named segment here on crash course: biolo-graphy. his name was william prout. in the early 1800s,he became fascinated with human digestion especially our urine. that's becausehe thought the best way to understand the
human body was through chemistry, and thebest way to understand body's chemistry was to understand what it does with food. by dayhe was a practicing physician, but every morning before breakfast he did research in his homelaboratory in london. and there he did many great things. like, being the first to discoverthat our stomachs contained hydrochloric acid. and writing a breakthrough book about kidneystones called an inquiry into the nature and treatment ofgravel, calculus, and other diseases connected with a deranged operation of the urinary organs. and he was, of course, the first person todiscover the chemical composition of pure urea, the main component of urine.
for the record, here it is: co(nh2)2. andin the presence of water, urea gives off ammonia, which is why your pee smells. through his years of studying urine, proutcame to the conclusion that all "foodstuffs" fell into three categories: the saccharinous(carbohydrates), oleaginous (fats), and albuminous (proteins). indeed, he went so far as to saythat in order to be healthy, you needed to eat all three of these things and not justsheep kidneys and gin, which is what most of london was living on at the time. but like many great minds, prout was overlookedin his own lifetime, because while he was studying actual science, everyone else waswalking 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 can tell that much by color i wonderwhat you could tell by taste. now he isn't understand that there were biologicalmolecules he didn't understand what these things were,but he did understand that there were three ingredients necessary for life. and it turnsout that all organisms either need to synthesize or ingest those ingredients in order to live. we're going to start out with the most basicof these ingredients for life: carbohydrates. you've no doubt heard of them. you may,in fact, be avoiding them like the plague.
but fact is that nothing, and no one, canavoid carbohydrates, because they are the source of all energy that we have availableto us. carbohydrates are made up of sugars, and thesimplest of them are monosaccharides. mono for one, and saccharides for the actual rootof the word sugar. 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. all biological energy is originally capturedfrom the sun by plants as glucose through photosynthesis. and every cell that needsenergy 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 (c6h12o6), but arranged differently.these subtle chemical difference do matter. fructose, for example, is significantly sweeterthan glucose. it's also processed by our bodies in different ways. and then there are disaccharides which -- likethe name says -- are just two monosaccharides put together. the most famous of these issucrose, which is simply a glucose molecule and a fructose molecule joined by a covalentbond. mono- and disaccharides are pretty much littleniblets of energy that are really easy for our body to process, but when these carbohydratesstart 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 structuralcompounds. these are the polysaccharides. instead ofbeing just two or three monosaccharides put together, polysaccharides can contain thousandsof simple sugar units. and because they're so big and burly, they'regreat for building with. in plants, cellulose is the most common structural compound. it'sjust a bunch of glucose molecules bound together and it is the most common organic compoundon 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 storingenergy and not just structurally but just as an energy store. and that's where we getbread. now, really interesting thing here: bread is made up of starch, the most simpleof which is called amylose. amylose and cellulose looks almost exactly identical, but one isgrass and the other is bread. like, chemistry! [well said.] plants store glucose in the form of starch,and it comes in lots and lots of different forms, from roots and tubers to the sweetflesh of fruits, to the starchy seeds of the wheat plant that end up being milled intoflour. ground-up grain is the main ingredient inthe bread, of course, most of the calories,
or energy content, comes from carbohydrates.when i eat this -- and i am going to eat the hell out of it -- i'm going to be eatingall of the chemical energy that this wheat plant got from the sun in order to feed it'snext generation of seeds that we then stole for our own use. now we, as human beings, can't grow fruitsor tubers, so we have to store our energy in a couple of different ways. the way thatwe tend to store carbohydrate energy is in glycogen, which is very similar to amyloseor starch, but has more branches and is more complicated. it's basically made up of theglucose we have left over after we eat and it sits in our muscles where it's ready tobe used and it's also stored in our livers.
it's generally a pretty short term store.if we don't eat for a day pretty much all of our glycogen gets depleted. but over the longer term, the way we storeenergy is through fat! all of our mom's worst enemies: the fat.which turn out to be really important and are the most familiar sort of a very importantbiological molecule: lipids. lipids are smaller and simpler than complexcarbohydrates, and they're grouped together because they share an inability to dissolvein water. this is because their chemical bonds are mostly nonpolar, and since water, as welearned in the previous episode despises non polar molecules, the two do not mix. it'slike oil and water.
in fact, it's exactly like oil and water! and if you've ever read a nutrition labelor seen this thing called the television, you're probably pretty conversant in theway we classify fats. but then 99% of us have no idea what those classifications actuallymean. fats are made up mainly of two chemical ingredients:glycerol, which is a kind of alcohol, and fatty acids, which are long carbon-hydrogenchains that end in a carboxyl group. when you get three fatty acid molecules togetherand connect them to a glycerol, that's a triglyceride -- they feature prominently inthings like butter, peanut butter, oils, and the white parts of meat.
these triglycerides can either be saturatedor unsaturated. and i know that when we put the word "fat" and "saturated" รข intothe same sentence it sounds like an evening at kfc, but here we're talking about beingsaturated with hydrogen. as you hopefully remember from our first lesson:carbon is very nimble in how it uses its four electrons. it can form single, double or triplebonds. this means that if the carbon atoms in a fattyacid are connected to each other with single bonds, all of the carbon atoms end up connectedto at least 2 hydrogen atoms. and of them even picks up a third. so the fatty acid issaturated with hydrogen. but when some of the carbons atoms are connectedto each other with double bonds all of those
carbons' electrons are spoken for, so they'renot able to pick up those hydrogen atoms. this means that they're not saturated withhydrogen and they are unsaturated fatty acids. to demonstrate, may i direct your attentionto this jar of peanut butter? here you can kind of see both kinds of fats.the liquid stuff you see at the top here: that is the unsaturated fat, which we generallythink of as oils. the pasty stuff down here also contains lots of unsaturated fat butalso contains saturated fat, which doesn't have any double bonds and so it can pack moretightly and form solids at room temperature. and there are also other fat classificationsthat you've heard of. trans fats, which everyone tells you neverto eat. they're right, don't eat them! they
don't exist in nature and are basically unsaturatedfatty acids that instead of kinking go straight across and so they're super bad for you. don'teat them. omega-3 fatty acids are unsaturated at the3 position, which is like, right there [where?]. and that's the only difference, but the reasonthat these are important is because we can't synthesize them ourselves. they're essentialfatty 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 thatwe also need to talk about. so remember that triglycerides are three fattyacid chains connected to a glycerol? swap
one of those fatty acids for a phosphate groupand you have a phospholipid. these make up cell membrane walls. since that phosphategroup gives that end polarity, it's attracted to water. and the other end is nonpolar andit avoids water. so if you were to scatter a bunch of phospholipids into some water,they would automatically arrange themselves like this with hydrophobic ends facing eachother, and hydrophilic ends sticking out to face the water. every cell in your body usesthis natural structure to form its cell membrane in order to keep the bad stuff out and thegood stuff in. another class of lipids is the steroids. steroidshave a backbone of four interconnected carbon rings, which can be used to form hundredsof variations. the most fundamental of them
is cholesterol, which binds with phospholipidsto help form cell walls. but they can also be activated to turn into different lipidhormones. 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 probablythe most complicated chemical compounds on the planet. in fact, they are so amazing thatwe're going to so a separate episode on them, and how they're created by dna. but rightnow, in you, there are tens of thousands of proteins doing everything they can to keepyou alive. there are enzymes regulating chemical processes,helping you digest food. there are antibodies
connecting themselves to invaders like bacteriumand viruses so that your immune system can get them. there are protein endorphins thatmess around with your brain and make you feel emotions [gross!] but they're everywhere, they do everything! and proteins do all of this stuff using only20 different ingredients. and these are the amino acids. just like fatty acids, amino acids have acarboxyl group on one end. on the other end they have an amino group. amino acid! now hey, i don't know if you've noticedthis, but this is the first time nitrogen
has shown up in our food. this is super important,because despite the fact that nitrogen is everywhere -- it's like 80% of the air -- wecan't just pull it out of the air and put it into our bodies. we have to get nitrogenfrom food. and so we have to eat foods that are high in protein like this egg, which byit's very virtue, because all the white part is protein, it contains a goodly amount ofnitrogen. now in the middle of the amino and the acidgroup is a carbon. it shares one of its electrons with good ol' hydrogen, and the other electronis 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 thereare 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 in there, you get valine,an amino acid that does a lot of stuff, like protecting and building muscle tissue. ifyou put this in there, you get tryptophan, which may be best known for its role in helpingyou regulate mood and energy levels. amino acids form long chains called polypeptides.proteins are formed when these polypeptides not only connect but elaborate and franklyreally elegant structures. they fold. they coil. they twist. if they were sculptures,i would go the museum every day just to look at them. and i'd walk straight past the nudes withouteven looking. but protein synthesis is only possible ifyou have all of the amino acids necessary,
and there are nine of them, that we can'tmake 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 inbuilding up our own protein. some foods, especially ones that contain animalprotein, have all of the essential amino acids including this egg and that concludes this triple-decker sandwichof biological awesomeness, which is all we
need to be happy, healthy people. and i'm sure, because of that, it's goingto be delicious. nope. thank you for watching this episode of crashcourse. i will be discussing something else very interesting next week. i don't even knowwhat it is. don't forget. go back and reinforce what you'velearned today by going back and watching bits that you feel like you may not have got completely. we'll also, of course, be available on facebookand twitter if you would like to ask us questions or give us suggestions there.
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