Biology 1010 Lecture 5 Organic Molecules


– [Instructor] This is thelast part of chapter two in your book. So we’re still on chapter two, but this is actually the fifth lecture and therefore the fifthquiz on organic molecules. So we still haven’t really gotten that far as far as the organization of life. We’ve talked about ADAMs, why they interact with one another. We’ve talked about molecules,particularly water. Now let’s talk about the mostimportant molecules for life, and those are what the buildingblocks or organic molecules as we call them.And most of us know the food version of these organic molecules thatwe consume on a daily basis. But there’s so much more to it than that. It’s not just about food. It’s about structure, it’s about function. So there’s a lot of thingsyou’re gonna learn new today, besides just the fundamentalsof what a carbohydrate is and what a lipid is,and what a protein is, and when nucleic acids are.Now before we get into that, there’s one more property ofwater we haven’t talked about. And I didn’t include itin that other lecture, in lecture four, because itfits better with this one. And that is that in organic chemistry, which is essentially metabolism. Organic chemistry andmetabolism are the same thing. It’s just all the chemistryin cells in a living organism. And we’ve already talked about metabolism, the way that which cells and living organisms process energy, how they make energy, how they use energy, that’s all organic chemistry is. The reason why we call itorganic chemistry is because all of these molecules have attheir foundation carbon. When we say something is carbon based, that’s what we mean by organic. Now the word organic todayis used in different ways from the way in which we grow our food, and the like.There’s many definitions of organic. But the way in which we use it in biology, it literally means carbon-based molecules. Because you’ll see at the foundation of eachof these groups, carbon, that ADAM is that at center to build these biological molecules that are the building blocks for life. So where does water come into play? Because water is not an organic molecule, but it plays a key role in this. Water is involved in all metabolism. That’s another property of water that you’re gonna betested on in this lecture, your quiz five, lecture five. All of the metabolic processes of breaking down carbohydrates, assembling molecules into proteins and DNA and all these things, water is at its core.Without water, you don’tundergo these reactions. So that’ll be the firstthing that we discussed today before we get into each of these four basic biological groups. Here are the four groups which we can categorizeall organic molecules into and most are familiar. Everybody has heard of carbohydrates. What do you think of whenyou think of carbohydrates? – [Students] Breads, grains. – [Instructor] Breads, grains, sugars, things of that sort. But we’ll show today thatthose are actually the minimum. The majority of organicmolecules that exist on our planet are not for food. They’re actually for structure. Plants and a great number of animals and otherorganisms use carbohydrates as their skeletal structures and their supportstructures for their cells, which really can’t be usedas a source of energy. So when we think ofcarbohydrates, we think food. When other organismsdeal with carbohydrates, yeah, there’s food, but they also use it fortheir overall structure. We don’t. We don’t necessarily use carbohydrates for structural components. We use other aspects ofbiological molecules. Lipids. When we talk about lipids, again, we know about triglycerides.You’re gonna learn thedifference between saturated and unsaturated fatstoday on a chemical level, and you’re gonna learn aboutthings like phospholipids, which aren’t used for energy, but are critical for life because all living thingsbeing made of cells, will find that the major component of all cells membranes are this organic moleculecalled phospholipids. Proteins. This is probably one ofthe most diverse groups. As such, we’re only goingto study the fundamentals of what proteins are and how they’re made.But in the human body alone, there are about 400,000,just the human body alone, 400,000 different proteins. And that’s not including other organisms. A lot of them have some ofthe same proteins that you and I have, but there’sdiversity within all life. And then of course the nucleic acids. We usually don’t think of food when we think of nucleic acids. We don’t have diets high nucleic acids. So what are nucleic acids? Well, it’s pretty muchyour genetic information. It’s your DNA and what we call our RNA. But it also plays anotherrole in energy transfer. There’s a molecule inthe nucleic acids group that is essential formetabolic energy transfer that we’re gonna talk about. So those are the four groups. So let’s first start with water’s role.These are two concepts that you’re gonna havetwo separate questions on, dehydration synthesis and hydrolysis. So let’s talk about whatthey are and what’s going on and there’s some more terminology you’re gonna have to learn. Dehydrate. What does to dehydrate something mean? Or when you’re dehydrated. You’re lacking water and this is not hydrating me by the way. In fact they put so much saltand other things in the soda that you’re actually dehydrating yourself when you drink soda. I still drink it, but you’renot hydrating yourself when you drink soda withall of that sodium in it and everything else. Your body has to excrete morewater than it actually can get out of the soda. Anyway, so when you’re dehydrated, you’re essentially are losing water. Well, in that fashion, this process calleddehydration synthesis is the organic chemistry of how all moleculesare assembled together.So let’s look at some terminologyyou’re gonna have to know. Each of the four basicbiological groups has the building blocks, which we call monomers. Mono, what do you think mono stands for? And I’m not talking about the disease. – [Students] One. – [Instructor] One. Okay. So monomers are single units. Now for each group they can vary. For carbohydrates thereare things like glucose, for lipids there are thingslike glycerol and fatty acids, for proteins there arewhat’s called amino acids. You’ve probably heardof amino acids before. And then the nucleic acids group, they’re called nucleotides. So the monomers vary in theiroverall chemical structure, but no matter what theiroverall chemical structure are, they are the building blocksfor each of those groups. So when we build structuralorganic molecules, like our proteins, like our carbohydrates, when we store it for longtermenergy, triglycerides, which are the saturatedand unsaturated fats, these are larger building blocks. And even your DNA. In fact your DNA, the smallest DNA is about33 million monomers long. That’s the smalleststrand of DNA you have. So what happens? Well, when you have theseindividual building blocks that you typically get from your food.As you’re eating your food, you’re breaking down theproteins and the fats and the carbohydratesfrom other organisms, and you get this stockpile of monomers. Well then we restructurethem into the proteins and the carbohydrates thatwe need for ourselves. So when monomers are assembled together, then they form long strings of monomers, which we no longer call monomers anymore, we call them polymers. So poly means many. So dehydration synthesis,why is it called dehydration? Because as you can seehere in any reaction, whether it’s proteins,nucleic acids, carbohydrates, or lipids, all of thesereactions will remove a hydroxyl group and a hydrogen atom from the two monomers and remove water, and in that process will covalently bond the two monomers together.Remember I told you that adash means a covalent bond. So this process is essentially building, taking smaller units andbuilding them into larger units. So if we were to definedehydration synthesis, we would say that it assemblesmonomers into polymers. And let me say that again. So dehydration synthesisassembles monomers, covalently bonds them together, assembles monomers into polymers, longer chains that in some casesare hundreds of units long, and others are millions of units long. – [Student] The bottom one is a polymer. – [Instructor] This isa polymer right here.Yep. When you get these longstreams of monomers, we call it a polymer. The top part are the individual monomersbeing assembled together. It is just done over andover and over and over again. This is also an energy storage process. Where you build these together, you actually store energy. And we do this during periods of time when we’re not eating, our body will take some ofthe excess food and energy and assemble it together and then store it for later periods of time when we need that energy. Now, the opposite called hydrolysis. Hydro again stands for water. Lysis means to break apart. So hydrolysis is just the reverse. It takes polymers,breaks the covalent bond between the individualunits by using water and essentially reverses this process. It breaks a covalentbond and it breaks them into their individual monomers.So an example of thisis every time we eat. When we eat starch. Starch is a long polymer of individual glucose molecules. And when we eat that, our body will start breakingthe individual covalent bonds, using water and other thingswe’ll talk about later in subsequent chapters and break them down into their individualmonomers like glucose. That’s one of the reasonswhy you get such a sugar high when you have what wecall high fructose syrup, because the fruitose is a pure monomer. There’s no need to break it down. Your body just gets instant energy. And that’s why you get thecrash afterwards as well.So that’s why starches andother large molecules tend to last longer because yourbody slowly breaks them down and releases energy as you need it. You don’t get this huge spike in energy where you start going a little crazy. All right. So hydrolysis is polymers arebroken down into monomers. This is what happenswhen we extract energy from these molecules. This is why we eat, to extract the energy from these molecules bybreaking the covalent bond and by doing so, we get energy out of them.So let’s start with the one we’re allpretty much familiar with, and that is carbohydrates. Carbohydrates, one of the main purposes of this group is energy. So don’t get me wrong, even though I say that it’s not the mostabundant carbohydrates, it’s all about energy. Plants, animals, fungi, bacteria, they love carbohydrates. It’s the easiest organicmolecule to break down and get energy from. That’s why we go for the carbs first. It’s because our cells and the way that organic chemistry works, it’s really easy to get energy from them. Easier than getting energy from fats. When you exercise, if you do that thing, you burn your carbohydrates first and then your body startsdigging into the fat reserves, which is why you have to typically work out for longer periods oftime than just quick bursts, because your body will say, well, I got the store of carbohydrates, I’m gonna go for that first. Okay. Now, the name actually tellsyou what they’re made of. Carbo has to do with carbon, hydrates like water, what’s water made of? – [Student] Hydrogen and oxygen.- [Instructor] Hydrogen and oxygen. So guess what? Carbohydrates are made of carbon, hydrogen and oxygen. That’s their fundamental structure. So as they get assembled together, let’s look at theirfundamental building blocks, which we call, instead of saying monomers now, we have specific names for each group. These monomers for thecarbohydrates, these simple sugars, we call them monosaccharides. So when we say monosaccharides, I don’t have to tell youwhich group I’m talking about. You know that they are monomersof the carbohydrate group. So monosaccharides. What are some examples of these? They can vary in theirstructure and shape, but they pretty muchhave the same purpose. They’re pretty much used for energy. There’s no other realpurpose for monosaccharides. They’re just energy. When they start gettingbuilt into larger structures, then they take on different functions. But in their monosaccharideform, it’s energy. The three on the right. These are the buildingblocks for the carbohydrates. Glucose is by far one ofthe more prominent ones that’s used in biology.But there’s others. Like fructose. That’s what’s in most of yourcandy and other sugar drinks and whatnot, high fructose corn syrup. That’s it. It’s just pure fructose monosaccharides that are being pumped into your body. And then there’s a littleless known called galactose. So glucose, fructose, and galactose. These are three types of monosaccharides. You will not need to knowtheir structure and their shape and other things like that. You just need to knowthose three names, okay? And that they are monosaccharides.Glucose, fructose and galactose. Okay? Now, those are the building blocks. So let’s start building. When you start undergoing what we call dehydration synthesis, which we just talked about, in the carbohydrate groups, you take a hydroxyl from onesugar, a hydrogen from another, and you covalently bond them together. So they ended up havingthis oxygen between them, but the covalent bond bonds them together. Well now that there’s two sugars, we call it a disaccharide.Di means two. Now this is the type ofsugar that you typically deal with when you bake. We usually don’t usehigh fructose corn syrup when we bake. What do we use? We use sucrose. That’s table sugar. That’s what you buy at thestore in those big bags, which we call sugar. It’s actually sucrose or a disaccharide. Now again this is also used for energy. We put it in to make things sweet. Our body can and does breakit down through hydrolysis into glucose and fructose. So it’s a very simple sugar as well, but it’s not a monosaccharide. We call it a disaccharide. There’s two other types of disaccharides that you’re probably familiar with that I’m not evengonna ask you for sucrose what the two monosaccharides are. But let’s talk about some examples of some other disaccharides. Lactose. What’s that found in? Milk. Okay. So lactose sugar isalso a disaccharide made from two monosaccharides. And then there’s one more. Maltose. Anybody venture a guesswhere you might have that or what it’s used for typically? Like a malt liquor? It’s usually the sugar usedin a fermentation process.They use the malt in the maltingprocess for fermentation. So there’s different typesof disaccharides in sugars. Let’s talk real quickly about lactose. I’m lactose intolerant, severely. And most people are. In fact, if you’re not lactose intolerant, if you can break down thelactose sugars and milk, then you are a mutant. Not a very powerful mutant, but you are a mutant. I don’t think you wouldjoin the X-Men anytime soon but the reason why you’re a mutant is because the normal process in humans is we stopproducing a protein called an enzyme later on whenwe reached adulthood, where we no longer need thoselactose sugars from the milk. Now there’s other thingsthat you could get from milk but most of the time we replace milk with beer or something else. So we don’t need milk. We need it when we’re young and our body produces that enzyme. But as we get older,we stop producing that. But evolution, we’ll talk about, especially here in the UShas selected for individuals that do, because of our diet, have the ability to retainthe function of that enzyme and therefore break it down.Now, if you really want tohave your ice cream and milk without the side effects, youcan go down and buy enzymes, they’re called Lactaid from a Walmart or any other Walgreens or whatnot, and they temporarily give you that ability to break down the lactosesugars through hydrolysis. But we’ll learn in lecture seven, when we talk about enzymes, how if your body doesn’t make an enzyme, you don’t undergo that process,specifically hydrolysis or dehydration synthesis.When you lack those enzymes, there’s anything from a mild irritation in breaking down milk sugars to death if it’s an enzyme that’s actuallycritical for the function of certain organic processes. And this is where inheritedgenetic diseases typically come about is when we’remissing that protein due to the genetics wereceive from our parents. It can actually be very life threatening. Now lactose intoleranceis not life threatening, but others can be. Okay. So sucrose, lactose and maltose. You just need know them as disaccharides. You don’t need to knowwhich ones make them up, that glucose and fructose make sucrose. I can’t even remember whichones make lactose and maltose. I know galactose is in here somewhere. So just know those as disaccharides. They’re also only used for energy. There’s no other purpose for these disaccharides but energy. All right. Now let’s talk about themore complex structures of carbohydrates, whatwe call polysaccharides.Again these are the polymers. So anything typicallyover about 100 monomers, we call a polysaccharide. I make that distinction right now because at the very end of this portion I’ll show youone more type of saccharide that doesn’t really fit intowhat we’re describing here. So polysaccharide. There are four thatyou’re gonna learn about, and that you’ll need toknow for testing purposes. Well, three out of the four are up there. So we have cellulose, chitin, that’s the onethat’s not up there, starch, everybody’s heard of, and glycogen, which noteveryone necessarily knows what it is. All right. Let’s start with the onesthat we’re familiar with, or somewhat familiar with. Starch and glycogen.These are almost identical. As you can see, each one of these greenhexagons is a monosaccharide. So these are long, long streams of thesemonosaccharides attached through dehydration synthesis. The four of these polysaccharides, okay? Starch is how plantsstore their carbohydrates. So that’s why plant materialtypically is high in starch. Corn, rice, wheat, and all these thingshave these the starch. Potatoes and the likehave starches in them that we use for eating and whatnot. But we don’t store it, animals don’t store theirpolysaccharides as starch. When we eat the starch, we break it up into individuallittle monosaccharides and we get energy out of it. And whatever’s left over, we restructure it throughdehydration synthesis into a slightly different molecule. It’s a little more highly branched as you can see called glycogen.We put that in our liver. Now why do we do that? Because in order to maintainhomeostasis in our blood, we need to have reserves of sugars. But we don’t reserve themas the individual monomers. We reserve them as these longerenergy storage molecules, which we call polysaccharides. For animals, we store as glycogen. But the same thing happens. When our blood sugar starts getting low, in order to maintain homeostasis, we start breaking off themonomers through hydrolysis, by taking water andbreaking the covalent bond.And then we reestablishthat blood sugar level. Okay? Our body is constantlyspending time to make sure that we have enough and adequate sugar in our blood so that it gets to our brain and our cells andgets to the rest of our body. So those are two examples of long term energystorage for carbohydrates. Okay? Now let’s talk about the other two. Notice the structuraldifference of cellulose. So where is cellulose found? Well, plants not onlystructure their monosaccharides into energy storage, but they also use it forstructural support of their cells. What am I talking about? Wood, fiber, that’s cellulose. So cellulose is a protectivecarbohydrate, very thick, very tough layer. I mean, wood is very tough because of all of thesefibers of cellulose. Now this is not an energy molecule, not even for plants.Why? Well it gets into the fact that these are linearrather than branched. Again in lecture seven, when we talked about enzymes, we’ll show that due to thefact that this is branched, we can break it down throughdehydration synthesis. But due to the fact thatcellulose is linear, we can’t. Yeah, the energy’s there, that’s kind of the Holy grail of trying to take plant materialand actually extract it and make ethanol and things of that sort, which is adifficult process to do. But the energy is there and some organisms can get energy from it. For example termites. In fact, it’s not even the termites that get the energy from it.There’s a little microbe inside their gut that can convert the celluloseinto monosaccharides, and then the termitegets energy from that. So cellulose. Let’s look at the plant fibers. They’re held togetherdue to their polarity by hydrogen bonding. Here’s another example of how hydrogen bondingplays its role biologically, just like water has its attraction to itself due to hydrogen bonding, so do the fibers or strands of cellulose have that weak attraction. Now collectively becomes very strong. Individually the hydrogen bonds are weak but collectively they’re strong. So like celery. Celery that has a lot of fiber in it. Not a lot of calories, not a lot of energy you canactually get because most of the celery is water and cellulose.So fiber is good for your diet, but you don’t actuallyget any energy out of it. Now other things can highlycompact the cellulose and that’s where wood comes into play. And that’s where trees get theirvery rigid structure is due to these massive strands ofinterwoven cellulose fibers that form around their cells and give their cells a rigidity that you and I just don’t do. All right. Now, so cellulose is by far one of the most abundantpolysaccharides on earth, because it’s the primarycomponent of plants. It’s the primary structurethat surrounds the plant cells and gives them their rigidity. Now chitin. Everybody wants to saychitin when they see it. It’s chitin. Chitin is a carbohydratethat is primarily found as the exoskeleton of crustaceans and insects, crabs, lobsters,and the insect clade.This is their, when you step on something and you hear that crunch, that’s chitin. When you go to Red Lobster and you crack open theirshell, that’s chitin. You don’t get any energy from chitin. If you’ve ever tried chewing it, you don’t get any energy. You want the meat, the protein that’s inside of their legs or their body or whatnot. So that hard shell, that exoskeleton is pretty much what protects these animals from– It’s their skeleton, just like we have an internal skeleton, they have an external skeleton.But it’s not made of calcium, it’s made of chitin, which is a carbohydrate. So that’s just another example. Now chitin can vary in its overall form, which is why you’re notseeing its structure. But it’s still undigestible in terms of getting energy from it. So cellulose and chitin are what we call structural polysaccharides. They’re not used for energy. They’re used for structure for plants, for animals that have an exoskeleton. It’s used in fungi. Fungi do the same thing as plants, they surround theircells with carbohydrate, but they don’t do it as cellulose, they do it as chitin. That’s why fungi are soresilient in their environments and so difficult to get rid of is because they can withstandextreme environments. I mean, they live in extreme environments. They’re constantly degrading things and waste products. It’s not an easy place to get food. So they need to protectthemselves by covering their cells with this hard substance called chitin. All right.So those are the main groupsin the carbohydrate groups. Now there’s one more. This one doesn’t really fit the mold, but you still need to know about it because throughout the semester, you’re gonna be seeing this when we talk about blood type, when we talk about organelles of the cell, like the golgi apparatus and what not. So it’s gonna come up several times. So it’s important that we understand it.It’s not a polysaccharide because it’s not hundreds of units long. It’s not a mono or disaccharidebecause it’s more than two. So if it’s somewhere inbetween about three to 100, we call it an oligosaccharide. So what is an oligosaccharide? Because it’s not used for structure, it’s not used for energy. So what is it used for? Well, we know that if you need blood, let’s say you have blood loss or you’re donating bloodbecause or whatnot, that blood types need to match. A with A, B with B, AB with AB, and O, which isactually a universal donor. We’re not worried about theRH factor later on the plus or the minus but the O– So we know that there’scompatibility and incompatibility between our cells andit’s not just our blood, it’s our organs. You do a heart transplant, you need to have a good donor match. What is it that they’re trying to match? Well, on the surface of allof your cells, we have these what we call oligosaccharides, which are essentially just three to 100 carbohydrate monomers that are covalently bonded to each other.So what is the purpose? The purpose is cell recognition. How do we know whenour bodies get infected with the bacteria or fungus? It’s because bacteria and fungus have theirown oligosaccharides. And when our immune system sees those, it says, oh, that’s not me, and tries to destroy it. So as our immune system develops, we learn to ignore ourown oligosaccharides and destroy anything else. And that’s why when theytry to find a good match, a donor for an organ orfor blood or whatnot, they need to have almostidentical oligosaccharides on that tissue, otherwise it’s gonna be rejected by the body’s immune system. So these oligosaccharidesare attached to the surface of all your cells. For your blood, that’s how we determine blood type.If you have one type ofoligosaccharide on your blood, you might be blood type A. If you have a differentoligosaccharide on your blood, you’re blood type B. If you have none of theones we usually consider for blood type, that’s what O is. O is actually lacking these. And that’s why O can be given to anybody minus the other factors, the RH factor, the plus, or the minus, because there’s nothingto recognize as foreign. That’s why O blood typeis the most desirable is because it’s lacking theserecognition molecules that will be rejected if the body says, hey, this isn’t my blood, this is some foreign object. So that’s what oligosaccharides are. They’re in all your cells, they’re attached to thesurface of all your cells. Each person has kind ofa unique set of these. The more genetically related you are, the more likely you are to have these samestructural oligosaccharide, which is when they look for donors, they first look for genetic relatives because it’s more likelyto occur within people who are genetically similar to you.Lipids. This one is not as clearcut as the carbohydrates because there is a variety ofgroups within the lipid group. It’s not like carbohydrates where there’s three monomers that pretty much build everything. Lipids, there’s a lot of diversity. The unifying concept of all lipids is that they are either completely, or at least mostly hydrophobic. What does hydrophobic mean again? – [Student] Repel water. – [Instructor] They repel water. They don’t like water. And the main reason for that is because they don’t formpolar covalent bonds and are therefore neutral. And water doesn’t like neutral substances. It likes polar, it likes ionic.So water and oils andlipids don’t mix primarily because lipids don’thave any charge to them, and therefore willseparate out from water. That’s why they’re hydrophobic. All right. So we know about a lot ofthe lipids that we have in our diet, but let’s look at what makes thedifference between saturated and unsaturated fats. Those are what we usually thinkof when we think of lipids as far as a food source, but there are other structures as well that become important. So there are four main groups in this. Two of which I’m goingto primarily focus on. The triglycerides and the phospholipids. We’ll mention sterols and waxes. There may be question on sterols, but the majority of thequestions in this group are on these two because theseplay the most relevant role in all living organisms. So the triglyceridesand the phospholipids. Now, yes we do have monomersand polymers in this group, but they’re not like the other groups where you have millionsof monomers put together to form polymers or even hundreds of monomers put together to form polymers.So technically speaking, dehydration and synthesisand hydrolysis still apply to this group, but you’renot gonna see the large, large structures that are found in the other four groups or the three of the other four groups, the carbohydrates, the proteins, and the nucleic acids. Okay? So as I mentioned, there’s a lot of diversitywithin this group. Now when we think lipids as a food source, we usually think triglycerides. Triglycerides are the saturated and the unsaturated fats in our diet. So let’s look at thestructure of it and then look at what saturated andunsaturated actually mean.So remember I told you howglycerol is technically a sugar, but it’s only found in the structural componentof a triglyceride. That’s why we don’tconsider a monosaccharide in the carbohydrate group, because it belongs in the lipid group. That’s what triglycerides are made of. So the glycerol is three carbons with some hydrogen and oxygen. But really what makes it afat are these huge long tails of carbon and hydrogen, whichwe call fatty acid tails. Now there’s three ofthem hence triglyceride. You have the glycerol and threefatty acids attached to it, and that’s why we call it a triglyceride.All triglycerides have thesame fundamental structure. Some can be a little bit longer, some have little bitlonger chains than others. They don’t always havethe same exact length. But notice that they’re very simple. They’re just carbon and hydrogen chains. Remember carbon and hydrogensshare covalent bonds equally. And that’s why this moleculehas no polarity to it, has no charge to it. It is absolutely neutral, and that’s why water and oil do not mix. All right. Now, what is saturatedand unsaturated fats mean? Well, it has to do withthe covalent bonding of the fatty acids tails. If all of the carbons are single, covalently bonded to eachother and they’re saturated with the hydrogens, that’s what we call a saturated fat. It’s when the tails of the triglyceridehave the maximum number of hydrogens attachedto the carbons, okay? But occasionally you’ll get fats that have double covalent bonds in them. Well what that does is because these two carbonsare sharing four electrons instead of just two,that reduces the number of bonds it can form with other atoms.Hence you get these gaps wherethere’s no hydrogen bound to the carbons, and so they’re unsaturated. Now we have monounsaturated fats, we have polyunsaturated fats. That just tells you how many double covalent bonds there are. If there’s one, it’sa monounsaturated fat. If there’s many, it’s a polyunsaturated fat. So structurally, what’s thedifference between these two and where do we find them? Well, here’s this kindof a bubble filling model of a saturated fat.Notice all of the tailsare perfectly linear, they’re all saturated with hydrogens, and it’s very compact. These are what we wouldconsider beef fats, the more solid fats. Lard and the like that really aren’t asgood for you health wise, because though they pack a punch, they’ve got a lot of energy to them, they’re harder to digestthan the unsaturated fats. So saturated tend to circulate through our cardiovascularsystem more often, they have a higher chance of being deposited in our arteries and causing clogs and things of that sort. But pound for pound, fatshave twice the amount of energy as carbohydrates.I mean look how mightycovalent bonds there are here. And every covalent bondgives you potential energy. So that’s why though, if you have a pound ofsugar and a pound of fat, you’re gonna get twice theamount of chemical energy out of the pound of fat, because of how condensedit is and how many of those you can have. All right. So what does an unsaturated fat, especially polyunsaturated fat look like? It looks like this. So because of the double covalent bonds, the tails are no longer linear. They’re just kind of all over the place. Well that creates a less, they’re less dense andtherefore more fluid. So unsaturated fats are things like oils. They’re much more fluid and not as compact. Now these are much easier to break down and don’t spend as much timein our cardiovascular system, which is why these tendto be more good for you. And you’re not losing yourselfup on the inside with oil so it’s not how it works.But you wanna think about it that way. Think about it that way, that they’re better for you. Now, can we turn in apolyunsaturated fat into a saturated? Absolutely. That’s what margarine is. Margarine is where theyhydrogenate the triglyceride. Meaning they break thedouble covalent bonds and they add hydrogens to it, thus turning it into a saturated fat. So what is margarine? It’s a solid oil. That’s why I don’t touch the stuff. It’s just nasty. So margarine, there’s prosand cons to all things. Due to the chemical process where they create these trans fats, it makes it very difficult forthe body to break them down. So anyway, we won’t get into all the health reasons or whatnot. But as far as fats go, the saturated fats arethings like the cheeses, and the ice cream, and the lard, and the butter and whatnot where when you get to theoils that you get from seeds and other parts of plants andother tissues and whatnot, those are the unsaturated fats. So that’s probably the maindifference between the two. It comes down to the overallnumber of covalent bonds between the carbons and the hydrogens.The more double covalent bonds there are, the more fluid the triglyceride is, and there’s where you get the oils. Okay. Now, that’s our food source. Now notice they’re puttogether in the same way that the other molecules we’ve talked about are put together. The individual monomersare the fatty acids and the glycerol. When you remove waterfrom each of these bonds, that’s dehydration synthesis, you covalently bond them together and you make a triglyceride. So in that fashion, you still have dehydration synthesis. So what’s hydrolysis? Well we do the opposite. We come in here, we breakthese covalent bonds.So when you get atriglycerides in your diet, first you break off allthe fatty acid tails, then your body comes inhere and starts chopping off these covalent bondsthrough hydrolysis, and those two carbonsactually pact quite a while. You get quite a bit of energy from that, which is why fats give youmore energy than carbohydrates. And that’s why your body, it’s a little harder to get at, which is why it says no, I’mgonna keep that in reserve. So triglycerides are goodfor long energy storage. And yes, you do form triglycerides if you have too much sugar in your body. And it all depends uponthe individual’s genetics and their metabolism on howfast they convert excess sugars into not only glycogen but they can reconvert thecarbohydrates into fatty acids and yes, you can increase your fat tissue by just eating carbohydrates. You don’t have to say,well, this is low in fat. So anyway, there’s alwaystrends and other things and I just try to dispelsome of these myths. All right. Phospholipids are almost identical in their overall structureto triglycerides.Let’s break it down. It has a glycerol, justlike a triglyceride. It has fatty acid tails. And those tails can be saturated or unsaturated just like triglycerides. But instead of havingone more fatty acid tail, which is why we don’tcall it a triglyceride, attached to that thirdcarbon is a phosphate and a nitrogen group. Now this is what makes thismolecule not only unique, but essential for life is that group, that phosphate and that nitrogen group.The phosphate group is negatively charged and the nitrogen groupis positively charged, which creates a polarity to this head. And we call this portion of the phospholipid the phosphate head or the hydrophilic head. When something is charged, it likes water. So this molecule has a personality crisis so to speak, because themajority of it hates water. These hydrophobic tailsbeing neutrally charged, don’t like water one bit. But this head loves water. So what happens is whenyou put phospholipids into a watery environment, remember all livingthings are mostly water, it does this.It creates these bilayers. Two layers of phospholipids, where the heads are oriented on the out and inside of the cell, and the tails are oriented on the inside wherethey’re not near water. This creates a fat layerthat protects the cell. We call this the cell membrane. And all cells have it, which is why this is one ofthe most crucial molecules for life is because allcells are surrounded by these phospholipidsbilayers as we call them. And that’s what helpsseparate the external and internal environments of the cell, where it’s able to maintain homeostasis. Every living organism has these. This is not used for energy. It is purely for structure. All cells have this. Not only on the outside, but as we’ll learn in the next lecture, on the inside as well.These phospholipids form the majority of what we call organellesor the organs of the cell that each have specific functions. The majority of them have at their foundation, these phospholipids. So it forms a very importantstructural component for the outside of the celland the inside of the cell. Now, less talked about, but still important to look at, this is where things startedgetting a little crazy because unlike triglycerides and phospholipids, sterolsare totally unique. They do not have evenclose to the resemblance of what triglycerides and phospholipids have attheir fundamental structure. And these really don’t form polymers. This group, the sterols and the waxes don’treally form huge polymers or even close to the polymers, like triglycerides and phospholipids.So what are sterols? We usually think whenpeople think sterols, they think steroids. And those are actually different. So don’t confuse the two. Sterols and steroids are different. So what are sterols? Well, they’re fats becausethey fit the definition that they are hydrophobic. But notice their structure. It has no resemblance to the triglyceride. So what does it look like? Well the main fundamental structure of all sterols is what we call a fourfused hydrocarbon ring. Okay? Just remember that word. Four fused hydrocarbon ring. It’s not even like sugar. Sugars have these big gaps in oxygen in betweenthem and form these long. These are actually fused together. That’s why we say fourfused hydrocarbon rings. What is the most prominent sterol? Cholesterol. So cholesterol is not atriglyceride, but it is a fat. And our body uses itfor a number of things.It uses it and puts itin our cell membranes to increase their fluidity, we put it in other partsof a cell as a hormone so to speak, and we convert it into various hormones. Cholesterol gets turned intotestosterone and estrogen, which are also sterols. So testosterone, we know about, estrogen, we know about. By the way, the myth that there’s moreestrogen or testosterone in male or female, let me just take that away. Men in your testes, you have a higherconcentration of estrogen, which is used to create your sperm thanwomen have circulating through their body. So we use both, women use both testosterone and estrogen. Yes, there are differencesin where we use them and how we use them, but ultimately testosterone and estrogen are both in male and female.Just depends upon where you look. Vitamin D, cortisone. Cortisone is an important hormonal signal. And vitamin D plays a key role from our skin being activated by light, and then creating thevitamin D that we need for various aspects of our body. But not all organismstypically use sterols. You don’t get bacteria using testosterone. You don’t get other microorganismsusing a lot of these. So that’s why it’s notnecessarily talked about as much, but it is important to at least understand that cholesterol is not a triglyceride. It’s a sterol as we call it. Now I have got some beehives. So I love talking about this. I forgot to bring in my comb. Usually when I do, people start ruining it and they squish it and whatnot. I’ll bring it in next time. The waxes are also again very unique. Now they are lipids, but there’s somewherein between a saturated and unsaturated fat.And they’re not really triglycerides. They do have fatty acid tails, but they are combined with alcohol or other carbon structures. So what’s so important about waxes? Well they are hydrophobicand they’re great for like in the bees forstoring the liquid honey. We use wax in our earto be able to collect and prevent organisms and such, help with dust and otherthings that’s necessary. But not all organisms use waxes. So wax, that’s why you’renot even seeing the structure here is a water repellent,pliable substance. So it is hydrophobic, and it’s used in veryunique circumstances, but not all organismsnecessarily use them.That’s why this one’s kindof an odd ball as well. The proteins group is the most diverse of the four basic biological groups. In the human body alone, you have 400,000 different proteins. That’s a lot. And so ultimately, the question becomes what are the fundamentalsof the protein groups? Since we can’t go over all 400,000, what makes a protein a protein? What are the fundamentals? All right. So let’s start with thebasic building blocks.Monomers. What are the monomersof the protein group? Well we call them amino acids. Now you’ve heard of amino acids before. Typically you hearabout them in nutrition, where you talk about essential amino acids and non essential amino acid. Let me tell you thedifference between them. Essential amino acids are amino acids that you can’t make yourself. So you have to get them in your diet. You cannot manufacturethem through metabolism. So you have to get them inthe food that which you eat. Non essential acids areones that you can make from other molecules thatyou consume on a daily basis. So that’s really thedifference between them. You have your essential ones that you need to get through your diet, andthen your non essential ones, which you can manufacturein your own cells.So what is an amino acid? Well, the name, it gets its name becauseof the chemical groups that are universal for all amino acids. On one end, you have a nitrogen and two hydrogens which we call an amine group. And then you have acarbon which is attached to in the center, and then on the otherend of that carbon is what we call a carboxyl group.Now, without into thedetails of how this is done, the carboxyl group actuallyreleases a hydrogen ion, which makes it an acid, hence amino acid. That’s why they’re called aminoacids because all monomers of the protein group, all amino acids have thisfundamental structure. Now what’s this R group right here? That’s what makes amino acids different. There are 20 amino acidsthat all living things use as their building blocks. They are the universal buildingblocks for all proteins. In some situations, it mightbe a simple hydrogen atom. That’s one of the most simpleamino acids called glycine. In other situations, they might be huge carbon ringstructures with some nitrogen in them as well, like tryptophan. Here’s another one called cystine. You’re not gonna have tomemorize any of the amino acids, but these are just some examples of how amino acids can vary substantially.And there are 20 of these building blocks. So let’s look at how they’re put together. No matter what we call R or functional group is, they all have the same basic fundamentals of how they’re assembled together. Same processes we talked about before. Hydrogen and hydroxyl group get removed through dehydration synthesisand the covalent bond exits. Now, the book and otherswill refer to this as a peptide bond, butit is not a new bond that you haven’t learned. It’s a covalent bond. Why do they call it a peptide bond? Because chemically, chemistsbecause of the nature of this bond, call it a peptide bond. So the reason why I point that out is because it makes it easy to understand what the polymers of all proteins are, they’re called polypeptide chains. That’s the universalword for all proteins. All proteins When they’reassembled together from their monomers into a polymer, we callthem a polypeptide chain. It doesn’t matter whichprotein you’re talking about, all proteins are polypeptide chains. Essentially, just long strings of amino acids assembled together through dehydration synthesis, okay? So make sure you understandpeptide bond is no different than a covalent bond, it’sjust how chemists name it.Now the same processoccurs when we eat proteins for a food source. We break them down through hydrolysis. We add water, we break the covalent bond, we get energy out of it. So we can get energy out of proteins and carbohydrates and fats. Well, what’s interestingabout proteins is not that they’re not just for food, they’re not just for energy, but they’re what make you who you are.Let’s look at the composition of what actually is a protein. Proteins are not justsimple linear structures. There is a three dimensionalshape in which they fold into that gives them a veryunique role in the cell or in your cells. Let me give you an example. We know that wrenches andscrewdrivers are tools that are used for various jobs. They pretty much madeof the same material. Fundamentally they’re made of metal. But based upon what mold they were put into when that metal was shaped, will determine what job they can do. You can’t use a wrench forwhat a screwdriver would do, and you can’t use a screwdriverfor what a wrench would do. And the same thingapplies to proteins here. Proteins essentially havethis hierarchy of folding that is based upon their ability to covalently bond, hydrogen bond, and here’s where weget some ionic bonding. Yes, there is some ionic bondingin the protein structure. Remember we talked about ionicbonds, typically don’t form, but this is the one exceptionwhere in some scenarios, when the protein folds, there is some ionic interactionsbetween the protein chains.So let’s look at this hierarchy, because this is whatI’m gonna test you on. The primary structure of aprotein is essentially the order of the amino acids. Now, the order is just what order do they getcovalently bonded in? Alanine, threonine, cystine, tyrosine, glutamate, glycine and whatnot. What order do they get put in? Well just like you understandhow in the English language, the different orderthat the letters are put in have different meaning for the words, the same thing is true for proteins.What order are the amino acidsgoing, are covalently bonded to each other, predetermine how thatprotein is going to fold and therefore function. If you put them in the correct sequence, then they will foldproperly into that globular or three dimensional shape,like a wrench or a screwdriver so to speak as I gave you that analogy. But all the primarystructure is, is the order of the amino acids. Nothing else. How do we get that order? Well this is the relationship between your geneticmaterial and your proteins. Your DNA, which is foundin all of your cells, has that template that tells your cell what order to put the amino acids in and therefore howto make your proteins. So in lecture 10, so ways off, but lecture 10 is when we’re going to discuss very deeply thisrelationship between how you go from the blueprint to the actual house.It’s kind of the differencebetween having a blueprint of a house and the actual house itself. The DNA would be the blueprint, the house would be the protein. That’s how you construct it as your blueprint tells you how to do so. Now the secondary structureis where you start to get initial folding. It’s not quite ready at this point, but you do get some of the– Think about origami. In the initial stages, you’re just kind of folding it. It does have some dimension to it, but it’s not what you want it to be yet. It’s just the initial stages of it. So you start getting theseloops of these little sheets and whatnot, but proteinsreally don’t function on that level.Now where does the secondarystructure come from? It primarily comes fromthe hydrogen bonding because amino acids, like other moleculeshave polarity to them. Now there are some amino acidsthat are neutrally charged, but there are a lot of other amino acids that have a polarity to them. And then there are someamino acids that are ions. So there’s a great amountof variety of amino acids. Some are neutral, someare positive charge, some are negative charge, some are polar, which they have both charges. There’s a great deal of dynamics. So you can see here that these loops and sheets actually formbecause of the polarity of these amino acids. Like water and likecarbohydrates and whatnot as I showed you, this is another exampleof hydrogen bonding as it exists in biology.Well once you get throughthe initial secondary stage or secondary structure of folding, then we get to the most important one, which is what we callthe tertiary structure. So what’s a tertiary structure? So essentially the three dimensional shape that the protein will take on, and that gives us its function. This is the difference betweenthe wrench and a screwdriver and a hammer. They each have respective jobs, even though they’re madeof the same material and one can’t do the job of another. Okay? So tertiary, you’ll seeon the quiz times the use of the language threedimensional or globular, those all mean the same thing. So tertiary, globular, three dimensional, these are all space filling models of how the protein is structured. This is pretty much howall proteins function on this level, is this tertiary structure.And we’ll give some examples of these. Now the last one isn’tactually much different than this one. It’s called quaternary structure. What is quaternary structure? It’s essentially multiplepolypeptide chains, all combined together into an even larger threedimensional structure. So the only difference between a tertiary and quaternary structure is how many polypeptide chains you have. For a single tertiary structure, it’s just one polypeptide chain folded. But for a quaternary structure, a perfect example of this is hemoglobin, which is in your blood. Hemoglobin actually has fourdifferent polypeptide chains, each individually folded, and then what holds themtogether in the middle? Iron. That’s why you have a lotof iron in your blood. So there’s some iron thatholds these four together.That’s what carries youroxygen and your carbon dioxide through your blood. Okay? So the only differencebetween these two is just how many proteins are involved? How many polypeptide chains? So if you see me describemultiple polypeptide chains forming a larger structure,that’s quaternary. But as you can see, they’re really not muchdifferent than each other. In fact, this is generally the rule. This is generally the exception. There are more proteins that form these higher conflict structures in your body than single proteins. Now this is just to give you an example of some of the proteins. You’re not gonna haveto memorize any of these but some of these will come up quite a bit throughout the semester. So it’s a good and important to at least give you a previewabout what we’re doing.Muscle. Your muscle cells have two major proteins. There’s actually more thantwo, but two major protein, actin and myosin, which interlink andultimately are the proteins that cause the force of contraction. So your muscles, which are cells are able to function because they have anabundance of these proteins. Antibodies. Your body produces 10million different variations of antibodies to try to respondto any infectious disease. Carbohydrates, lipases, proteinases, this is a huge group we’regonna spend a lot of time on lecture seven called enzymes.Guess what’s actually doingthe dehydration synthesis and the hydrolysis. It’s enzymes. So there are proteins that are actually puttingmolecules together and breaking them down. So it’s not just happeningspontaneously in your cells. These enzymes are whatactually break it down. If you remember I talkedabout lactose intolerance. People who are lactoseintolerant can’t break down the lactose sugars because they fail to produce this enzyme that does that. And no two enzymes do the same job. Each one has their own tertiary structure and therefore does only one job. It’s like trying to take awrench to do a screwdriver’s job. It just won’t work.Okay? So each protein has a specific job. If you don’t make thatprotein, you don’t do that job. In some cases it justcauses a mild irritation of milk proteins. In other cases, it canbe life threatening. So, let’s see, insulin. Insulin is a protein we’regonna talk about quite a bit because it’s necessary for your body to maintainhomeostasis and pull glucose out of the blood stream into your cells.We know if you have type 1 diabetes, your body doesn’t produce insulin, and so you have to have insulin injections to regulate your blood glucose levels. Type 2 diabetes is your bodydoesn’t respond to insulin and there are othermechanisms such as exercise that can actually helpmitigate the absorbance of glucose into your bloodstream. Keratin. Keratin is one of themore diverse proteins because it’s found in somany different tissues in your body and it can be compacted in any number of different ways. It forms your hair, it’s inyour skin, it’s in your nails, it’s in the horns and beaksof various other organisms. So it can be really, really tough. It could be slightly tough. It can be very pliable like in your skin. It can be tough like in your nails. There’s many other things, but keratin has pretty much one main job. It’s a waterproof protein.And that’s why your skin hasso much of it and your hair, and your nails. It’s very tough and it’s verywater waterproof and it helps to maintain homeostasis for your skin. So there’s just so manydifferent proteins. We can’t go through them all. Now, this is the last concept though that you will be tested on. And this is the reason whywe’ll explain it’s not good to let your fever go up to about 105, 106 if you have a fever. Your body artificially resetsyour internal thermostat when you have a fever because a slightly highertemperature increases metabolism, and that helps your body to be able to fight off the infection.That’s why you get a fever. However, it shuts offyour ability to sweat and as your body temperature rises, when you get to a certain point, there starts to become an issue. Proteins will only remainstable at certain temperatures. If the temperature starts to go higher and higher due to the heat, the proteins will actuallystart shaking and disassembling in that tertiary structure. Remember hydrogen bonds are weak. And so what happens is if youraise the temperature enough, then the proteins do this. They essentially unravel. Now what they don’t do is this. They don’t snap back together. Okay? It’s not like a rubber band. If they unravel, the cell has to chew them up through hydrolysis andremake them all over again. When your cells get too hot,like when you have a fever, your proteins undergo this process. We call it denaturing. So you’re gonna need to knowwhat denaturing is as well as what can cause thedenaturing of your proteins.So denaturing is essentiallya loss of its quaternary or tertiary structure. It goes back to this. It just unfolds to its primary structure. It’s like melting down awrench or a screwdriver. You have this molten metalthat doesn’t do anything because it doesn’t have anyshape or any structure, okay? That’s why you don’t want yourtemperature to get too high because when the proteins denature, the cells can’t do theirjob, the cells die, and then you start havingmassive issues from there. Now, temperature isn’t the only thing that can actually be nature your proteins. That’s one thing that candisrupt the hydrogen bonds. Guess what? Since proteins are also heldtogether by some ionic bonding, as well as hydrogen bonding, if you change the saltconcentration, sodium chloride, potassium, calcium, anynumber of different ions, if you increase it too much, then it disrupts the hydrogen bonds and the protein falls apart.So proteins in too high of a salt solution willcause them to denature. They’ll break apart. So it’s not just about heat. And the last one is pH. Remember all pH is, is a measure of the hydrogen ion concentration. Well, proteins are designedto work at very specific pH. Not all proteins work at a neutral pH.Some could work in veryacidic environments. Like a pH of 2.7, some workin more basic environments, like a pH of eight or nine. Each protein is specifically designed to work at a specific pH. So if you change that pHby adding hydrogen ions or adding hydroxide ions, the same principle appliesas it does with salt. The ions, the hydrogen andthe hydroxide will disrupt the hydrogen bonding of the proteins and cause them to denature. So changes in pH, changesin salt concentration and changes in temperature,pretty much heating things up. If you cool things downyou can stop the proteins from moving, but that’show we preserve proteins for long periods of time. They don’t denature by freezing them, but they do denature by heating them up. So I will test you on what things can actuallycause denaturation. So what things don’tdenature your proteins? Well, let me give you a prime example that you’ll probably see on your quiz.Light. Light doesn’t denature proteins. In fact, it protects us. We have a defense mechanism. When you go outside and you’re exposed to notonly sunlight, but UV light, your body reacts by producing a protein that absorbs the light called melatonin. Not melatonin. Melanin. Sorry, melanin. Melanin production. So melanin is produced byyour melanocytes in your skin that’s why your skin gets darker.It’s a defense mechanism. Why? Because UV radiation can damage your DNA. And so your cells producethis protein, melanin to absorb the light. And they’re not denatured by that. So that’s just an exampleof something you would look for on this one where I say, which is the bond would notcause your proteins to denature.One might be freezing them. That doesn’t cause them to denature or exposing them to UV light or even just regular light. Doesn’t cause your proteins to denature. In fact, we are kind of light driven. Vitamin D production, we need light for that to occur. So we do need some sunlightto be able to remain healthy and maintain homeostasis. But UV light is damaging andthat’s why your body reacts to it by producing the melanin. Now, last organic group, nucleic acids. Here we are coming backto where I mentioned that there are some sugars which are technically carbohydrates, but they don’t form the building blocks of the carbohydrate group, which is why we don’t includethem into the monosaccharides. Two of those sugars arecalled deoxyribose and ribose, and that’s where DNAand RNA get their names. DNA literally stands fordeoxyribonucleic acid and RNA stands for ribonucleic acid. So the names are derived from the sugar that makes up their monomers. Now, the sugars aren’tthe only thing that makes up their monomers.Here is the basic building blocks of all DNA and RNA molecules. There is a phosphate group, a sugar, which will differ between DNA and RNA. DNA uses a sugar called deoxyribose, RNA uses a sugar called ribose. And then this is the key part right here. The nitrogenous base. This part of the monomer iswhat provides the information. Okay? Your DNA and RNA are prettymuch just blueprint molecules. They’re blueprints for how your cells need to make the proteinsto be able to function. So I’ll explain in a secondhow that blueprint works, but this monomer, we havea specific name for it. It’s called a nucleotide. So make sure you understandthat that is the monomer of the nucleic acids group. It’s called a nucleotide. So what makes up a nucleotide? A phosphate group, a sugar, and what we call a nitrogenous base. Now there are many different types of nitrogenous bases. For DNA there’s four and RNA there’s four.And they share most of them in common. Though there are some subtle differences. DNA uses– Now the reason why we callthem nitrogenous bases is because they got a lot of nitrogen in them and carbon andhydrogen and whatnot. So DNA uses four basis called guanine, cytosine, thymine and adenine. RNA on the other hand doesn’t use thymine. It uses guanine, cytosine,adenine and it uses uracil.Now this is just a precursor. You’re not gonna haveto memorize these yet, but in lecture 10 you will. So might as well learn them now. But DNA and RNA arealmost exactly the same. They just have one base thatthey don’t share in common. DNA exclusively uses this base, RNA exclusively uses this base but the other three, they both use as far as their nucleotides. So if the nucleotides are the monomers, what are the polymers? Well, by the nature of saying DNA and RNA, those are the polymers. What do I mean? The shortest strand of DNA in any one of your cells is33 million nucleotides long. Yes, million. They’re the one of the longest polymers in your body. And some of your chromosomes have as much as 100 millionnucleotides to them.So between, if you countup all of the nucleotides in a single cell, you have about 5 billionnucleotides for every cell. Okay? So this is by far, one of the more importantorganic molecules because of the data that it holds, the blueprint that it holds. Now there are some fundamentaldifferences between DNA and RNA and their structure. Let’s look at those. DNA is your genetic hereditary material. This is one aspect thatI’ll test you on for DNA. It is what gets passed on fromone generation to the next. You have a baby, howdo you make that baby? I don’t know if you knowhow to make that baby, but you’re fusing the DNAbetween two individuals. So men will pass on half ofthe DNA through their sperm, women will have the other halfof the DNA and their oocyte or the egg. When that fuses together, that’s the geneticmaterial that you pass on. This is about reproduction.But RNA is a messenger molecule. It tells the cell, it gives the cell theinformation that’s contained on the DNA. So you’ll understand moreabout this in the next lecture when we talk about cellbiology and where DNA and RNA are found and whatnot. But DNA is kind of likehaving this huge cookbook with all the recipes in it. Well, when you’re makingyour brownies so to speak, you don’t want your kids to start messing up your original recipe. So what do you do? You make a copy of that page. You don’t care if thatgets exposed to the flour and the sugar and the markersand all the good stuff that your kids are doing when you’re baking your brownies. That’s really the main difference here. DNA is the hereditary material, RNA is just a copy of portionsof your DNA to tell the cell what to do. Notice that RNA is just a single strand and DNA is actually thisdouble helix structure.And this provides greaterstability for this to be a longterm informationstorage molecule. Notice how it’s heldtogether in the middle. What do you think is holdingthe two strands together? Hydrogen bonding. Okay? So individually again,hydrogen bonding is weak but collectively it’swhat holds the strands of your DNA together. Now how are these assembled together? The same process we’ve talkedabout, dehydration synthesis. So here’s one nucleotide,phosphate, sugar, and a base. It then is covalently bonded right here to the next nucleotide,phosphate, sugar, base. Covalently bonded here to the next nucleotide,phosphate, sugar, base, all the way down the line. So the backbone of DNA and RNA is actually where the covalent bondingoccurs for dehydration synthesis. The middle of the DNA is actuallyjust held together weakly by hydrogen bonds. Now why is that important? Because in order to copy DNA,it’s like opening up a book.It has to be able to be openand accessed very easily. As such, the DNA has to be separated and then put back together very easily, which is why it needs hydrogen bonding instead of covalent bonding. Because the DNA is constantlybeing opened and closed, open and closed. Now there’s one more moleculein the nucleic acids group besides DNA, RNA. And it doesn’t play itsrole in information. It plays its role in metabolism.What am I talking about. It’s called ATP, adenosine triphosphate. Why is this a nucleotide? Well, let’s look at it. It’s made up of a phosphate, a sugar, and a nitrogenous base. A nucleotide. So that’s why it belongsto the nucleic acid group. Now later on we’ll discussall the ins and outs of this. For now just acceptthat this is the battery that fuels all metabolism. When your cells need energy, this is what they tap into. You’re like, why isn’t it a glucose? Glucose gets turned into this. Lipids get turned into this. Proteins get turned into this. So we’ll discuss in lectureseven, how that’s done. But that’s really what ATP is. It’s that double A batteryor that triple A battery or whatever battery that plugs in to everymetabolic process in your cell.So that’s why this isalso an important molecule to understand, it is anucleic acid or a nucleotide because its fundamentalstructure is a phosphate, sugar and base. We’ll talk more later about what those other phosphates are and why. So now you know ATP, DNA and RNA. These are all nucleic acids. Now ATP is a monomer. It is not a polymer. It’s just a single unit.So ATP is an example of a monomerof the nucleic acid groups where DNA and RNA are theexamples of the polymers. Now RNA isn’t usually as long as DNA. RNAs can range anywhere from several hundred toseveral thousand nucleotides. So they’re still pretty long. They’re not millions ofnucleotides long like the DNA, but several thousand is still pretty long. So RNA and DNA are thepolymers of that group..


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