The Science of Everything Podcast - Episode 18: Biochemistry Basics

Episode Date: June 20, 2011

An overview of biochemistry, covering the basic properties, structure and functions of nucleic acids, lipids, carbohydrates and proteins. Also includes a discussion of the nature of organic molecules and the importance of carbon in living organisms. Recommended pre-listening is Episode 15: Chemical Bonding.

You're listening to The Science of Everything podcast, episode 18. Biochemistry basics. So in today's episode, I'm going to talk about the basic principles of biochemistry, which is the chemistry of living things and organic molecules. And I'm going to talk about in particular the basic properties, structure, and functions of the four main classes of bioorganic molecules, which are proteins, nucleic acids, lipids, and carbohydrates. And before I do that, though, I'm going to give a brief.

brief outline of what organic molecules are and why they're so important in living organisms and just generally about what biochemistry is about. So biochemistry is kind of the foundational field for the study of biology because to understand biology you have to understand cells because every living thing is made up of cells and to understand cells you have to understand the molecules from which they are made and those molecules are biomolecules and the study of those biomolecules is biochemistry. All organic molecules are made from carbon. And carbon is, therefore in a sense, the building block of life. Everything that we know that is alive is made largely from carbon, covalently bonded to atoms of

hydrogen, oxygen, sulfur, nitrogen, a few other elements nearby on the periodic table. Carbon is a relatively rare element in the natural world. It only accounts for 0.03% of the Earth's total crust, but it accounts for almost 20% of the total mass of a human body. So carbon is substantially concentrated and well ever represented in, in terms of mass, in living creatures. So why is carbon so important? The reason is because carbon has four valence electrons. That is, it has four electrons in its outermost shell, and that atomost shell has a capacity of eight. So four valence electrons provides the largest number of bonding opportunities, because, as mentioned in the previous episode, atoms tend to fill up their outermost shell to have eight electrons

in it. It's just more stable that way. So if you have five or six electrons, you're only need to gain three or two more in order to make up that eight in the atomost shell. So that only provides you with three or two bonding opportunities. But four electrons in your valence shell like carbon has provides the largest number of bonding opportunities, namely four. So that means that means that any elements in the same group on the periodic table as carbon is will have that same number of valence electrons and therefore the same number of bonding opportunities. So you might expect that life could be made from those things as well because they also have a large number of bonding opportunities. Silicon, for example, has the same, also has four valence electrons. The

difference though is that as atoms get larger, they tend to get, they tend to have a tougher time forming large, complicated molecules which are necessary for life. And so carbon being nice and small, but also having the four valence electrons is really the ideal, the ideal sort of backbone or building block of life. Okay, so carbon's important because that has four valence electrons, but why, and that's the maximum number of bonding opportunities you can have, but why a bonding opportunity is so important? Well, the reason I've hinted to is because the more bonding opportunities you have for a given atom, the larger and more complicated molecules you can form, and because life is complicated, it needs big, complicated molecules. So many molecules that we study in physics, maybe have

3, 5, 10, 15 atoms would be a fairly large one. But the kind of molecules we talk about in living organisms, particularly like nucleic acids and proteins, can have millions of atoms in them. They are just enormous for molecules. You can even see some of these molecules macroscopically, like, for example, DNA, when it's condensed into a chromosomal form, is essentially one large molecule, or at least mostly,

and you can see it, not macroscopically, but you can see it just with a light microscope. You don't have to use electron tunneling microscopes as you normally would to see a molecule. So these things can become enormously long. And to have that, you need to have the large number of bonding opportunities that comes with four valence electrons. Another important thing about carbon is that the four valetons

permits it to form non-polar bonds. If you remember, non-polar bonds are ones that are sort of symmetrical. So in the case of oxygen, for example, it only has two valence electrons. and so when it forms a bond with two hydrogen atoms to form a water molecule, the resultant molecule is a bit bent because the two non-bonding electron pairs that are left over repel each other a bit more strongly than the two bonding electron pairs because the two bonding pairs sort of have the hydrogens attached to them,

whereas the non-bonding electron pairs do not, and so they're more highly negatively charged, so they repel each other more. So the whole molecule as a whole is a polar, asymmetrical. It's sort of bent. And I talked about that in a previous episode. But with carbon, you can avoid that because having four

bonding electrons permits you to be completely symmetrical because you can have one bonding electrons on each sort of side of the atom spread equally around in all directions, and they can all bond in the same way. And so you can get very large symmetrical bonds happening. And in fact you can form very long chains of

carbon molecules without them bending or becoming asymmetrical or polar in any way, which could disrupt the process and force the molecule to sort of end. If you can just keep building on and on, kind of like Legos, then you can form very large molecules, and that's what carbon permits by having the four valence electrons. Okay, so as I mentioned before,

there are four main types of macromolecules, as we call them, or biomolecules. They're just big organic molecules that occur in living organisms, proteins, nucleic acids, lipids, and carbohydrates. And I'm going to talk about each of those in turn shortly, but first I have a couple of other preliminary points that I want to cover. First is how macromolecules form in a general sense, because I said these can be up to millions of atoms long. How does a molecule that big come into existence? Well, a very common way

that they form is by smaller units called monomers joining up together, linking up to each other to form what are called polymers, and I have discussed these in a previous episode. So you can think of these macromolecules, in particular nucleic acids and proteins, as being very long, long chains, but with many small repeating units in them. So each of these units, each of these monomers may only have a few dozen atoms in them. So, I mean, that's still reasonably large for a molecule, but still much closer to ordinary size. But you put many of them together, you form a macro molecule. Generally, the way that these monomers combine into chains,

the way they bond together, is either by what's called dehydration synthesis or hydrolysis. And basically, this is where, in dehydration synthesis, you remove a hydrogen atom from one monomer and a hydroxyl, which is just an oxygen and a hydrogen, from the other monomer, and those two come together to form H2O, which is water. So a water is removed,

and then the two monomers bond together. So it's called dehydration, because one water molecule is removed for each monomer joining that you have. Hydrolysis is the opposites where you break apart a polymer by adding a water molecule. You know, one hydrogen goes to one monomer,

hydroxyl goes to the other and the monomers split apart. So the fact that you can have dehydration, synthesis and hydrolysis shows that water is once again playing another very important role in biology, as I mentioned it in previous episode, that it does. But also that some macromolecules can become unstable

if there's too much water around or too little water around because water can either cause them to disintegrate through hydrolysis or to combine together in dehydration synthesis. I should mention there are other forms. of polymerization which involve the elimination or incorporation of small molecules into the chain as you build it up. But that's the general method that these large macromolecules form.

You pull the monomous, you bring the monombs together, they bond together, and a small molecule like water or something like that is either released or incorporated into the chain as it builds up. Another important concept is that of functional groups. Functional groups are small units of atoms other than carbon and hydrogen, so not including carbon and hydrogen, but small groups of those other atoms that occur in various different places in organic molecules. And the reason that this is an important concept is because there are a number of different functional groups that occur frequently, like the hydroxyl functional group, which is a very simple functional group, which just basically has an oxygen bonded to a hydrogen atom, but that found in ethanol, for example.

Others include sulfur or fluoride, other common organic substance, or other common elements that are found in organic substances. But the thing is that wherever functional groups occur, if you have the same functional group, it often leads to similar chemical properties, even if it's in a completely different molecule, macromolecule. The same functional group often yields similar properties. So looking for what functional groups of particular macromolecule

has can be useful in sort of inferring its properties or understanding its properties. Okay, one final general concept before we get into the four types of macromolecules, and that is the concept of an enzyme. Now, an enzyme is a protein, so a protein, remember, is one of the four types of macromolecules. So an enzyme is a macromolec that functions as a catalyst. Okay, what's a catalyst? A catalyst is a chemical substance of some sort, in this case a protein,

that serves to speed up chemical reactions. The key point about enzymes is that they are not consumed in the chemical reaction process. So unlike reactants, they are not used up. They don't go away. They do not change chemical form in the process of the reaction. And so once they've been incorporated, in one reaction process, they're free to then be engaged in another reaction and then another one, and they just keep going and keep cycling through different reactions.

So apart from the fact that they can keep doing that, they can keep being involved in different reactions, they speed reactions along, which is really the crucial point about them. And the way they do it is by changing the reactants relationship to each other in space. Like often they physically bring their reactants closer to each other, or arrange them in a slightly different shape or something like that to help permit bond. to occur and to help the reaction take place. Because remember, for every chemical reaction, you first have to sort of break existing bonds or pull electrons and atoms out of their potential wells, so pull electrons away from protons or whatever, pull them into a higher level of potential

energy before they can then move into a new and ultimately lower than initial level of potential energy. But you need that initial investment to then get to the ultimately final lower energy level. and enzymes reduce that initial investment that you need by changing their orientations or shapes or whatever of the reactants. And so they're essential in biological, in living organisms, because almost all biological functions would occur far too slowly if enzymes were not present to speed up the reactions. And biological functions, well basically everything that happens inside our body is a biological function, and therefore consists of a chemical reactions, many chemical reactions, very complicated ones, involving, digestion and sending action potentials around and contracting muscles and all of these things require chemical reactions to occur.

And if those chemical reactions go too slowly, then you die, basically. And enzymes permit the chemical reactions to occur sufficiently rapidly in order for life to continue. So enzymes are vital for the new organisms. And because proteins act as enzymes, proteins, therefore are very important. And a number of diseases, in fact, are caused by the presence or absence of certain enzymes, which maybe, in particular, some types of food allergies, for example, can be caused by lacking an enzyme required to break down a certain nutrient or something. Okay, so, nucleic acids. Nuclearic acids are information stores.

The purpose is to replicate themselves and store information regarding how to make life, basically. So specifically, there are two different types of nucleic acids, DNA and RNA. DNA stands for deoxo-ribonucleic acid and RNA stands for just ribonucleic acid. And those particular names just refer to the parts of the molecules that make up the monomers that form the DNA and RNA molecules. But anyway, so don't worry too much about the names. I'll just call them DNA and RNA. Now, nucleic acids are very long polymers made up of repeating units called nucleotides.

So each of these nucleotides is a monomer, and there are five. different types of nucleotides. There are four that are used in DNA molecules and four that occur in RNA molecules. Now, three of them are the same DNA and RNA, but there's one that's different, so I'll come back to that, but that means that there's five different nucleotides in total that are used in DNA and RNA. Okay, so we've got this monomer, which is a nucleotide, many nucleotides lined up, joined together, form a nucleic acid, an RNA or an DNA molecule. Now, each of these nucleotides itself consists of a couple of different units. First, of all, it consists of a five carbon sugar. A sugar is a form of a carbohydrate, which we'll talk about

later, but basically it's a ring of five carbon atoms sort of all bound together. It sort of looks like a hexagon if you see it represented in chemical form, as a chemical formula. So you've got this hexagon of carbon atoms in the middle, and then bonded to that central hexagon are a phosphate group. A phosphate group is just a phosphate atom bonded to three oxygen atoms. And finally, there is also what's called a base, or a nitrogenous base. And this is, the different bases consist basically of some carbons, some nitrogen, some oxygens, and some hydrogens, the normal candidates in organic molecules. But anyway, there are five different versions of this base. and depending upon which version of the base is used,

that determines the sort of type of nucleotide that it is. Now, remember, I said there are five different monomers that go into the polymers to make nucleic acids. Well, each of the five monomers has exactly the same base, has exactly the same five carbon sugar, and exactly the same phosphate group, plus there are a couple of other hydrogens and oxygens attached to the, five carbon group, but all of that's the same between each of these five different types of monomers.

The only thing that differs is the nitrogenous base. And in all cases, it's fairly similar. It's carbons in a ring and some nitrogens and stuff like that, but the exact positioning of some oxygens and some carbons and nitrogen and so on differs between the five different nitrogenous bases. And so it's just that difference in the base there that determines what kind of monomer it is. The five bases are called aden, guine, cytosine, uricel, and. and thiamine. And they're often abbreviated, particularly in genetics as AG, C, U, and T. And that's just for simplicity because they tend to occur in particular patterns which we're interested in. Now, I said before that nucleic acid store information, but if they're just a bunch of these monomers,

carbon, nitrogen, oxygen atoms and whatever, linked together, then how can they store information? The answer is the order of the nucleotides in the polymer determines, it carries information itself. It's sort of similar to a computer really because a computer carries information in the form of zeros and ones and the order of those zeros and ones determines what information you have. Similarly, the order of the bases in a nucleic acid determines the information that it carries.

And there's a very sophisticated cellular machinery that knows in a sense, or, is able to read that information and use it to do stuff. In particular, the information that is coded in nucleic acids is used to produce proteins. That's another topic in and of itself, so I can't really go into details here, but suffice it to say that the information that's stored in nucleic acids, particularly DNA and RNA, is generally used to make proteins. Well, it does some other stuff too.

And the order of the monomers within the DNA or RNA molecule stores the information about how to make the protein or whatever. And because the only things that differ, the only part of the monomers that are different, is the nitrogenous base, then it's really the order of the bases that we're interested in, not so much the order of the monomers themselves, because most of them are just the same.

Now, you've probably seen a representation of DNA before, and it's in that sort of double helix structure. RNA is similar. It also forms a sort of a conform to spirals, but it doesn't have a double helix. and that's because the base that is used in hydrogen, not the base, you remember I said that there's a five-carbon backbone pentagon thing that forms the core of each of these,

that each of the monomers, of each of the monomers in the nucleic acid. I said that that five-carbon backbone is the same in all of them. Not exactly true, because there is a slight difference between the five-carbon sugar in DNA compared to RNA, that there is a small difference. In fact, it's a hydroxyl group that replaces a hydrogen, so basically one extra oxygen atom in that whole five-carbon thing. And that actually changes the RNA backbone sufficiently

to prevent it from forming double helices like DNA does. So one extra oxygen atom in each of those molecules makes RNA behave substantially differently to DNA. And one of the reasons DNA forms that double strand, the double helix strand, where you've got two separate strands wound together, is because it is more stable like that. And also, each strand actually stores separate copies of the information. It's the same information, but it's just stored in a complementary way. So as a crude analogy, you can think of it like if there's a one on one strand, then there's a zero on the other strand,

and if there's a zero on one strand, then there's a one on the other strand. And so they're complementary to each other in that way. So plus for minus. It's not exactly like that, but that sort of gets the general idea. So they store the same information as the key point, and having a double copy of the information helps to repair errors and things like that. And so it's very, because the DNA molecules carry information about how to build proteins and how the organism needs to function and so on, it's very important that you keep that information, pristine, you keep it accurate.

And so that's why you need the extra stability for the double strand, and you need the redundancy in keeping two forms of the same information. and so on. Okay, and DNA molecules can be very long. Remember the double helix structure that you probably seen? Well, that whole thing is a single molecule. Or you can sort of think of each strand as its own separate molecule, but they're just intertwined together. And each of those molecules can be millions, even hundreds of millions of base pairs or monomers long. So just imagine and lining up hundreds of millions of these little monomers next to each other and forming just an enormously long molecule.

The only way we can fit all that DNA into ourselves is because it is wrapped around itself and curled in extremely complicated patterns. If we just had it in pulled out straight, it would be, I don't know exactly how long. I don't have to look that up, but it's substantially long. Certainly not enough to fit in its cell. Okay, so that's it for nucleic acids. Basically, they store information, and they're very big and long. Now I want to move on to lipids.

Lipids are a loosely defined group of molecules with the sole common characteristic of being insoluble in water. That means they don't dissolve in water. They're mostly made of oxygen, carbon and hydrogen. So whereas before, nucleic acids are a very tightly defined group of molecules. They have a similar structure, a very similar structure. And DNA and RNA are really the two big ones. There are some other ones too, but they're the two big ones.

Lippids, however, are much looser group. They can be very different from each other. they just share a broad property of being insoluble in water. Also, unlike nucleic acids and also unlike proteins, lipids are generally not formed from monomers joining together into polymers. They're generally just sort of single monomers in of themselves, or maybe a few, sort of like a few monomers coming together to form a bigger molecule, but even there, that it's not exactly like that. So they tend to be much smaller than, say, nucleic acids or proteins, but they're still quite large as far as

molecules go. And the reason that, I mean, you might think why do we have this sort of amorphous group, which is a pretty broad category. The reason is because the fact that lipids are insoluble in water is very important, because water, remember I have said, is the biological solvent. It plays a crucial role in life. It's just everywhere, really. You need water for life to exist, particularly in complex life like humans. And, you know, there's water inside every cell. And so, if something is in soluble in water, it's going to behave substantially differently in many different contexts than something that is soluble in water. So, lipids tend to have important behaviors in common, which is why we group them together.

Oh, another thing about lipids, I should just mention, is that they tend to have, remember I said that they're composed mostly of oxygen, carbon, and hydrogen atoms. Well, particularly, they tend to have large numbers of just carbon-hydrogen bonds. And carbon-hydrogen bonds turn out to have a very high energy yield for just a single bond and two atoms of the small size like that, it has a very high energy yield bond, just the way the chemistry works out. And because lipids tend to have a large number of those, lipids are a very efficient energy storage molecules.

In fact, they can store about twice as much energy weight for weight as carbohydrates can. Carbohydrates also serve as energy storage molecules, but as I've just said, lipids are more efficient at storing energy. And so the more common name for lipids are fat, and lipids and fats, sort of more or less the same thing. So when we talk about body fat or putting on fat or whatever, that's actually just deposits of lipid molecules that are stored in particular ways. And the reason the body stores the excess energy like that

is because it's a very efficient way of storing it. In fact, you wouldn't want to store excess energy in the form of carbohydrates because then eating the same amount of excess calories would lead you to put on twice as much weight, because remember I just said that fats or lipid molecules wait for weight store twice as much energy as carbohydrates. So it's actually good that the body's found a more efficient way of storing energy than carbohydrates or proteins.

The downside to that, though, is that if you eat fat, you're getting twice as much energy as if you ate the same weight of carbohydrates or proteins. So that's why we have to be careful about not eating too much fat. Okay, so a bit more about lipid molecules. One type of lipid molecules are called fatty acids. These are kind of the simplest type. Fatty acids are just long chains of hydrocarbons that end in a carboxyl group. And a carboxal group is just one of those functional groups I talked about earlier.

It's got carbon, oxygen and some other stuff. So a hydrocarbon, as I've discussed previously, is just a long chain of carbons with hydrogens bonded to them. So carbons and hydrogens, hence hydrocarbon, simple name. So fatty acids are long chains of hydrocarbons with a carboxal at the end. And there are many different types of fatty acids, but they basically, particularly just differ from each other based on how long they are and how many, how saturated they are with hydrogen atoms. And fatty acids are very useful for storing energy. Another form of lipids are called triglycerides. Now, glycerol is a type of organic molecule with

a hydroxyl group with three carbons and then a hydroxor group bonded to each of those three carbons. But anyway, the details of that aren't important. Just the key idea is that glycerol is a particular type of organic molecule, and triglycerides are so named because they have one molecule of glycerol and then three fatty acid chains, sort of one attached to each of the three carbons in the glycerol. So it's sort of like the glycerol atom grew three hydrocarbon tails, so hence the name triglycerides. So they're kind of like beefed up versions of fatty acids. And so triglycerols are particularly used to store energy in fat cells. Now there are two types of fats, saturated and unsaturated fats, and I mentioned.

this before, the word saturation just refers to how many hydrogen atoms each carbon atom has in the tails. The maximum possible number of hydrogen atoms that each carbon can have in the tails is two, because each carbon in the tails, apart from the very end one, is bonded to one carbon above it, and one below it, and remember they only have four valence electrons, so they can only form four bonding sites, so we've already counted for two, the remaining two, you can have one one hydrogen each. However, if the carbon has a double bond with each of its carbon neighbors, then it doesn't have any spare bonding sites left, and so it won't have any hydrogen atoms bonded to it, or it could have one double bond and one hydrogen. And of course, different proportions of

carbon atoms within the tail could have more or less numbers of double bonds and hydrogen. So the more saturated you are, the more hydrogen bonds you have in that tail. And remember I said that the more hydrogen bonds, the hydrogen carbon bonds are a good way of storing energy. So the more carbon-hydrogen bonds you have, the more energy you can store. And so that's one reason why saturated fats are generally worse than unsaturated fats, because they have more energy. Another reason is that the saturated fats, because remember I said that they have all the carbons, if a fat is completely saturated, it means that every carbon atom in the tail is fully loaded up with hydrogen atoms. so there are no double bonds there.

But because there are no double bonds, there are no kinks in the tail. So the tails are just completely straight with carbons down and hydrogens on all sides. So these straight hydrocarbon chains can, because they're straight, they can pack together in a very dense relationship. If you have double bonds,

they tend to go out in strange angles and form kinks and things like that, so the tails can't pack together very tightly. But with saturated hydrocarbons, they can pack together closely. And this tends to make them solid or near solid at room temperature. Whereas unsaturated fats, because of all the kinks that can't pack together, they tend to be liquid at room temperature.

And so, in fact, as you get more saturated, you tend to the fatty acid, or the fat tends to become more viscous and eventually solidifies. So animal fats tend to have saturated fatty acid chains, whereas plant fats tend to have unsaturated tails. And in fact, fats are much more common than we would think. Things like beeswax, earwax, olive oil, and corn oil are all lipids. They're all similar sort of fatty acid chains and triglycerides and things like that. Carbon hydrogen bonds. Saturated fats are also a problem because, as I mentioned, they tend to be solid, or at least more solid-like. And so they're worse for fucking arteries, basically, which blocks off blood flow and then can lead to heart attacks or strokes and other things.

So that's why we need to avoid too much saturated fat. Okay, one final point that needs to be made about lipids. That's the phenomenon or the group of molecules called phospholipids. Now, phospholipids have a phosphate group bonded to a glycerol, and two fatty acid tails. So unlike the triglyceride, they only have two fatty acid tails, and instead of one tail, they have an extra phosphate group bonded to the glycerol. Remember, a phosphate group's just a phosphate atom with three oxygens onto it. So it's kind of like you can think of as a modified triglyceride with one less tail.

So it's got two tails instead of three. Now, why do we care about phospholipids? Because they form the major component of cell membranes. Cell membranes are the kind of elastic bag sort of container that protects cells and that separates them from the outside. Phospholipids form these membranes. In fact, that they line up in two separate layers. One pointing outside the cell and one pointing inside the cell, and one pointing inside the cell, and this forms, and do we say, they form the membrane. The reason they're so good at that is because phospholipids are half of them, polar and therefore tends to bond to water, namely the phospholipid head, the part that has the phosphate group bonded to it, it is polar and so tends to react with water. And so the phosphate heads tend to point in the cell, in toward the cell and out away from the cell, both of which environments have a lot of water in them.

So if you've got the two heads facing outwards, the two tails, the hydrocarbon tails, must be facing inwards pointing towards each other. And these tails, because they're non-polar, remember, we've just got carbons and hydrogens, they're sort of symmetrical, they're basically non-polar, they do not tend to react with water, which is non-polar. And if you're not sort of familiar with these polar-non-polar terms, I refer you back to the earlier episode where I talked about this chemical bonding. Anyway, non-polar and polar tend not to mix very well. So small polar molecules, for example, water and lots of other things, can't get through the cell membrane.

They can't pass through the non-polar region of the hydrogabond tails that are pointing in towards each other. And so that's why the membrane forms such an effect, barrier separating the inside from the outside of the cell. What's even cooler about phospholipids is that in an aqueous solution, so in water, they actually spontaneously arrange themselves into these sort of lipid bilayer barriers, just because of the forces that are acting on them. The tails tend to get pushed together, and the heads tend to get pushed apart towards the water, and then they tend to line up against each other, and so they just naturally form these lipid bilays, which is very much like a cell membrane. And so

I talked about this briefly in the episode about the origins of life, where I said that you can have things like my cells or lipid bilay spontaneously forming, and then early sort of protobiont self-coping molecules, perhaps RNA molecules, would have been sort of trapped within these early cell membranes, and then copied themselves, and then the membranes could have split into two, and then you could have had early sort of very simple forms of cells. But that's all possible because these lipid bilays form spontaneously, which is just a very interesting phenomenon, and all basic chemical principles.

Okay, so I've talked about nucleic acids, talked about lipids. Now I'm going to move on to carbohydrates, the third major group of organic molecules. Carbohydrates are also kind of a loosely defined group. Lipids and carbohydrates are sort of loose to groups, whereas nucleic acids and proteins are tighter, more tightly defined. But carbohydrates are just, they contain carbon and hydrogen and oxygen in a two, in a one to two to one ratio. So they have two hydrogens for every one carbon and every one oxygen. So it's just a certain ratio. And that's why they're called carbohydrates.

They have carbon and they're hydrated in a sense because they have hydrogen and oxygen, which make up water. Like lipids, they also have a large number of CH bonds because they're mostly carbon and hydrogen and oxygen. So lots of CH bonds, so they're also good stores of energy, just like lipids. Now, there are a number of different types of carbohydrates, mostly defined by how big they are, in a sense. The smallest and simplest types of carbohydrates are called monosaccharides. Now, the word saccharide just effectively means sugar.

And so carbohydrates are basically just sugars. So when you talk about lipids, those are sort of basically fats. Carbohydrates are sort of basically sugars. Nuclearic acids aren't really anything. They're just nucleic acids. They're not really nutritionally that important. They're not used to store energy so much, but lipids and carbohydrates are. So monosaccharides, simple sugars, they can have as few as three carbon atoms,

although up to five and six are more common, but they often form small, like hexagon or pentagon shapes of these carbon atoms bonded together, pretty small. They sometimes form straight linear molecules, but mostly of those little rings I talked about, the pentagons and hexagons. There are many different isomers of these simple monosaccharides. For example, glucose and fructose have exactly the same chemical formula.

They're just the, you know, the carbon atoms, or not carbon, but the hydrogen atoms moved here, or the oxygen atoms moved here, or the bondings around. arrangement slightly different or something like that. And this might not sound very important if the oxygen has just been moved on carbon along, but it actually can make a significant difference in chemical behavior. So it does in fact matter. And you're probably heard of glucose and fructose. They're both just simple monosaccharides, which are different forms of sugar, really. Okay,

disaccharides is the next one. Dysaccharides, die from two. It's basically, dieaccharides are just two monosaccharides joined together. And so it's sort of like a polymerization in that sense, except it's not many packed together, it's just two, hence a disaccharides. They are often, discharides are often formed within the body to facilitate transportation of monosaccharides around, because if you buy them together, they become easy to transport. Sucrose is a common example of a disaccharide. It's made from one glucose and one fructose monomer,

both put together to form the sucrose. And sucrose is more commonly called sugar. It's basic table sugar. It's produced mostly, we get it mostly from plants, notably either sugar cane or sugar beet. But it can be produced, I mean, if you have sources of fructose and glucose, then you can make it using chemical reactions. And one of the things that we need to do in metabolism

is to break the bonds, break that bond that joins the two monosaccharides together so that it can be metabolized properly. And lactose is a particular type of disaccharide that's commonly found in milk, in mammalian milk. And if people are lactose intolerant, or at least one form, of that is that they lack the enzyme needed to break that disaccharide into two, and so they can't digest it. And so it basically just sits around in the system and gives upset stomachs and causes other problems. So that's one example of why enzymes are so crucial. You need them

to break up these disaccharide and other things. And finally, the final type of saccharides are the polysaccharides, poly just meaning many. So they're formed from many, many, many monosaccharides joined together, up to hundreds or even thousands of them. And they're a very good way to store energy because you've got lots of the monosaccharides, lots of those carbon hydrogen bonds, and therefore lots of energy potential. Polysaccharides are particularly important in plants. They, where a special type of polysaccharide, made from glucose monomers, is called cellulose. And cellulose is used for structural support in plants. So that's what makes plants rigid and sort of bend back into shape when you move them. It's the cellulose.

Most animals, including humans, cannot break down the chemical bonds of cellulose. And so they they can't digest it. That is why we can't eat many raw plants. We can't eat grass or wood, for example. We can't digest the cellulose. However, that cellulose has an awful lot of energy with all those carbon hydrogen bonds, and you can see that if you burn wood. It'll burn for a long time, it produces a lot of energy. That's all coming from the carbon hydrogen bonds, mostly in the cellulose, that's where you're driving your energy from. There's another form of, a slightly altered form of

cellulose called chitin, and it is used to make the tough exoskeleton in many arthropods, like crabs, that shell on the outside of a crab, it's made from Chittin, which, as I said, is an ultra-form with cellulose. So, crabs and trees actually have more in common than you might otherwise think. Okay, so I've talked about nucleic acids, which store information. I've talked about lipids and carbohydrates, which store energy, and I use to transport energy around, and also form the cell membranes, and they do other things. They can also act as hormones, chemical signaling molecules, basically. But you may be thinking that, well, yeah, but what about everything else that's done in the body? Because,

what I've mentioned so far, and this seems to be a small subset of what the body does. And you're right. And the answer is that everything else, almost, I mean, almost everything else you can think of that the body does is done by proteins.

Proteins are just the universal workhors of living organisms. There's a list of some of the functions of proteins that I have for you, and I'll just go through some of them. Proteins form enzymes, as I said, so they speed up the chemical reactions that living organisms need to survive. they act in defensive purposes, so the white blood cells in the immune system are made largely of proteins.

They act as for transportation. So there are proteins embedded in cell membranes that allow certain things to come and go in and out of the cell. There are also other molecules that transport stuff inside the cell or between cells. Those are generally proteins. muscle cells are made from filaments which slide relative to each other, those filaments are made of proteins. Many of the structural elements of the body, things like hair, ligaments, joints, parts of bones, organs, just most of the structural bits of the body are made from proteins. Also, many proteins serve as hormones and as neurotranspins and things like that, so sending messages between cells. So you can see that just like almost everything that the cell does,

does, therefore the body does, is done by proteins, or at least involves proteins. So by far, I would argue that proteins are the most important of the four types of macromolecules. And like nucleic acids, proteins are just made up of big, long chains of monomers, except these monomers are different to the nucleic acid monomers. The monomers that make up proteins are called amino acids. There are 20 different types of amino acids which make up proteins in living organisms that we know, or at least in humans. I think some more exotic organisms have a couple of different types of prediocids.

of amino acids, but basically there are 20. There are many more amino acids that are not used in living organisms, but 20 that are used in life. Each amino acid has a single central carbon atom, bonded two. Okay, remember the carbon atom has four bonding sites. So one of those bonding sites has taken up by hydrogen. Another one of them is taken up by an amino group,

and I'll come back to that. One is taken up by a carboxyl group. Remember I mentioned that, it was just the carboxid group, it's just a carbon and oxygen and hydrogen. and the final bonding site is a side group called the R group. This R group is unique for every different type of amino acid. So remember I said it was the nitrogenous base, which differs between the five different types of nucleic acid

to determine which monomer it is. Well, in the case of amino acids, it's the R group that differs, and therefore gives each amino acid its unique property. And the R group can vary from a single hydrogen to quite a complicated carbon ring with oxygen and stuff like, so there's no particular pattern to those. They can be all sorts of different things. The amino group, the thing I said to come back to,

that's just nitrogen with a few hydrogens attached to it. So it's basically that the part of an amino acid molecule that's the same is you've got essential carbon, then a couple of other carbons, some other hydrogens, and an amino group, nitrogen there. That's the same. And then there's this other part, the R group, which differs and can be large or small depending on which type of amino acid it is.

And amino acids come together, form in a covalent bond, and what's called a peptide bond, it's just a particular type of bond, to form the big long chains of polymers that make up proteins. Now, a single string of amino acids, maybe up to 100 units, amino acids long or something like that, is called a polypeptide, it just means a many-peptide bonds, so it's a polypeptide,

and if it's a really short string of amino acids, it's just a peptide. But anything longer than that is really a protein. I mean, a polypeptide, which you may hear is basically the same as a protein. generally though it's smaller and maybe it doesn't do as much. But proteins just a particularly long polypeptor, just many amino acids, hundreds or thousands, or even tens of thousands, joined together. Now, proteins have very intricate structures.

It's not just the order of amino acids in the protein and also the number of amino acids and protein that determines its functions. It's also the particular way that protein folds in on itself because proteins are very long, and they don't just exist and be long strands, or even just curl up randomly, they fold in very intricate, specific ways. And there are different levels of that structure, primary structure, secondary structure,

tertiary structure, quaternary structure, and then even some subsidiary levels within that. And there are even diseases, for example, cyclonemia, that are caused solely by misfolding of proteins or slight changes in the amino acids, which then cause proteins to misfold. And there is even a specific, I don't know what you call exactly, perhaps a disease vector or something, that's called prions that are simply misfolded proteins, particularly in the brain. Mad cow disease is an example. So mad cow disease, it's not a bacteria, infectious and a fungal infection, it's not a virus,

it's nothing like that, it's not cancer, it's just a misfolded protein in the brain, which causes very strange behavior and death. And prions are kind of scary because there's not much you can really do about them. You know, you can't, the immune system can't really do anything much about them. The antiviral agents won't work, antibacteriol, agents won't work, antifungal agents won't work, even temperature and radiation generally won't really help, because it's just a misfold of proteins, so there's not much you can do about them. And the study of exactly how proteins fold in the particular way they do is a very fascinating

one, and it's still not very well understood. But it's thought to somehow involve the interaction of the different side groups, little chains, shortchanged of molecules that sort of come off the main big long polymer, and also functional groups on the side of amino acids. It's thought that these interact in a certain particular way, which then sort of funnels the protein to fold in its particular way. You think of a funnel, it starts off with a wide mouth and then converges to a narrow end. A protein's folding sort of thought to be like that.

It starts off at a very unstructured state, just kind of a big long line or whatever, and then it gradually gets closer and closer to its folded level with the interaction of the side grips, and it comes to a sort of a lower and lower energy state until it finally reaches the bottom end of the funnel where it's its most compact and lowest energy state. But fundamentally, it's just positive and negative charges

of the different atoms and ions interacting within the protein and between different amino acids and the protein, pulling and pushing and causing it to fold up in the right way. That's not a very satisfactory answer, but it's nothing magical. It's just chemistry writ large, really, and it's extraordinarily complicated, but it's still basic chemistry. Well, basic chemistry, but really complicated

because there are just so many different atoms and therefore so many permutations. you heat up proteins or put them in ionic concentration or pH or something that's too high or low, they can unfold, which is what's called denaturing. And if proteins unfold, they don't function properly because they need to be in the right, folded in just the right way to do whatever is they're supposed to do, whether it is defense or metabolism or acting as enzymes or whatever. So if they unfold, they don't work.

And if they don't work, you probably die. And so that's why, if, for example, pH goes too high or too low, it can be a problem. So for example, if you have too much carbon dioxide in your blood or too little, it will change the pH of your blood. And that in turn can cause proteins to denature or to misfold. And therefore, that can cause you to die because your proteins that give you alive aren't working anymore. Similarly, if you store food or other living organisms in very high salt environments, that can also denature the proteins because it's a, the ionic concentration has gone up because you've got lots more salt dissolved in the water. And so once again,

can denature and the whatever it is you've stored there can die. That's why food can be preserved in salt because bacteria and other things can't grow on the food because it's too salty for them and therefore the proteins inside the bacteria are denature and it can't really work. Okay, so that's about all I wanted to cover for this introductory podcast. We've covered proteins, nucleic acids, lipids and carbohydrates. I'm definitely going to talk more about these in future episodes because there's much, much more to say, particularly about proteins and nucleic acids. I mean, there's all of genetics and molecular biology and much more of biochemistry that focuses on how proteins fold, how they work, how nuclear acids work, how nuclear gases

work, how nuclear acids are red and how they are used to make proteins and so on. But all in good time. So, yeah, that's it for this week. If you enjoyed this episode, please, please contact me and send me an email. I haven't received much feedback for the podcast, and I'd really like to know who is listening. And also, any reviews that you might want to post on iTunes. or somewhere else would be most appreciated. Anyone you want to tell about the podcast as well, love to get more listeners, that would be great. So thanks for listening, and I'll talk to you next time.