Triglycerides – TRANSCRIPT

Okay, we’re gonna start off with some of the summary basic structure, look at the function and the differences between saturated and unsaturated fatty acids, which are one of the components. Okay, let’s start with the basic structure.

They contain three elements: carbon, hydrogen, and oxygen. And just those three elements, no nitrogen, no sulphur, nothing like that.

So, triglycerides are made up of three fatty acids and a molecule of glycerol. I’m going to probably colour-coordinate these, actually and do glycerol (for reasons you’re gonna see) do glyceryl in green.

Three fatty acids and the general arrangement is going to look like, (and this is just a tiny little sketch here): We have glycerol in green. It’s actually joined by an ester bond and I might actually just be a little bit fancy and put…oh no, it’s gonna be too tight if I put my ester bonds in…you’re gonna get it in full detail in just a moment. And then, these are my fatty acids. I’m gonna do this one with a slight kink in it. And again, all will be revealed.

The bonds that join them together here are called ester bonds. So they’re joined by three fatty acids, one for each. This is joined by three ester bonds.

And obviously, they’re made by condensation reaction. It’s the type of reaction, if you ever get asked: What type of reaction is it? It’s either condensation or hydrolysis. Are they doing joining together? In this case, we’re joining the glycerol to three fatty acids. So it’s a condensation reaction. It produces three molecules of water.

And the fatty acids can come in various different forms and they are either called saturated or unsaturated. In fact, I’m going to put all the fatty acids as a key term. I’ve drawn it in blue up here just because I wanted to make it clear on the diagram.

Okay. So again, we’re going to explain what all of these things mean.

Well, let’s draw out this tiny little diagram here in a little bit more detail. So, we have this molecule of glycerol, and we do need to know the atomic structure of these things, which is why I am drawing them out just here. So I’m gonna start off with…it’s got three carbon atoms. (I’m just thinking about my spacing a little bit).

I’m gonna do my carbons a little bit more spaced down. (So I’ve already made a mistake there but I think I can correct it). These are actually…I’m going to make this into an oxygen. These are OHs, but I’m going to do the H, which takes part in this condensation reaction, so I’m going to label them in red. And then the three fatty acids, one for each of these carbon atoms, essentially.

So again, we have…and my fatty acids in blue, so I’m matching my colours up. This is our carboxylic acid group. So it’s a carbon onto a double bond oxygen.

And then I’m going to just represent this by an R Group, which means that this is the bit, the carboxylic acid bit, is the bit that is common to all fatty acids. The R is going to be a hydrocarbon tail. So carbons and hydrogens, and we’re going to look in more detail at saturated and unsaturated in a moment. So, we have glycerol plus three fatty acids produces triglyceride plus three molecules of water because there are three condensation reactions taking place here between these groups.

And so what do we get? Well, the green part of the glycerol isn’t going to change. So, all the hydrocarbons are just carbon and hydrogen…so the only thing we need to worry about with glycerol is just these OH groups, but it’s not going to be an issue, here. I’m just gonna think which ones do I want to represent inside of my bonds. I think I’m gonna do all of my…okay…So the newly formed bond I’m going to highlight. We’ve got the oxygen here, which bonds onto a carbon which is double-bonded to an oxygen and that is our ester bond.

And then we have our R group, which is going to be a hydrocarbon. So this is going to be a carbon atom in reality, but we’re going to call it R because it’s going to change depending on which type of fatty acid it is. Okay. So this is our ester bond. If you’re asked to circle it, it’s important that we include both the carbon that’s double-bonded to the oxygen and the oxygen that’s attached to that. So it’s the carbon and both oxygens.

And I’m just going to label that. I guess I need to draw my H2Os. We’ve got obviously one, two, three and they’re forming three molecules of water up here. This is my ester bond.

Okay, so far so good. Glycerol, three fatty acids. I suppose we can put some little arrows in here…forms a triglyceride and three molecules of water by condensation reaction.

Okay, so what are the functions of these things? Well, why do we bother with triglycerides? Well, they are an energy source for aerobic respiration.

You could say that they are a respiratory substrate, but that’s getting more into the respiration side of things later on the A-level. But yeah, we can break these things down and we can respire them to release energy and make ATP.

They act as thermal insulation. A little bit of fat in winter keeps us a little bit warm. So I’m gonna put, e.g., polar bears have obviously a decent layer of fat to keep them protected from the cold.

We also have electrical insulation. They do not conduct electricity. An example, again we’ll come across this later in the course, is the myelin sheath.

We also have some buoyancy. If I can spell it…U O Y A N C Y…correct me in the comments if my spelling is not correct. Yeah, they’re pretty lenient with spelling unless it can be confused with another key term or it’s not clear what you mean mitosis, meiosis, maltose, maltase, that kind of thing. So if it is similar to another word, be careful that your writing is nice and neat.

So…seals…obviously spend some time floating on the surface and fat helps them to do that. And there’s also some physical protection around organs. So, if you get punched, then you don’t just damage your organs because they’re unprotected. They have a layer of fat around them which helps cushion any blows.

Okay. Well now let’s dive in and look at these little fatty acids a little more that we’ve just signified so far as an R Group. So, they are gonna be a hydrocarbon chain with this carboxylic acid group on the end and a carboxylic acid group is a C double bond O with an OH on the end.

So, let’s look at saturated fatty acids. Saturated means that they are full up and they are full up of hydrogen. They cannot contain another atom of hydrogen no matter what you do to them. So, to be a fatty acid, they need to have the carboxylic acid group. So that’s gonna be our C double bond O and our OH. So this is our carboxylic acid group and now we’ve got just a hydrocarbon chain.

So I’m just going to draw a couple just for demonstration. Let’s draw three carbon atoms. Let’s draw actually a fourth one here. And this one has hydrogens all around it. So this is like our ending carbon.

And you might get question, it’s very rare, that’s like: what’s the generic formula for the structure of this fatty acid: a saturated fatty acid or they give you a random fatty acid. Is it saturated or unsaturated? Well, we can just look at…the end here is slightly different. We’ve got a carbon with three hydrogens on it. And we’ve got the carbon with the C double OH on it and all the other carbons in between are saturated, which means they have single carbon, carbon bonds and all the other bonds are hydrogen.

So, if we were looking at the generic formula, we can sort of treat this end piece as CH3. We can look at the carboxylic acid group on the end and then we can look at everything in the middle of it…it depends on how many carbon atoms are in the middle. But there’s two hydrogen atoms for every carbon atom that’s not included on either end that might seem a little bit complicated, but it really isn’t too bad.

Okay, I think I’m gonna draw my unsaturated so we can compare it for differences.

Obviously, this chain of carbon atoms could be a lot longer…could be a hundred carbon atoms in that hydrocarbon. I’m only drawing a few just for convenience sake. So, again, to be a fatty acid, It must have this carboxylic acid group on the end. So that is a given. And now we’re going to draw a couple of carbon atoms. These ones are going to have hydrogens on either side. Each carbon atom can make four, these are covalent bonds. So you can see this one has got one two, three, four. Now, this one is going to double bond onto the next carbon and this actually happens at a bit of an angle. So, I haven’t drawn that particularly well, but if you imagine that just sloping down a little bit down here.

Now this carbon has got one, two, three. It’s already got three so it can’t do a hydrogen on either side. So, it can only do one more hydrogen here and same with this one. These bonds are shared. So this is one, two, it’s gonna make a carbon down here…this one is straight. This is where the kink is supposed to be, and again, we can only add one more because I’ve got one, two, three, four carbon atoms there and let’s say that this is our last one so it’s just got hydrogens on all sides. Okay.

Let’s label a few things here. So this is our carboxylic acid group. You can call it a carboxyl group/ carboxylic acid. It’s an acid because it can dissociate some of its hydrogen, but that’s more chemistry than biology, so let’s not get too involved in that.

And every fatty acid is going to have one of those. The length of the carbon atom chain is gonna vary. Let’s put a little bit of notes down around our saturated fatty acid. So it does not have carbon-carbon double bonds. Do NOT have…you could say double bonds between carbon atoms or you can call it a carbon-carbon double bond. So if we were drawing that it would look something like this: carbon double bonded onto carbon. It doesn’t have any of those. Every one of these bonds is a single which means you can’t fit any more hydrogen in.

If we were to break this double bond, we could add a hydrogen here. We can add a hydrogen here and hence this one being unsaturated with hydrogen.

They basically cause an increase in cholesterol and low-density lipoproteins, so they’re not ideal for our health.

What are lipoproteins? Well, sometimes these are called LDLs…Basically lipids are insoluble. Triglycerides are lipids and they’re not soluble in water or the blood. So in order to transport them, fatty acids and triglycerides are transported by these lipoproteins. We bind them onto a protein and then we can sort of move them around a little bit more straightforwardly.

Alright, then unsaturated. What have we got down here. Well, they DO have carbon-carbon double bonds. Which obviously we are representing, here. They contain less hydrogen than saturated fatty acids.

If it were to have more than one carbon-carbon double bond, let’s say there was a carbon-carbon double bond here and here, we would call it a poly unsaturated. Obviously, this would be a mono unsaturated and it could be a polyunsaturated. It’s basically never examined, but it’s good to just be familiar with some of that language.

Also, we might get…if when we do get the double bonds…the double bonds have a kink because the bonding angle isn’t straight. I’m going to say they are kinked at each double bond. It’s a bit lazy just to call it a double bond because obviously we’re specifically referring to the double bond between carbon atoms. Not to, for example, this double one between the carbon and the oxygen over here in the carboxylic acid group, because every fatty acid has those as well. So really you should refer to it as carbon-carbon double bond or a double bond between carbon atoms and this gives us our little kink which is why these carbon atoms are off at an angle, and these ones are in a straight line.