Okay, so we're going to talk about our next macromolecule or macromolecules, lipids and nucleic acids. So starting with lipids, these are hydrophobic molecules. And how do we know that? Is because there are non-polar covalent bonds because they're hydrocarbon chains.
You can see this squiggly line down here. Remember those are just carbons at all of those points and the hydrogens are... filled in. So we know that those are non-polar and will not want to interact with water.
They are fearful, hydrophobic of water. And this is due to the fact that they want to aggregate and send water off on its side. That's why oil and water separate.
Lipids are not categorized as polymers because they're not covalent bonds. The interactions that are happening between them are non-covalent, and they are the van der Waals interactions, which are very similar to the hydrophobic interaction. So they're just sticking together to stay away from water, because water is polar, water has the charge, whereas our non-polar molecules do not, so they want to move away.
There are many different types of lipids in our body and they all have different functions because they have different structures. So things like fats and oils, we can use those actually for energy in our body. Phospholipids are structurally oriented in our body, creating our plasma membrane or our lipid bilayer. We also have carotenoids and chlorophylls found in plants that are going to help.
absorb the light so that we can go through photosynthesis. Steroids, you might have heard of steroids before, but what those are, they're hormones that signal through our body different responses to our environment. Furthermore, vitamins play an essential role in how our body metabolizes our food sources.
Around all of our nerves, we have a fat layer. called myelin, and also on our skin, which helps it be hydrophobic and repel water. So in our body, fats are stored as triglycerides.
So what this is, is three fats that are attached to what's called a glycerol model. And we're going to look at that. They're very hydrophobic because of the non-polarity in those fatty acid tails. There is a little polarity, but very, very little.
And where we see the polarity is when we're looking at the carboxylic acid group that's on the end of the fatty acid tail. But if you're thinking fatty acids, you should automatically put it in a non-polar hydrophobic. that glycerol is going to attach those three fatty acids.
So specifically, this image is going to show the condensation reaction. So here's our glycerol backbone, which have each of these oxygen, which are called hydroxyl groups on it. You can see our fatty acid tail that's primarily just...
carbons and hydrogens. At the end have a carboxylic acid on it and this carboxylic acid and this hydroxyl group is going to have water leave. If water leaves the reaction, we're going through a condensation reaction creating a larger molecule and in this case it's a triglyceride.
In your body these are how our fatty acids are transported through our bloodstream. They're packed into other proteins and delivered as triglycerides. So the length can vary.
There isn't always 16 carbons. It's a very common number, but there can be medium chain and short chain fatty acids as well. There's a difference between saturated fatty acids.
You might have heard of that before if you look on a food label. They will always label how much saturated fatty acids versus unsaturated fatty acids there are in a food source. What that's saying is what is saturated with hydrogen specific. So fatty acids that are fully saturated with all the hydrogens, there are no double bonds and they're only hydrogens. They are going to pack closely together.
and potentially are going to be harder to be separated because we're increasing the amount of those hydrophobic non-covalent interactions. So unsaturated fatty acids, what they are, they are the same fatty acid chain, except this time we have double bonds. We could have more than one double bond. This will cause kinks in the chain. which won't allow it to pack closely together and be held together by those non-covalent interactions.
Let's look at the examples for this. So saturated fatty acids, you can see here that all the carbons have their four valence shells filled either by bonding to another carbon and then two hydrogens. So this is a saturated fatty acid. where all of the carbons are bound just to one or two other carbons and then bonded to hydrogens in the person.
This causes tight packing, so those carbons can get really close together, increasing those non-covalent interactions. And this is why things like butter are hard and solid at room temperature, is because they are packed. together, creating a lot of those interactions.
So there's a lot more strength holding those together. Unsaturated fatty acids, you can see that we have double bonds, and then we're not fully saturated with hydrogen. So all of our valence shells are still fulfilled for these carbons as we have one, two, three, and four, but it is a double bond being held together so those electrons are being shared so there's two pairs of electrons being shared between these carbon carbon this causes a kink and these kinks prevent them from tightly packing and that's why it's found as an oil in at room temperature so these double bonds create more fluidity and therefore an oil at room temperature.
Another example of a lipid is a phospholipid. So phospholipids, if you break that down, what does phospho sound like? Hopefully you think phosphate.
So it is the same kind of setup where we have glycerol as a backbone, holding these fatty acid chains. but it's also attached to a phosphate. And that phosphate, you'll notice, has a lot of oxygens associated with it. And whenever we see oxygens, we want to think polar covalent bonds.
And polar covalent bonds have molecular dipoles that are going to allow it to be hydrophilic. So our phosphate is hydrophilic. where our fatty acid tails are hydrophobic.
This is called an anthropathic molecule because we have two different ends that are going to be hydrophobic and hydrophobic. So what this does is it creates things like a lipid bilayer. Phospholipids are what make up the mass majority of our lipid bilayer.
And so the hydrophilic end will be towards the aqueous solution. And so the aqueous solutions are extracellular as well as intracellular. And all the fatty acid tails that are hydrophobic are going to stick together and be in the center of that bilayer. That's why it's called a bilayer is because we have two different layers of phospholipids. Another category of lipids are steroids.
Remember that these are just carbons. It's just simplifying the drawing. So most of this molecule, this steroid cholesterol, are carbons and hydrogens. We do have one little hydroxyl group over here.
So it is categorized as amphipathic because this is hydrophilic and this is hydrophobic. But the mass majority of this molecule is hydrophobic. And so steroids, cholesterol is what forms most of the hormones in our body. It's just the starting point. Cholesterol is also really important for our lipid bilayer, as you'll learn in future lectures.
So we also have vitamins in our body and vitamins such as vitamin A. can be hydrophobic as it is categorized then as a lipid because it's primarily carbons and hydrogens. So cholesterol here you see is the starting point and we can make things like progesterone in our body by using different enzymes to add different functional groups. You might have heard of cortisol before.
cortisol is elevated under stressful conditions, as well as testosterone and estrogen. So all of these are derived from a lipid called cholesterol. So hopefully you'll take a second and go through these questions just to catch up on the content, but I'm going to move on to nucleic acids. So nucleic acids, what they are, are the foundation of what we call the central dogma. The central dogma is when we have DNA, right?
That's the blueprint for our genes and our phenotype. So the DNA can go through two different paths. If it's within one cell, then we want to go through my time.
and make a copy of it, we can go through DNA replication. So that's going to be happening within the nucleus, and then we're going to separate and create our own individual cell. DNA then also can be transcribed.
Transcribed happens first to form RNA. RNA is also categorized as a nucleic acid. It's just a ribonucleic acid. And we'll talk about specifically why it's called. So our RNA is sent out from the nucleus where the DNA is found into the cytosol.
And then it is translated because that happens later at the ribosome to make a polypeptide. And these polypeptides are what... fold into our proteins. So here's the nuts and the bolts of nucleic acids. So you can see that we have many different components and there are three parts to a nucleotide.
So the three different parts are, let's start with the easy one, phosphate. So we always have a phosphate group attached. The next planet is a sugar. So this is a one, two, three, four, five carbon sugar. Therefore, we categorize that as a pentose.
And specifically, its name is ribose in this case. And ribose on the second carbon has a hydroxyl group present. Deoxyribose, which is found in DNA. does not have that hydroxyl group on the second carbon. Everything else is the same, but we are missing deoxy.
So we are removing the oxy from ribose for deoxyribose. So that's what we find on DNA. Then we have a base.
That's the third component, phosphate, pentose sugar, and then a base. These bases are primarily the same between DNA and RNA, except for one exception. So we have cytosine. Cytosine and thiamine are categorized as a pyrimidine.
They're only one single ring structure. You don't need to worry about memorizing these specific atoms that are present. But what you should recognize is that there's only one ring in cytosine and thiamine versus the purines have a double ring structure. So the double ring structures are categorized as purines. A good way to remember this is that pure agony of remembering these.
So the purines, so pure, and then A, G are agony. So these are the double ring structures. So the difference between DNA and RNA is that thiamine is found in DNA. whereas your cell is found in this.
So this is one area that we can say that they all come together and they form the phosphate, the ribose, and the base. So RNA, another difference between DNA and RNA is that it's single-stranded. You can see that we have just one group of new ribonucleotides that are covalently bonded. These covalent bonds are called phospho because there's a phosphate, di, which is two, and then that ester is referring to those oxygens. So the phosphodiester is the covalent bond that's holding together the individual monomers, the ribonucleotides of the polymer.
RNN. It's also very directional in this case, where we have what's called the five prime end because of the fifth carbon being down here on the bottom. The three prime end is up at the top because we have the third carbon being present. So five prime, three prime.
So DNA now has that double stranded DNA. So we are having a phosphodiester bond that's still holding together one whole side of these polymers. So the nucleotides are coming together as monomers and then being held together by the covalent bond of phosphodiester to create the polymer of DNA. But... we are going to make it double stranded.
And how it's held together is specifically through hydrogen bonds. These hydrogen bonds are formed between the bases of one purine and one pyrimidine. So you can see here that we have a purine that's based paired with a pyrimidine.
The hydrogen bond remember are two electronegative atoms like oxygen and nitrogen with a hydrogen bond in between. Only one of them is covalently bonded. The other is the hydrogen.
Depending on which purine and pyrimidine are base paired, there is a varying number of hydrogen bonds. So the guanine and cytosine are always going to have three hydrogen bonds versus the purine having two. This is going to result in a strength difference. The more bonds or interactions that you have, the more strength holding these guanine and cytosine together versus the A's and the T's, the adenine and the thi-. So notice too that we have the uracil on the RNA, thiamine is found on the DNA.
So that's another way you can tell a difference between DNA and RNA, including double-stranded versus single-stranded, and then the sugar. So noticing that if the sugar is the ribose or the deoxyribose, they have different roles and they have different functions. Okay.
With that, that is nucleic acids and lipids. Please let me know if you have any questions. questions. Thank you.