Review 1: Nucleic Acids, Lipids, & Membranes
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Let's turn our attention toe lipids as we transition to talking about the membrane. Now many lipids and biological systems contain fatty acids and fatty acids, just like nucleotides have a sort of unique naming and numbering convention. And if we take a look at this example here of CIS Oleic acid, Cecil ache acid being the common name of this molecule, this molecules formal name would be one and then in parentheses. Delta with a superscript nine. Um, and the reason for these numbers are 18 which is the number of carbons in the chain. One the number of double bonds, and you put a colon between those two and then in parentheses. Delta and nine represents the number of the carbon participating in the double bonds. So if you look at our chain here, carbon number nine is where the double bond starts. So again, this molecules formal name would be 18 1 Delta nine, and then it would be Octa decade groups, actor mhm decking awake acid and the OIC Acid, of course, is because of the car box will group right there. So let's take a look at this other molecule, which has the common name EPA. That's sort of generically how it's referred to. And let's think about what numbers we would put in here. So why don't you take a minute, maybe pause the video and try to figure this out yourself and I'm going thio. Explain how we would number this So if you count out our chain or simply look at the numbers provided you see that it's carbons long and it contains 123 for five double bonds, so this would be 20 colon five and then in parentheses. Delta 58 11 17 So five, eight, 11 14 and 17. So this is on Lee one way of naming and numbering fatty acids. You might also notice that in red we have the letter of the Greek letter Omega and numbers starting at the end of the chain. And this is actually referring to a sort of different naming numbering convention for fatty acids, which is, uh, mostly used by nutritionists and biologists. Not so much biochemists, and that is the omega system of naming and numbering fatty acids. So you might see that counting backwards, we have a double bond starting at Carbon three and also one at carbon six. And you may have heard, um, you know, sort of in the media people talking about omega three and omega six fatty acids And these are fatty acids that actually have to be acquired through your diet and are essential for us. Um, and we have to acquire them through a diet because we actually can't synthesize fatty acids that air this long. Uh, anyhow, um, looking at this molecule you have here, you can see that this is an omega three fatty acid because it has this omega three double bond. If it didn't have that, and it just had if it just had this omega six double bond, we would call this an omega six fatty acid. And, you know, generally speaking, omega three fatty acids you tend thio acquire from vegetables and nuts and fish, and omega six is tend to come more from animal products specifically like red meat type products. So beef, butter, milk, that sort of stuff. So you don't need thio necessarily. Um, you know, memorize thes molecules, but you do need to understand how the numbering convention works for fatty acids and also you need to understand how the Omega numbering convention works. Moving on naturally occurring fatty acids are, um, that air unsaturated are always cysts. And unsaturated, of course, refers to the degree of unsaturated or, basically, how maney double bonds or present in the hydrocarbon. So whenever you have naturally occurring unsaturated fatty acids, the double bond is always in the CIS form, like we saw above with, um, with sis Oleic acid and, of course, with EPA. No, in terms of properties of fatty acids. As the chain length increases, the melting point also increases. So you can kind of think of this as a result of Vander Waals interactions with longer the chain. The stronger the vander Waals interactions, meaning the stronger the inner molecular forces between the molecules, meaning the higher the melting point. Um additionally, the longer the chain on the fatty acid with less soluble that fatty acid is so smaller chain fatty acids tend to be far more soluble than longer chain fatty acids, so longer chain fatty acids, um, are conversely less soluble in water. Unsaturated actually greatly reduces the melting point fatty acids, so even having just one double bond present in your fatty acid will uh, plummet the melting point of the molecule. And uhh! This does come with a caveat. And that caveat Is that trans Fats, Right? So we were saying that unsaturated in is always assist in naturally occurring fatty acids, but you can have fatty acids that have, um, trans bonds in them. And those air the so called trans fats that everyone is really worried about and doesn't want to eat and transfats actually have higher melting points. And this is because even though they're unsaturated despite unsaturated in, they're trans double bonds are linear. So if we were thio, look at a, uh, chain with the CIS bond right there. That sys bond creates a kink in the chain like you see up here in Oleic acid. It actually makes the chain kinked, whereas trans fats still actually have a straight chain form, even though they have a double bond in it. And that means that trans fats can actually fit together more tightly, or those trans fatty acids can fit together more tightly, whereas thesis fatty acids aren't going to be able to fit together as tightly so again, that's going to increase the strength of the Inter molecular forces because they're going to be closer. Those die polls will be closer together, so trans fatty acids will actually have higher melting points despite being unsaturated now, Usually they are the simplest form of a fat molecule that will see in biology that uses a fatty acid, Artress legless roles. And these air basically storage lipids. They store energy for later use in the body, generally long term energy storage. And they're made from glycerol, a glycerol backbone combined with three fatty acids that are attached by Esther Bonds. So here is your lists are all backbone and in red I'm gonna mark those s Oops. Here we go. Read. I'm gonna mark those Ester bonds, right. There's the ester bonds between the fatty acids and the glycerol ALS. And what's important to note is, if Onley one chain is unsaturated, it's always on carbon. Two of the glycerol. So here we have carbons 12 and three. So if there's Onley one unsaturated fatty acid, it's always gonna be the middle one. Basically, it's always going to be on carbon, too. If you have more than one unsaturated fatty acid in your tricycle cholesterol, um, you'll have you know you'll have one in the two position and then one either in the one or three position, and it's less strict there. So just remember, if Onley one chain is unsaturated, it's always gonna be on carbon, too. And also notice right here that on carbon three we have on omega three fatty acid, right? All right with that, let's flip the page.