Fatty Acids - Online Tutor, Practice Problems & Exam Prep

Fatty acids are amphipathic molecules with a hydrophobic hydrocarbon tail and a hydrophilic carboxylic acid head. They can be saturated, containing only single bonds, or unsaturated, featuring at least one double bond. Unsaturated fatty acids are classified as omega-3 or omega-6 based on the position of the first double bond from the methyl end. Shorthand notation for fatty acids indicates the number of carbons and double bonds, aiding in their identification. Common fatty acids include lauric, myristic, palmitic, stearic, and arachidonic acids, essential for understanding lipid structures.

Fatty Acids Concept 1

When it comes to fatty acids, we're going to say that most fatty acids contain an even number of carbons, typically 12 to 26, with a generic or general formula of C3C2NCOOH. N can vary based on the length of the fatty acid chain. Now, we're going to also say that fatty acids are amphipathic molecules, meaning they have both non-polar and polar parts. We're going to say that this depiction, this image on the right represents a fatty acid. The fatty acid itself has a hydrophobic tail, and that's because the tail is made up of only hydrocarbons, only carbons and hydrogens making it non-polar. And because it's non-polar, it's hydrophobic. We're going to say the carboxylic acid has a hydrophilic head. Hydrophilic means water-loving. And why is that? Because the carboxylic acid head is polar.

If we take a look here at this image, based on the length of the fatty acid chain, we're going to say this represents Lauric acid. Remember that the hydrocarbon tail would be hydrophobic, and then the carboxylic acid head would be hydrophilic. We say that typically our fatty acids are between 12 and 26 carbons. Only one of these carbons is part of a polar part. The rest of the tail is non-polar. So we're going to say here, the larger the hydrocarbon tail, the more non-polar the fatty acid. Therefore, overall fatty acids are non-polar. So just remember when looking at a fatty acid, we have two parts to it: the hydrophobic hydrocarbon tail and the hydrophilic carboxylic acid head.

Fatty Acids Example 1

Which of the following statements about fatty acid structure is correct? A. Carboxylic acid group of the fatty acid is polar. Well, that's true, it's hydrophilic and does not interact with aqueous environments. This part is false. Because the head is polar, it should interact with aqueous environments, meaning water. Fatty acids contain a nonpolar head with a polar tail. Now here's the opposite. They have a polar head and a nonpolar tail. Fatty acids are amphoteric. Remember, amphoteric means that it can exist as an acid or a base. It's not amphoteric; it's amphipathic, meaning it has a polar and a nonpolar section. Fatty acids consist of a hydrophilic head, true, and a hydrophobic tail, that's also true. So here, the only statement that's correct would be option D.

Which of the following fatty acids would you expect to be more soluble in cyclohexane?

• A. Palmitic acid (16 Cs)
• B. Stearic acid (18 Cs)
• C. Lauric acid (12 Cs)
• D. none of the above

Fatty Acids Concept 2

So in this video, we're going to learn the distinction between a saturated versus an unsaturated fatty acid. Now, when we say saturated, these are the fatty acids that contain only carbons single bonded to carbons. When we say unsaturated, these are the fatty acids containing at least one carbon double bonded to a carbon. So again, saturated, they're all single bonded to one another. In an unsaturated, there are at least two carbons double bonded to each other. Now, mono- and poly- prefixes indicate one and multiple double bonds respectively. Mono- meaning one, poly- meaning many. We're going to say here, naturally occurring fatty acids contain what we call cis double bonds. Remember, cis means same side. This is different from trans which means opposite side. If we take a look here, we have a saturated fatty acid in the form of lauric acid. Here, it's this portion that we're looking at in terms of saturation. It's just a bunch of carbons single bonded to each other, and that's why it is a saturated fatty acid. Below it, we have Oleic Acid and Linoleic Acid. Linoleic Acid, an unsaturated fatty acid. And we're going to say here that linoleic acid, it has two double bonds so it would be polyunsaturated. Also remember, if we look at the double bond, we would say that this bond points down, this bond points down, they're on the same side pointing the same direction that's why it's cis. Same with this one. Here goes our double bond here, double bond here, and the bonds coming off are pointing in the same direction down. These would be two cis bonds. Okay. So that's what we mean by cis in nature. Right? So remember, when we say saturated that means that the hydrocarbon tail, the non-polar portion has no double bonds. It's all single bonded carbons to one another. If it is unsaturated, there's at least one double bond somewhere on this hydrocarbon tail, where two carbons are double bonded to each other. Alright. So just keep that in mind.

Fatty Acids Example 2

In this example, it says, classify each fatty acid as saturated with an "S", monounsaturated with "mono", or polyunsaturated with "poly". So in the first one, we can definitely say that this is an unsaturated fatty acid because of the presence of our double bonds or pi bonds. We would say that there are 1, 2, 3, 4 of these double bonds or pi bonds. That would mean that this is a polyunsaturated fatty acid. For the next one, the same thing again. We have 1, 2, 3 double bonds this time. Again, these are sites of unsaturation. Since there's more than 1, this would be a polyunsaturated fatty acid. And then finally, for the last one, we look at the hydrocarbon tail. There are no double bonds that we can see, no pi bonds. Therefore, this would be a saturated fatty acid. Okay. So here we just put "S". So this is how we classify each of the 3 fatty acids that we see within a given example question.

Fatty Acids Concept 3

In this video, we're going to take a look at omega fatty acids. Now remember, we have alpha, which means beginning, and omega, which means the end. So, omega must have something to do with the end of our fatty acid chain. Here we're going to say, unsaturated fatty acids can be classified by the first double bond, numbering from our methyl carbon. The methyl carbon is the end carbon of my fatty acid chain, and therefore, it represents my omega carbon. If we take a look here, it says we have an omega-3 fatty acid. That means the first double bond is located at the 3^rd carbon. If this is our methyl group right here, so this is our omega carbon. And we're going to say we count 1, 2, 3 to get to the double bond. So carbon number 3 is where we get to our double bond. That's why this is an omega-3 fatty acid.

In an omega-6 fatty acid, the first double bonded carbon is located at the 6^th position. Here we're going to say, here is our omega again, this methyl group right here, and just count to see how long it takes you to get to the double bond. We go 1, 2, 3, 4, 5, 6. We had to count to 6 to get to that double bond. That's why this is an omega-6 fatty acid.

So, again, just remember, when we talk about omega fatty acids, they can be omega-3 or omega-6. And here, we look at the methyl group at the end of the fatty acid chain, and count to see how far it takes us, how long it takes us to get to the double bond. Does it take us to the count of 3, making it an omega-3 fatty acid, or do we have to count to 6 to make it an omega-6 fatty acid?

Fatty Acids Example 3

In this example, it says, "Label the following unsaturated fatty acids based on Omega classification." So, with Omega, we're looking at the methyl group in each one, and all we have to do is count to see how long it takes us to get to the double bond.

So for A, we count 1, 2, 3, 4, 5, 6. We had to get to the 6th carbon to get to our double bond, making this an Omega 6 Fatty Acid. For the next one, let's count. Here's 1, 2, 3, 4, 5, 6, 7, 8, 9. In this one, we have a new type of omega that we haven't seen yet. This is an Omega 9 fatty acid, but the process is still the same. The omega carbon is the methyl carbon, the carbon at the end. Count from the omega carbon to the double bond, seeing how long it takes us to get there, what carbon do we land on. That tells us the type of omega classification. So, for option A, we have an Omega 6 fatty acid, and then for option B, we have an Omega 9 fatty acid.

Fatty Acids Concept 4

In this video, we're going to take a look at fatty acid shorthand notations. Now we're going to say fatty acids are assigned shorthand notations for easy naming. Here, this is based on the number of carbons followed by the number of double bonds, separated by a colon. If we take a look at the top fatty acid, in blue, this would be the number of carbons total for the fatty acid. Remember, this is a carbon, part of the carboxylic acid group. So, we go 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. We have 12 total carbons, so this will be 12. And then we have a colon, we have no double bonds at all, so this would be 0. So, the shorthand notation for this fatty acid would be 12:0. For the next one, the total number of carbons is what? 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 total carbons. So, this will be 16, and then we have one double bond involved, so this would be :1. So, this would be 16:1 as the shorthand notation for this particular unsaturated fatty acid.

Fatty Acids Example 4

Here in this example it says, "Provide a shorthand notation for the following fatty acid below." Alright, so remember our shorthand notation for fatty acid is based on: 1, the number of carbons the fatty acid possesses, followed by a colon, and then the number of double bonds the fatty acid possesses. So, if we take a look here, we're going to see how many carbons this possesses? It possesses 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 total carbons. So we'd have 18, colon, and then followed by the number of double bonds that it possesses. It possesses 1, 2. Remember, it's carbon-carbon double bonds that it possesses. It possesses 2 of them, so this would be 2. So the shorthand notation of this particular unsaturated fatty acid would be 18 followed by a colon followed by the number 2. Alright, so this would be our final answer.

Fatty Acids Concept 5

When it comes to remembering fatty acids, we're going to say that to be able to draw more complex lipids, we first need to memorize structures of the common fatty acids. And we're going to say here that we have a list of some common fatty acids from 12 carbons all the way up to 20. So we have 12, 14, 16, 18, and 20. We have lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid. Now, how exactly will I remember these different types of common fatty acids? Well, first, remember we're starting out with the number 12. We're going up 2 at a time till we get to 20. These are our common types of saturated fatty acids. None of them have double bonds. And what we can do here is our memory tool number 1. This will help us to remember the order of these different types of common saturated fatty acids. And here, the memory tool is that "Lori's Mystic Palace Stores Art." Here, looking at the first letter of this memory tool will help us to remember the names of these different types of saturated fatty acids. Alright, so "Laurie's" is lauric acid, "Mystic," we're going to say, is myristic acid, "Palace" is palmitic acid, "Stores" is stearic acid, and then "Art" is arachidic acid. Right? So just keep this memory tool in mind when we're trying to remember the common types of fatty acids starting out with 12 carbons all the way up to 20.

Fatty Acids Example 5

This example question says, without looking at the table above, identify the number of carbons present in each saturated fatty acid. So remember, our memory tool one says that "Lori's Mystic Palace stores art." So here, L M P S, and A. And when it comes to these common fatty acids, they start out with 12 carbons, and they go to 20. So we have 12 carbons for Lorie's, then 14 for Mystic, 16 for Palace, 18 for Stearic, and then 20 for Arachidic. Here, the first letter in this memory tool is connected to the first letter of these different types of fatty acids. So Lauric is with Lauric acid, which has 12 carbons. We already know that after this is 12:0 because it has no double bonds, we don't care about the number of double bonds. We want the number of total carbons. Next, Mystic M here, Myristic, so this is 14. Palace is for Palmitic, so that's 16. S is for Stearic, that'd be 18 and then 20 for Arachidic Acid, A for Art. So this is the number of total carbons we have for each of these saturated fatty acids based on our memory tool 1. So remember, keep it around to help you start out figuring out how many carbons and double bonds we have for each one of these saturated fatty acids.

Provide a condensed structural formula for a fatty acid with 18 carbons (18:0) and give its common name.

• A. Storic acid
• B. Palmitic acid
• C. Stearic acid
• D. Palmitoleic acid

Fatty Acids Concept 6

In this video, we'll take a look at some of the most common types of unsaturated fatty acids and memorize them using our memory tool number 2. So here, our memory tool number 2 says that, 16 palms occupy lovely lush 20 acres. So, 16 palms. Our first unsaturated fatty acid here has 16 carbons, and it has one double bond. So here this is palmitoleic acid, and then here we have oleic acid, here this would be 18, we see it has only 1 double bond.

Next, we have Linoleic acid which is still 18 carbons, but 2 double bonds, so 2. Then we have linoleic acid, these 2 are so close together. Alright. So here, we're going to have 18 and then 3. Next, we have arachidonic acid, which is 20 because of 20 acres. Then we see that it has 4 double bonds, so this is 4.

Now, a couple of things to note in terms of these double bonds. The ones in purple, the first four, the double bonds start at Carbon 9 from the carbonyl group. Alright. So we count to see how far they are to see where it starts. Alright. So if we looked, look at any of them. 1, 2, 3, 4, 5, 6, 7, 8, 9. They all start 9 carbons on carbon number 9. Now here for Arachidonic Acid, it's the 5th acid, and the double bond starts at carbon number 5 from the carbonyl carbon. Right? So we have 1, 2, 3, 4, and 5. Carbon 5, 5th carbon in this group of common unsaturated fatty acids. Alright. So, just remember, utilize memory tool 2 to help you memorize some of these common unsaturated fatty acids.

Fatty Acids Example 6

In this example, it says, provide shorthand notations for each fatty acid. These represent our unsaturated fatty acids. Our memory tool number 2 tells us that 16 palms occupy lovely lush 20 acres. So here if we take a look, we have p, o, l, and l, and a. Alright. So if we take a look here, for palms, we're dealing with Palmitoleic acid, which would be 16:1. Here we have occupy which is Oleic acid, we go up by 2 and stay the same in terms of the number of Pi bonds, so still 1. Then here, these three here represent 18 carbons, and the number of Pi bonds increases. So, 18:1, then 18:2, then 18:3. This is Linoleic acid. This is Linolenic acid. And then we have 20 acres which is Arachidonic acid. Here we go up by 2 again, so 20:4. Alright. So we can see that we have 16, then these three stay at 18, and it's the number of Pi bonds that's increasing. Then we go up to 20 here and still, the number of pi bonds increases by just one more to 20:4. Alright. So here if we take a look, Linoleic acid is lovely, so this would be 18:2. Occupy is Oleic acid, so this would be 18:1. Arachidonic Acid is 20 acres, so that would be 20:4. And then Linolenic acid is lush, so that's 18:3. So this would be the shorthand notation for each of these unsaturated fatty acids.

Provide a skeletal structure for Linolenic acid.

• A.
• B.
• C.
• D.

Here’s what students ask on this topic:

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids contain only single bonds between carbon atoms, making their hydrocarbon tails straight and allowing them to pack closely together. This results in a solid state at room temperature. Unsaturated fatty acids have at least one double bond between carbon atoms, causing a kink in the hydrocarbon tail. This kink prevents tight packing, making these fatty acids liquid at room temperature. The double bonds in unsaturated fatty acids can be in the cis or trans configuration, with cis being more common in nature. Cis double bonds create a more pronounced bend in the fatty acid chain, further preventing tight packing.

What are omega-3 and omega-6 fatty acids?

Omega-3 and omega-6 fatty acids are types of polyunsaturated fatty acids classified based on the position of the first double bond from the methyl end (omega end) of the fatty acid chain. In omega-3 fatty acids, the first double bond is at the third carbon atom from the methyl end. In omega-6 fatty acids, the first double bond is at the sixth carbon atom from the methyl end. These fatty acids are essential for human health, playing crucial roles in cell membrane structure and function, and must be obtained through the diet as the body cannot synthesize them.

How are fatty acids named using shorthand notation?

Fatty acids are named using shorthand notation that indicates the number of carbon atoms and the number of double bonds in the molecule. This is written as C:D, where C is the total number of carbon atoms and D is the number of double bonds. For example, a fatty acid with 16 carbon atoms and one double bond is written as 16:1. This notation helps quickly identify the structure of the fatty acid without needing to draw it out fully.

What are some common types of fatty acids and how can they be memorized?

Common types of fatty acids include lauric acid (12 carbons), myristic acid (14 carbons), palmitic acid (16 carbons), stearic acid (18 carbons), and arachidic acid (20 carbons). A useful mnemonic to remember these is 'Lori's Mystic Palace Stores Art,' where each word's first letter corresponds to the fatty acid's name. For unsaturated fatty acids, another mnemonic is '16 Palms Occupy Lovely Lush 20 Acres,' representing palmitoleic acid (16:1), oleic acid (18:1), linoleic acid (18:2), linolenic acid (18:3), and arachidonic acid (20:4).

What does it mean for a fatty acid to be amphipathic?

A fatty acid is amphipathic because it has both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts. The hydrophobic part is the long hydrocarbon tail, which is nonpolar and does not interact well with water. The hydrophilic part is the carboxylic acid head, which is polar and can form hydrogen bonds with water. This dual nature allows fatty acids to play a crucial role in forming cell membranes, where they arrange themselves into bilayers with hydrophobic tails facing inward and hydrophilic heads facing outward.