Fatty Acids - Online Tutor, Practice Problems & Exam Prep

Fatty acids typically have an even number of carbons (12-26) and follow the formula CH₃CH₂NCOOH, exhibiting amphipathic properties with a hydrophobic tail and a hydrophilic head. Saturated fatty acids contain only single carbon bonds, while unsaturated ones have at least one pi bond, categorized as mono- or polyunsaturated. 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 CH3CH2nCOOH. 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 nonpolar 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 nonpolar. And because it's nonpolar, 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 to 26 carbons. Only one of these carbons is part of a polar part. The rest of the tail is nonpolar.

So we're going to say here, the larger the hydrocarbon tail then the more nonpolar the fatty acid. Therefore, overall fatty acids are nonpolar. 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 react 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 is 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

In this video, we're going to take a look at saturated versus unsaturated fatty acids. Now, when we say saturated, we're saying that the fatty acids contain only carbon single bonded carbon bonds. And, when we say unsaturated, that means the fatty acids contain at least a pi bond. Meaning that there's going to be 2 carbons, at least 2 carbons with a pi bond between them. Now, here when we use the terms Mono and Poly prefixes, they indicate 1 and multiple double bonds respectively. And we're going to say here when it comes to these fatty acids in terms of nature, we're going to say naturally occurring fatty acids contain a cis configuration. And remember, another way we can look at cis is the z configuration. Here, if we take a look, we have saturated versus unsaturated within this image. In a saturated fatty acid, here we have lauric acid as our example. It is basically a chain here with no pi bonds anywhere with a fatty acid at the end. When we go into the realms of unsaturated, in the first one we have oleic acid. Oleic acid possesses 1 pi bond. Therefore, we'd say that it is a monounsaturated fatty acid. Then we have Linoleic acid. This one possesses 2 pi bonds. Because it possesses more than 1 pi bonds, we'd say that it is a polyunsaturated fatty acid. And if you look at both of our unsaturated fatty acids, you would see that the configuration would be z or cis around that pi bond. So just remember these are naturally occurring fatty acids. Later on, we'll talk about how a trans or e configuration could occur, but for right now, just realize that naturally occurring fatty acids tend to adopt a cis or a z configuration.

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, 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". This is how we classify each of the 3 fatty acids that we see within the given example question.

Fatty Acids Concept 3

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 16:1 as the shorthand notation for this particular unsaturated fatty acid.

Fatty Acids Example 3

Here in this example, it says, "Provide a shorthand notation for the following fatty acid below." Alright, so remember our shorthand notation for fatty acids is based on first, 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 4

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 until we get to 20. These are our common types of saturated fatty acids. None of them have pi 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 4

This example question asks, "Without looking at the table above, identify the number of carbons present in each saturated fatty acid." Remember, our memory tool one says that Lori's Mystic Palace stores art. So here, L M P S A. When it comes to these common fatty acids, they start out with 12 carbons and go up to 20. We have 12 carbons for Lori's, then 14 for Mystic, 16 for Palace, 18 for Stearic, and then 20 for Arachidic Acid, A is for Art. Here, the first letter in this memory tool is connected to the first letter of these different types of fatty acids. Lauric acid has 12 carbons. We already know this as 12:0 because it has no double bonds. We do not 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, which is 16. S is for Stearic, that'd be 18, and then 20 for Arachidic Acid. 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 each of these saturated fatty acids has.

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 5

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 pi bonds. 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. 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 at 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 5

In this example, it states, "provide shorthand notations for each fatty acid." These here 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, l, and a. Alright. So, taking a closer look, for "palms", we're referring to palmitoleic acid, which is represented as 16:1. Here we have "occupy", which is Oleic acid, where we increase the length by 2 carbons and maintain the same number of Pi Bonds, resulting in 18:1. Then here, these three are all 18 carbons, but the number of Pi Bonds increases: first 18:1, then 18:2, and then 18:3. This latter sequence includes Linoleic acid and Linolenic acid. Then we have "20 acres", which corresponds to Arachidonic acid. Here, we increase by 2 carbons to 20, and the number of Pi Bonds goes up by one more to 20:4.

We can see that we start with 16 carbons, then these three remain at 18 carbons, with an increasing number of Pi Bonds. Then we progress to 20 carbons, where the number of Pi Bonds increases by just one more to 20:4. Alright. So here, Linoleic acid is "lovely", which would be represented as 18:2. "Occupy" is Oleic acid, so this would be 18:1. Arachidonic Acid is "20 acres", so this notation is 20:4. Linolenic acid is "lush", so it's represented as 18:3. These are the shorthand notations 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 general formula for fatty acids and why do they typically have an even number of carbons?

The general formula for fatty acids is CH₃(CH₂)_nCOOH, where n varies based on the length of the fatty acid chain. Fatty acids typically have an even number of carbons, usually ranging from 12 to 26. This is because they are synthesized by the sequential addition of two-carbon units derived from acetyl-CoA during fatty acid biosynthesis. This process inherently results in fatty acids with an even number of carbon atoms.

What is the difference between saturated and unsaturated fatty acids?

Saturated fatty acids contain only single bonds between carbon atoms, making them fully 'saturated' with hydrogen atoms. In contrast, unsaturated fatty acids have at least one double bond (pi bond) between carbon atoms. If there is one double bond, the fatty acid is monounsaturated; if there are multiple double bonds, it is polyunsaturated. The presence of double bonds introduces kinks in the fatty acid chain, affecting its physical properties and how it interacts with other molecules.

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, separated by a colon. For example, a fatty acid with 12 carbons and no double bonds is written as 12:0. If a fatty acid has 16 carbons and one double bond, it is written as 16:1. This notation helps quickly identify the structure and degree of unsaturation of the fatty acid.

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

Common saturated 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: Lauric, Myristic, Palmitic, Stearic, and Arachidic.

What is the significance of the cis configuration in naturally occurring unsaturated fatty acids?

In naturally occurring unsaturated fatty acids, the double bonds typically have a cis configuration, meaning the hydrogen atoms are on the same side of the double bond. This cis configuration introduces a bend or kink in the fatty acid chain, affecting its packing and physical properties. Cis configurations are important for maintaining fluidity in cell membranes and are generally more beneficial for health compared to trans configurations, which are associated with negative health effects.