Triacylglycerols: Study with Video Lessons, Practice Problems & Examples

Triacylglycerols, also known as triglycerides, are glycerolipids composed of three fatty acid chains linked to a glycerol molecule via ester linkages formed through dehydration synthesis. They serve as long-term energy storage, providing more energy per unit mass than carbohydrates, and act as thermal insulators under the skin. Triacylglycerols can be classified as simple, containing identical fatty acids, or mixed, with varying fatty acids. Specialized cells called adipocytes store these lipids, crucial for maintaining body temperature and energy reserves.

Triacylglycerols

In this video, we're going to begin our introduction to Triacylglycerols. Now before we get started, I first want to point out that over here we have a modified version of our original lipid map, but you can still see that the lipids are branching off into 2 major groups, which are the fatty acids and the isoprenes over here on the right. But again, we're going to cover the isoprenes much later in our course after we finish covering all of the fatty acids and all of the fatty acid-based lipids. And so now that we finished talking about fatty acids, we're finally going to transition into our first class of fatty acid-based lipids, which are the glycerolipids. And so glycerolipids are literally defined as lipids with fatty acid chains that are linked to a glycerol molecule. And so notice down below over here on the left-hand side, we're showing you the structure of a glycerol molecule. So we can go ahead and label it as glycerol. And of course, the glycerol prefix in glycerolipids indicates that a glycerol molecule is going to be in its structure and these are lipids with glycerol. And because they are branching from the fatty acids, we know that fatty acids are going to be found in their structures. Now, moving forward from this point, we're going to talk about 2 different classes of glycerolipids. The first class is going to be the triacylglycerols and so we'll introduce the triacylglycerols here in our next lesson video. So I'll see you guys there.

Triacylglycerols

So now that we've introduced glycerolipids, in this video we're going to talk about the first type of glycerolipid, the triacylglycerols. And so taking a look at our map here, we can see that the glycerolipids fall right here at this position, so they are indeed fatty acid-based lipids. And then branching off of the glycerolipids, we have the triacylglycerols. And you can see the word glycerol itself embedded within the word triacylglycerol. So we know it's going to have a glycerol molecule and be considered a glycerol lipid. Now when it comes down to it, triacylglycerols are also known as triglycerides. And so you may see that your textbook or your professors will use triacylglycerols and triglycerides interchangeably with each other. These triacylglycerols, as the name implies with the tri, these are just lipids with 3 fatty acid chains linked to a single glycerol molecule. And so, again, the prefix tri here is just referring to the 3 fatty acid chains that are linked. Now these 3 fatty acid chains that are linked to this single glycerol molecule are going to be linked via ester linkages, and these ester linkages are formed by dehydration synthesis reactions, and we can see all of this down below in our image in this first box that we see over here. And, so notice that this molecule that we see over here on the far left is our glycerol molecule And so we can go ahead and label it as glycerol. And then over here, what we have are 3 fatty acid chains. And notice that these fatty acid chains are variable or they can be variable. And so here we have a shorter fatty acid. Here we have a longer fatty acid. And then here we have an unsaturated fatty acid. And so these 3 fatty acids can be linked to the glycerol molecule here via dehydration synthesis reactions, where a water molecule can be released, and in the process, it links the glycerol molecules here to the fatty acid chains, and it links them via these ester linkages, which we have boxed here in blue. And, again, this is exactly what we described up above in our text. Now, what's important to note is that the fatty acid chains of triglycerides can either be identical to each other or they can be different from each other. Notice again that in our example here, we had 3 fatty acids that were different from each other. However, they can be identical to each other as well. Now, if the triacylglycerol contains 3 identical fatty acids, then these are referred to as simple triacylglycerols. However, if the fatty if the triacylglycerol contains a mixture of different fatty acids, then they're called mixed triacylglycerols. And so we can see that over here in our image as well. Notice that in this box, we have simple Triacylglycerol right here because we have 3 identical fatty acid chains linked to the glycerol molecule. And then over here on the right, what we have is mixed triacylglycerol because notice that there is a mix of fatty acid chains. These 2 may be identical but this one over here is not identical and so collectively they're referred to, as a mixed group. And then last but not least, what I want to leave you guys off with is that, sometimes these fatty acid chains that we see here, they're just referred to as chains, and so you can think of chains branching off of the glycerol molecule. And other times these fatty acids are referred to as tails and so you can think of the tails here branching off of the glycerol molecule. And so you'll see interchangeably, that I will use chains and tails to refer to these fatty acid chains, and your professors and textbooks will also do the same. And that is some common use of vocabulary to refer to these fatty acid chains. And so this here concludes our introduction to triacylglycerols and in our next lesson video, we'll be able to talk about the function of these triacylglycerols before we actually transition into the next group of glycerolipids. And so, again, that concludes this video, and I'll see you guys in our next one.

What type of bond connects the fatty acid chains to the #1, #2, and #3 positions of glycerol in triacylglycerols?

• A. Phosphodiester bonds.
• B. Disulfide bonds.
• C. Ether Bonds.
• D. Ester Bonds.
• E. Dehydration Bonds.

Draw the structure of a triacylglycerol that contains all 18:0 fatty acids. Is this a simple or mixed triacylglycerol?

a) Simple triacylglycerol. 

b) Mixed triacylglycerol. 

• A. Simple triacylglycerol.
• B. Mixed triacylglycerol.

Triacylglycerols

In this video, we're going to talk about some of the functions of triacylglycerols. Now, triacylglycerols primarily function in the long-term storage of fatty acids, and as you'll see down below in our image, when it comes to fatty acid storage, fatty acids are almost never stored as free individual fatty acids like what we see over here. Instead, the fatty acids, when it comes to their storage, they're going to be stored as triacylglycerols like what we see over here. And the fatty acids themselves can actually be completely oxidized to provide even more energy per unit mass than carbohydrates. And so, when these fatty acids are stored as triacylglycerols, the triacylglycerols are really acting as long-term energy storage molecules, and so they're acting practically as these batteries because batteries can provide long-term energy.

Another function of triacylglycerols is that they can also serve as thermal insulators under our skin to help maintain body temperatures. And so, what you'll notice in our image down below, we have this skinny figure over here and then we have this bigger figure over here. The skinny figure is asking, "Aren't you cold?" And the bigger figure, who's clearly going to have a lot more triacylglycerols, is saying, "Nope." And so, by having the extra triacylglycerols underneath your skin, that can help maintain body temperatures and help keep your body warm.

Now, the specialized cells that synthesize and store triacylglycerols are called adipocytes. Adipocytes are also known as fat cells. And so, over here, what you can see is we have the scanning micrograph of adipocytes. These big white blots that you see within these cells are really just the triacylglycerols and where they're being stored within the cells.

This here concludes our introduction to triacylglycerol functions, and we'll be able to get some practice applying these concepts in some of our next videos, so I'll see you guys there.

The function(s) of triacylglycerols in animals include:

a) Storage for long-term energy.

b) Encoding genetic information. 

c) Short-term energy storage. 

d) Thermal insulation of body temperature. 

e) A and D. 

f) A & C.

• A. Storage for long-term energy.
• B. Encoding genetic information.
• C. Short-term energy storage.
• D. Thermal insulation of body temperature.
• E. A and D.
• F. A & C.

Here’s what students ask on this topic:

What are triacylglycerols and how are they structured?

Triacylglycerols, also known as triglycerides, are a type of glycerolipid composed of three fatty acid chains linked to a glycerol molecule. The structure involves ester linkages formed through dehydration synthesis reactions. The glycerol molecule serves as the backbone, and each of its three hydroxyl groups (OH) forms an ester bond with the carboxyl group (COOH) of a fatty acid. These fatty acids can be identical or different, leading to simple or mixed triacylglycerols, respectively. The ester linkages are crucial for the stability and storage function of these molecules.

What is the primary function of triacylglycerols in the body?

The primary function of triacylglycerols in the body is long-term energy storage. They store fatty acids, which can be oxidized to provide more energy per unit mass than carbohydrates. Additionally, triacylglycerols act as thermal insulators under the skin, helping to maintain body temperature. Specialized cells called adipocytes, or fat cells, synthesize and store these lipids, making them crucial for energy reserves and thermal regulation.

How are triacylglycerols synthesized?

Triacylglycerols are synthesized through a process called dehydration synthesis. This involves the formation of ester linkages between the hydroxyl groups of a glycerol molecule and the carboxyl groups of three fatty acids. During this reaction, water molecules are released. The general reaction can be summarized as:

${\mathrm{Glycerol}}_{}+3{\mathrm{Fatty}}_{}{\mathrm{Acids}}_{}\to {\mathrm{Triacylglycerol}}_{}+3H_{}{2}_{}{O}_{}$

What is the difference between simple and mixed triacylglycerols?

Simple triacylglycerols contain three identical fatty acid chains linked to a glycerol molecule, whereas mixed triacylglycerols have varying fatty acid chains. In simple triacylglycerols, all three fatty acids are the same, leading to a uniform structure. In mixed triacylglycerols, the fatty acids can differ in length, degree of saturation, or both, resulting in a more complex structure. This variability can affect the physical and chemical properties of the triacylglycerol.

What role do adipocytes play in the storage of triacylglycerols?

Adipocytes, also known as fat cells, are specialized cells that synthesize and store triacylglycerols. These cells are found in adipose tissue and are crucial for maintaining energy reserves and thermal insulation. The triacylglycerols stored in adipocytes can be mobilized and broken down into fatty acids and glycerol when the body requires energy. The large lipid droplets within adipocytes are primarily composed of triacylglycerols, making these cells essential for long-term energy storage and temperature regulation.