What is Fatty Acid? – Composition & Structure (Video)
Understanding the Omega Fatty Acids
What Are Fats and Why Do You Need Them?
When you see the word fat, you may think of butter, mayonnaise, the cholesterol in meats and eggs, and even the fatty tissues in your own body. But technically speaking, these aren’t all fats. Instead, they’re examples of a broader category of substances known as lipids-compounds that contain carbon, oxygen, and hydrogen and which are hydrophobic (hydro = water, phobic = fearing), meaning they don’t dissolve in water. If you were to drop lipids, such as butter or olive oil, into a glass of water, you would see them rise to the top and sit on the water’s surface. This repelling of water enables lipids to play a unique role in foods and in your body.
To answer our original question, fat is the common name for just one type of lipid, known as a triglyceride. Because this is the type of lipid found most abundantly in foods, food labels and nutrition sources refer generally to this category as dietary fat-not dietary lipid-so fat is the term we’ll use in this text.
Fats Serve Multiple Functions in Foods and in Your Body
Fats perform a variety of functions in cooking. They give a flaky texture to pie crusts and other baked goods, and they make meat tender and soups and puddings creamy. The flavors and aromas that fats provide can make your mouth water as you eye crispy fried chicken or smell baking cookies. Foods that are higher in fats contribute to satiety, that feeling of fullness you experience after eating. In your body, fats are essential for energy storage and insulation. Two other types of lipids are also important as components of the membranes surrounding your cells and play a key role in transporting proteins in your blood. Three types of lipids are found in foods and in your body: triglycerides (fats), phospholipids, and sterols. Two of the three, triglycerides and phospholipids, are built from a basic unit called a fatty acid. So let’s start our discussion of the structure of lipids with the fatty acids.
Fatty Acids Are Found in Triglycerides and Phospholipids
All fatty acids consist of a chain of carbon and hydrogen atoms, with an acid group (COOH) at one end. There are more than 20 different fatty acids. They can vary by (1) the length of the chain, (2) whether the carbons have a single or a double bond between them (C ¬ C or C “C), and (3) the total number of double bonds. The way carbon bonds occur in different types of fatty acids is what makes some fatty acids healthier than others.
There are three main types of fatty acids:
Saturated fatty acids. When each carbon in a fatty acid chain is bonded with two atoms of hydrogen, as we saw in Figure 5.1, the chain is considered saturated with hydrogen. It cannot hold any more.We therefore call such a fatty acid a saturated fatty acid. For example, stearic acid is a saturated fatty acid. It has 18 carbons, all of which are bound, or saturated, with hydrogen. Long fatty acids, such as stearic acid, are strongly attracted to one another, and are relatively straight, so they are able to pack tightly together in food, and thus become solid fats at room temperature. Stearic acid can be found in cocoa butter (in chocolate) and in the fatty part of meat. Shorter saturated fatty acids (with fewer than 12 carbons) have a weaker attraction to one another, and so do not pack tightly together. Because of this, foods that contain them are liquid at room temperature. Whole milk contains short-chain saturated fatty acids. Fats made up of mostly saturated fatty acids are called saturated fats. As you will learn later on in the text, saturated fats and other solid fats should be minimized in the diet, as they are not healthy for your heart.
Monounsaturated fatty acids (MUFAs). Take a look at the fatty acid. Do you notice that, at one place in the chain, two carbons are each bound to only one atom of hydrogen, and are joined twice to each other? This double carbon bond means that the carbons are not “saturated” with hydrogen atoms at that point in the chain. This makes the chain unsaturated. Because a double bond occurs at just one point in the chain, the molecule is called a monounsaturated fatty acid (recall that mono- means one). Like stearic acid, oleic acid contains 18 carbons, but two of them are paired with each other rather than hydrogen, so it has one double bond. This one double bond makes oleic acid a monounsaturated fatty acid. It also makes it crooked. That is, double bonds cause a kink in the chain of the fatty acid. This kink keeps unsaturated fatty acids from packing together tightly. Thus, unsaturated fatty acids are liquid at room temperature. For instance, oleic acid is found in olive oil. You can see the effect of straight versus kinked fatty acid chains on foods. As you might expect, fats made up of mostly unsaturated fatty acids are called unsaturated fats. Whereas saturated fats are unhealthy, unsaturated fats are considered important to your health.
Polyunsaturated fatty acids (PUFAs). A polyunsaturated fatty acid (poly = many) contains more than one double bond and is even less saturated with hydrogen than a monounsaturated fatty acid. For instance, linoleic acid contains two double bonds and is polyunsaturated. It is found in soybean oil. Like monounsaturated fats, polyunsaturated fats are considered healthy. Incidentally, your body can make most of the fatty acids it needs, but there are two that it cannot make, and both are polyunsaturated. Because you must consume them in your diet, they’re known as essential fatty acids. They are linoleic acid and alpha-linolenic acid. We’ll discuss these essential fatty acids in more detail later in this text.
Triglycerides Contain Three Fatty Acid Chains
Triglycerides are the most common lipid found in foods and in your body. Each triglyceride compound is made up of three fatty acid chains (tri = three) connected to a glycerol “backbone.” Glycerol is a compound containing carbon, hydrogen, and a type of alcohol. The three fatty acids join to the glycerol backbone to form the triglyceride. Any triglyceride can contain a variety of different fatty acids. The more common name for triglycerides is fat, and this is the term we’ll use throughout this text. Most of the lipids that you eat and that are in your body are in the form of fat. Many fatty foods, such as butter, lard, and the fat in meats, are solid at room temperature so are often referred to as solid fats. Oils are lipids that are liquid at room temperature.
Phospholipids Contain Phosphate
Like fats, phospholipids contain a glycerol backbone, but instead of being made up of three fatty acids, they contain two fatty acids and a phosphate group (a compound containing the mineral phosphorus). The portion where the phosphate is attached to the glycerol is referred to as the head, which is hydrophilic (philic = loving), so it is able to attract water. In contrast, phospholipids’ fatty acid tails are hydrophobic.
Phospholipids make up the phospholipid bilayer in cell membranes. Their water-loving heads face outward to the watery areas both outside and inside your cells, and their fat-loving tails line up with each other in the center, creating a phospholipid membrane that surrounds the cell and acts as a barrier. The cell membrane allows certain substances, such as water, to enter the cell but keeps others, like protein, from leaking out. You can visualize this phospholipid layer as being like a picket fence, acting as a barrier surrounding each cell. The major phospholipid in your cell membranes is lecithin. Even though lecithin plays an important role in your body, you don’t have to worry about eating large amounts of lecithin in foods. As with all phospholipids, your body is able to make all the lecithin it needs. Because of its unique water- and fat-loving attributes, lecithin is used in many foods as an emulsifier, which helps keep incompatible substances, such as water and oil, mixed together. For example, an emulsifier is sometimes added to commercially made salad dressings to prevent the fat from separating and rising to the top of the dressing. The emulsifier’s nonpolar, fat-attracting tail surrounds the droplets of fat, which orients the polar, water-attracting head of the emulsifier toward the watery solution of the dressing. This keeps the fat droplet suspended in the dressing and allows these two incompatible substances to stay blended together. We’ll see the process of emulsification again when we discuss how the body uses fat.
Sterols Have a Unique Ring Structure
Unlike phospholipids, sterols are lipids that do not contain glycerol or fatty acids. Instead, they are composed mainly of four connecting rings of carbon and hydrogen. The best known sterol is cholesterol. Though cholesterol’s association with heart disease has blemished its reputation, it plays an important role in your cell membranes and is the precursor of some very important compounds in your body. As with lecithin, don’t be concerned about meeting your daily need for this important substance through your diet, since your body manufactures all the cholesterol you need.
Message
Lipids are hydrophobic compounds made up of carbon, hydrogen, and oxygen. The three types of lipids are triglycerides, phospholipids, and sterols. Fatty acids, which consist of a carbon and hydrogen chain and an alcohol group, are the basic structural units of triglycerides and phospholipids. Triglycerides are formed from three fatty acids connected to a glycerol backbone and are the most prevalent lipids in your food and body. Phospholipids are made of two fatty acids and a phosphate-containing group attached to a glycerol backbone. Phospholipids are an important part of the structure of cell membranes. Cholesterol is an important sterol in your cell membranes and is the precursor to other essential compounds.
Cocoa butter melts at body temperature. This is why solid milk chocolate melts in your mouth.
Keeping a Salad Dressing Blended
To prevent the fat from separating out in a salad dressing, an emulsifier is added. The emulsifier’s fat-attracting tails surround the droplets of fat, whereas the water-attracting heads remain oriented toward the watery portion of the solution or dressing. This allows the fat droplet to stay suspended and blended in the dressing.
Structure of a Sterol
Rather than being made from fatty acids attached to a glycerol backbone, sterols have a carbon ring configuration with hydrogen’s and oxygen attached. Cholesterol is the best-known sterol.
Three Types of Lipids
The three types of lipids vary in structure. Triglycerides and phospholipids are built from fatty acids, whereas sterols are composed of carbon rings.
Fatty acids differ by the length of the fatty acid chain, whether or not there are double bonds between the carbons, and (if there are double bonds) how many double bonds they contain.
Saturated fatty acids are able to pack tightly together and are solid at room temperature.
The double bonds in unsaturated fatty acids cause kinks in their shape and prevent them from packing tightly together, so they tend to be liquid at room temperature.
A triglyceride consists of three fatty acids attached to a glycerol backbone. Note that a single triglyceride can contain different fatty acids.
Phospholipids’ Role in Your Cell Membranes
1. Because the phosphorus-containing head is polar, it attracts charged particles, such as water located both outside and inside your cells.
2. Its fatty acid-containing tail is nonpolar, so it mingles and lines up with other nonpolar molecules such as the fatty acid-containing ends of other phospholipids.
3. This creates a two-layer membrane that surrounds the cell and acts as a barrier, allowing certain substances to enter the cell but keeping others from leaving.
Terms:
Lipid – A category of carbon, hydrogen, and oxygen compounds that are insoluble in water.
Hydrophobic – Having an aversion to water
Fatty acid – The basic unit of triglycerides and phospholipids.
Saturated fatty acid – A fatty acid that has all of its carbons bound with hydrogen.
Saturated fats – Fats that contain mostly saturated fatty acids.
Monounsaturated fatty acid (MUFA) – A fatty acid that has one double Bond
Unsaturated fatty acid – A fatty acid that has one or more double bonds between carbons.
Unsaturated fats – Fats that contain mostly unsaturated fatty acids polyunsaturated fatty acid (PUFA) A fatty acid with two or more double bonds essential fatty acids The two polyunsaturated fatty acids that the body cannot make and therefore must be eaten in foods: linoleic acid and alpha-linolenic acid.
Linoleic acid – A polyunsaturated essential fatty acid; part of the omega-6 fatty acid family.
Alpha-linolenic acid – A polyunsaturated essential fatty acid; part of the omega-3 fatty acid family.
Triglyceride – Three fatty acids that are attached to a glycerol backbone. Also known as fat.
Glycerol – The three-carbon backbone of a triglyceride.
Oils – Lipids that are liquid at room temperature.
Phospholipids – Lipids made up of two fatty acids and a phosphate group attached to a glycerol backbone.
