What Are Fats? - Functions & Molecular Structure

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  • 0:00 Definition of Fats
  • 0:48 The Structure of Fats
  • 2:26 Saturated and Unsaturated Fats
  • 3:06 The Function of Fat
  • 4:03 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

There are probably many images that come to mind when you hear the word 'fat.' This lesson is all about fat and will explore the structure and function of this often misunderstood lipid.

Definition of Fats

Chances are, you are familiar with fats. Maybe you've read the nutritional labels for foods and try to avoid eating too much fat, or maybe you've shivered in the cold and thought, 'I need some extra fat to stay warm!' When you hear the word 'fat', different images probably come to mind, like a big gob of goo or a chunk of meat dripping with oils. But fats are much more complicated than gobs of goo that you try to avoid.

Fats are large molecules that are classified as lipids and are made up of glycerol and fatty acids. What do those vocabulary words mean, exactly? Let's go through them next, while we also go over the structure of fasts. We'll also learn about the functions of fats, including energy storage and body insulation.

The Structure of Fats

Fats are classified as lipids, or a group of compounds which are substances made up of two or more elements that do not dissolve in water. For example, what happens when you place olive oil in water? It floats on top because it does not dissolve. Olive oil is classified as a lipid.

Glycerol is part of the structure of fat and is made up of three carbon atoms. Each carbon atom can bond, or attach, to four other atoms. One of those bonds is made with a hydroxyl-group, or a hydrogen and oxygen. The other three bonds are with carbon and hydrogen atoms. Take a look at the image below to get a better idea. Note: O stands for oxygen, H stands for hydrogen, and C stands for carbon.


Fats are also made up of fatty acids, which have a long chain of carbons. On one end of the chain there is a carboxyl-group, or a carbon double bonded to an oxygen and single bonded to an oxygen and hydrogen. Double bonds are depicted by using two lines, which you can see in the image below.

carboxyl group

A fat is formed when a glycerol joins with three fatty acids. Fats are also called triglycerides. In the image below, you are looking at a fat, or triglyceride. Take a moment to review the picture. Note there is one glycerol connected up to three fatty acids. Also note the double bonds; they will be important in distinguishing between saturated and unsaturated fats. The zigzagging lines are a shortcut chemistry folks use, but they just represent the carbon chain.


Saturated and Unsaturated Fats

There are two main types of triglycerides: saturated fats and unsaturated fats. Unsaturated fats have at least one double bond in the long carbon chain, whereas saturated fats do not have at least one double bond. Most animal fats, like bacon grease and butter, are saturated fats and are solids at room temperature. Unsaturated fats are typically liquid at room temperature and consist of oils.

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