Triglyceride — Structure & Function

Energy Storage

Lipids that store energy are called triglycerides. In many organisms, extra carbohydrates (polymers made of simple sugars like glucose) are stored as triglycerides in fat tissue.

Triglycerides are excellent long-term energy storage molecules because they will not mix with water and break down. We can also eat them (in delicious fried foods) and break them down to get energy.

They are made of a glycerol backbone attached to three fatty acid chains.

Glycerol is a simple sugar alcohol. Fatty acids are carbon chains attached to a carboxylic acid group ($-COOH$), as seen below.

The bonds between the glycerol molecules and fatty acids are covalent bonds called ester bonds. They are formed from a condensation reaction which can be seen in the picture below. It's called condensation because water molecules are formed (they condense) during the reaction.

What Is a Saturated Fat?

You've probably heard of saturated and unsaturated fats on TV ads, nutrition labels, and billboards. The difference between their structures is really small. Let's take a look:

Saturated fats have straight chains because the chain part of their structure contains only single carbon-carbon bonds. Saturated fats pack together closely and are solid at room temperature. Saturated fats are typically found in animal products. Butter is a good example.

Unsaturated fats have a kink in their chain caused by double or triple carbon-carbon bonds. Because of the kinks, these fats can't pack together very closely. This makes them liquid at room temperature. They are typically found in plant products. Vegetable oil is a good example.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Triglyceride}}$ : A molecule made of a glycerol backbone attached to three fatty acid chains

$\color{#8925AE}{\text{Macromolecule}}$ : A polymer that has a large (macro) molecular mass. There are four main types in organisms: carbohydrates, proteins, lipids, and nucleic acids

$\color{#8925AE}{\text{Saturated}}$ : When each carbon atom in the fatty acid chain is linked by a single bond.

$\color{#8925AE}{\text{Unsaturated}}$ : When fatty acids have at least one carbon-to-carbon double bond.

$\color{#8925AE}{\text{Lipid}}$ : Fats and oils (like cholesterol)

(Video) What Is Fat?

by George Zaidan on TED-Ed

This video gives a good description of the different kinds of animal and plant fats. It also explains the difference between cis and trans fats.