Difference Between Glycerol and Fatty Acids

Main Difference – Glycerol vs Fatty Acids

Glycerol and fatty acids are two molecules that are involved in the formation of a triglyceride molecule. Triglyceride molecule consists of a single glycerol molecule, attached to three fatty acid molecules. It is a type of lipid mainly found in the cell membrane. Phospholipids are another type of lipids which contains a single glycerol molecule attached to two fatty acids molecules and one phosphate molecule. The main difference between glycerol and fatty acids is that glycerol is a trihydric alcohol whereas fatty acids are organic compounds with a carboxylic group. Fatty acids can be either saturated or unsaturated. Based on the degree saturation of fatty acids, the physical properties of triglycerides are changed.

Key Areas Covered

1. What is Glycerol
      – Definition, Characteristics, Structure, Role
2. What are Fatty Acids
      – Definition, Characteristics, Structure, Role
3. What are the Similarities Between Glycerol and Fatty Acids
      – Outline of Common Features
4. What is the Difference Between Glycerol and Fatty Acids
      – Comparison of Key Differences

Key Terms: Alcohols, Carboxylic Acids, Cis Fatty Acids, Glycerol, Fatty Acids, Phospholipids, Saturated Fatty Acids, Triglycerides, Unsaturated Fatty Acids

What is a Glycerol

Glycerol is a colorless, viscous substance, and is a component of lipids such as triglycerides and phospholipids. It contains three carbon molecules. Glycerol is a trihydric alcohol that contains three hydroxyl groups at each of the three carbon molecules. It is formed as a by-product in the soap manufacture. It is used as a laxative and emollient. The chemical formula of glycerol is shown in figure 1.

Difference Between Glycerol and Fatty Acids

Figure 1: Glycerol

The lipids that contain glycerol are called glycerolipids. Glycerol is the basis of all triglycerides and phospholipids since it connects fatty acids together. The triglyceride model is shown in figure 2.

Figure 2: Triglyceride Model

Triglycerides contain three fatty acids attached to the glycerol backbone. However, phospholipids contain two fatty acid molecules and one phosphate molecule attached to the glycerol backbone.

What are Fatty Acids

Fatty acids refer to a type of carboxylic acids that contain a hydrocarbon chain with a terminal carboxylic acid and are the constituents of lipids such as triglycerides and phospholipids. They are predominantly non-polar molecules due to the long hydrocarbon chains in their structure. Carboxylic group occurs at a terminal of the hydrocarbon chain. The structure of a fatty acid molecule is shown in figure 3.

Difference Between Glycerol and Fatty Acids_Figure 3

Figure 3: Palmitic Acid

Based on the degree of saturation, fatty acids contain two categories: saturated fatty acids and unsaturated fatty acids. Each carbon of the saturated fatty acids is joined to the adjacent carbon by a single bond. Unsaturated fatty acids contain double bonds in the hydrocarbon chain. Saturated fatty acids are straight molecules as an average. But, each double bond of the unsaturated fatty acids produces a kink in the molecules. Based on this, two types of unsaturated fatty acids can be identified: cis fatty acids and trans fatty acids. Cis fatty acids cannot produce a solid form due to the large bends they have in their structure. Saturated and unsaturated fatty acids are shown in figure 4.

Main Difference - Glycerol vs Fatty Acids

Figure 4: Saturated and Unsaturated Fatty Acids

Based on the degree of saturation of the fatty acid molecules, triglycerides are classified as saturated fat and unsaturated fat.

Similarities Between Glycerol and Fatty Acids

Both glycerol and fatty acids are components of triglycerides and phospholipids.
Both glycerol and fatty acids are soluble in water.
Both glycerol and triglycerides contain functional groups, which contribute to the polarity of both molecules.

Definition

Glycerol: Glycerol is a colorless, viscous substance, which is a component of lipids such as triglycerides and phospholipids.

Fatty Acids: Fatty acid is a carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group, especially any of those occurring as esters in fats and oils.

Types

Glycerol: Glycerol is a trihydric alcohol.

Fatty Acids: Fatty acids are carboxylic acids with hydrocarbon chains.

Functional Group

Glycerol: Glycerol contains three hydroxyl groups.

Fatty Acids: Fatty acids contain a carboxylic group.

Number of Carbons

Glycerol: Glycerol contains three carbon molecules.

Fatty Acids: Fatty acids may contain 10-30 carbon molecules (most recently, 12-18).

Polarity

Glycerol: Glycerol is a polar molecule.

Fatty Acids: The hydrocarbon part of the fatty acids is non-polar but, the carboxylic group is polar.

In Triglycerides

Glycerol: A single glycerol molecule is involved in the formation of a triglyceride molecule.

Fatty Acids: Three fatty acid molecules are involved in the formation of a triglyceride molecule.

In Phospholipids

Glycerol: A single glycerol molecule is involved in the formation of phospholipid molecules.

Fatty Acids: Two fatty acid molecules are involved in the formation of a phospholipid molecule.

Conclusion

Glycerol and fatty acids are the two structural components of lipids such as triglycerides and fatty acids. Glycerol is an alcohol with three hydroxyl groups in the adjacent carbons. Fatty acids are long hydrocarbon chains, which are capped by a terminal carboxylic group. Glycerol molecule serves as the backbone of the triglycerides and phospholipids. Fatty acid molecules are attached to the glycerol molecules by ester bonds. The main difference between glycerol and fatty acids is the role of each type of molecule in the formation of triglycerides and phospholipids.

Reference:

1.“Introduction: Common Macromolecules- Lipids and Biomembranes.” Learn Biochemistry, Available here.
2.“Fatty Acids and Triacylglycerols.” UW Courses Web Server, Available here.

Image Courtesy:

1. “Glycerin Skelett” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Eie-TRIGLYCERIDE” (CC BY-SA 3.0) via Commons Wikimedia
3. “Palmitic acid structure” By Edgar181 – Own work (Public Domain) via Commons Wikimedia
4. “221 Fatty Acids Shapes-01” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia