What is the Difference Between Saponifiable and Non-saponifiable Lipids

The key difference between saponifiable and non-saponifiable lipids is that saponifiable lipids contain ester linkages and can be hydrolyzed into smaller molecules, while non-saponifiable lipids do not contain ester linkages and cannot be hydrolyzed into smaller molecules.

Lipids are a diverse group of organic compounds that includes fats, oils, hormones, and other membrane components. They are non-polar molecules and are insoluble in water. Lipids produce high energy and are responsible for various functions within the human body. They act as an energy storage molecule to provide energy in the absence of carbohydrates. They also act as an insulator and take part in the thermal regulation of the body. Lipids can be classified into two classes based on saponification, a chemical reaction by which esters are hydrolyzed into smaller product molecules. The two groups are saponifiable and non-saponifiable lipids.

CONTENTS

1. Overview and Key Difference
2. What are Saponifiable Lipids
3. What are Non-saponifiable Lipids
4. Similarities –  Saponifiable and Non-saponifiable Lipids
5. Saponifiable vs Non-saponifiable Lipids in Tabular Form
6. Summary – Saponifiable vs Non-saponifiable Lipids

What are Saponifiable Lipids?

A saponifiable is a lipid containing long-chain fatty acids and forming esters. These lipids have the ability to undergo saponification reaction under basic conditions. Furthermore, ester hydrolysis can take place in saponifiable lipids, yielding fatty acids. The main examples of saponifiable lipids are triacylglycerides, glycerophospholipids, sphingolipids, and waxes.

The function of these lipids depends on their structure. Triacylglycerides are utilized as the primary chemical energy storage form in the body. It is a common form of fat in the bloodstream. It is composed of three fatty acid chains linked by a glycerol molecule. Glycerophospholipids are complex structures that consist of a glycerol molecule with two fatty acids, a phosphate, and a small molecule attached to it. They act as major constituents of membranes that are bilayers. Sphingolipids are made of a backbone that consists of a sphingoid base with a fatty acid chain attached by an amide bond at the 2^nd carbon atom. They are amphipathic molecules having hydrophobic and hydrophilic properties. They function as structural components of membranes, cell signaling modulators, and mediators. Waxes are made up of long-chain fatty acids linked through ester oxygen to long-chain alcohol. They usually act as a waterproof layer for coatings such as leaves and feathers.

What are Non-saponifiable Lipids?

Non-saponifiable lipids are lipids that do not form esters. They are mainly composed of ring structures. Two major types of non-saponifiable lipids are terpenes and steroids. Terpenes include certain fat-soluble vitamins such as vitamin A, vitamin E, and vitamin K, carotenoids, and certain coenzymes such as coenzyme Q and ubiquinone. Terpenes are composed of two or more isoprene units which are five carbon units. These isoprene units bond together through a head-to-tail organization. For example, two isoprene units form monoterpene, and this is responsible for the characteristics such as odour and flavour of plants. Steroids are an important type of lipids that consist of a system fused of cyclohexane and cyclopentane. They are derivatives of a complex compound perhydrocyclo-pentanophenanthrene, which has three fused cyclohexane rings and a terminal cyclopentane ring.

Steroids consist of hormones such as oestrogen, progesterone, corticosterone, and some vitamins such as vitamin D3. Steroids that act as hormones affect cellular activities by influencing gene expression, and steroids that act as vitamins influence the activities of cellular enzymes. Other types of steroids, such as cholesterol, are constituents of plasma membranes that influence structure, permeability, and transport.

What are the Similarities Between Saponifiable and Non-Saponifiable Lipids?

• Saponifiable and non-saponifiable lipids are major types of lipids.
• They contain carbon atoms in the structure.
• Moreover, their elemental composition is carbon, hydrogen, and oxygen
• They act as structural components.
• They are amphipathic molecules.

What is the Difference Between Saponifiable and Non-saponifiable Lipids?

Saponifiable lipids contain esters of fatty acids, while non–saponifiable lipids do not contain esters of fatty acids. Thus, this is the key difference between saponifiable and non–saponifiable lipids. Besides, saponifiable lipids are composed of long-chain linear fatty acids, while non–saponifiable fatty acids are composed of fatty acids forming ring structures. Moreover, saponifiable lipids mainly act as structural compounds, while non–saponifiable lipids can act as both structural and storage compounds.

The below infographic presents the differences between saponifiable and non-saponifiable lipids in tabular form for side-by-side comparison.

Summary – Saponifiable vs Non-saponifiable Lipids

Lipids are a group of biomolecules that are composed of carbon, hydrogen, and oxygen. They act as energy stores as well as thermal insulators in the body. Lipids are classified into two classes, namely saponifiable and non–saponifiable lipids. Saponifiable lipids contain esters of fatty acids, while non–saponifiable lipids do not contain esters of fatty acids. So, this is the key difference between saponifiable and non–saponifiable lipids. The four main types of saponifiable lipids are triacylglycerols, glycosphingolipids, sphingolipids, and waxes. The main non-saponifiable lipids are terpenes and steroids. While saponifiable lipids are mainly structural, non-saponifiable lipids have both structural and biochemical functions.

Reference:

1. “2 Types of Non-saponifiable Lipids: Terpenes and Steroids (with Diagram).” Biology Discussion, 27 Aug. 2015.
2. “Saponifiable Lipids.” Unacademy, 18 Apr. 2022.

Image Courtesy:

1. “MFGM structure” By Mead Johnson Nutrition (CC BY 4.0) via Commons Wikimedia
2. “Figure 03 03 10” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia