Lipids – Structure, Function and Examples

Glass containers filled with oils

Core Concepts

In this article, you will learn about lipids, the structure of lipids, the function of lipids and a few examples of lipids.

Topics Covered in Other Articles

What are Lipids?

Lipids are macromolecules that are soluble in organic solvents and insoluble in water. They are abundant in biological systems and play multiple roles in plants and animals. They have a unique structure that allows them to form lipid bilayers and make membranes. Therefore, there are many subclasses of lipids, and these are described below. Also, cooking oils and beeswax (produced from honeybees) contain these incredible molecules.

Glass containers filled with oils and different lipids
Source: Wikimedia Commons

What are Lipids made of?

Lipids consist of 3 main elements: carbon (C), hydrogen (H) and oxygen (O). Additionally, these elements form hydrocarbons chains and hydroxyl groups. Importantly, these chains are held together by carbon and hydrogen bonds.

Types of Lipids

They are three types of lipids: Trigylercerides, Phospholipids and Sterols.


Triglycerides, the most common, are classified as fats and oils. These are in our diets and body fat tissues. The molecular structure of this lipid consists of a glycerol molecule and three fatty acids. Glycerol is a compound of hydrogens, carbons, and hydroxyl groups (-OH). Whereas fatty acids are long chains of carbons that have hydrogen molecules attached. Also, a carboxylic acid group (-COOH) is directly attached to one end of the hydrocarbon chain. So, glycerols and fatty acids attach through ester linkages which are formed through condensation reactions and broken through hydrolysis reactions.

The molecular structure of a triglyceride, a type of lipid
Source: Wikimedia Commons

Also, there are two types of fatty acids: Saturated and Unsaturated fatty acids.

Saturated fatty acids are hydrocarbon chains that are linear and unbranched. The structure consists of carbon-carbon single bonds (C-C) with a carboxylic group. The label indicates the number of hydrogen molecules bonded to each carbon. At the same time, unsaturated fatty acids have one or multiple carbon-carbon double bonds. This suggests that a few hydrogen molecules bonded to each carbon.

Molecular structures of saturated and unsaturated fatty acids
Source: Wikimedia Commons


Phospholipids are complex structures that have an abundance in biological membranes. The molecular structure of this lipid consists of a glycerol molecule, one or two fatty acids, an alcohol group and a phosphate group. Importantly, the phosphate (head) contains an electrical charge while the fatty acids (tail) contain a neutral charge. Therefore, this allows the head of the lipid to be hydrophilic (water-loving) and the tail to be hydrophobic (water-hating).

Molecular structure of a phospholipid, a type of lipids structure
General structure of a phospholipid. Source: Wikimedia Commons

These lipids are known for the formation of biological membranes. These membranes act as barriers to prevent molecules from either leaking out or diffusing in. Also, they contain transport systems which allow specific molecules to enter the cell or have unwanted molecules exit the cell. The phospholipids would arrange themselves as a structure called a bilayer. Importantly, the hydrophobic heads of the phospholipids will align together while the hydrophilic tails will be in contact with the inside and outside of a cell.

Graphic showing the structure of a lipid bilayer
Alignment of lipid molecules to form a membrane. Source: Wikimedia Commons


Sterols, the least common, are unique structures that are present in foods (from animals). The molecular structure derives from a gonane, a tetracyclic hydrocarbon with no double bonds. Additionally, a hydroxyl group replaces a hydrogen molecule at position 3. 

a type of sterol molecule, one of many types of lipids
Source: Wikimedia Commons

Cholesterol is a waxy sterol that is present in animal cells. It is essential for many metabolic processes such as the production of vitamin D, hormones and bile. They are produced by the liver and most cells in the human body. Additionally, the waxy sterol is transported around the body with substances called lipoproteins. They form complexes with special proteins to transport cholesterol throughout the body. Then, there are two main types of cholesterol: high-density lipoprotein (good cholesterol) and low-density lipoprotein (bad cholesterol).

For more information, see this page.

Functions of Lipids

  • Storage of energy: Excess fat stored in fatty tissue. Normally, stored fat acts as an energy reserve.
  • Contribution to taste, smell and texture of food: Fat contains compounds that contribute to aromas and flavours.
  • Insulation and protection: Fat stored underneath the skin helps in the insulation of extreme temperatures in the body.
  • Signalling and regulation: Lipids (triglycerides) control the internal climate of the body which maintains temperature.

For more information, see this page.

Examples of Lipids

Some well-known examples that contain lipids are:

  • Butter
  • Milk
  • Coconut oil
  • Olive oil
  • Soybean oil
  • Fish oil
  • Cholesterol
  • Hormones
  • Beeswax
  • Earwax