Question

What structural features do a triacylglycerol and a phosphatidyl ethanolamine have in common? How do the structures of these two types of lipids differ?

Short answer

Both have glycerol and fatty acids but differ in the third attachment: triacylglycerol has a third fatty acid whereas phosphatidyl ethanolamine has a phosphate and ethanolamine group.

Step-by-step solution

Identify Common Features

A triacylglycerol and a phosphatidyl ethanolamine both contain glycerol as a backbone structure. They also have fatty acid tails attached to this glycerol backbone.

Structure of Triacylglycerol

Triacylglycerol consists of one glycerol molecule bonded to three fatty acid tails through ester bonds, forming a simple lipid.

Structure of Phosphatidyl Ethanolamine

Phosphatidyl ethanolamine also consists of a glycerol backbone with two fatty acid tails. However, instead of a third fatty acid, it has a phosphate group attached to the third hydroxyl group of the glycerol molecule with an ethanolamine group attached to the phosphate.

Compare The Differences

The main difference lies in the third position of the glycerol backbone. Triacylglycerol has a third fatty acid, while phosphatidyl ethanolamine has a phosphate group and an ethanolamine instead.

Key concepts

Triacylglycerol

A triacylglycerol, also known as a triglyceride, is a type of lipid commonly found in fats and oils. It is composed of a glycerol backbone bonded to three fatty acid molecules via ester bonds. The primary function of triacylglycerol is to store energy.
Triacylglycerols are simple lipids because their structure includes only glycerol and fatty acids without any additional groups. They are highly hydrophobic and form the main constituents of body fat in humans and animals. The three fatty acids can be the same or different, giving rise to various types of triacylglycerols.

Phosphatidyl Ethanolamine

Phosphatidyl ethanolamine is a type of phospholipid found in biological membranes. Like triacylglycerol, it contains a glycerol backbone and fatty acid tails. However, its structure differs significantly due to the presence of a phosphate group and an ethanolamine group.
In phosphatidyl ethanolamine, the glycerol backbone is bonded to two fatty acids at the first and second positions. The third position features a phosphate group attached, which in turn is bonded to an ethanolamine group. This makes phosphatidyl ethanolamine an important component of cell membranes, contributing to their fluidity and functionality.

Glycerol Backbone

Both triacylglycerols and phosphatidyl ethanolamine share a common structural feature: the glycerol backbone. Glycerol is a simple polyol compound with three hydroxyl groups.
The glycerol backbone serves as the foundation to which fatty acids and other groups are attached. In both types of lipids, the hydroxyl groups of glycerol participate in forming ester bonds with fatty acids. This central feature is crucial for the formation and function of these lipids in biological systems.

Fatty Acids

Fatty acids are long hydrocarbon chains with a carboxyl group at one end. They are key components of both triacylglycerols and phosphatidyl ethanolamine.
Fatty acids can vary in length and in the number and position of double bonds, leading to diverse properties. In lipids, fatty acids are typically linked to the glycerol backbone via ester bonds. Their hydrophobic nature is essential for the formation of lipid bilayers and for storing energy in the form of fats.

Phosphate Group

A phosphate group is an essential part of phosphatidyl ethanolamine but not found in triacylglycerols. This group consists of a phosphorus atom bonded to four oxygen atoms, and it is charged and hydrophilic.
In phosphatidyl ethanolamine, the phosphate group is attached to the glycerol backbone's third hydroxyl group. This phosphate group is further attached to an ethanolamine group, forming a complex structure. The presence of the phosphate group makes phosphatidyl ethanolamine amphipathic, with both hydrophobic and hydrophilic properties, allowing it to play a crucial role in cell membrane structure and function.