The key difference between glycolipids and phospholipids is that glycolipids contain a carbohydrate group attached to the lipid residue, whereas phospholipids contain a phosphate group attached to the lipid residue.
Glycolipids and phospholipids are two types of lipid-containing substances we can find in cell membranes. They differ from each other according to the chemical structure and function. However, both these compounds contain lipid residues.
CONTENTS
1. Overview and Key Difference
2. What are Glycolipids
3. What are Phospholipids
4. Side by Side Comparison – Glycolipids vs Phospholipids in Tabular Form
5. Summary
What are Glycolipids?
Glycolipids are lipids containing carbohydrates. Here, the lipid and the carbohydrate are linked to each other via a glycosidic bond, which is a type of covalent bond. The carbohydrate in the glycolipid structure can be either a monosaccharide or an oligosaccharide. The most common lipid residues that can form glycolipids are glycerolipids, and sphingolipids. They have glycerol and sphingosine as their backbones, respectively. Fatty acids get attached to this backbone.
The lipid residue contains two parts: polar head group and nonpolar tail group. In a cell membrane, the outer surface of the membrane is made of polar head groups, while the inner part is made of nonpolar tail groups. The saccharides attach to this cell membrane through the polar head group. This ligand component is also polar; thus, it allows the glycolipid to be soluble in the aqueous environment around the cell.
Figure 01: Subtypes of Glycolipids
When forming the glycolipid, the sugar molecule binds with a free hydroxyl group of the lipid residue in the backbone through the anomeric carbon of the sugar component. A glycosidic bond forms between the anomeric carbon of sugar molecule and the hydroxyl group of the lipid. There are different types of glycolipids such as glyceroglycolipids and glycosphingolipids
What are Phospholipids?
Phospholipids are lipid residues containing phosphate groups. These are the most common lipid components in cells and they mainly act as structural components. We can find these components in bio-membrane structures like lysosomal membrane, mitochondrial membrane, endoplasmic reticulum membrane, and Golgi apparatus membrane.
Figure 02: Structure of the Cell Membrane
Phospholipids are amphipathic compounds containing a polar, hydrophilic head and two hydrophobic, nonpolar tails. In a cell membrane, there is a bilayer of phospholipids (two layers of phospholipids). The polar heads are at the outer surfaces and nonpolar tails are in between the two phospholipid layers.
What is the Difference Between Glycolipids and Phospholipids?
The key difference between glycolipids and phospholipids is that glycolipids contain a carbohydrate group attached to the lipid residue, whereas phospholipids contain a phosphate group attached to the lipid residue. Therefore, glycolipids contain a carbohydrate moiety, while there are no carbohydrate moieties in phospholipids. In other words, there are no additional phosphate groups in glycolipid structure, but there is a phosphate group in phospholipid. When considering the chemical structures, glycolipid contains a hydrophilic head and hydrophobic tail while phospholipids contain a hydrophilic head and two hydrophobic tails.
The following infographic summarizes the difference between glycolipids and phospholipids in tabular form.
Summary – Glycolipids vs Phospholipids
Glycolipids and phospholipids are two types of lipid-containing substances we can find in cell membranes. The key difference between glycolipids and phospholipids is that glycolipids contain a carbohydrate group attached to the lipid residue whereas phospholipids contain a phosphate group attached to the lipid residue.
Reference:
1. “1.4: Glycolipids.” Physics LibreTexts, Libretexts, 16 Sept. 2019, Available here.
2. “Glycolipids.” Nature News, Nature Publishing Group, Available here.
3. “Glycolipid.” Wikipedia, Wikimedia Foundation, 6 Dec. 2019, Available here.
Image Courtesy:
1. “Glycolipids” By RicHard-59 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “0302 Phospholipid Bilayer” By OpenStax – (CC BY 4.0) via Commons Wikimedia