Difference Between Fluid Mosaic Model and Sandwich Model

The key difference between fluid mosaic model and sandwich model is that fluid mosaic model states that cell membrane is a fluid phospholipid bilayer in which proteins are either partially or wholly embedded while sandwich model described the cell membrane structure as a lipid layer sandwiched between two protein layers.

There are several models which explain the structure of the cell membrane. Fluid mosaic model and sandwich model are two such models. Fluid mosaic model declares that large protein (glycoprotein) molecules are embedded within the bilayer of phospholipids. It is the most accurate model of the cell membrane. Sandwich model, on the other hand, states that a phospholipid bilayer is sandwiched between two layers of proteins. It was the first model to describe the cell membrane structure.

CONTENTS

1. Overview and Key Difference
2. What is Fluid Mosaic Model 
3. What is Sandwich Model
4. Similarities Between Fluid Mosaic Model and Sandwich Model
5. Side by Side Comparison – Fluid Mosaic Model vs Sandwich Model in Tabular Form
6. Summary

What is Fluid Mosaic Model?

Fluid mosaic model is the most accurate model that explains the structure of the cell membrane. According to this model, glycoproteins (large protein molecules) are embedded partially or completely in the phospholipid bilayer. This model also includes both integral and peripheral proteins. The mosaic nature of the cell membrane is mainly due to the homogenous distribution of proteins in the lipid bilayer. Apart from phospholipid and proteins, there are carbohydrates molecules on the exterior surface of the cell membrane. They are found bound to either to proteins (forming glycoproteins) or to lipids (forming glycolipids). There are cholesterol molecules, as well.

In brief, the fluid mosaic model identifies the cell membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. G.L. Nicholson and S.L. Singer proposed the fluid mosaic model in 1972.

What is Sandwich Model?

Sandwich model is the first model that explained the structure of the cell membrane. This model was proposed in 1935 by Hugh Davson and James Danielli. It states that the lipid layer is sandwiched between two protein layers. In simple words, it describes that phospholipid bilayer lies between two layers of globular proteins.

According to the sandwich model, the cell membrane is trilaminar and lipoproteinous. There are two layers of proteins; one facing the inte­rior of the cell and the other facing the external milieu. Hence, proteins do not span the lipid bilayer according to the sandwich model.

What are the Similarities Between Fluid Mosaic Model and Sandwich Model?

• Fluid mosaic model and the sandwich model are two different models that describe the structure of the cell membrane.
• These models attempted to describe the positions of proteins in the cell membrane.
• Both mention the presence of glycoproteins and phospholipid bilayer.

What is the Difference Between Fluid Mosaic Model and Sandwich Model?

Fluid mosaic model is the model that states large protein molecules are embedded partially or completely within the lipid bilayer while the sandwich model described the cell membrane structure as a lipid layer sandwiched between two protein layers. So, this is the key difference between fluid mosaic model and sandwich model. According to fluid mosaic model, proteins are embedded either partially or completely. In contrast, according to the sandwich model, there are two layers of proteins, and protein layers coat the outer surface. G.L. Nicholson and S.L. Singer proposed the fluid mosaic model in 1972 while Hugh Davson and James Danielli proposed the sandwich model in 1935.

Below infographic compares both models and lists the differences between fluid mosaic model and sandwich model.

Summary – Fluid Mosaic Model vs Sandwich Model

The fluid mosaic model describes the plasma membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. It also describes how proteins are partially or completely embedded in the phospholipid bilayer. This is the most accurate model that explains the structure of the cell membrane. Sandwich model is the first model that described the cell membrane. According to the sandwich model, the phospholipid bilayer is sandwiched between two protein layers. According to the sandwich model, proteins do not span across the membrane. Thus, this is the summary of the difference between fluid mosaic model and sandwich model.

Reference:

1. “Cell Membranes and the Fluid Mosaic Model | Boundless Anatomy And Physiology”. Lumenlearning.Com, 2020, Available here.

Image Courtesy:

1. “Cell membrane detailed diagram en” By LadyofHats Mariana Ruiz – Own work. Image renamed from File:Cell membrane detailed diagram.svg (Public Domain) via Commons Wikimedia
2. “MembranaAspectoTrilaminar” By Alejandro Porto – Basada en fotografía TEM de Kristen M. Harris, PI, (CC BY-SA 3.0) via Commons Wikimedia