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Membrane Fluidity

Membrane Fluidity

Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are generally able to move about in the plane of the membrane, giving the membrane its flexible nature called fluidity. Two other features of the membrane contribute to membrane fluidity: the chemical structure of the phospholipids and the presence of cholesterol in the membrane.

Membrane Fluidity

Membrane Fluidity

Membrane fluidity is explained by the fluid mosaic model of the cell membrane, which describes the plasma membrane structure as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.
Mosaic nature of the membrane
The mosaic characteristic of the membrane helps the plasma membrane remain fluid. The integral proteins and lipids exist as separate but loosely-attached molecules in the membrane. The membrane is a relatively...

Fluid Mosaic Model

Fluid Mosaic Model

Scientists identified the plasma membrane in the 1890s and its principal chemical components (lipids and proteins) by 1915. The model for plasma membrane structure, proposed in 1935 by Hugh Davson and James Danielli, was the first model to be widely accepted in the scientific community. The model was based on the plasma membrane's "railroad track" appearance in early electron micrographs. Davson and Danielli theorized that the plasma membrane's structure resembled a sandwich with the analogy of...

Membrane Domains

Membrane Domains

The membrane domains concentrate specific lipids and proteins at one place within the membrane, which helps in cell signaling, adhesion, and other critical cellular processes. These domains can differ in size, composition, function, and lifespan.
Protein Domains
The membrane comprises a group of distinct proteins responsible for carrying out a cell's specific function. For example, the plasma membrane of the human sperm, or a single germ cell, contains a unique set of proteins in the anterior...

SNAREs and Membrane Fusion

SNAREs and Membrane Fusion

Once a transport vesicle has recognized its target organelle, the vesicular membrane needs to fuse with the target membrane to unload the cargo. Transmembrane proteins called SNAREs present on organelle membranes and their vesicles, mediate vesicle fusion.
SNAREs exist in pairs that symmetrically interact and catalyze the fusion of the lipid bilayers in vesicle and target organelle. v-SNARE in the vesicle membrane are single polypeptide chains that bind to a complementary t-SNARE, composed of 2...

Rab Cascades

Rab Cascades

Rab GTPases act in a regulated cascade during membrane fusion, helping the lipid bilayers mix. The Rab family of proteins are active when bound to GTP, and inactive when bound to GDP. Hence, they act as guanine nucleotide-dependent molecular switches. Rab-GTP recognizes and binds to long or short-range tethering proteins to capture the target vesicle. These tethers coordinate with SNAREs on the vesicle and the target membrane to assemble the trans SNARE complex that locks the mixing bilayers.

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Related Experiment Video

Updated: May 22, 2026

SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy

SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy

Published on: August 24, 2016

SNARE proteins and 'membrane rafts'.

Thorsten Lang¹

¹LIMES-Institute, Laboratory for Membrane Biochemistry, University of Bonn, Bonn, Germany. tlang@gwdg.de

The Journal of Physiology

|May 5, 2007

Summary

The original lipid raft hypothesis is revised. SNARE protein clusters, previously debated, are now recognized as dynamic membrane rafts, crucial for cellular processes like vesicle fusion.

Area of Science:

Cell Biology
Membrane Biophysics
Biochemistry

Background:

The original lipid raft hypothesis proposed specific membrane domains enriched in cholesterol and sphingolipids.
Detergent-resistant membranes (DRMs) were used to isolate these putative lipid rafts and associated proteins.
SNARE proteins, involved in vesicle fusion, were found in DRMs, suggesting raft association.

Purpose of the Study:

To re-evaluate the definition and characteristics of membrane rafts.
To determine if SNARE protein clusters fit the revised definition of membrane rafts.
To clarify the relationship between SNAREs, cholesterol, and membrane microdomains.

Main Methods:

Critique of the detergent-based criterion for identifying lipid rafts.

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Construction of Model Lipid Membranes Incorporating G-protein Coupled Receptors (GPCRs)

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Last Updated: May 22, 2026

SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy

SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy

Published on: August 24, 2016

Visualizing Intracellular SNARE Trafficking by Fluorescence Lifetime Imaging Microscopy

Visualizing Intracellular SNARE Trafficking by Fluorescence Lifetime Imaging Microscopy

Published on: December 29, 2017

Construction of Model Lipid Membranes Incorporating G-protein Coupled Receptors (GPCRs)

Construction of Model Lipid Membranes Incorporating G-protein Coupled Receptors (GPCRs)

Published on: February 5, 2022

Review of recent consensus definitions for membrane rafts.

Analysis of SNARE protein localization and behavior in relation to membrane domains.

Main Results:

The term 'lipid rafts' has been replaced by 'membrane rafts' in a revised model.
Membrane rafts are defined as small, dynamic, sterol- and sphingolipid-enriched domains.
SNARE clusters meet the criteria for bona fide membrane rafts, despite prior challenges.

Conclusions:

The original concept of lipid rafts based on detergent resistance is outdated.
SNARE clusters are now understood as dynamic membrane rafts involved in membrane fusion.
This revised understanding impacts the study of intracellular trafficking and membrane dynamics.