What is the liquid ordered state?
What is the liquid ordered state?
The liquid ordered phase is a liquid crystalline phase of a lipid bilayer, and is of significant biological importance. It occurs in many lipid mixtures combining cholesterol with a phospholipid and/or sphingolipids e.g. sphingomyelin. This phase has been related to lipid rafts that may exist in plasma membranes.
What is ld phase?
These include the liquid disordered (Ld) phase characterized by fast translational diffusion and low acyl chain order, the liquid ordered (Lo) phase with fast diffusion and high chain order, and the solid gel (Lβ) phase having slow diffusion and high chain order.
What is membrane gelling?
One property of a lipid bilayer is the relative mobility (fluidity) of the individual lipid molecules and how this mobility changes with temperature. This response is known as the phase behavior of the bilayer. The solid phase is commonly referred to as a “gel” phase.
What causes lipid rafts?
One type of microdomain is constituted by cholesterol and sphingolipids. They form because of the segregation of these lipids into a separate phase, demonstrated by Biltonen and Thompson and their coworkers. These microdomains (‘rafts’) were shown to exist also in cell membranes.
What is bilayer made up of?
phospholipid molecules
A bilayer is composed of two sheets of phospholipid molecules with all of the molecules of each sheet aligned in the same direction. In a water medium, the phospholipids of the two sheets align so that their water-repellent, lipid-soluble tails are turned and… … common of which is the bilayer.
What is TC of a lipid?
The phase transition temperature is defined as the temperature required to induce a change in the lipid physical state from the ordered gel phase, where the hydrocarbon chains are fully extended and closely packed, to the disordered liquid crystalline phase, where the hydrocarbon chains are randomly oriented and fluid.
Why is cholesterol essential for lipid rafts?
Cholesterol is thought to serve as a spacer between the hydrocarbon chains of the sphingolipids and to function as a dynamic glue that keeps the raft assembly together (1). Cholesterol partitions between the raft and the nonraft phase, having higher affinity to raft sphingolipids than to unsaturated phospholipids.
How do raft lipids stabilize small rafts?
Small rafts can sometimes be stabilized to form larger platforms through protein–protein and protein–lipid interactions” [42]. Raft lipids have been proposed to exist in a more ordered state, similar to the liquid-ordered (l o) phase described in model membranes [2, 43].
How do rafts form?
Two different models of raft formation have been proposed. The first model, supported by most data, suggests that rafts form by phase separation. Thus, structural features of lipids that affect Tm and promote phase separation will also promote raft formation.
Are cell rafts in ternary mixtures of lipids liquid ordered?
Cellular rafts are enriched in cholesterol and sphingolipids, and their potential correspondence with the liquid ordered ( Lo) phase in ternary mixtures of lipids has been recognized since the early 2000s 3, 4.
What are lipid rafts and membrane domains?
Lipid rafts are defined as cholesterol- and sphingolipid-enriched membrane domains and numerous studies have attempted the lipid characterization of caveolae and raft domains. Lipids do not always mix uniformly in membranes, but can cluster to form microdomains.
