Membrane Dynamics: -Transbilayer Movement of Lipids Requires Catalysis

At physiological temperature, transbilayer—or “flip flop”—diffusion of a lipid molecule from one leaflet of the bilayer to the other (Fig. 11–16a) occurs very slowly if at all in most membranes. Transbilayer movement requires that a polar or charged head group leave its aqueous environment and move into the hydrophobic interior of the bilayer, a process with a large, positive free-energy change. There are, however, situations in which such movement is essential. For example, during synthesis of the bacterial plasma membrane, phospho lipids are produced on the inside surface of the mem brane and must undergo flip-flop diffusion to enter the outer leaflet of the bilayer. Similar transbilayer diffusion must also take place in eukaryotic cells as membrane lipids synthesized in one organelle move from the inner to the outer leaflet and into other organelles. A family of proteins, the flippases (Fig. 11–16b), facilitates flip flop diffusion, providing a transmembrane path that is energetically more favorable and much faster than the uncatalyzed movement.

FIGURE 11–16 Motion of single phospholipids in a bilayer. (a) Move ment from one leaflet to the other is very slow, unless (b) catalyzed by a flippase; in contrast, lateral diffusion within the leaflet (c) is very rapid and requires no protein catalysis.

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مواضيع ذات صلة

The Composition and Architecture of Membranes:- Lipids and Proteins Diffuse Laterally in the Bilayer

Membrane Dynamics:- Acyl Groups in the Bilayer Interior Are Ordered to Varying Degrees

The Composition and Architecture of Membranes:- Covalently Attached Lipids Anchor Some Membrane Proteins

The Composition and Architecture of Membranes:- The Topology of an Integral Membrane Protein Can Be Predicted from Its Sequence

The Composition and Architecture of Membranes: -Integral Proteins Are Held in the Membrane by Hydrophobic Interactions with Lipids

The Composition and Architecture of Membranes:- All Biological Membranes Share Some Fundamental Properties

The Composition and Architecture of Membranes:- Each Type of Membrane Has Characteristic Lipids and Proteins

Working with Lipids:- Mass Spectrometry Reveals Complete Lipid Structure

Working with Lipids:- Gas-Liquid Chromatography Resolves Mixtures of Volatile Lipid Derivatives

Working with Lipids:- Adsorption Chromatography Separates Lipids of Different Polarity

Working with Lipids:- Lipid Extraction Requires Organic Solvents

Lipids as Signals, Cofactors, and Pigments: -Plants Use Phosphatidylinositols, Steroids, and Eicosanoidlike Compounds in Signaling