#membrane properties

Plasma Membrane

Which property of phospholipids is essential for the formation of the lipid bilayer?

Formation continuous bilayer aqueous milieu requires molecules possessing opposing solubility tendencies same structure thermodynamic principle driving self assembly. Phospholipids classic amphipaths containing hydrophilic headgroup phosphate plus choline ethanolamine serine inositol capable ionic hydrogen bonding water and two hydrophobic long chain fatty acids fourteen to twenty four carbons driving entropic hydrophobic effect via release ordered water clathrates surrounding tails increasing system entropy. Above critical micelle concentration nanomolar they self assemble bilayer sheets clos

Ref: Tanford C., Science 1978, Amphipathic phospholipids bilayer assembly hydrophobic effect and thermodynamics.

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Properties of Plasma Membrane

Which feature of lipid bilayers makes them selectively permeable?

Selective permeability originates from continuous oily interior separating cytosol from extracellular milieu. Phospholipid tails containing fourteen to twenty four carbon hydrocarbon chains exclude water creating low dielectric slab with Born energy penalty greater than one hundred fifty kilojoules per mol for moving sodium potassium chloride through effectively blocking ions and large polar molecules like glucose nucleotides sucrose. Small nonpolar gases oxygen carbon dioxide nitrogen dissolve readily and cross by solubility diffusion while water crosses slowly via transient pores permeabilit

Ref: Alberts et al., MBOC 7th ed., Chapter 11: Permeability of hydrophobic core and channels.

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Properties of Plasma Membrane

Which of the following statements about membrane fluidity is true?

Regulation of fluidity reflects balance between order and disorder of fatty acyl chains governing membrane physical properties and protein function. Saturated acyl chains straight all trans conformation maximize van der Waals contacts small area per lipid about forty eight square angstroms low fluidity high transition temperature. Cis double bond introduces kink thirty degree bend reducing contact area to about sixty square angstroms increasing free volume lowering transition temperature fifty degrees increasing lateral diffusion coefficient and rotational freedom measured by fluorescence anis

Ref: Singer and Nicolson, Fluid Mosaic Model and Fluidity Dependence on Unsaturation, Science 1972.

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Plasma Membrane Proteins

Which of the following properties affects membrane protein mobility?

Diffusion behavior of membrane proteins governed by hydrodynamic and cytoskeletal factors. Saffman-Delbruck model relates diffusion coefficient D to membrane thickness h viscosity mu m and protein radius r through D proportional to natural log of membrane to protein size. Number of transmembrane domains increases effective radius and frictional drag because each helix engages annular lipids diffusing as complex and more extensive hydrophobic surface contacts viscous acyl chains. Single-pass glycophorin diffusion coefficient about five times ten to minus nine centimeters squared per second fast

Ref: Kusumi et al., Paradigm Shift in Membrane Protein Diffusion and Corral Model, Annu Rev Biophys.

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