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#membrane fluidity

14 public questions tagged with this topic.

Basics of Cell Biology

Which component of the plasma membrane is responsible for fluidity?

Membrane fluidity describes lateral mobility, rotation, and flexing of components, parameter influencing permeability, fusion, and signaling complex formation. Phospholipids primarily determine fluidity through acyl chain composition: presence of cis double bonds as in oleoyl 18:1 and arachidonoyl 20:4 introduces kinks preventing close packing, lowering melting temperature Tm and increasing lateral diffusion coefficient about 10^-8 cm2/s measured by fluorescence recovery after photobleaching and fluorescence anisotropy. Shorter chains also increase fluidity. Cholesterol buffers fluidity by int

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Phospholipids and Fluidity Regulation.

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Plasma Membrane

Which of the following stabilizes the plasma membrane by modulating its fluidity?

Modulation membrane order cholesterol textbook example fluidity homeostasis buffering mechanism dual action concentration dependent. Cholesterol inserts three beta hydroxyl near phospholipid ester carbonyl forming hydrogen bond rigid tetracycle parallel upper ten carbons acyl chains restricting trans gauche isomerization high temperatures decreasing lateral diffusion coefficient from one to zero point five micrometer squared per second and passive permeability small solutes two to three fold measured calcein leakage assays. Low temperatures cholesterol disrupts all trans crystalline lattice in

Ref: Krause & Regen, JACS 2005, Cholesterol regulates fluidity stability buffering phase transition mechanism.

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Glycolipid and Phospholipid

Which of the following is NOT a function of sterols?

Sterols exhibit pleiotropy including biophysical modulation precursor provision signaling regulation but not direct ion conduction through pore formation or carrier mechanism. In plasma membrane cholesterol increases order parameter thickness decreases passive proton sodium permeability stabilizes liquid ordered rafts organizing receptors transporters signaling complexes cytoskeleton linkers. Metabolically cholesterol transported inner mitochondrial membrane StAR STAR D4 transfer cleaved CYP11A1 cytochrome P450 side chain cleavage to pregnenolone first step mineralocorticoids glucocorticoids a

Ref: Brown & Goldstein, J Lipid Res 2009, Cholesterol multifunctions not ion transport regulation.

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Properties of Plasma Membrane

Which molecule has the lowest transition temperature (Tm)?

Transition temperature dependence reflects chain packing efficiency influenced by length unsaturation. DOPC dioleoyl phosphatidylcholine contains two eighteen carbon chains each with cis delta nine double bond bending chain thirty degrees creating double kinks and large cross sectional volume reducing van der Waals contacts. Its Tm about minus seventeen to minus twenty Celsius lowest among common PCs. POPC one palmitoyl saturated sixteen plus one oleoyl unsaturated Tm minus two, DPPC dipalmitoyl two saturated sixteen packs tightly all trans Tm forty one due to high cooperative enthalpy, DMPC d

Ref: Lewis et al., Biochemistry 1987, Phosphatidylcholine Tm table DOPC lowest.

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Properties of Plasma Membrane

Which component of membranes helps maintain fluidity at lower temperatures?

Preservation of fluidity when temperature drops relies on lipid composition adjustments preventing gel formation that would freeze transporters. Cholesterol with rigid tetracyclic nucleus and three beta hydroxyl inserts among phospholipids orientation hydroxyl near carbonyl oxygen aligning ring parallel to upper acyl chains. At low temperatures it sterically hinders all trans chain crystallization by creating free volume and disrupting van der Waals lattice lowering order parameter measured by DPH anisotropy from zero point eight to zero point four. At high temperatures same rigid ring dampens

Ref: Mourtsen & Zuckermann, FEBS Letters 2004, Cholesterol broadens transition maintains fluidity.

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Properties of Plasma Membrane

Which lipid movement occurs the fastest in a membrane?

Biological membranes support diverse motions separated by orders of magnitude based on activation energy required to traverse hydrocarbon core. Lateral diffusion within same leaflet requires only breaking weak van der Waals contacts and creating small free volume achieving diffusion coefficient about ten to minus eight centimeters squared per second meaning lipid circumnavigates Escherichia coli in microseconds and mammalian cell in seconds. Axial rotation and wobbling of acyl chains are even faster nanoseconds observed by ESR. In contrast flip flop forcing zwitterionic or anionic headgroup th

Ref: Alberts et al., MBOC 7th ed., Chapter 10: Rates of lipid movement lateral vs transverse.

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Properties of Plasma Membrane

Which factor is responsible for phase transitions in phospholipid bilayers?

Lipid phase behavior reflects cooperative melting of hydrocarbon lattice from ordered gel to disordered liquid crystalline phases. Transition temperature Tm defines midpoint where fifty percent of chains contain gauche kinks and lateral expansion occurs, measured by differential scanning calorimetry as sharp endothermic peak representing enthalpy change. Tm rises with longer saturated acyl length because more CH2 groups increase van der Waals energy and with high sphingolipid content forming hydrogen bonding network at amide and hydroxyl groups. Cis unsaturation introduces permanent thirty deg

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Phase transitions Tm and calorimetry.

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Properties of Plasma Membrane

What happens to membrane fluidity when the fatty acid chains are shortened?

Fluidity of biomembranes reflects balance between van der Waals cohesion and steric freedom of acyl chains introduced by kinks. Shortening fatty acid chains from eighteen to fourteen carbons reduces surface area for London dispersion forces, weakening chain chain attraction and lowering cooperative melting enthalpy and phase transition temperature. The transition temperature Tm drops sharply, so at physiological thirty seven degrees a larger fraction exists in liquid crystalline disordered state characterized by frequent trans gauche isomerizations and rapid lateral diffusion near ten to minus

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: Fatty acid chain length and membrane fluidity.

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Properties of Plasma Membrane

What happens when cholesterol is added to a membrane at high temperature?

Dual effect of cholesterol on membrane order described as condensing and fluidity buffering arises from rigid steroid ring system intercalating among phospholipid acyl chains. At temperatures above phospholipid Tm chains highly disordered with many gauche conformers large area per lipid fluid low order. Cholesterol hydroxyl moiety positioned near phospholipid carbonyl oxygen forms hydrogen bond, rigid tetracyclic rings restrict chain isomerization reducing number gauche kinks order parameter S increases from zero point two to zero point five measured deuterium NMR, lateral diffusion coefficien

Ref: Ohvo-Rekila et al., Cholesterol Interactions and Membrane Fluidity Biphasic Effect, Prog Lipid Res 2002.

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Properties of Plasma Membrane

Which of the following affects the transition temperature (Tm) of membranes?

Phase transition of lipid bilayers from lamellar gel L beta where acyl chains fully extended ordered tight orthorhombic packing low mobility to liquid crystalline L alpha where chains disordered gauche isomers high mobility monitored by differential scanning calorimetry DSC exhibiting endothermic peak at Tm and by fluorescence anisotropy probes DPH TMA-DPH showing sharp decrease. Factors affecting Tm: chain length longer sixteen to eighteen carbons increases van der Waals interactions raising Tm dipalmitoyl phosphatidylcholine sixteen zero Tm forty one degrees centigrade distearoyl eighteen ze

Ref: McElhaney, Lipid Phase Transition and Chain Length Effect, Biochim Biophys Acta 1984.

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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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Eukaryotic Cell - Cell Wall and Cell Membrane - Fluid Mosaic Model

A change makes the lipid bilayer of a cell membrane much less fluid. Which group of processes is most likely to be affec

Membrane fluidity results from lateral movement of proteins within the quasi-fluid lipid bilayer. This property is important in cell growth, formation of intercellular junctions, secretion, endocytosis and cell division.

Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Eukaryotic Cell - Cell Wall and Cell Membrane - Fluid Mosaic Model

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