#lipid composition

Plasma Membrane

Which type of lipid is NOT a part of the plasma membrane?

Biological membrane formation is governed by amphipathic geometry where polar headgroup cross-section balances hydrophobic tail volume, satisfying packing parameter close to 1 for bilayer assembly and stability. Phospholipids such as phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, sphingolipids like sphingomyelin and cerebroside, and cholesterol as small amphiphile intercalated among chains all meet this criterion and readily incorporate into 5 nanometer fluid mosaic film with integral proteins diffusing laterally. Triglycerides, triacylglycerols composed of glycerol esterif

Ref: Lehninger Principles of Biochemistry, 8th ed., Chapter 10: Triglycerides vs Membrane Lipids.

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Glycolipid and Phospholipid

Which of the following is NOT abundant in lipid rafts?

Isolation detergent resistant membranes quantitative shotgun lipidomics show selective lipid sorting excluding certain anionic glycerophospholipids and enriching sphingolipid cholesterol species. Sphingomyelin cholesterol ceramide cerebrosides galactosylceramide gangliosides GM1 associate preferentially due saturated acyl chains fourteen to twenty four carbons hydrogen bonding amide hydroxyl enabling tight packing into liquid ordered phase high chain order low fluidity lateral diffusion moderate. Glycolipids project bulky headgroups outward stabilizing raft extracellular leaflet sterically hin

Ref: Levental I et al., PNAS 2010, Lipid raft composition PS depleted not enriched and coupling.

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Properties of Plasma Membrane

What is the primary determinant of lipid bilayer curvature?

Spontaneous curvature stems from imbalance between optimal headgroup repulsion and hydrocarbon chain pressure described by Israelachvili packing parameter P equals v divided by a times l. When headgroup area a large relative to volume v molecule resembles inverted cone P less than one yielding positive curvature forming micelles as lysophosphatidylcholine with one chain generating outward bulges. Small headgroup like PE PA DAG yields cone P greater than one favoring negative curvature invaginations and HII tubes needed for fusion fission. PC sphingomyelin balanced a and v give cylinder P about

Ref: McMahon & Gallop, Nature 2005, Mechanisms membrane curvature determinants headgroup size.

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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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