Skip to content
Login Register

#membrane lipids

22 public questions tagged with this topic.

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.

View Details
Plasma Membrane

What is the role of phosphatidylinositol in the membrane?

Phosphatidylinositol's inositol ring protruding into cytosol can be phosphorylated to produce phosphoinositides that act as transient second messenger precursors. Upon activation of GPCR coupling to Gq or RTK activating PLC-gamma, phospholipase C cleaves PIP2 into diacylglycerol which stays embedded to recruit C1 domain of protein kinase C and Munc13 for exocytosis, and soluble IP3 that binds tetrameric IP3 receptor calcium channels on ER releasing calcium that activates calmodulin and NFAT. Concurrently class I PI3K phosphorylates PIP2 to PIP3 which accumulates transiently and recruits protei

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 15: Phosphoinositide Signaling Cascade.

View Details
Plasma Membrane

Which of the following forms mixed bilayers with phosphoglycerides?

Phosphoglycerides and sphingomyelin can co-assemble into stable mixed bilayers because both possess two hydrophobic tails and cylindrical geometry compatible with lamellar phase, unlike lysophospholipids that form micelles or cardiolipin that favors hexagonal inverted phases due to small headgroup. Sphingomyelin's fatty acid amidated to sphingosine resembles phosphatidylcholine's diacylglycerol moiety in hydrophobic thickness, allowing van der Waals matching and hydrophobic mismatch avoidance, enabling fluid mosaic continuity. Moreover sphingomyelin synthesis itself links the two classes: sphi

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Mixed Bilayers of Sphingomyelin.

View Details
Plasma Membrane

Which of the following molecules is the main precursor for sphingolipids?

Building sphingolipids requires creation of sphingoid long-chain base de novo in endoplasmic reticulum membrane through highly regulated steps essential for barrier formation. Serine palmitoyltransferase, heterodimer of SPTLC1 and SPTLC2 regulated by ORMDL feedback inhibition and small subunits ssSPTa/b that determine acyl chain preference, condenses L-serine and palmitoyl-CoA producing 3-ketodihydrosphingosine, reduced by 3-ketodihydrosphingosine reductase KDSR to dihydrosphingosine, also called sphinganine. Dihydrosphingosine is N-acylated by six ceramide synthases CerS isoforms with fatty-a

Ref: Lehninger Principles of Biochemistry, 8th ed., Chapter 21: Sphingosine Precursor and S1P Signaling.

View Details
Plasma Membrane

Which type of linkage stabilizes the structure of ceramide?

Ceramide comprises sphingosine, an 18-carbon amino alcohol with trans double bond between C4-C5, linked to fatty acid of 14 to 26 carbons via amide bond at C2 amino position providing chemical stability. Reaction catalyzed by ceramide synthases CerS1-6 in endoplasmic reticulum shows chain-length specificity determining biological outcome such as apoptosis versus differentiation. Amide linkage is more resistant to hydrolysis than ester bond and participates actively in intermolecular hydrogen bonding through NH as donor and carbonyl oxygen as acceptor, interacting with adjacent hydroxyl groups

Ref: Lehninger Principles of Biochemistry, 8th ed., Chapter 10: Ceramide and Sphingolipid Metabolism.

View Details
Plasma Membrane

Which of the following is NOT a function of cholesterol in the plasma membrane?

Cholesterol's structure with rigid tetracyclic ring system and short iso-octyl tail allows it to insert into phospholipid bilayers with hydroxyl near phospholipid carbonyls and ring system interacting with upper acyl chains. At low temperatures it disrupts tight packing of saturated chains, preventing transition to gel phase and preserving lateral diffusion essential for protein function, while at high temperatures its rigid ring restricts chain motion, decreasing permeability to small polar molecules, protons, and sodium ions, maintaining electrochemical gradients. Within membranes cholestero

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Cholesterol Functions and Steroidogenesis.

View Details
Plasma Membrane

Which of the following linkages is found in sphingomyelin but not in phosphoglycerides?

Phosphoglycerides use glycerol backbone where fatty acids are linked to sn-1 and sn-2 hydroxyls via O-ester bonds, susceptible to phospholipase A1 and A2 hydrolysis generating lysophospholipids and free fatty acids like arachidonic acid. Sphingomyelin architecture departs: its backbone is sphingosine, containing long-chain amino alcohol with double bond, where fatty acid attaches at amino group at C2 through N-amide bond formed by ceramide synthase in ER, producing ceramide intermediate. This amide bond affords additional hydrogen bond donor and acceptor, raising melting temperature and streng

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: Sphingomyelin Structure, Amide Linkage.

View Details
Plasma Membrane

What is the primary function of glycolipids in the plasma membrane?

Glycolipids are restricted to the exoplasmic leaflet where their oligosaccharide chains, assembled in Golgi by glycosyltransferases and glycosidases, face extracellular milieu forming glycocalyx extending beyond protein domains. This topology makes them poorly suited to regulate fluidity, which is governed by fatty acid saturation and cholesterol content, or to transport ions, mediated by channels and pumps. Their principal contribution lies in recognition and signaling. Carbohydrate moieties constitute ABO and Lewis blood group antigens, selectin ligands like sialyl Lewis X that direct leukoc

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Glycocalyx and Cell Recognition.

View Details
Plasma Membrane

Which of the following phospholipids is primarily involved in apoptosis?

Phosphatidylserine is normally confined to the cytoplasmic leaflet of the plasma membrane at greater than 85% asymmetry, maintained by P4-ATPase flippases ATP11A and ATP11C that use ATP to translocate aminophospholipids inward while floppases move lipids outward. Early in apoptosis, effector caspase-3 cleaves and inactivates flippases and simultaneously activates calcium-dependent scramblases such as Xkr8 and ANO6, causing rapid collapse of asymmetry and exposure of phosphatidylserine on the external surface. This externalized lipid functions as dominant eat-me signal recognized by dedicated p

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Lipid Asymmetry and Apoptosis.

View Details
Plasma Membrane

Which of the following is a major glycolipid found in the plasma membrane?

Gangliosides are prominent glycosphingolipids of vertebrate plasma membranes, characterized by a hydrophobic ceramide anchor embedded in the outer leaflet linked to a complex oligosaccharide carrying one or more sialic acid residues. This bulky carbohydrate headgroup projects into the extracellular space and participates in the glycocalyx, mediating cell-cell recognition, modulation of receptor tyrosine kinases such as EGFR, and adhesion during neural development and immune synapse formation. Unlike sphingomyelin which incorporates phosphocholine as headgroup via phosphodiester bond, or phosph

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Membrane Structure, Glycosphingolipids and Gangliosides.

View Details
Plasma Membrane

Which of the following membrane lipids carries a negative charge at physiological pH?

Electric field across membrane influenced anionic phospholipids clustered inner leaflet physiological pH seven point four generating negative surface potential crucial signaling recruitment. Phosphatidylserine headgroup contains phosphate pKa less two carboxyl pKa three amine pKa nine net charge minus one neutral pH despite zwitterionic potential measured zeta minus fifteen millivolts inner leaflet ten to fifteen percent total phospholipid outer almost zero. Approximately PS binds Annexin V calcium dependent detection apoptosis C2 domains PKC synaptotagmin polybasic KRas via electrostatic attr

Ref: Levental & Grzybek, Annu Rev Physiol 2010, Phosphatidylserine anionic negative charge electrostatic signaling and clearance.

View Details
Glycolipid and Phospholipid

Which type of lipid interaction is disrupted by methyl-β-cyclodextrin?

Lipid raft integrity pharmacologically perturbed using methyl beta cyclodextrin torus shaped oligosaccharide seven glucose units hydrophobic interior cavity zero point eight nanometer diameter fitting sterol. Cavity fits cholesterol high affinity one to two stoichiometry extracting sterol membrane into soluble inclusion complex without hydrolyzing phospholipids at low concentrations below ten millimolar preserving phospholipid mass. Removal dismantles cholesterol sphingolipid condensed complexes driven van der Waals packing hydrogen bonding amide hydroxyl interactions transforming liquid order

Ref: Zidovetzki & Levitan, Biochim Biophys Acta 2007, Cyclodextrin cholesterol sphingolipid raft disruption mechanism and reversibility.

View Details