Phospholipid Structures and Composition Quiz

Phospholipid Structures and Composition

• Phospholipids can form micelles, lipid bilayers, monolayers, or vesicles depending on their structure and geometry
• Micelles consist of lipids arranged in a sphere with hydrophilic groups pointing outward and hydrophobic groups meeting at the center
• In a bilayer, lipids are arranged in a plane with hydrophobic groups pointing outward on both ends and towards each other in the middle
• Vesicles are similar to spherical bilayers, containing an aqueous core
• Glycerophospholipids have two fatty acyl chains and a phosphoalcohol esterified to a glycerol backbone
• Phosphate is connected to an alcohol through a phosphoester linkage in glycerophospholipids
• Phospholipids can have different head groups, acyl chain types, and number of acyl chains, leading to structural variations
• Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol are important in signaling cascades
• Phosphatidylcholine and phosphatidylethanolamine are the main lipids in cell membranes
• Plasma membrane, mitochondria, and endoplasmic reticulum have varying lipid compositions
• The lipid composition of a membrane varies between cell types and organelles
• Membrane lipid compositions are depicted in three pie charts, showing differences in lipid percentages

Micelle Formation and Neutral Lipids

• Micelles have hydrophobic tails oriented toward the core and hydrophilic head groups oriented toward the solvent, maximizing interaction with water while shielding the tails.
• Micelle formation results in an apparent gain of organization and loss of entropy, but the overall entropy change is positive due to liberated water molecules.
• The free energy (ΔG) of micelle assembly is negative, making the process spontaneous, illustrating the hydrophobic effect.
• A 3-part figure illustrates the micelle structure, amphipathic molecule hydrogen bonding, and micelle surrounded by water molecules.
• The critical micellar concentration (CMC) is the concentration at which micelles form and varies for different amphipathic molecules.
• Below the CMC, amphipathic molecules partition into membranes; above it, membranes begin to dissolve.
• Fatty acids are stored as neutral lipids, lacking charged groups, esterified to glycerol or cholesterol.
• Monoacylglycerol, diacylglycerol, and triacylglycerol are formed by esterifying fatty acids to glycerol.
• A 2-part figure shows the structures of monoglycerides, diglycerides, and triacylglycerols, including saturated, monounsaturated, and polyunsaturated fats.
• Saturated fats contain only saturated fatty acids, monounsaturated fats have a single double bond, and polyunsaturated fats have multiple double bonds.
• The structures of monoglycerides and diglycerides are displayed in Part A, and the different triacylglycerol structures are shown in Part B.
• Glycerides containing saturated fatty acids are called saturated fats, those with at least one fatty acid with a single double bond are termed monounsaturated fats, and those with multiple double bonds are known as polyunsaturated fats.