Which statement is true about the basis for lipoprotein separation by ultracentrifugation?

• A. It is based on density only
• B. It is based on protein and TG content
• C. It is based on color
• D. It is based on viscosity

Answer: (B)

Lipoprotein separation by ultracentrifugation relies on buoyant density. The particles differ in how much protein versus lipid they contain, so their densities vary. Proteins (apolipoproteins) add density, while lipids—especially triglycerides—lower density. Because different lipoproteins have different protein-to-lipid ratios, they settle at different points in a density medium under high centrifugal force. So the underlying idea is density, which is determined by composition—protein and triglyceride content—so variations in those components create the distinct fractions. Color or viscosity aren’t the basis for separation, and while density is the key property, the composition explains why those density differences exist.