The turbid layer in lipoprotein ultracentrifugation corresponds to which particle?

• A. Chylomicrons
• B. HDL
• C. LDL
• D. VLDL

Answer: (D)

The main idea here is that lipoproteins separate by buoyant density when spun at high speed, so particles with different lipid content settle into distinct zones. The turbidity you see in a particular layer signals a band rich in lipid-containing particles of intermediate density.

VLDL has an intermediate density, roughly 0.95–1.006 g/mL, because it carries a lot of triglycerides. In the ultracentrifugation setup, it sits between the very top layer of chylomicrons (the least dense, forming a creamy top layer) and the denser LDL and HDL fractions. That intermediate position makes the VLDL-containing layer appear turbid, due to its lipid-rich composition.

Chylomicrons, being the least dense, rise to the very top as a creamy layer rather than the turbid band. HDL is the most dense, settling toward the bottom, with LDL occupying a middle-to-lower zone. So the turbid layer corresponds to VLDL because of its intermediate density and triglyceride-rich makeup.