Introduction to Lipids: Videos & Practice Problems

Hypothesis: Increasing headgroup negative charge reduces micelle stability with bile salts due to electrostatic repulsion. Design: prepare phospholipids with neutral (phosphatidylcholine), zwitterionic (phosphatidylethanolamine), and negatively charged (phosphatidylserine) headgroups in identical concentration; add physiological bile salt levels; measure micelle size distribution and critical micelle concentration by dynamic light scattering and surface tension assays. Outcome measures: CMC, average micelle size, and stability over time. Expect charged headgroups to alter CMC and reduce stable micelle formation compared with neutral headgroups.

Hypothesis: Headgroup charge has no effect; design: mix random lipids and observe under a light microscope; outcome: presence or absence of any visible structure is recorded without quantitation.

Hypothesis: Only chain length matters; design: vary acyl chains but keep headgroups constant and correlate color change to micelle formation, assuming optical color is a valid proxy for micellization.

Hypothesis: Increasing positive headgroup charge will transform all micelles into rigid crystals; design: prepare positively charged phospholipids and measure caloric output when crystals form.