A cell membrane can contain hundreds of different lipid molecules, but our understanding of the dynamics of cell membranes is very limited. As a result of a collaboration between the ILL and ESS on the deuteration of lipids from cell cultures, we can now produce 100s of milligrams of lipid extracts from yeast and other microbial cell cultures, sufficient for neutron spectroscopy studies of their dynamics. We recently carried out the first QENS experiment on IRIS to probe the dynamics of the phospholipid extract from P. pastoris yeast, and found that there is a significant difference in their average molecular dynamics compared to model lipids such as POPC and DMPC. We now propose to continue our investigation on IRIS to probe the effect of ergosterol and its drug-resistance related precursors on yeast phospholipid dynamics.