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 IN16B at ILL to investigate the ns dynamics of total lipid extracts from P. pastoris yeast, and found that their average molecular dynamics are considerably faster than single lipid membranes such as DMPC, and could not be observed on the timescale probed by IN16B. We now propose to continue our investigation on IRIS to probe faster dynamics that should allow a comparison to DMPC and the polyunsaturated lipid PLPC.