1. In the present review, we suggest that a few common processes linked to membranes consume the majority of energy used by most organisms. 2. Membranes may act as metabolic pacemakers through changes in lipid composition, altering membrane characteristics and the working environment of membrane proteins. 3. Experiments involving membrane exchanges show predictable changes in protein activities (sodium pump) that are dependent upon the type of membrane used. 4. Potential mechanisms discussed include fluidity, electrical fields, surface area requirements of lipids and peptide-lipid interactions.