The first systems of molecules having the properties of the living sta
te presumably self-assembled from a mixture of organic compounds avail
able on the prebiotic Earth. To carry out the polymer synthesis charac
teristic of all forms of life, such systems would require one or more
sources of energy to activate monomers to be incorporated into polymer
s. Possible sources of energy for this process include heat, light ene
rgy, chemical energy, and ionic potentials across membranes These ener
gy sources are explored here, with a particular focus on mechanisms by
which self-assembled molecular aggregates could capture the energy an
d use it to form chemical bonds in polymers. Based on available eviden
ce, a reasonable conjecture is that membranous vesicles were present o
n the prebiotic Earth and that systems of replicating and catalytic ma
cromolecules could become encapsulated in the vesicles. In the laborat
ory, this can be modeled by encapsulated polymerases prepared as lipos
omes. By an appropriate choice of lipids, the permeability proper-ties
of the liposomes can be adjusted so that ionic substrates permeate at
a sufficient rate to provide a source of monomers for the enzymes, wi
th the result that nucleic acids accumulate in the vesicles. Despite t
his progress, there is still no clear mechanism by which the free ener
gy of light ion gradients, or redox potential can be coupled to polyme
r bond formation in a protocellular structure.