PHYSICAL PRINCIPLES OF CELL BOLOGY

This thread is meant to include key principles we have gleaned.

ENERGY STORAGE - The cell stores energy not by having "fuels" which are "burned" but rather by maintaining processes (reactions/flows) out of equilibrium.  A key example is that [ATP] is maintained much higher than the value to which it would equilibrate given the ADP and Pi in the cell.  ATP is an example of an 'activated carrier', but there are numerous others.  Besides carrier molecules, energy is also stored by out-of-equilibrium gradients across membranes -- such as of ions and protons. In fact, ATP synthesis is driven by non-equilibrium proton [H+] concentrations maintained across the appropriate membrane.

ENERGY TRANSDUCTION - Energy is regularly converted among different carriers and 'devices' in the cell.  A sequence of activated carriers with high-energy electrons create a proton gradient, which in turn is used to generate ATP.  The constant downhill flow of (free) energy - from original source (food or light) to cellular waste - keeps the cell operating in an orderly way.  The flow of energy provides the power for information to flow in a single direction -- e.g., from a signal outside the cell to the nucleus.