Though metabolic reactions include formation and breakdown of non-protein biomolecules such as sugars, lipids, etc., gene mutations affect the metabolism.
All the metabolic reactions are driven by enzymes. Enzymes are proteins that have catalytic powers. Mutation in the genes of any of the enzymes of metabolic pathways would affect the pathway.
The answer is nuclear fusion, since this is such a dominant source of energy as opposed to nuclear fission which takes place as well but at much smaller rates.
