I'm not a chemist, neither a molecular biologist. But I'm fascinated with science.
The way I understood, DNA is a macro-molecule which is made of atoms. And in reproduction, either mitosis or meiosis then mating, or in RNA creation mutation can happen. And mutation means a letter molecule in the chain of DNA can become another letter.
From the other side I know that by combining a known set of reactants, we get the same products, ALL the times. In other words, chemical reactions are deterministic and no matter how much we try, H2 + O results in water, and not in solphuric acid for example.
At this point I'm stuck. And I can't find an answer. How mutation happens in DNA while it's the outcome of chemical reactions and those reactions are deterministic?