If you add too little salt, the dough is tough and sticky. If you add too much, water flows out of yeast cells by osmosis. Then nutrients are lost and production of carbon dioxide slows down. After dough rises a couple of hours in a warm place, it's ready to go into the oven. There, heat causes pockets of gas in the dough to expand.
Enzymes are biological catalysts.
Proteins are polymers of amino acids. Van Nostrand Reinhold. American Health, pp. Bake your own bread. The cookbook decoder.