Gluten is formed when flour is mixed with water and kneaded. Both the gliaden and glutenin proteins unite with the water and then commingle to form sheets of flexible gluten. Gluten is the component that traps gases and air that cause the dough to rise. The yeast feeds on the sugars and produces carbon dioxide and alcohol. The carbon dioxide enlarges the air bubbles in the dough and the alcohol converts to gas and makes the air bubbles even larger. Gluten also holds on to the starch granules, allowing them to bend around the air bubbles. Then, as the bread bakes, the gluten proteins begin to cook, releasing water into the starch granules, firming the proteins, and providing the desired crumb.