How does ethanol affect yeast respiration?
As the amount of ethanol present increases, the pH of the yeasts living environment decreases. Because of this, the enzymes of the yeast start to denature – this means that they start to change shape as the bonds that hold them together are broken or changes. This alters the shape of the active site of the enzyme, rendering it useless. (Enzymes work via a ‘lock and key’ method, where the substrate/s the enzyme modifies fit perfectly into the enzymes ‘active site’, which has such a specific shape that only those substrate/s for that enzyme can fit into it. Any change of the shape of this active site means that the substrate/s can no longer fit into it, and so the enzyme cannot function, leaving it ineffective. If a yeast organism has no enzymes, it cannot respire and so it will die.
