So if we're examining, let's say, glucose, the open chain form of glucose looks like this. And if we're examining, let's say, fructose, well, then the fructose open chain form looks like this. Now, although the open chain form of sugar molecules does exist to a very a small extent inside our body, these open chain sugar molecules actually undergo a cyclic reaction to form ring structures. Why? Well, because the ring structure of the sugar molecule is lower in energy and more stable than its open chain counterpart. Now, what exactly is this reaction that takes place that allows that less stable or higher in energy open chain form to transform into the more stable, lower in energy ring structure form?