I've had some students who were taking biochemistry in preparation for professional training. And if your goal is work in a clinical profession, much of the standard biochemistry curriculum will seem abstract and impractical. So I want to highlight a recent story in the Washington Post where a boy with a set of unusual symptoms was eventually diagnosed with a rare genetic disease in a pathway that all biochemistry students study. The boy, Peter Mathiasen, suffered recurrent, inexplicable bouts of hypo- (but also sometimes hyper-) glycemia and ketosis. After a number of years, a specialist diagnosed him with a glycogen storage disease. In particular, Peter as found to have a deficiency in the enzyme phosphorylase kinase.
Normally, the liver regulates the level of glucose in the blood. When glucose is high, as is the case after a meal, the liver will absorb the glucose and store it in the form of a polymer called glycogen. When blood glucose is low, enzymes in the liver break down the glycogen and release glucose into the blood. The enzyme directly responsible for breaking down glycogen is called phosphorylase, so-called because it uses inorganic phosphate to break the bonds between glucose molecules in glycogen. Phosphorylase needs to be activated by the addition of a phosphate to its structure (yes, all these phosphate additions can get confusing...). The enzyme that does this is phosphorylase kinase.
Since Peter has a genetic deficiency in the regulation of phosphorylase, glycogen breakdown and glucose release by the liver is defective. What's really remarkable about this story is that the treatment is simple: Peter drinks a mixture of cornstarch in water before bedtime, and sometimes during the day if he's particularly active. The breakdown of the cornstarch in the digestive tract is slow enough that it provides his body with a steady source of glucose.
You can read the whole story here: http://bangordailynews.com/2012/05/23/health/after-five-years-boys-rare-ailment-revealed-and-treated-with-a-pantry-staple/