It has been an absolute pleasure (for the majority of my adult life) to have had the opportunity to immerse my thoughts in the study of intermediary metabolism, to have been engaged in metabolic research involving alcohol metabolism, and then to have had the privilege of teaching this material to college students with a curiosity of physiological chemistry. Below are a few metabolic pathways (thousands exist) that remind me of a very exciting research and teaching career. To all my former Biological Sciences 170 students who happen upon this page - thank you for sharing those memorable times.

Aside from the few remarks below, no significant effort is made to explain the importance of these metabolic pathways. I hope the few comments provided, however, conjure up some curiosity.

The first pathway, shown below, describes the catabolism of carbohydrate (glucose) to lactate via anerobic glycolysis, which by definition occurs under anaerobic conditions. The next time you exercise and feel that "burn," you will begin to appreciate this pathway and the reason why heart rate and respiration increase with muscle lactate production. Essentially, your lungs and heart are trying their best to deliver and replenish the additional oxygen used and needed during intense muscular activity. I have a great section on this material in "Smart Weight Loss." Reading "Smart Weight Loss" is a much easier way to understand nutrition and exercise metabolism without pronouncing funny names and staring at strange diagrams. This is one of the reasons I wrote "Smart Weight Loss."
The next metabolic pathway, shown below, is essential for the synthesis of urea (ureagenesis) from various nitrogen sources. Not a pathway we spend too much time thinking about on a daily basis until it is time to appreciate the vital role our kidneys and liver play in the elimination of nitrogen in the form of urea.
The next metabolic pathway, shown below, describes the oxidation (burning) of fatty acids (fat). The best way to lose extra or unwanted adipose tissue (fat) is to do more of the following:
The diagram below depicts the basic interrealtionship between amino acids (protein), triglycerides (fat), and carbohydrates (sugars). Memorizing metabolic pathways, like the one below, is the best
way to start seeing the overall "picture" up close.
The next metabolic pathway, shown below, describes the production of ketone bodies (ketogenesis) from fatty acids. Look for "acetone." It is the ketone body that gives you the "bad breath" syndrome when blood insulin levels are low. Seriously, it is critical that the liver makes ketone bodies whenever blood insulin levels are low. You have a healthy curiosity if you are wondering why?
You will appreciate the next pathway, shown below, when you are hungry. There are important times when your liver is told ("instructed") to make glucose (sugar) via a process called gluconeogenesis. Start looking for "lactate" near the bottom of the diagram (just outside the mitochondrion) and then carefully follow the arrows to the top of the diagram to locate "glucose." Note that the cytosolic enzyme "Pyruvate Kinase" catalyzes an irreversible (unidirectioanl) reaction between phosphoenol pyruvate (PEP) and pyruvate. Not much room here to discuss why it happens the way it does, but note that pyruvate must enter the mitochondrion to eventually get metabolized to phosphoenol pyruvate (PEP). In an unfed state, all reactions between phosphoenol pyruvate (PEP) and glucose in liver tissue are reversible. Do you see where the sugar "glucose" is produced and how we got there from "lactate?" The topic of gluconeogenesis gets very interesting when the regulatory (hormomal/enzymes) details are presented. Also interesting to note is that the lactate used for glucose production in liver tissue is generated in muscle tissue from anaerobic glycolysis?
The last diagram, shown below, pretty much explains why I took all the big words and complicated diagrams out of my Smart Weight Loss book. I have always found it fascinating that there are so many different ways to essentially make the same point.
The diagrams above are excerpts from the Review of Physiological Chemistry.