A Note From Ray Haring . . .

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 spent many years in a metabolic research laboratory investigating alcohol's affect on liver function and cellular 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.

A day in a life teaching my favorite class.
(Tap photo for a glimpse of my Biological Sciences 170 class)

A day in a life remembering researching metabolic pathways with my major professor, Dr. Richard A. Freedland,

Chair, Department of Molecular Biosciences, UC Davis School of Veterinary Medicine.

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 inter-relationship 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 unfed, on a caloric restricted diet, or when you are generating glucose from lactic acid (lactate) during bouts of anaerobic activity. Carbon flux to glucose from amino acids (derived from protein degradation) are not shown in this diagram. The following pathway, however, describes the metabolic events 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 (unidirectional) 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 look for pyruvic acid (pyruvate) and notice that pyruvate is just one step closer to glucose than lactate. Remember, lactate used for glucose production in liver (hepatic) tissue is generated in sketetal muscle tissue from anaerobic glycolysis, ie., "burning" or oxidizing glucose as a source of fuel when muscle cells are running a bit low on oxygen during intense physical activities. Although the steps are not shown or mentioned in the diagram below, certain amino acids generated from protein degradation can be used to make pyruvate and Citric Acid Cycle intermediates after they have been stripped (deaminated) of their nitrogen group. Simply, this means our bodies will increase rates of protein degradation in order to make glucose (gluconeogenesis) during periods of food restriction. Think simple. Does it make sense to try to keep the sugar (glucose) level from falling into the hypoglycemic (low) range during an intentional or unintentional restriction of food intake? Yes! The liver is pretty smart at times!

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.