The Citric Acid Cycle (via Khan Academy)


“Hans Adolf Krebs received the Nobel Prize in Physiology for his “discovery of the citric acid cycle.” He was knighted in 1958.”–Via Wikipedia. Now you can put a face to the architect of your biochemical nightmares during this week.  

Just when you think you’re out of the woods after Glycolysis–you say to yourself: “I can take a breather”–the Krebs Cycle (a.k.a. The Citric Acid Cycle, or the oxidation of citrate) makes its appearance.

It can be just as complex, if not more, than Glycolysis. But the main thing that we have to take into account about this catabolic pathway–and catabolism of carbohydrates is all about accounting–is the redox reactions mediated by the enzymes of this pathway. This short animation should give us a brief review of how oxidation and reduction (redox) occur.

The following animation–embedded here via Khan Academy–shows a very good summary of the Citric Acid Cycle (notice the importance that the lecturer gives to “the big picture”, which in the Krebs Cycle means the enzyme regulated oxidation of a carbohydrate).


Glycolysis, or how cells break down carbohydrates.


Glycolysis (via McGraw Hill: How Glycolysis Works)

Eons of emergent changes and mutations, aided by natural selection, have made it possible for cells to make efficient use of the available energy on this planet. And the source of this energy is the Sun.

With these two sentences we welcome what can be considered the hardest, and most despised, part of any Bio course: Cellular Respiration. Cells are powered by combustion; but these have to occur in a controlled way. Enzymes–a synchronized and highly complex cascade of enzymatic events– will manage this controlled release of energy. This process begins with Glycolysis. The following videos are very good explanations of how Glycolysis works. Keep in mind that these are complex events. They are summarized as best as possible, but some effort has to be put in order to understand them: