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).

Oxidate It Or Love It / Electron to the Next One

We’ve reached “El Cuco” of High School Bio. Cellular Respiration–especially the stage that follows Glycolysis: Aerobic Respiration, in which chemiosmosis and the ETC (Electron Transport Chain) play a very important role–is a very complex set of biochemical reactions. In order to make energy from glucose, a lot has to happen; and all of this can be quite overwhelming:

This will not appear on your test.

This will not appear on your test.

The Krebs cycle can be tedious, difficult and boring; and I am well aware that my efforts on this blog do not guarantee that we will have a blast discussing this biohemical pathway. But I want to share this music video (via The Rhymebosome); maybe somethings about the Krebs cycle can actually be worthwhile:

Their best intentions are clear but a mouthful of complex words remains inevitable. Fortunately, Pulitzer Prize science writer, Jonathan Weiner, comes to the rescue with these two parragraphs (via

To power all of its molecular machinery … each cell contains anywhere from a few hundred to a few thousand mitochondria. And every one of those mitochondria contains a large collection of rotary motors. With every breath you take, you set off a long series of actions and chemical reactions that make those rotary motors spin around and around in every living cell of your body like zillions of turbines, windmill vanes, or airplane propellers. These rotary motors turn out a concentrated energy food, an energy-rich molecule called adenosine triphosphate, or ATP.

And this ATP, more than any other molecule in the cellular inventory, makes all the rest of the machines go. This is the fuel of all our mortal engines. Without ATP it would be useless for us to breathe in air, to drink and to eat. Without ATP, even the smallest piece of action in our bodies would slow down and stop.