Scientific Nutrition Update 25: Glycolysis

The full glycolysis pathway

This episode is all about starting to teach the basics of biochemistry.  In this case we are looking directly at the glycolysis pathway.  If you really don’t care about the underlying science feel free to skip this episode.

Script:

For today’s episode we are going to talk about glycolysis.  This is one of those occasional episodes where I focus in on one specific area or pathway in my area of expertise, biochemistry.  This is going to focus more on the pure science, and less on applications. This episode is meant for those nerds like me who really love to get down and dirty in the nitty gritty.  If all you care about is directly applicable tips, I’m going to recommend that you move on.

 

So what is glycolysis? Glycolysis is one of the basic carbohydrate metabolic pathways that is also one of the most basic energy generation pathways.  It is the pathway that breaks glucose down into pyruvate, which can enter the citric acid cycle. It is basically the beginning of a whole bunch of different pathways and because of that is really important.  It is also a pathway that stays almost exactly the same no matter what organism you look at, suggesting it has a really long evolutionary history. It is also an anaerobic process, meaning that it does not require oxygen to progress, however the products often enter aerobic pathways afterwards.

 

So briefly, glycolysis is a process that converts glucose into two pyruvate molecules, while also taking NAD+ and ADP and converting them into their high energy forms NADH and ATP.  This is a energy production pathway, meaning that it creates more high energy molecules like ATP than it consumes. What distinguishes glycolysis is its universality, and the fact that it can proceed anaerobically.  

 

Glycolysis however is relatively inefficient and as such is pretty tightly controlled.  Most critically at the phosphofructokinase enzyme which is responsible for converting fructose-6-phosphate to fructose-1,6-bisphosphate.  This step represents High levels of ATP which we have already establishes is the high energy substance inhibit this enzyme, preventing the process from advancing when it is unnecessary.  However, the action of this enzyme is promoted when there is a greater concentration of AMP which is a lower energy form of this molecule, thus promoting more energy creation when it is needed.  

 

There is also an earlier regulation point at hexokinase that can help prevent it from progressing this far.  That enzyme is inhibited by the presence of glucose-6-phosphate which is the product of this enzyme. Suggesting that if the glucose-6-phosphate is not being used it will prevent more from being formed.

 

There is also a final regulation point at pyruvate kinase which is the final step.  This is inhibited by ATP. This step is really about controlling the flow, we do not want to be continually producing ATP if there are sufficient supplies, so this final regulation helps control the flow rate.  

 

So why do you need to know this? You do not.  This is learning for the sake of learning. It is also important to understand some of these basic pathways, because many of the more interesting and advanced pathways interact with these simple ones and so then these become really important.  

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