Glycolysis - A Biochemical pathway

How does human body derive energy from Glycolysis!

If you have heard your parents telling you that if you eat a healthy diet you will grow up to be strong and energetic then you must have wondered how the food that you eat actually ends up giving you the energy we so desperately need!

Human body has so many functions that it is involved in, and if you care to go into the nitty gritty of the said functions you will have found new respect for the remarkable ways our body serves us in every hour of everyday throughout lifetime. Glycolysis is one of the words that has been thrown around in our biology classes time and time again. So, Let’s dive in to learn what that is and how it is a very important biochemical pathway.

Glycolysis means breaking down of glucose (a simple hexose) into two molecules of Pyruvate-3 carbon molecule. Glycolysis is an oxygen independent metabolic pathway and is likely a very ancient pathway. Pyruvate the end-product of glycolysis is important because it is at a crossroads with many metabolic pathways serving as a precursor to the synthesis of several biomolecules and to produce large number of ATP molecules (the energy currency of our body) under aerobic conditions. Pyruvate under aerobic condition is completely degraded into carbon dioxide and water during citric acid cycle and oxidative phosphorylation, the complete oxidation of glucose into CO2 and H2O is highly exergonic, the free energy change is -2840 KJ/mole (that’s a lot)

The glycolysis pathway can be studied under 10 steps. The initial five steps known as the Preparatory steps are as follow: - Here, one glucose molecule is converted into glyceraldehyde3 phosphate and dihydroxyacetone phosphate (3carbon molecules) powered with several biochemical enzymes in under five progressive steps. (fig 1:in blue)

The next five steps called Pay off phase (fig2) yield 2 ATP in which only glyceraldehyde 3 phosphate enters the pay-off phase, so it is necessary that DHAP (dihydroxy acetone phosphate) be converted into(glyceraldehyde 3 phosphate) GAP during the preparatory phase.

It is important to note that in 7th step (Fig 2) for each glucose molecule cleaved results in two molecules of 1,3 BPG, the conversion of two molecules of 1,3 Bisphosphoglycerate (1,3 BPG) into two molecules of 3 phosphoglycerate (3PG) it yields two molecules of ATP, such production of ATP is called Substrate level phosphorylation. Ultimately, two molecules of Pyruvate are produced as phosphoenol pyruvate is acted upon by pyruvate kinase in the 10th step. Let’s overview the entire pathway the reactants, products and the number of energy molecules involved. (fig3) We observe the overall production of two ATP molecules from glycolytic pathway, it does seem a little underwhelming to derive just 2 energy packets after undergoing such a rigorous pathway, but recall that the glucose molecule is not yet fully oxidized since pyruvate was the end product, and not CO2. Under aerobic condition pyruvate will be oxidized by different pathways and over 30 molecules of ATP will be produced per molecule of glucose. This results in -2872 KJ of free energy change, so much amount of energy is being processed as you live and breathe throughout this article. Such comprehensive and energy intensive processes occur in our cells all the time and this is only one of those processes. In consequence, this underscores our responsibility to learn about and to take care of our bodies, which tirelessly work to provide us with best of the living experience.