Glycolysis Pathway

Glycolysis pathway is the metabolic process, by which glucose (C6 H12 O6) is broken down into two molecules of pyruvate (CH3 CO CO OH), which then enters the Krebs Cycle as Acetyl CoA. It is a sequence of ten chemical reactions in two phases. It envolves enzymes that act as catalists, which make possible the conversion, or degradation, of one molecule into another. We can also say that glycolysis is the anaerobic catabolism of glucose, occurring virtually in all cells cytosol. The free energy, which is stored in 2 molecules of pyruvic acid (pyruvate), is somewhat less than that in the original glucose molecule. The free energy released in this process is used to form the high energy compounds, ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).

Phases of glycolysis

First phase- Once glucose has gotten into the cell cytosol, it is degraded into glucose-6-phosphate by the enzyme hexokinase through phosphorylation reactions. Next, Glucose-6-phosphate is converted into fructose-6-phosphate by the enzyme isomerase. Fructose-6-phosphate is catalized into fructose-1,6-bisphophate by the enzyme phospho-fructo-kinase using ATP as energy. Then, fructose-1,6-bisphophate is broken down by the enzyme aldolase into two molecules: glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

Second phase- Glyceraldehyde-3-phosphate is transformed into 1-3bisphospho-glycerate by the enzyme glyceraldehyde-3-phosphate dehydrogenase, with the coenzyme NAD, which is reduced to NADH. Next, the 1-3bisphophoglycerate is catabolized into 3-phosphoglycerate by the enzyme phosphoglycerate-kinase, with one molecule of ATP being released in the process. The molecule 3-phosphoglycerate is in turn converted into 2-phosphoglycerate by the enzyme phosphoglycerate mutase. Then 2-phosphoglycerate is catalized into phosphoenol pyruvate by the enzyme enolase/MG2. Finally, phosphoenol pyruvate is broken down into pyruvate by the enzyme pyruvate kinase, producing another molecule of ATP in the process.

To enter the Krebs cycle, the pyruvate must be catalized into acetyl CoA by the enzyme pyruvate dehydrogenase.

Below, a glycolysis pathway diagram, which shows the metabolic conversion of glucose into pyruvate.