Summary
Highlights
Glycolysis begins with a six-carbon glucose molecule. The first reaction converts glucose into glucose 6-phosphate, catalyzed by the enzyme hexokinase. Kinases are enzymes that transfer phosphate molecules. In this step, hexokinase takes a phosphate from ATP and attaches it to the sixth carbon of glucose, producing glucose 6-phosphate and converting ATP to ADP.
Next, glucose 6-phosphate is acted upon by phosphoglucomutase, an isomerase enzyme. Isomerases rearrange molecules to produce an isomer without adding or removing atoms. This reaction converts the glucose hexagon shape into a fructose pentagon, resulting in fructose 6-phosphate, with the phosphate remaining at the sixth carbon.
Fructose 6-phosphate then reacts with phosphofructokinase one, another kinase. A phosphate molecule is transferred from ATP and attached to the first carbon of the substrate, creating fructose 1,6-bisphosphate. This is the last energy-requiring step of glycolysis and marks the end of the preparation or investment phase.
Fructose 1,6-bisphosphate is split into two molecules: dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, catalyzed by the enzyme aldolase. These two molecules are isomers and are kept in equilibrium by triose phosphate isomerase. Glyceraldehyde 3-phosphate is the molecule fully utilized in the pathway, meaning one glucose molecule eventually yields two molecules of glyceraldehyde 3-phosphate.
The next step is catalyzed by glyceraldehyde-3-phosphate dehydrogenase, which performs the first oxidation-reduction reaction of glycolysis. Glyceraldehyde 3-phosphate is oxidized to 1,3-bisphosphoglycerate. Hydrogen is moved from glyceraldehyde 3-phosphate to an NAD molecule, producing NADH. Simultaneously, an inorganic phosphate is added to the first carbon.
1,3-bisphosphoglycerate then proceeds to the next step, catalyzed by phosphoglycerate kinase. In this reaction, a phosphate is removed from the first carbon of 1,3-bisphosphoglycerate to make ATP, leaving 3-phosphoglycerate as the product.
Next, 3-phosphoglycerate is acted upon by phosphoglycerate mutase, which is a mutase enzyme that changes the structure of molecules. The phosphate group is moved from the third carbon to the second carbon, yielding 2-phosphoglycerate.
2-phosphoglycerate is then converted to phosphoenolpyruvate by the enzyme enolase. This step is easy to remember as both the enzyme and product contain the word 'enol'. Water is also produced during this reaction.
The final step of glycolysis catalyzes phosphoenolpyruvate to pyruvate. This reaction is carried out by pyruvate kinase. This is the last energy-forming step of glycolysis, where ATP is made from ADP through the transfer of a phosphate molecule, completing the biochemical reaction of glycolysis.