Glycolysis Enzymes Quiz

Glycolysis: Breaking Down Glucose through Enzymatic Processes

Glycolysis, a central metabolic pathway, is the series of chemical reactions by which glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (a three-carbon compound). This process generates energy in the form of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide, reduced form) that can be used by cells to perform various functions. The enzyme involvement in glycolysis is a crucial aspect of this process, and we'll delve into the enzymes that facilitate each of the ten steps.

Step 1: Hexokinase

Glycolysis begins with the phosphorylation of glucose by hexokinase (or glucokinase). This enzyme uses ATP as the phosphate donor, creating glucose-6-phosphate (G6P) and adenosine diphosphate (ADP).

Step 2: Phosphoglucose isomerase

Phosphoglucose isomerase catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate (F6P). This reaction does not involve a net gain or loss of ATP, but it is essential for the progression of glycolysis.

Step 3: Phosphofructokinase-1 (PFK-1)

Phosphofructokinase-1 is a key regulatory enzyme in glycolysis. This enzyme catalyzes the phosphorylation of fructose-6-phosphate to produce fructose-1,6-bisphosphate (F1,6BP) using ATP as the phosphate donor.

Step 4: Aldolase

Aldolase cleaves fructose-1,6-bisphosphate into two three-carbon molecules: glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).

Step 5: Triose phosphate isomerase (TPI)

Triose phosphate isomerase catalyzes the interconversion between the two triose phosphate molecules, G3P and DHAP.

Step 6: Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)

Glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidation of G3P to 1,3-bisphosphoglycerate (1,3-BPG) and the reduction of NAD+ to NADH.

Step 7: Phosphoglycerate kinase (PGK)

Phosphoglycerate kinase is another important regulatory enzyme in glycolysis. This enzyme transfers the phosphate group from 1,3-BPG to ADP, forming 3-phosphoglycerate (3-PG) and ATP.

Step 8: Phosphoglycerate mutase (PGM)

Phosphoglycerate mutase catalyzes the interconversion of 3-phosphoglycerate to 2-phosphoglycerate (2-PG).

Step 9: Enolase

Enolase catalyzes the dehydration of 2-phosphoglycerate to phosphoenolpyruvate (PEP).

Step 10: Pyruvate kinase (PK)

Pyruvate kinase is the final enzyme in glycolysis. This enzyme catalyzes the formation of pyruvate from PEP, while transferring the phosphate group to ADP, generating ATP.

Glycolysis is a fundamental process for cells to generate energy, and its regulation ensures that energy production is balanced with the cell's needs. Understanding the enzymatic steps and their individual roles is essential for appreciating the intricacy of this metabolic pathway.

References: Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J, et al. Molecular Cell Biology, 4th ed. New York: W.H. Freeman, 2000. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, and Walter P. Molecular Biology of the Cell, 6th ed. New York: Garland Science, 2014.