Energy-investment phase
Energy Investment Phase
In the initial phase of Glycolysis, 2 ATP molecules are used to ultimately convert a six-carbon glucose to two molecules of 3 carbon phosphorylated glyceraldehyde- 3-phosphate (G3P)
· Step 1: Glucose is phosphorylated into Glucose-6 phosphate by hexokinase and an ATP molecule. This Process requires an Mg2+ concentration to occur and once this step is initiated, the entire process must go to completion.
· Step 2: Glucose 6 phosphate is prepared for another phosphorylation through an aldose-ketose conversion which changes Glucose-6-phosphate into fructose-6-phosphate. The enzyme used to accomplish this is phosphoglucoisomerase.
· Step 3: Fructose-6-phosphate is phosphorylated by Phosphofructokinase (PFK) and an ATP. This enzyme also requires Mg2+ and is the key regulatory step. The product of this reaction is Fructose-1, 6-bisphosphate
o Phosphofructokinase (PFK) is complex allosteric enzyme which affects the rate at which glycolysis occurs in the cell. It is positively affected by high levels of ADP and AMP which signify a lack of energy and a need for Glycolysis. PFK is, in turn, inhibited by the presence of molecules such as ATP and citrate (a product of the Krebs cycle)
· Step 4: Fructose-6-phosphate undergoes hydrolysis and its ring structure is broken and separated into two trioses, Dihydroxyacetonephosphate (DAP) and Glyceraldehyde 3-Phosphate(G3P).
· Step 5: The subsequent energy yielding reactions make use of G3P and not DAP. Therefore a final isomerization reaction takes place in which DAP is converted into its structural isomer G3P. This reaction is regulated by triosephosphate isomerase.
Total investment: 4ATP (2 per Glucose molecule)
In the initial phase of Glycolysis, 2 ATP molecules are used to ultimately convert a six-carbon glucose to two molecules of 3 carbon phosphorylated glyceraldehyde- 3-phosphate (G3P)
· Step 1: Glucose is phosphorylated into Glucose-6 phosphate by hexokinase and an ATP molecule. This Process requires an Mg2+ concentration to occur and once this step is initiated, the entire process must go to completion.
· Step 2: Glucose 6 phosphate is prepared for another phosphorylation through an aldose-ketose conversion which changes Glucose-6-phosphate into fructose-6-phosphate. The enzyme used to accomplish this is phosphoglucoisomerase.
· Step 3: Fructose-6-phosphate is phosphorylated by Phosphofructokinase (PFK) and an ATP. This enzyme also requires Mg2+ and is the key regulatory step. The product of this reaction is Fructose-1, 6-bisphosphate
o Phosphofructokinase (PFK) is complex allosteric enzyme which affects the rate at which glycolysis occurs in the cell. It is positively affected by high levels of ADP and AMP which signify a lack of energy and a need for Glycolysis. PFK is, in turn, inhibited by the presence of molecules such as ATP and citrate (a product of the Krebs cycle)
· Step 4: Fructose-6-phosphate undergoes hydrolysis and its ring structure is broken and separated into two trioses, Dihydroxyacetonephosphate (DAP) and Glyceraldehyde 3-Phosphate(G3P).
· Step 5: The subsequent energy yielding reactions make use of G3P and not DAP. Therefore a final isomerization reaction takes place in which DAP is converted into its structural isomer G3P. This reaction is regulated by triosephosphate isomerase.
Total investment: 4ATP (2 per Glucose molecule)