The 10 Steps of Glycolysis Diagram | Quizlet

Step 1

A phosphate group is transferred from ATP to glucose, making glucose-6-phosphate. Glucose-6-phosphate is more reactive than glucose, and the addition of the phosphate also traps glucose inside the cell since glucose with a phosphate can't readily cross the membrane.

Enzyme = Hexokinase

- Glycolysis takes places in the cytosol of the cell.

Step 2

Glucose-6-phosphate is converted into its isomer, fructose-6-phosphate.

Enzyme = Phosphoglucose Isomerase

Step 3

A phosphate group is transferred from ATP to fructose-6-phosphate, producing fructose-1,6-bisphosphate. This step is catalyzed by the enzyme phosphofructokinase, which can be regulated to speed up or slow down the glycolysis pathway.

Enzyme = Phosphofructokinase

Step 4

Fructose-1,6-bisphosphate splits to form two three-carbon sugars: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate. They are isomers of each other, but only one—glyceraldehyde-3-phosphate—can directly continue through the next steps of glycolysis.

Enzyme = Fructose Biphosphate Aldolase

Step 5

DHAP is converted into glyceraldehyde-3-phosphate. The two molecules exist in equilibrium, but the equilibrium is "pulled" strongly downward, in the scheme of the diagram above, as glyceraldehyde-3-phosphate is used up. Thus, all of the DHAP is eventually converted.

Enzyme = Triose Phosphate Isomerase

- This ends the "energy investment phase" of glycolysis. Two ATP molecules have been used up and two 3-carbon molecules that are isomers of each other (DHAP and G3P) have been produced.

Step 6

Glyceraldehyde-3-phosphate, one of the three-carbon sugars formed in the initial phase, loses two electrons and two protons, reducing NAD+ to NADH and producing an H+.This reaction releases energy, which is used to attach another phosphate to the sugar, forming 1,3-bisphosphoglycerate.

Enzyme = Glyceraldehyde-3-Phosphate Dehydrogenase

Step 7

1,3-bisphosphoglycerate donates one of its phosphate groups to ADP, making a molecule of ATP and turning into 3-phosphoglycerate in the process. This is the first substrate-level phosphorylation.

Enzyme = Phosphoglycerate Kinase

Step 8

3-phosphoglycerate is converted into its isomer, 2-phosphoglycerate.

Enzyme = Phosphoglycerate Mutase

Step 9

2-phosphoglycerate loses a molecule of water, becoming phosphoenolpyruvate (PEP). PEP is an unstable molecule, poised to lose its phosphate group in the final step of glycolysis.

Enzyme = Enolase

Step 10

PEP readily donates its phosphate group to ADP, making a second molecule of ATP. As it loses its phosphate, PEP is converted to pyruvate, the end product of glycolysis.

Enzyme = Pyruvate Kinase

- This ends the "payoff phase" of glycolysis. 2 ATP and 1 NADH are produced from each of the 3-carbon sugars (Glyceraldehyde-3-phosphate), leading to the formation of 2 pyruvate molecules, 4 ATP, and 2 NADH.

- The "net" production is 2 ATP molecules!

TERM

Regulatory Step #1

DEFINITION

This is the first irreversible step of glycolysis. It is highly exergonic.

TERM

Regulatory Step #2

DEFINITION

This is the second irreversible step of glycolysis. It is highly exergonic. PFK is an allosteric enzyme regulated by the energy status of the cell.

TERM

Regulatory Step #3

DEFINITION

This is the third (and final) irreversible step of glycolysis. It is highly exergonic.