Stages of Glycolysis

Glycolysis is one of three processes which occur in cellular respiration. It involves a glucose molecule going through a number of stages to produce 2 molecules of pyruvate in the end. This pyruvate is then passed on to another process of cellular respiration known as the Krebs cycle where another set of stages take place. The three most common stages of glycolysis are:

1. Phosphorylation: Where a phosphate is removed from ATP and added to glucose.
2. Lysis: Involving the splitting of fructose bisphosphate.
3. Dehydrogenation: Involving the removal of hydrogen from triose phosphate.

However the above mentioned processes are just a summary of the major stages taking place. Now we’ll look at the 7 stages of glycolysis:

Stage 1
ATP donates a phosphate group to the glucose molecule containing 6 carbons. This is done to make the glucose molecule more reactive to continue through stages to come.

Stage 2
After the phosphate has been added the entire glucose phosphate molecule gets reorganized to form a fructose phosphate molecule.

Stage 3
A second ATP then comes along and further donates another phosphate group to the fructose phosphate again making it more active. Now fructose bisphosphate is formed.

Stage 4
After the addition of yet another phosphate to fructose phosphate forming fructose bisphosphate, the molecule then splits into two triose phosphate molecules each containing 3 carbons. The original molecule of fructose bisphosphate contained 6 carbons therefore when it splits each molecule would therefore have 3 carbons attached.

Stage 5
In this stage two things happen:

1. Hydrogen atoms are lost from both triose phosphate molecules and gained by NAD. There is no net change in the concentrations of NAD and reduced NAD, because two oxidized NAD(one for each molecule of triose)are reduced when hydrogen is added forming 2 reduced NAD(again one for each molecule).
2. Inorganic phosphate is again added to each triose phosphate molecule therefore making it more reactive.

Stage 6
Just after adding a phosphate group another is removed from each triose bisphosphate molecule. 2 ADP molecule gains these phosphate and forms 2 ATP (remember 1 from each molecule).

Stage 7
Two things happen in this stage:

1. Another phosphate group is removed from each triose phosphate molecule 2 ADP molecules gains this phosphate to form 2 ATP molecules. The net synthesis of ATP in glycolysis is 2 because 2 ATP’s are lost in the first stages but in the end 4 ATP’s are produced.
2. A water molecule is removed from each triose phosphate molecule. 2 pyruvate molecules are formed in the end.

The diagram below shows a representation of the stages above. Read through the stages and try to identify them in the diagram below.

Tip: Click on image to see larger view

Stages of Glycolysis

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