Introduction of Glycolysis Steps

1. Chemical Principles in Biology
(CHEM-430)
Dr. Hira Khalid
Assistant Professor Chemistry
(HEC Approved Supervisor)

2. Glycolysis
 Glycolysis is the process that allows the simple sugar glucose, which comes from
your food, to be broken down into usable energy. It’s part of a larger process
called cellular respiration
 Glycolysis -the simple sugar glucose is broken down in the cytosol
 Pyruvate, the product from glycolysis, is transformed into acetyl CoA in the
mitochondria in preparation for the next step
 The citric acid cycle - where electron carriers, NADH and FADH2, are made in the
mitochondria
 Oxidative phosphorylation - this process occurs in the mitochondria, and uses
the electron transport chain to produce ATP, the bulk of usable energy for the cell

3. Glycolysis Process
 Over the course of several steps, glycolysis breaks down one glucose molecule into
two molecules of another compound called pyruvate. Pyruvate is essentially ½ of a
glucose molecule because it contains half the carbons from glucose. Glycolysis can
be broken down into two phases: the investment phase and the reward phase.

4. Step 1 : To break down glucose, energy has to be used. ATP transfers its
phosphate group to glucose to produce a new 6-carbon molecule,
glucose-6-phosphate.

5. Step 2: Next, the glucose-6-phosphate molecule is rearranged, and ATP
is used again to add another phosphate group to the molecule. There
are now two phosphate groups attached to the glucose-6-phosphate
molecule.

6. Step 3: An enzyme comes along and cuts glucose-6-phosphate into two, 3-carbon
molecules. This is the end of the investment phase. The molecules are starting to look a
lot more like two pyruvates
The reward phase
In the reward phase, ATP and NADH are made. This is the payoff of the original
molecule of ATP invested in the first phase.
Step 4 : The enzyme Aldolase splits fructose 1, 6-bisphosphate into two sugars that are
isomers of each other. These two sugars are dihydroxyacetone phosphate (DHAP) and
glyceraldehyde 3-phosphate (GAP).

7. Step 5: The enzyme triophosphate isomerase rapidly inter-converts the molecules
dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GAP).
Glyceraldehyde phosphate is removed / used in next step of Glycolysis.

8. Step 6: Another phosphate group is added to the 3-carbon molecule, and NADH from
the reaction.

9. Step 7: ATP is formed as a phosphate group is removed from the 3-carbon molecule and
added to ADP

10. Step 8: The second ATP is created as the phosphate group leaves the 3-carbon molecule, and is
added to ADP. Pyruvate has been made!

11. Step-9 The enzyme enolase removes a molecule of water from 2-phosphoglycerate
to form phosphoenolpyruvic acid (PEP)

12. Step 10: The enzyme pyruvate kinase transfers a P from phosphoenolpyruvate (PEP) to ADP
to form pyruvic acid and ATP Result in step 10. The second ATP is created as the phosphate
group leaves the 3-carbon molecule, and is added to ADP. Pyruvate has been made!

13. During glycolysis a total of four ATP are made. Recall that the original 6-carbon glucose is
split into two 3-carbon molecules at the end of the investment phase. This means that the
two 3-carbon molecules both go through the reward phase, both yielding two ATP.
Remember two ATP were used in the investment phase, so we have a net production of two
ATP. To summarize for emphasis:
-2 ATP in investment phase
+2 ATP reward phase for first pyruvate
+2 ATP in reward phase for second pyruvate
Additionally, two NADH compounds, two water molecules, and two pyruvates are created.