Glycolysis
- 6-carbon glucose --> two 3-carbon pyruvates.
- Glyco = “sugar”; lysis = “split”.
- Occurs in the cytoplasm of the cell.
- 10 reactions each catalyzed by an enzyme.
- This is a complicated process, but don’t worry – students only need to identify and understand the important parts. So what’s important? The points in the pathway where things are made or used are the most important.
- Two ATP are used in steps 1 and 3. The phosphate groups are added to the glucose molecule so they can later be removed and energy can be harvested.
- In steps 4 and 5 the molecule is split into DHAP and G3P. An enzyme converts DHAP to G3P. This produces two molecules of G3P.
- Step 6 produces two NADH (one from each G3P). NAD+ takes hydrogen atoms and reduces to NADH. In step 7, two ATP molecules are produced by substrate-level phosphorylation. The phosphate group is transferred to ADP.
- At this point the ATP debt is paid.
- Some rearranging occurs.
- In step 10, two ATP molecules are produced by substrate-level phosphorylation and pyruvate is formed.
Energy Yield for Glycolysis
A total of 4 ATP were produced. 2 ATP were used in steps 1 and 3.
This is a net production of 2 ATP and 2 NADH.
2 mol ATP x 31 kJ/mol ATP = 62 kJ
Total free energy in 1 mole of glucose = 2870 kJ
Energy conversion efficiency = 62 kJ/2870 kJ x 100% = 2.2%
Glycolysis alone is not very energy harnessing. The remaining energy is trapped in 2 pyruvate molecules and 2 NADH produced during glycolysis. Therefore, glycolysis is sufficient for small organisms, but humans need much more energy to run.
The process now continues into the mitochondria via pyruvate oxidation.
A total of 4 ATP were produced. 2 ATP were used in steps 1 and 3.
This is a net production of 2 ATP and 2 NADH.
2 mol ATP x 31 kJ/mol ATP = 62 kJ
Total free energy in 1 mole of glucose = 2870 kJ
Energy conversion efficiency = 62 kJ/2870 kJ x 100% = 2.2%
Glycolysis alone is not very energy harnessing. The remaining energy is trapped in 2 pyruvate molecules and 2 NADH produced during glycolysis. Therefore, glycolysis is sufficient for small organisms, but humans need much more energy to run.
The process now continues into the mitochondria via pyruvate oxidation.