Stage 2: Glycolysis
Before glucose can be converted into ATP, it has be broken down into two
pyruvate molecules (the ionized form of pyruvic acid). This process is known as
glycolysis. Glycolysis takes place in the cytoplasm and can occur without the presence of oxygen and is the
primary energy source for most organisms. This process consumes two ATP molecules, and produces four ATP molecules and two
NADH2+ molecules. Glycolysis is summarized below:
1. Glucose 6-phosphate is formed when the 6th carbon on the glucose molecule
is phosphorylated by an ATP molecule.
2. Glucose 6-phosphate is converted into a 5-carbon ring isomer, fructose
3. Fructose 6-phosphate is phosphorylated by another ATP to form fructose 1,
4. Fructose 1, 6-diphosphate is processed by an enzyme into two
glyceraldehyde 3-phosphate molecules.
5. Two molecules of glyceraldehyde 3-phosphate are oxidized, losing hydrogen atoms and gaining
phosphate groups to form 1, 3-diphosphoglycerate. Two molecules of NAD+
are converted into NADH2+ in the process.
6. Two 1,3-diphosphoglycerate molecules phosphorylate ADP
(adenine diphosphate) to yield two molecules of 3-phosphoglycerate
and two ATPs are produced.
7. The phosphate groups on 3-phosphoglycerate move to the 2nd carbon, forming
8. The two 2-phosphoglycerate molecules are dehydrated and forms two
high-energy phosphoenolpyruvate molecules.
9. The two phospoenolpyruvate phosphorylates two ADPs and
produces two more ATPs and two
molecules of pyruvate.
After the glucose molecule has been converted two pyruvate, it is then sent
to the Kreb Cycle to be converted into
more usable forms of energy.
Go on to Stage 3: Aerobic Respiration