Important Facts about Glycolysis:
The major steps of glycolysis are outlined in the graphic
on the left. There are a variety of starting points for glycolysis;
although, the most usual ones start with glucose or glycogen
to produce glucose-6-phosphate. The starting points for other
monosaccharides, galactose and fructose, are also shown.
Glycolysis - with
white background for printing
There are five major important facts about glycolysis which
are illustrated in the graphic.
1) Glucose Produces Two Pyruvic Acid Molecules:
Glucose with 6 carbons is split into two molecules of 3 carbons
each at Step 4. As a result, Steps 5 through 10 are carried out
twice per glucose molecule. Two pyruvic acid molecules are the
end product of glycolysis per mono- saccharide molecule.
2) ATP Is Initially Required:
ATP is required at Steps 1 and 3. The hydrolysis of ATP to
ADP is coupled with these reactions to transfer phosphate to
the molecules at Steps 1 and 3. These reactions evidently require
energy as well. You may consider that this is a little strange
if the overall objective of glycolysis is to produce energy.
This energy is used in the same way that it initially takes heat
to ignite the burning of paper or other fuels - you need to expand
some energy to get it started.
3) ATP is Produced:
Reactions 6 and 9 are coupled with the formation of ATP. To
be exact, 2 ATP are produced at step 6 (remember that the reaction
occurs twice) and 2 more ATP are produced at Step 9. The net
production of "visible" ATP is: 4 ATP.
Steps 1 and 3 = - 2ATP
Steps 6 and 9 = + 4 ATP
Net "visible" ATP produced = 2.