Page 131 - Demo 1

by nearly all of the organisms on Earth. The process does not use oxygen and
is, therefore, anaerobic. During glycolysis, glucose (a 6-carbon molecule) is
broken down to two molecules of pyruvate (also pyruvic acid, a 3-carbon
molecule).

Glycolysis is divided into (1) the energy-investment phase, when some
ATP is used to begin the reacons, and
Figure 57. Simplified Diagram of
(2) the energy-harvesng phase, when Glycolysis both NADH and ATP
are produced. Source:
https://archive.cnx.org/resources/20abe48ad463ab7
b120a27a2ad706a7c98bb1e53/Figure_08_01.jpg

1. Energy-investment Phase

In this phase, the starng molecule of glucose gets rearranged, and two
phosphate groups are aached to it. The phosphate groups make the
modified sugar, now called fructose-1, 6-bisphosphate, unstable ---
allowing it to split in half and form two phosphate-bearing three-carbon
sugars. Because the phosphates used in these steps come from ATP, two
ATP molecules get used up.

The three-carbon sugars formed when the unstable sugar breaks down
are different from each other. Only one glyceraldehyde-3-phosphate
(G3P) can enter the next step. However, the unfavorable sugar, DHAP,
can be easily converted into the favorable one, so both finish the pathway
in the end.

2. Energy-harvesting Phase
In the second half of glycolysis, the three-carbon sugars formed in the
first half of the process go through a series of addional transformaons,
ulmately turning into pyruvate. In these reacons, two ATP molecules and
one NADH molecule are made. Overall, it makes four ATP and two NADH
because this phase takes place twice, once for each of the two three-
carbon sugars.
Each reacon in glycolysis is catalyzed by its own enzyme. The most
important enzyme for the regulaon of glycolysis is phosphofructokinase,
which catalyzes formaon of the unstable, two-phosphate sugar molecule,
fructose-1, 6-bisphosphate. Phosphofructokinase speeds up or slows
down glycolysis in response to the energy needs of the cell.

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