Page 317 - Biology_F5

Biology for Advanced Level Secondary Schools
(c) Oxidation by dehydrogenation releasing energy that powers the cell. The
In this step, an enzyme removes one removal of the third phosphate from ATP
hydrogen atom and two electrons from each converts ATP back into ADP, which is

three-carbon molecules. Both hydrogen used again in cellular respiration to make
atoms are modified to hydrogen ions, more ATP.
positively charged particles. The hydrogen
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ion and two electrons from each three- When the two 3 carbon compounds are
carbon molecule are transferred as a unit separated from the phosphate groups, the
to a large molecule called Nicotinamide three-carbon compounds are converted
Adenine Dinucleotide (NAD) to form into two molecules of pyruvate, each
two molecules of reduced NADH. The composed of three carbons, three
hydrogen ions and electrons stored in oxygen, and three hydrogen atoms.

each molecule of NADH are used to make When glycolysis is complete, important
ATP in later stages of cellular respiration products are produced; two molecules
during oxidative phosphorylation of the of NADH, two molecules of pyruvate
electron transport chain. (pyruvic acid) and two molecules of ATP.
NADH and pyruvate are used in the next
In the final step of glycolysis, two steps of cellular respiration and the ATP
hydrogen atoms are removed from each molecules are used for reactions in the cell

three-carbon compound. These hydrogen that require energy.
atoms bond to free-floating oxygen
atoms in the cytoplasm to form water. The process can be detailed as follows:

This step prepares the two three-carbon Glyceraldehyde-3-phosphate or
compounds for action by the next enzyme 3-phospho-glyceraldehyde (3-PGAL) is
in the pathway. This enzyme removes the converted into 1, 3-biphosphoglycerate or 1,
phosphate group from each of the three- 3-diphosphoglyceric acid (1,3-diPGA) by
carbon compounds. Each phosphate glyceraldehyde-3-phosphate dehydrogenase
group then bonds to a single molecule enzyme where NAD is reduced into
of adenosine diphosphate (ADP). ADP NADH . Then 1, 3-diPGA is converted to
2
is composed of three carbon-based rings 3-phophoglycerate or 3-phosphoglyceric
and a tail of two phosphate groups. The acid (3-PGA) by phosphoglycerate kinase

addition of the third phosphate group to enzyme, this process involves the loss of
the tail forms ATP. In this step, two new phosphate group (Pi) from 1,3-diPGA to
ATP molecules are produced; this is the form (3-PGA), and the Pi is transferred to
substrate-level phosphorylation. When a molecule of ADP to form the first ATP
cells require energy, another enzyme molecules. Actually, two molecules of
breaks off the third phosphate group, ATP are formed because there were two

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