BOTANY Higher Secondary Second Year - Textbooks Online

5. DHAP and glyceraldehyde-3-phosphate are interconvertible by the
action of triose phosphate isomerase. These five series of reaction constitute
hexose phase and produce two molecules of 3-carbon compound called 3phosphoglyceraldehyde.
In hexose phase two ATP molecules are consumed.
6. A molecule of glyceraldehyde-3-phosphate is phosphorylated and
oxidized to 1,3-bisphosphoglyceric acid in the presence of glyceraldehyde-
3-phosphate dehydrogenase. During this reaction, one NADH 2 is formed.
7. 1,3-bisphosphoglyceric acid is dephosphorylated to a molecule of
3-phosphoglyceric acid by phosphoglyceric kinase. During this reaction
one ATP is formed. This type of ATP synthesis is called direct
phosphorylation or substrate level phosphorylation.
8. A molecule of 3-phosphoglyceric acid is then converted into a
molecule of 2-phosphoglyceric acid by phosphoglyceric mutase. In this
reaction, phosphate molecule is shifted form third carbon to second carbon.
9. A molecule of 2-phosphoglyceric acid is dehydrated to a molecule
of 2-phosphoenol pyruvic acid by enolase. Removal of water molecule
from the substrate is called enolation.
10. A molecule of 2-phosphoenol pyruvic acid is dephosphorylated
to pyruvic acid and ADP is phosphorylated to ATP. This reaction is
catalyzed by pyruvic kinase. Thus, in the triose phase, two molecules of a
molecule of 3-phospho glyceraldehyde produce 2 molecules of pyruvic
acid.
In glycolysis, 4ATP and 2NADH 2 molecules are formed and 2ATP
molecules are consumed in hexose phase. Hence, the net gain is 2ATP
and 2NADH 2 .
Oxidative decarboxylation of pyruvic acid
The two molecules of pyruvic acid formed from a glucose molecule
move into mitochondria and are oxidized, decarboxylated to two molecules
of acetyl coenzyme A (acetyl Co~A). These 2 carbon compounds are
formed by
Pyruvic dehydrogenase
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