Biology Times (^19)
March
Step-II: Oxidative decarboxylation of pyruvic acid/Link reaction/Gateway reaction/transition reactions.
Step-III: Krebs cycle and
Step-IV: Electron transport system.
Step - I: Glycolysis
Glycolysis is the first step in the breakdown of glucose into three carbon molecules called pyruvates.
Glycolysis consists of an energy requiring phase followed by an energy releasing phase. Glycolysis is also
called as EMP pathway as it was discovered by three German scientists Embden, Meyerhof and Parnas.
Glycolysis occurs in cytoplasm (extra mitochondrial process) and is a universal pathway in all biological
systems.
Glycolysis occurs in all living organisms (prokaryotes and eukaryotes). The principal reactions associated
with the classic glycolytic and fermentative pathways in plants are almost identical with those of animal
cells.
Step1: Glucose is phosphorylated to Glucose 6-phosphate by ATP in the presence of enzyme hexokinase or
glucokinase and Mg2+
Step 2: Glucose 6-phosphate is changed to its isomer Fructose 6-phosphate with the help of the enzyme
phosphoglucoisomerase
Step 3: Fructose 6-phosphate is further phosphorylated by means of ATP in presence of enzyme
phosphofructokinase and Mg+. The product is Fructose 1, 6-bisphosphate.
Step 4: Fructose 1, 6-bisphosphate splits up enzymatically to form one molecule each of 3-carbon compounds
Glyceraldehyde phosphate or 3-phosphoglyceraldehyde(PGAL) and Dihydroxyacetone phosphate
(DHAP) by the enzyme aldolase.
Step 5: DHAP is isomerised to Glyceraldehyde 3-phosphate by enzyme Triose phosphate isomerase
Step 6: In the presence of enzyme Glyceraldehyde-3-phosphate dehydrogenase, glyceraldehyde 3-phosphate
loses hydrogen to NAD to form NADH 2 and accepts inorganic phosphate to form 1,3-bisphosphoglycerate
Step 7: In this step 1,3-bisphoshoglycerate is converted to 3-phosphoglycerate by the enzyme
phosphoglycerokinase. Phosphate group is transferred to a molecule of ADP that yields an ATP. This is
first substrate level ATP synthesis.
Step 8: 3-Phosphoglycerate is changed to its isomer 2-Phosphoglycerate by enzyme phosphoglyceromutase
which transfers the phosphate from third to second carbon.