Glycolysis

GLYCOLYSIS
In the pathway of glycolysis, glucose (6 carbons molecule) is split into two pyruvate (3-carbon molecule) under aerobic conditions; or lactate under anaerobic conditions, along with production of a small quantity of energy.
Summary of glycolysis (Embden-Meyerhof pathway)

The whole reaction is summarized as
Glucose + 2 Pi + 2 ADP --> 2 Lactate + 2 ATP


? Notes
• Steps 1, 3 and 9 are key enzymes; these reactions are irreversible. Steps 5, 6 and 9 produce energy. Steps 5 and 10 are coupled for regeneration of NAD+.
• The steps 1, 2 and 3 are called the preparatory phase, The next steps are together called the energy producing phase.
• Hexokinase and glucokinase may be considered as iso-enzymes; their properties are compared in Table below. Glucokinase is under the influence of insulin; but hexokinase is not.
• The phosphorylation of glucose to glucose-6-phosphate traps it within the cells to be metabolized.
• The enzyme phosphofructokinase (PFK) is an allosteric, inducible, regulatory enzyme. It is an important key enzyme of this pathway. This is an activation process, the energy being derived by hydrolysis of ATP. This irreversible step is the rate limiting reaction in glycolysis.
• The energy of bisphospho glycerate (1,3-BPG) is trapped to synthesize one ATP molecule with the help of bisphospho glycerate kinase. This is an example of substrate level phosphorylation (where energy is trapped directly from the substrate without the help of the complicated electron transport