Explain the phase of glycolysis.

Explanation

1. Preparatory phase : Glucose enters the glycolysis from sucrose which is the end product of photosynthesis. Glucose is phosphorylated into glucose-6- phosphate by the enzyme hexokinase, and subsequent reactions are carried out by different enzymes. At the end of this phase fructose - 1, 6 - bisphosphate is cleaved into glyceraldehyde - 3 phosphate and dihydroxy acetone phosphate by the enzyme aldolase. These two are isomers. Dihydroxy acetone phosphate is isomerised into glyceraldehyde-3-phosphate by the enzyme triose phophate isomerse, now two molecules of glyceraldehyde 3 phosphate enter into pay off phase. During preparatory phase two ATP molecules are consumed in step - 1 and step-3.
2. Pay off phase : Two molecules of glyceraldehyde - 3- phosphate oxidatively phosphory lated into two molecules of 1,3 - bisphospho glycerate. During this reaction `2NAD^+` is reduced to `2NADH + H^+` by glyceraldehyde - 3- phosphate dehydrogenase at step 6. Further reactions are carried out by different enzymes and at the end two molecules of pyruvate are produced. In this phase, `2ATPs` are produced at step 7 and 2ATPs at step 10. Direct transfer of phosphate moiety from substrate molecule to ADP and is converted into ATP is called substrate phosphorylation or direct phosphorylation or trans phosphorylation. During the reaction at step 9, 2 phosphoglycerate dehydrated into Phospho enol pyruvate a water molecule is removed by the enzyme enolase. As a result, enol group is formed within the molecule. This process is called Enolation.