Question

Under actual cellular conditions, how many strongly exergonic reactions take place in glycolysis?

How many strongly endergonic reactions take place in gluconeogenesis?

please answer all

Answer 1

Gluconeogenesis and glycolysis are coordinated so that within a cell one pathway is relatively inactive while the other is highly active.

In glycolysis three strongly exergonic reactions takes place. These three highly exergonic steps are:

Step 1, involving conversion of glucose to glucose-6-phosphate by enzyme Hexokinase.

Step 3, in which fructose-6-phosphate is converted into fructose-1,6 bisphosphate with the help of enzyme phosphofructokinase.

Step 10, involving conversion of phosphoenolpyruvate to pyruvate by enzyme pyruvate kinase.

These 3 reactions have large, negative ∆G drops and are also considered regulatory steps which include the enzymes hexokinase, phosphofructokinase, and pyruvate kinase.

The processn of gluconeogenesis is highly endergonic until it is coupled to the hydrolysis of ATP or GTP, effectively making the process exergonic.

While most steps in gluconeogenesis are the reverse of those found in glycolysis, three regulated and strongly endergonic reactions are replaced with more kinetically favorable reactions.

Hexokinase, phosphofructokinase, and pyruvate kinase enzymes of glycolysis are replaced with glucose-6-phosphatase, fructose-1,6-bisphosphatase, and PEP carboxykinase/pyruvate carboxylase.

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