Sucrose is the start of glycolysis and the ending of gluconeogenesis in plants

 

Glycolysis is the breakdown of sugars

Gluconeogenesis is the making of sugars

 

Sucrose is broken down by one of three enzymes:

 

1.  Neutral invertase

2.  Acid invertase

3.  Sucrose synthase

 

Invertase breaks sucrose into fructose and glucose

 

Sucrose synthase breaks sucrose into fructose and UDPglucose in the presence of UTP and PPi

 

The glucose and fructose molecules are both phosphorylated by a hexokinase

 

Glucose + ATP a glucose-6-phosphate

Fructose + ATP a fructose-6-phosphate

 

The UDPglucose is converted to glucose-1- phosphate and UTP in the presence of PPi

 

UDPglucose + PPia UTP + glucose-1-phosphate

 

The glucose-1-phosphate is converted to glucose-6-phosphate by the enzyme phosphoglucomutase

 

The glucose-6-phosphate is isomerized to fructose-6-phosphate by the enzyme phosphoglucoisomerase

 

Glucose-6-phosphate n fructose-6-phosphate

 

Fructose-6-phosphate is phosphorylated to fructose-1,6-bisphosphate by one of two enzymes

 

fructose-6-phosphate n fructose-1,6-bisphosphate

 

1.  ATP-phosphofructokinase

2.  PPi-phosphofructokinase

 

PPi is not found in animals

 

PPi-phosphofructokinase, in some plants, is activated by fructose-2,6-bisphosphate

 

The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate is a regulation point in plant glycolysis

 

Fructose-1,6-bisphosphate is broken down to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate by aldolase

 

dihydroxyacetone phosphate is isomerized to glyceraldehyde-3-phosphate by the enzyme triose phosphate isomerase

 

Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate by the enzyme glyceraldehyde-3-dehydrogenase

 

1,3-bisphosphoglycerate is converted to 3- phosphoglycerate by phosphoglycerate kinase

 

3-phosphoglycerate is converted to 2-phosphoglycerate by the enzyme phosphoglycerate mutase

 

2-phosphoglycerate is converted to phosphoenolpyruvate (PEP) by the enzyme Enolase

 

Phosphoenolpyruvate is converted to pyruvate by the enzyme pyruvate kinase