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