Question

Question #7 (10 points) - Which steps of glycolysis are not reversible for gluconeogenesis? How are these steps reversed during gluconeogenesis?

Answer 1

The gluconeogenesis is the process of synthesis of glucose from non-carbohydrate substances like amino or organic acids. It is an anabolic process and is carried out in the Liver. The lactate formed in the muscle is exported to liver and converted to pyruvate and utilized for glucose synthesis through gluconeogenesis.

All amino acids except leucine and lysine and glycerol from fats can also be converted to glucose through gluconeogenesis. The process of gluconeogeneis is the reverse of glycolysis. But, the reactions 1, 3 and 10 are irreversible in glycolysis and these steps are carried out by different enzymes in gluconeogenesis. The step 1 of glycolysis is conversion glucose to glucose - 6 - phosphate by hexokinase enzyme.

The step 3 is conversion of fructose - 6 - phosphate to fructose - 1, 6 - bisphosphate by phosphofructokinase. The step 10 is conversion of phosphoenol pyruvate to pyruvate by pyruvate kinase. These irreversible reactions of glycolysis are ctalayzed by different enzymes in gluconeogenesis. The enzymes involved in gluconeogeneis catalyzing these steps include Glucose - 6 - phosphatase (step 1), Fructose - 1, 6 - bisphosphatase (step 3) and phosphoenol pyruvate carboxykinase (step 10 ) respectively. The use of different enzymes can reverse the substrates to products in gluconeogenesis.

GLUCOSE-6 GLUCOSE PHOSPHATSE GLUCOSE 6 PHOSPHATE FRUCTOSE 6-PHOSPHATE FRUCTOSE1,6- BIPHOSPHATASE FRUCTOSE-1,6-BIPHOSPHATE GLYCERALDEHYDE-3 PHOSPHATE DIHYDROXYACETONE PHOSPHATE 1,3 IPHOSPHOGLYCERATE GLYCEROL IRREVERSIBLE STEPS BYPASSED 3 PHOSPHOGLYCERATE 2 PHOSPHOGLYCERATE PHOSPHOENOLPYRUVATE CO2 PHOSPHOENOLPYRUVATE - GDP .... GTP CARBOXYKINASE OXALOACETATE -ADP PYRUVATE AMINOACIDS ATP CARBOXYLASE -CO, PYRUVATE FATTYACIDS