BCM 252 – Carbohydrate Metabolism
Study Unit 2
Gluconeogenesis
Gluconeogenesis: Making “new” glucose
• Glucose is the sole or major fuel source for:
→ Brain
→ Nervous system
→ Erythrocytes
→ Testes
→ Renal medulla
• The brain requires exclusively ~120 g glucose daily
→ ~160 for the whole body
→ Amount of glucose in body fluids ~ 20g
→ ~150g is stored as glycogen
• Between meals and fasts / after vigorous exercise:
→ Glycogen depleted and organisms need a method to synthesize glucose
Gluconeogenesis
• Gluconeogenesis: pathway that converts pyruvate and related three- and four-
carbon compounds to glucose
• Occurs in all animals, plants, fungi, and microorganisms
• Mainly occur in the liver in mammals
Gluconeogenesis across the kingdoms
• Notice that mammals cannot convert fatty acids to sugars
• Plant seedlings convert stored fats and proteins to sucrose required for
development
• Plants and photosynthetic bacteria convert CO2 to carbohydrates – Calvin Cycle
, Gluconeogenesis and Glycolysis share several steps
• Gluconeogenesis and glycolysis are not identical pathways running in opposite
directions
• 3 glycolysis reactions are essentially irreversible in vivo and cannot be used in
gluconeogenesis
→ Must be bypassed with exergonic reactions
Gluconeogenesis and glycolysis are partitioned between organs
• Glycolysis occurs mainly in the muscle and brain
• Gluconeogenesis occurs mainly in the liver
Study Unit 2
Gluconeogenesis
Gluconeogenesis: Making “new” glucose
• Glucose is the sole or major fuel source for:
→ Brain
→ Nervous system
→ Erythrocytes
→ Testes
→ Renal medulla
• The brain requires exclusively ~120 g glucose daily
→ ~160 for the whole body
→ Amount of glucose in body fluids ~ 20g
→ ~150g is stored as glycogen
• Between meals and fasts / after vigorous exercise:
→ Glycogen depleted and organisms need a method to synthesize glucose
Gluconeogenesis
• Gluconeogenesis: pathway that converts pyruvate and related three- and four-
carbon compounds to glucose
• Occurs in all animals, plants, fungi, and microorganisms
• Mainly occur in the liver in mammals
Gluconeogenesis across the kingdoms
• Notice that mammals cannot convert fatty acids to sugars
• Plant seedlings convert stored fats and proteins to sucrose required for
development
• Plants and photosynthetic bacteria convert CO2 to carbohydrates – Calvin Cycle
, Gluconeogenesis and Glycolysis share several steps
• Gluconeogenesis and glycolysis are not identical pathways running in opposite
directions
• 3 glycolysis reactions are essentially irreversible in vivo and cannot be used in
gluconeogenesis
→ Must be bypassed with exergonic reactions
Gluconeogenesis and glycolysis are partitioned between organs
• Glycolysis occurs mainly in the muscle and brain
• Gluconeogenesis occurs mainly in the liver
