Carbohydrate metabolism
Most important ones: glucose, galactose, and fructose
3 parts of carbohydrate metabolism
- Glycolysis
(aka Embden-Meyerhof pathway)
- Citric acid cycle
(aka Krebs cycle)
- Oxidative phophorylation
Other pathways in carbohydrate metabolism
- Glycogenesis
- Direct oxidative pathway
(aka hexose monophosphate shunt)
(aka pentose phosphate pathway)
- 2,3 bisphophoglycerate
(aka 2,3-diphosphoglycerate, 2,3-DPG)
Other notes on carbohydrate metabolism
Fructose
Fructose is converted to:
- fructose 6-phosphate by hexokinase, OR,
- fructose 1-phosphate by fructokinase
* Majority
* Independent of insulin
Fructose 6-phosphate can then be converted to:
- fructose 1,6-phosphate, OR,
- fructose 2,6-phosphate
Fructose 2,6-phosphate
[WG21:p295]
Potent regulator of hepatic gluconeogenesis
When level of F2,6P is high
-> Conversion of F6P to F1,6P increased
-> Increased glycolysis
When level of F2,6P is low
-> Conversion of F1,6P to F6P increased
-> Increased gluconeogenesis
Catecholamine
- Liver
* beta-receptor --> increase cAMP
* alpha-receptor --> increase intracellular [Ca2+]
* Both increase gluconeogenesis
--> Increase hepatic glucose output
- Muscle
* Same mechanism
* Absence of glucose 6-phosphatase
--> Lactate released from muscles
--> Converted to glycogen in liver
--> Increase hepatic glycogen content
- NE and E both increase FFA release into circulation
- E decrease peripheral utilization of glucose