Glucose metabolism Flashcards
What is the committed step of the pentoses phosphate pathway?
Dehydrogenation of glucose-6-phosphate
What’s the difference between glycogen stored in the liver and glycogen stored in the muscle?
Muscle glycogen is only available for local energy production (only used by the muscle)
Liver glycogen is used for blood glucose maintenance.
Name the four enzymes involved in glycogenesis.
Hexokinase (glucokinase)
Phospho-glucomutase
Glucose-1-phosphate uridyltransferase
Glycogen synthase
What are the two main enzymes found in glycogenolysis?
Phospho-glucomutase
Glycogen phosphorylase
What are the non-hexose sources that can be used to make glucose in gluconeogensis?
Lactate
Pyruvate
Glycerol
Certain amino acids
Where does gluconeogensis occur?
Mainly in the liver, with some contribution from the kidneys during prolonged starvation.
Which enzymes in glycolysis can’t be reversed and why?
Hexokinase/glucokinase
Phosphofructokinase
Pyruvate kinase
Because these all involve the use of ATP.
How are hexokinase/glucokinase and phosphofructokinase bypassed?
Hexokinase - G6Pase
Phosphofructokinase - fructose-1,6-bisphosphonate
Where is the enzyme glucose-6-phosphatase found and why?
In the lumen of the endoplasmic reticulum because it needs transporters for substrates and products to get in and out.
What stimulates and what inhibits the expression of G6Pase?
Stimulates - Adrenaline and glucocorticoids.
Inhibits - insulin
What is the intermediate molecule involved in the bypass of pyruvate kinase during gluconeogensies?
Oxaloacetate
What enzyme catalyses the conversion of pyruvate to oxaloacetate?
Pyruvate carboxylase (PCOX)
What enzyme catalyses the conversion of oxaloacetate to phosphoenolpyruvate?
Phosphoenolpyruvate carboxykinase (PEPCK)
What stimulates gluconeogensis?
Glucagon and adrenaline
- decreases glucokinase activity
- increases G6Pase and PEPCK activity
The effect is at the level of gene expression
Which tissues are dependant on glucose and why?
The brain - because FAs can’t cross the BBB
Erythrocytes - no mitochondria, so can’t oxidise fuels and the only energy is from glycolysis
