Metabolism 5 (glycogenesis + glycogenolysis) Flashcards
What is glycogenesis?
Formation of glycogen
What is glycogen?
What is the name of its protein core?
Polysaccharide
Glucose molecules bound by alpha 1,4 glycosidic linkages
Glycogenin
Where does glycogenesis occur?
What does it prevent?
Liver + muscle
Hyperglycaemia
Which type of glucose transporter is in:
> pancreas?
> liver?
> muscle?
GLUT2
GLUT2
GLUT4
Describe how glycogenesis is initiated in liver + muscle in the fed state
- Glucose in blood rises
- Transported to pancreas via GLUT2
- Beta cells secrete insulin
- Glucose transported to hepatocytes (GLUT2) + muscle cells (GLUT4)
- Glucose in liver + muscle increases
- Insulin stimulates glycogenesis in muscle + liver
How does insulin affect the glucose transporters in muscle cells?
Increases the no. of GLUT4 bound to the plasma membrane
What affects the storage + release of glycogen in the liver?
What is this glycogen used by?
Changes in blood glucose levels
NOT the liver
- glucose released into blood for other tissues to use
What does glycogen support in muscle cells?
What is this glycogen used by?
Aerobic + anaerobic energy conversion pathways
Muscle cells only
DON’T release glucose back into blood
What does the pathway that synthesises glycogen use?
Activated glucose
= UDP-glucose
= Uridine diphosphate glucose
Which is the rate limiting enzyme in glycogenesis?
What does this enzyme catalyse?
Glycogen synthase
Formation of alpha 1,4 linkages
Why is branching in glycogen important?
> increases solubility
> more branches = glucose can be released more readily
What does a branching enzyme catalyse?
Formation of alpha 1,6 linkages
What does glycogen phosphorylase target?
Alpha 1,4 glycosidic linkages
At which stage does glycogenolysis finish in the muscle?
What then happens to the final product?
G-6-P
G-6-P taken on to the glycolytic pathway
At which stage does glycogenolysis finish in the liver?
What then happens to the final product?
Glucose
Released into blood
How is glycogen metabolism regulated?
Covalent modification
Allosteric control
What is glycogen synthase activated by?
What does this do to the enzyme?
Insulin
Dephosphorylates
What is glycogen synthase inhibited by?
What does this do to the enzyme?
Glucagon
Phosphorylates
What is glycogen phosphorylase activated by?
What does this do to the enzyme?
Glucagon
Phosphorylates
What is glycogen phosphorylase inhibited by?
What does this do to the enzyme?
Insulin
Dephosphorylation
What are the 3 glycogen phosphorylase inhibitors in the liver?
ATP
G6P
Glucose
What are the 2 glycogen phosphorylase inhibitors in muscle?
ATP
G6P
What are the glycogen phosphorylase activators in muscle?
AMP
Ca2+
What is the glycogen synthase activator in liver?
G6P
What is the glycogen synthase activator in muscle?
G6P
What are glycogen storage diseases?
A class of more than 10 distinct disorders of glycogen metabolism
- characterised by increased or decreased amounts of glycogen
- affect mainly liver + muscle
What is the rate limiting enzyme of glycogenolysis?
Glycogen phosphorylase
What is the 1st step of glycogenesis?
Glucose -> G6P
Via hexokinase
or glucokinase in liver
What is the 2nd step of glycogenesis?
G6P -> G1P
Via Phosphoglucomutase
What is the 3rd step of glycogenesis?
G1P -> UDP-glucose
Via UDP-glucose pyrophosphorylase
What is the 4th step of glycogenesis?
UDP-glucose -> glycogen (alpha 1,4)
Via glycogen synthase
Using a glycogen primer
What is the glycogen primer made of?
Glycogenin + UDP-Glucose
What is the 5th step of glycogenesis?
Glycogen (alpha 1,4) -> glycogen (alpha 1,6)
Via branching enzyme
What is the 1st step of glycogenolysis?
Glycogen -> G1P
Via glycogen phosphorylase (1,4)
+ Transferase
+ Debranching enzyme (1,6)
What is the 2nd step of glycogenolysis?
G1P -> G6P
Via Phosphoglucomutase
What is the 3rd step of glycogenolysis?
G6P -> Glucose
Via G6Pase
