Glycogen Metabolism Flashcards
What are the names for glycogen synthesis and breakdown?
Synthesis - glycogenesis.
Breakdown - glycogenolysis.
What is the difference in the function of liver and muscle glycogen?
Liver: broken down between meals and released to maintain blood glucose levels for RBCs and brain.
Muscle: provides energy via respiration during bursts of physical activity.
What is the primary source of glucose overnight when hepatic glycogen is depleted?
Gluconeogenesis.
What are the links joining glycogen and what links introduce branches?
α 1-4 glycosidic links, α 1-6 glycosidic links.
What is the protein at the centre of glycogen?
Glycogenin.
What is the function of glycogenin and why is this important?
It has catalytic properties to add glucose molecules to itself. Glycogen synthase can only add glucose molecules to existing glycogen so glycogen primer of at least 4 glucose required to be attached to glycogenin.
Before glucose can be used in either glycolysis or glycogen synthesis, what needs to happen to it?
Needs to be phosphorylated by hexokinase to form glucose-6-phosphate.
What determines whether glucose-6-phosphate will be used for glycolysis or glycogen synthesis?
If glucose conc is low, used for glycolysis and vice versa.
What does glucose-6-phosphate need to be converted to before glycogenesis and what enzyme does this?
Glucose-1-phosphate. Phosphoglucomutase.
What is a special feature of phosphoglucomutase?
It can do forwards and backwards reactions.
What is glucoase-1-phosphate then converted to and what is required?
UDP-glucose. Uses a molecule of UTP and UDP-glucose phosphorylase.
What is released when glycogen synthase adds UDP-glucose to the end of the strand?
UDP molecule.
What happens to the released UDP molecule?
It is phosphorylated to form UTP. For each glucose added to glycogen, 1 ATP is consumed.
What about UDP-glucose makes it highly active?
The bond between glucose and the second phosphate group of uridine diphosphate.
What is the bond between UDP and glucose?
Phosphate ester linkage.
What is the rate limiting enzyme of glycogenesis?
Glycogen synthase.
What is the enzyme which introduces branching to glycogen and after how many residues does it do this?
Transglycosylase. Every 10.
What enzyme is glycogenolysis catalysed by?
Glycogen phosphorylase.
What does glycogen phosphorylase do?
Cleaves a glucose molecule from the glycogen and adds a phosphate to form glucose-1-phosphate.
What is the rate limiting step of glycogenolysis?
The reaction catalysed by glycogen phosphorylase.
What happens to the glucose-1-phosphate once it has been cleaved off glycogen?
It is the converted to glucose-6-phosphate by glucophosphomutase.
Once glucose has been converted into glucose-6-phosphate, what then happens in the liver?
Can be de-phosphorylated by glucose-6-phosphatase and the resulting glucose released into the blood stream via GLUT-2 transporters.
Once glucose has been converted into glucose-6-phosphate, what then happens in skeletal muscle?
Glucose-6-phosphate cannot be de-phosphorylated, is used to provide energy via glycolysis and the TCA cycle.
What does debranching require?
Additional enzymes.
What enzymes allow regulation in glycogenesis and glycogenolysis?
Glycogen synthase (glycogenesis), glycogen phosphorylase (glycogenolysis).
What hormone allows regulation of glycogenesis and how?
Insulin, indicates high blood sugar so stimulates glycogen synthase and inhibits glycogen phosphorylase.
What hormone allows regulation of glycogenolysis and how?
Glucagon, indicates low blood sugar so stimulates glycogen phosphorylase and inhibits glycogen synthase.
What other hormones can stimulate glycogen phosphorylase?
Adrenaline and cortisol.
What are glycogen storage diseases and how many types are there?
Group of diseases with increase glycogen deposits in liver or muscle or both. 10.
