Glyogenesis,glycogenolysis And Gluconeogenesis Flashcards
In which tissues does gluconeogenesis occur?
Liver
In which tissues does glycogenolysis occur?
Muscle, liver
Describe the structure of glycogen
Glycogen is a branched polymer of about 6000 glucose units linked by alpha 1 to 4 glycosidic bonds in the backbone and alpha 1 to 6 glycosidic bonds at the branch points. It is highly branched allowing for quick release at time of need.
What is the regulatory enzyme in glycogenesis? What does it do?
Glycogen synthase. It transfers glucose from UDP glucose to the extending glycogen chain. It is stimulated by insulin and inhibited by glucagon.
Describe glycogenesis.
Glucose is converted into G6P by glucokinase which is then converted into G1P by phosphoglucomutase which is then converted to the UDP glucose which is then added to the growing glycogen chain by glycogen synthase.
What is the regulatory enzyme in glycogenolysis? What does it do?
The regulatory enzyme in glycogenolysis is glycogen phosphorylase which breaks the a one to four glycosidic bonds and adds a phosphate to each glucose to form glucose one phosphate. It is stimulated by glucagon via G protein coupled receptors on the liver cell and inhibited by insulin via tyrosine kinase receptors.
Describe glycogenolysis.
Glycogen is broken down to form glucose 1 phosphate by glycogen phosphorylase; which is then converted into glycogen six phosphate by phosphoglucomutase. G6p may enter glycolysis or PPP or be converted into glucose by glucose 6 phosphatase.
Explain the effect of adrenaline on glycogenesis and glycogenolysis.
Adrenaline acts on beta adrenoceptors on the liver cell membrane or on muscle cells to activate glycogen phosphorylase- the regulatory enzyme of glycogenolysis. This leads to the break down of glycogen to release glucose… Which is used by the muscle or released into the blood by the Liver.
The activation of the beta adrenoceptor generates cAMP which activates PKA which inhibits glycogen synthase and activates glycogen phosphorylase.
Describe the effect of calcium on glycogenolysis and glycogenesis.
Influx of calcium into muscle cell after stimulation leads to the activation of glycogen phosphorylase which releases G6P which can be used for energy by going through glycolysis in the muscle cell.
Describe the cause of glycogen storage diseases.
Glycogen storage diseases are caused by genetic mutations in enzymes involved in glycogenolysis pathways. This means that glycogen six phosphate can’t be broken down to release glucose for energy. It is converted into glycogen instead —> build up of glycogen in the body cells which impairs their ability to function and hypoglycaemia on overnight fasting due to inability to access glycogen store.
What causes glycogen storage disease 1a?
Glycogen storage disease 1a or von Gierkes disease is caused by mutations in the gene coding for glucose 6 phosphatase leading to fasting hypoglycaemia due to inability to access glycogen store and accumulation of glycogen in the liver.
Describe the cause of glycogen storage disease II.
Pompes disease is caused by a mutation in the gene coding for acid Maltase, which breaks down glycogen in lysosomes. This leads to a build up of glycogen to toxic levels –> progressive multiple organ damage.
In which tissues does glycogenesis occur?
Liver and muscle
