Glycogen Questions Flashcards
What is the general structure of glycogen?
It consists of glucose connected by a-1,4 glycosidic linkages with branches at 1-1,6 glycosidic bonds, branches distributing at even intervals resulting in spherical structure.
What is the general mechanism of glycogen build-up?
When glucose enters the cell, it is phosphorylated into G6P, then isomerised into G1P by phosphoglucomutase-1 wheren then UDP-glucose is catalysed from this by UDP glucose pyro-phosphorylase, serving as an intermediate glucose donor for glycogen construction.
What initiates glycogen, and what initially elongates it?
Glycogenin, elongated by glycogen synthase, then branched by GDE introducing 1-1,6 glycosidic bonds at regular intervals.
How is glycogen breakdown cytosilically achieved?
Co-ordination of glycogen phosphorylase which release glucose-1 phosphate by removal of the a-1,4 glycosidic linkage, and GBE.
What happens to G1P derived from the cytosolic pathway proceeding glycogen degradation?
Isomerised into G6P, which can bed dephosphorylated to free glucose by the enzyme glucose 6 phosphotase, where glucose transporters secrete it.
How is glucose uptake facilitated in the brain?
GLUT1 across the endothelium of the BBB, accounting for majority of glucose taken up by the body.
How is glucose uptake facilitated in the skeletal muscle?
GLUT 1 on PM facilitating transport into the muscle fibre and GLUT4, found within intracellular storage vesicles which in muscle contraction/insulin stimulation, translocate into the PM.
How is glucose uptake facilitated in the Liver/Pancreas?
GLUT2 absorbs glucose from blood to tissue.
What does Franconi-Bickel disease derive from?
GLUT2 gene mutations with impaired utilization of glucose/galactose, leading to both hyperglycemia an hypergalactosemia.
What is the first enzyme involved in conversion of free glucose to G6P?
Hexokinase.
What do GKRP do in fasting?
They inhibit glucokinase action, limiting glucose utilization.
What do glucokinase mutations lea to?
Disordered glucose metabolism resulting in hypoglycemia
What does glucokinase deficiency lead to?
Hinderance of pancreation/hepatocyte glucose metabolism, leading to impaired insulin secretion from the pancrease, reducing glycogen synthesis in the liver
How is UDP-Glucose formed and when does it take place?
Formed from catalysis by UDP glucose pyrophosphatase, facilitating reversible conversion to UDP-glucose from reactants; UTP and G1P, in the presence of Mg2+., following G1P formation.
What is glycogenin?
A transferase catalysing transfer of glucose residues from the UDP-glucose to itself, forming the a-1,4 glycosidic linkages creating linear glucose polymers of about 10-20 glucose.
