Week 14: Glycogenesis & Glycogenolysis Flashcards
What is glycogenesis?
synthesis of glycogen from glucose
What is glycogenolysis?
breakdown of glycogen to form glucose
When glucose levels are low
What is glycogen?
Main storage form of glucose in liver and muscle cell
When is liver glycogen broken down?
between meals
Why is liver glycogen released?
released to maintain blood glucose levels for red blood cells and brain
What type of glycogen maintains blood glucose levels?
liver glycogen
When does muscle glycogen provide energy?
during bursts of physical activity
What influences glycogenolysis activity?
fluctuates depending on meal times
Recall where glycogenolysis fluctuates?
- Decreases at breakfast but increases shortly after
- peaks at lunch
- decreases in-between
What happens to the % of source of blood sugar according to dietary?
after meal time increases
What is the primary source of glucose overnight?
gluconeogenesis
when hepatic glycogen is depleted
What are the monomers of glycogen?
glucose molecules joined by alpha 1-4 glycosidic links
What link are the branches of glycogen on?
introduced by alpha-1,6 glycosidic links
What is the nonreduing end of glycogen?
provides directionality to glycogen
What are the two pathways glucose-6-phosphate can go?
- glycolysis
2. glucose-1 phosphate –> glycogen synthesis
What can glucose residues only be added to?
existing glycogen chain
What is the intermediate form of glucose?
UDP-glucose
active form of glucose
What does the activated form of glucose allow it to do?
joining to existing form of glycogen
What does a glycogen residue require to bind to glycogen chain?
a certain amount of glycogen to be present i.e glycogen primer
How many glucose residues does a glucose primer contain?
4
What is the primer attached to?
covalently attached to a protein called glycogenin
What enzyme converts G6P to G1P?
phosphoglucomutase
transfers phosphate on C6 to C1
What converts G1P to UDP-glucose
UDP-glucose pyrophosphorylase
What enzyme converts UDP-glucose to glycogen?
glycogen synthase
What can simple precursors be first converted to?
activated intermediates
Is G1P+UTP –> UDP+ pyrophosphate (PPi) reversible?
YES
What pulls the formation of UDP glucose forward?
the very active pyrophosphatase hydrolyses PPi so cant reverse anymore
What is the rate limiting enzyme of glycogen synthesis?
glycogen synthase
Can glycogen synthase introduce branches?
can not introduce branches
can not start new molecules
How many glucose molecules can glycogen synthase add to glycogen?
1 at s time
What is the branching enzyme?
transglycosylase
What bond will transglycoylse add a glucose?
alpha 1,6-glycosidic linkage on carbon 6
How often is a new branch created?
every 10 glucose residues
What regulates glycogenesis?
insulin & glucagon
What regulates level of the hormone?
stimuli= blood glucose levels
When does glycogenesis occur?
immediately after meals
What is high blood glucose levels also called?
hyperglycaemia
What hormone activates glycogen synthase? hyperglycaemia
insulin
What hormone inactivates glycogen synthase? hypoglycaemia
glucagon
What is glycogenolysis?
When we need to utilise the energy stored as glycogen
What catalyses glycogenolysis?
glycogen phosphorylase
What is the rate limiting step in glycogenolysis?
degradation of glucose to glucose-1-phosphate& then G6P
How many glucose molecules can be cleaved at a a time?
1
What happens when G6P is dephosphorylated in the liver?
dephosphorylated to glucose and released into blood stream
Can (skeletal) muscle cells dephosphorylate G6P?
NO, instead used to provide energy via glycolysis & TCA cycle
What does glycogenolysis depend on?
demand for blood glucose
What hormones regulate glycogenolysis?
hypoglycaemia, stress+hypoglycaemia, stress, hyperglycaemia
What is the source of glucagon?
pancreatic alpha cells
What hormones increases blood glucose levels in glycogenolysis?
glucagon, adrenaline, cortisol
What hormones decreases blood glucose levels in glycogenolysis?
insulin
What is the source of insulin?
pancreatic beta cells
What is the source of adrenaline?
adrenal medulla
What is the source of cortisol?
adrenal cortex
