Glycogenesis Flashcards
glycogenesis
glucose converted to glycogen
why do we need glycogenesis
to ensure a reserve of quick energy
major sites of glycogen synthesis and storage
liver and skeletal muscle
some glycogen in kidneys and heart
liver glycogen unique role
can be broken down to glucose to reenter the bloodstream
maintains blood glucose homeostasis
skeletal muscle glycogen storage role
majority of glycogen stores bc skeletal muscle is so common
which tissue has the greatest concentration of glycogen?
liver
glycogen stores in muscle: problem
an energy source that can’t directly contribute to blood glucose levels
muscles don’t have enzyme that converts phosphorylated glucose back into free glucose
how does glucose enter the cell?
(step 1 of glycogenesis)
glucose is phosphorylated by hexokinase in muscle or glucokinase in liver to become glucose-6-phosphate
ATP to ADP
glycogen is made up of
G6P (blood glucose) + gluconeogenic precursors = glycogen
hexokinase type 1 and 2 location
muscle, brain, adipose tissue
glucokinase (hexokinase type 4) location
liver and pancreas
hexokinase inhibition
allosterically inhibited by G6P (its product)
when cell has enough G6P, glucose entry into cell is slowed
glucokinase inhibition
not inhibited by G6P
hexokinase Km
low Km
function at max velocity at fasting blood glucose concentrations
glucokinase Km
high Km
functions at max velocity only when glucose levels are high (such as following a high-carbohydrate meal)
hexokinase and insulin
not induced by insulin in normal individuals
glucokinase and insulin in normal individuals
induced by insulin in normal individuals
hexokinase and insulin in insulin-resistant individuals
not induced by insulin
glucokinase and insulin in insulin-resistant individuals
not induced by insulin
which form of glycogen synthase (dephosphorylated or phosphorylated) is more active
dephosphorylated
insulin promotes dephos
what promotes dephosphorylation of glycogen synthase
insulin
this is how insulin stimulates glycogenesis
what is induced by insulin?
glucokinase!
what is an alternate source of glucose for glycogensis?
newly synthesized glucose from gluconeogenesis
step 2 of glycogenesis
transfer phosphate from carbon 6 of glucose to carbon 1
enzyme: phosphoglucomutase
step 3 of glycogenesis
uridine monophosphate combined with G1P to form UDP-glucose
energy from UTP to UMP (hydrolysis of anhydride bond)
in what form is glucose incorporated into glycogen?
UDP-glucose
step 4 of glycogenesis
UDP-glucose to glycogen
enzyme: glycogen synthase
what does glycogen synthase require
preformed glycogen as a primer
how is initial glycogen formed
glucose residue binds to glycogenin
when is glycogen synthase active
when it is dephosphorylated
when is glycogen synthase inactive
phosphorylated
insulin and glycogen synthesis
insulin stimulates dephosphorylation of glycogen synthase (activates it)
after 6 or 7 glucose molecules are added to glycogen chain,
branching of chain
branching enzyme
transfers 6 or 7 glucoses to C-6-OH group
forms alpha(1-6) bonds bc glycogen synthase can’t
why is branching important
increases molecule’s solubility and compactness
makes nonreducing ends of chains available so glucose can be cleaved rapidly and used for energy (glycogenolysis)
glycogenesis energy use
consumes energy bc an ATP and UTP are consumed for each molecule of glucose introduced
