Glycogen Flashcards
how is gluconeogensis regulated
by allosteric and substrate-level control mechanism
How is glycogen synthesized?
- Glucose units are activated for transfer by formation of sugar nucleotides
- UDP=glucose synthesis is driven by pyrophosphate hydrolysis..
- glycogen synthase catalyzes formation of alpha(1–>4) glycosidic bonds in glycogen.
How is Glycogen Metabolism controlled?
- Glycogen metabolism is highly regulated
- Glycogen synthase is regulated by covalent modification
- Hormones regulate glycogen synthesis and degradation.
when would we want to store glucose ?
- we have high concentration of glucose
- high levels of ATP(high energy states)
glycogen synthase
forms those alpha (1-4) glycosidic linkages
Glycogen phosphorylase is regulated by covalent modification…
phosphorylation converts the enzyme from a form that is allosterically regulated, to a form that is persistently active.
in the Phosphorylase (alpha) side
the equilibrium is shifted towards the R state so that the phosphoryaled enzyme is more active, with no requirement for an allosteric activator
That is, phosphorylation reduces the value of L ([T0]/[R0]) in the MWC mechanism
what is phosphorylase kinase regulated by?
phosphorylation
when is glucagon made?
in response to low blood sugar, and stimulates mobilization of glycogen
what does epinephrine do?
it prepares the organism for mobilization of large amounts of energy (‘fight or flight’)
why Cyclic AMP is a second messenger?
because it is the intracellular agent of an extracellular hormone. The enzyme that makes cAMP is membrane associated
why this cascade mechanism amplifies hormonal signal ?
because one hormone-receptor complex can activate many G proteins, and many cAMP molecules can be synthesized before the G protein dissociates
how does cAMP activates cAMP-dependent protein kinase?
cAMP binding causes dissociation of the C subunit, which is the active kinase, which phosphorylates phosphorylase kinase
Phosphocreatine
provides a short-term source of ATP in muscle, because it can phosphorylate ADP to make ATP
what’s the source of ATP during intense workout?
free ATP, phosphocreatine and anaerobic glycolysis
phosphocreatine prolongs ATP availability for a few more seconds
why can’t ATP persist for long periods of time during workout?
because ATP and phosphocreatine are quickly used up, and anaerobic glycolysis would cause acidosis
where do ATP come from in long term excise ?
glycogen breakdown and aerobic metabolism become important
Which type of ATP synthesis is slower?
synthesis by oxidative phosphorylation is slower than by anaerobic glycolysis, which in part explains the reduced speeds of runners running longer distances
what’s another source of ATP during LONG marathons ?
fat breakdown also becomes an important energy source. ATP synthesis from fat degradation is even slower than from glycogen breakdown, so speeds are slower. Elite runners consume ~equal amounts of fat and glycogen during marathon
what are the types of Glycogen storage diseases?
von Gierke’s disease
Cori disease
McArdle disease
von Gierke’s disease
(glucose-6-phosphatase). Glycogen is normal in structure but present in excess. Glucose-6-phosphate accumulates in liver (cannot be converted to glucose), stimulates glycolysis causing lactate acidosis
Cori disease
(debranching enzyme), only outermost branches of glycogen can be degraded. Symptoms similar to von Gierke
McArdle disease
(muscle glycogen phosphorylase). Limited ability to perform strenuous exercise, but gentle exercise is possible
what are other names for pentose phosphate pathway?
hexose monophosphate shunt or the phosphogluconate pathway
