BIOC 503 - Glycogen

fasting

glycogen is degraded for energy under ___ conditions

glucose, alpha 1-6

glycogen is a ___ polymer, with alpha 1-4 linking the monomers together, and __ allowing branching

fast regulation

The branching of glycogen allows for ___ as more ends can be added to/removed from at the same time

• aka faster building/disassembly compared to a linear structure which would only add or release 1 glucose at a time

advantages of glycogen granules

• large # of glucose molecules in a small space = reduced osmotic pressure

• branched structure allowing rapid synthesis & degradation

• subject to regulation and help manage glucose levels

muscles

The glucose released from glycogen in __ stays in the __

blood circulation

the glucose released from glycogen in the liver goes into the ___

glycogen degradation in muscles

• glycogen made into glucose 1 phosphate

• glucose 1 phosphate made into glucose 6 phosphate

• G6P goes into glycolysis to make ATP

glycogen degradation in liver

• glycogen made into glucose-1-phosphate

• glucose-1-phosphate made into glucose-6-phosphate

• G6P made into glucose by glucose-6-phosphatase

• glucose join blood circulation to be distributed to organs

UDP glucose

• made from glucose-1-phosphate and UTP

• hydrolysis of this molecule provides the energy to form glycosidic linkages

• aka uridine diphosphate glucose

reducing end

end of glucose with an aldehyde group that can be oxidized to carboxy group

non-reducing end

end of glucose with an hydroxy group that does not get oxidized nor reduced

glycogenin

glucose attached to reducing end by __ protein

glycogen synthase

enzyme adding glucose to the non-reducing end of glucose at the end of different branches by releasing UDP from UDP glucose

• DE-activated by PKA (glucagon and epinephrine)

• activated by phosphatase-1 (insulin)

• favors glycogen synthesis

branching enzyme

enzyme cutting 6-7 residues of a chain of glucose and transferring it to another place/chain creating alpha 1-6 linkages

glycogen phosphorylase

enzyme complex cutting alpha 1-4 linkages releasing glucose-1-phosphate

• activated by phosphorylase kinase (itself activated by PKA which responds to glucagon and epinephrine)

• de-activated by phosphatase-1

debrancher enzyme

type of transferase cutting 3 residues before branching point and adding them to the non-reducing end of another chain while hydrolyzing the alpha 1-6 linkages and release 1 glucose molecule.

glucose-6-phosphatase

enzyme ONLY found in the ER of liver cells (hepatocytes)

make glucose from G6P so it can be transported in capillaries

hypoglycemia

glucose-6-phosphatase deficiency, also called Von Gierke’s disease, causes sever ___ as the liver cells are unable to make glucose from glucose-6-phosphate so it can be released into capillaries and reestablish blood glucose levels

activated, inhibited

glycogen synthesis in liver is ___ by insulin, and ___ by glucagon

inhibited, activated

glycogen degradation in liver is ___ by insulin, and ___ by glucagon

epinephrine

hormone released from adrenal glands that acts as a regulator of glycogen synthesis and degradation in the same way glucagon does

• release triggered by stress or exercise

• ultimately increase blood sugar levels

glucagon, epinephrine

__ and __ both have receptor in the liver cells that increase the activity of adenylyl cyclase, thus increasing the level of cAMP. 

• the HIGHER concentration of cAMP ACTIVATES cAMP mediated kinase PKA

• active PKA phosphorylate and modify activity of other protein

insulin

when __ binds to its receptors on liver cells, it:

• activates phosphodiesterase to degrade cAMP

• activates phosphatase-1 to dephosphorylate proteins that previously got a phosphate group from PKA

phosphorylate kinase

enzyme activating glycogen phosphorylase & thus favoring glycogen degradation

• activated by PKA (glucagon and epinephrine)

• de-activated by phosphatase-1 (insulin)

glucagon receptors

muscles do NOT have ___

exercise

__ triggers epinephrine release and thus activates PKA, which activates phosphorylase kinase, and thus activate glycogen phosphorylase which promote glycogen degradation

Ca2+, AMP

muscle contraction causes ___ release and [__] increase, which also activates glycogen phosphorylase activation and promotes glycogen degradation

glucose uptake

insulin promotes ___ in muscles, as well as activating glycogen synthase and blocking glycogen degradation

high

In neurons, when blood glucose is ___, it is directly taken from CSF and stocked in astrocytes as glycogen

low

In the brain, when glucose levels are ___, the glycogen in astrocytes degraded to make lactate which is taken up by neurons and turned into pyruvate to make ATP