Chapter 15 Flashcards
Glycogen serves as the
main storage form of glucose in animals esp live and muscle
Purpose of glycogen in muscle
provides an immediate source of glucose for quick energy during physical activity
Purpos eof glycogen in the liver
acts as a reservoir to regulate blood glucose levels, releasing into bloodstream when necessary
Glycoggen structure
highly branched polymer made up glucose moleucles with branch points allowing it to release glucose rapidly from mutiple points
Beta granules
smaller glycogen particules found in the muscle cells
purpos beta granules
quick energy release
B granulues shape
arranged in chains
how many non reducing ends are there in beta granules?
2,000 non reducing ends per beta molecules
Alpha granules structure
larger clusters in liver that conisist of mutiple beta granules.
Purpose of Alpha granules
absent after 24 hrs
provide a slower but sustained release of cluose to maintain blood sugar
which granule is easier for enzymes?
Beta bc they are in free form alpha granules have embedded enzymes making it harder to bind
Gylcogen dimer
serves as a primer for glycogen synthesis
1-4 link
1-6 link
Glycogenolysis
break down of glycogen
Glycogenesis
glycogen building
glycogen phosphorylase
catalyzes glycogen breakdown
how do glycogen phossphorlyase aid in glycogen breakdown?
proteolytic cleavage or cuts glycogen chains by adding a phsophate
where does the glycogen phosphorylase work?
non reducing end
What’s required for the glycogen phosphorylase? [cofactor]
pyridoxial phosphate
Role of pyridoxial phosphate
speds up reaction by making it easier for the phosphate from IP to break down bonds in glycogen
repeattive
When glycogen is brokden down it rleeases a form of glucose called
glucose 1-phosphate
Purpose of phosphoglucomutase
convert glucose 1- phosphate to glucose 6 phosohate group
Fate of G6P in liver
G6P can further be converted to regular glucose whihc then enters the bloodsteeam to help maintain blood sugar levels
Fate of G6P in skeletal muscle
G6P will be used in glycolysis
Sugar nucleotide UDP glucose
What are sugar nucleotides
modified forms of sugars where a secific anomeric carbon is activtaed
hOW DO SUGAR NUCLEOTIDES SUCHAS udp ACTIVATE
ATTACHMENT OF A NUCLEOTIDE TO A SUGAR VIA a phosphate linkage
Purpose of UDP Glucose
main form of glucose used to build glyocgenn
What does it mean by UDP tag
Why is UDP good for synthesis purposes?
Irreversible function - UDP glucose doesnt easily reverse
nucleotide moetit
efficent leaving group
taggin function
What drives the formation of UDP-glucose?
the removsl of a by product PPI or phyrophosphate which release a alarge amount of energy.
What’s the energy releease for UDP formation
-19.2kj/mol
pushes reacin forward strongly
What are the main sources of glucose 6-phosphate>?
Hexokinase - converts glucose in blood to g6p
Liver conversion from lactate
What facilitates thr conversion of glucose 6 phosphate to glucose 1phosphate
Phosphoglucomutase
Why is g6p converted to g1p?
to become apart of udp glucose
udp glucose phos
glyogen syn
adds glucose units one by one to the non reducing end of the growing glyocgen chain using UDP glucose
Branching Enzyme
creates branches by breaking off a small glucose chain from the main chain and attaching it to a different point
Why does branching enzymes move branches?
allows for faster breakdownlater as it creates more point which glucose can be released
Whats the end result after rbanching enzymes are complete?
a highly branched efficent glycogen molecule ready for quick release
What is required for glycogen synthesis?
primer or gylcogenin
What is Glycogenin
1st reaction in glycogenin mechanism
Glycogenin attaches the 1st glucose molecule to tyrosine
o glycosidicic linkage
autocatalytic reaction
The first reaction in glycogenin mechanism is considered autocatalytics meaning?
glycogenin adds glucose to itself
2nd reaction in glycogenin mechanism
glycogenin then adds around 7 more flucose from udp glucose forming a shorter starer chain
what occurs after the short chain is in place?
enzymes can continue building and branching glycogen
Phosphorylase a
catalytically active form ready to break down glycogen
phosphorylase b
LESS active and predominates in resting muscle
catalytic anbolic vs
when is phsophorylayze activates?
high levels of glycogen ?
Skeletal muscles have no receptors for
glucagon
Phosphorylase b is converted to phosphorylase a to become active via
Phosohorylation of phosphroylaze b
Wha triggers the phosphorlyation of phosphorylase b
hormones
What hormone triggers phosphorylation of phoyslayes b in the muscle?
Epinephrine
What hormone triggers phosphorylation of phoyslayes b in the liver?
glucagon
glucagon vs epinephrine
catabolic vs fight or flight
When is epineohrine released?
in muscles during virgous muscle activity
when are amp levels high?
during high muscle acitity
AMP activation
AMP binds to phosphorylase b in muscle cells actviating during low energy states
ATP inhibition
high atp lvels block amp binding slowing glycogen
What does glucagon and epinephrine act upon?
Gsalpha ?
What do elevated cAMP initates?
an enzyme cascade
Enzyme cascade
domino effect on catalyst
A rise in camp activates Pka which will..
phosphorylates phosphorlyase b kinase
Purpose of phosphorylase b kinase
cataylzes the phsophorylation of glycogen phosphroylase b
What is CA 2+ a signal for
muscle contraction
CA 2+ binds to and activates
Phosphorylase b kinase
AMP Accumulation
during intense activity amp levels rise signaling low energy and activating phsphorylase kinase
Phosphorlayse kinase in turn activates
gylcogen phosphorylase, promoting glycogen breakdown fro energy
Phosphoprotein phosphate 1 PP1
REMOVES PHOSPHATE GROUPS DEACTIVATING PHOSPHORYLASE A BACK TO phosphorylase
How do phosphoprotein phosphate effect glycogen breakdown process?
slows it down
Explain the allsoteric control in liver enzymes
What happens in liver senses glucose levels
glycogen synthase a
unphosphorylated and catalytically active
glycogen synthase b
phosphorylated and inactive unless G6P is present
GSK3
CATALYZES THE PHSORYLATION OF GLYCOGEN Synthase a
What does insulin activate and inactivated?
Inactivate - GSK3
Activates - PP1
How does G6P acts allosterically with glycogen synthase b
to be a better substrate for PP1
What does GSK3 require prior to target glycogen synthase?
prior phosphorylation by casein kinase 2
Role of GSK3
gsk3 cannot phosphorylate glycogen synthase until
casein kinase 2 CKII has phosphorylated the glycogen synthase on a nearby reisude [a priming event]
insulin
insulin
Glycogen targeting proteins
act as scaffolds bringing together enzymes involved in glycogen metabolism
What do glycogen targeting proteins coordinate?
glycogen synthase
phosohorylase
PP1
allowing for efficent regulation in reponse to hormone leels
Insulin activates and inactiates hwat in the liver