Chapter 22 (Glycogen Breakdown and Synthesis) Flashcards
When ___ breaks down glycogen it must stay within the cell
muscle
because Glucose-6P cannot cross the cell membrane
When ___ breaks down glycogen it can go elsewhere throughout the body
liver
because the liver has Glucose-6-phosphatase
Only glucose units that are at least ___ units away from a branch point are cleaved
5
Glucose’s break off as
Glucose-1P
Then goes through phosphoglucomutase
Glycogen Debranching enzyme
Creates and breaks alpha(1-4) bonds
Phosphoglucomutase creates
A Glucose-1,6-BP intermediate
UDP-Glucose Pyrophosphorylase
Turns Glucose-1P into UDP-Glucose (transferes a UMP) Requires UTP Produces PPi (driving force behind the rxn) Irreversible
Glycogen Synthase
Attaches the Glucose in UDP-Glucose to a Glycogen (n+1) molecule
Requires Glycogen (n)
Produces a UDP
ONLY generates alpha(1-4) linkages yielding alpha-amylose
Most glycosyl groups in mammals are donated by ___
UDP-Glucose
In plants, starch is built from glucose units donated by ___
ADP-Glucose
Glycogen Branching Enzyme
Transfers 7 residue segments from the end of a chain to the C6-OH group Breaks alpha (1-4) bonds Creates alpha (1-6) bonds
Overall reaction for glycogen storage and utilization
Glucose + Pi + 2 NAD + ADP (arrow) 2 pyruvate + ATP + 2 NADH + H2O
Storage costs ___ ATP and utilization gives us ___ ATP
2
3
Internal cellular regulation is via ___ regulation
allosteric
High demand for ATP
Glycogen synthase is inhibited
Low demand for ATP
Glycogen synthase is favored
Regulation between cells occurs via ___
Hormones
insulin,glucagon,epinephrine
Difference between glucagon and epinephrine
Glucagon: long-term maintenance
activates liver gluconeogenesis
act in the LIVER and ADIPOSE only
Epinephrine: fight or flight
acts on LIVER and MUSCLE
Active form (A) of:
Glycogen synthase
Glycogen phosphorylase
dephosphorylated (-OH)
phosphorylated (-OPO3)
Glycogen phosphorylase regulation (allosteric)
Activator: AMP
Inhibitor: ATP, G6P, and glucose (in liver)
Glycogen synthase regulation (allosteric)
Activator: G6P
Least active form of enzyme
Tb
Most active form of enzyme
Ra
Insulin dephosphorylation (on/off)
Glycogen synthase: on
Phosphorylase kinase: off
Glycogen phosphorylase: off
Epinephrine/Glucagon phosphorylation (on/off)
Turns ATP to cAMP
Protein Kinase A (PKA): on
Phosphorylase kinase: on
Glycogen phosphorylase: on
Binding of epinephrine and glucagon activates a heterotrimeric ___ protein
G
Inactive when bound to GDP
Creation of cAMP
epinephrine/glucagon bind to G protein
GDP becomes GTP
Causes the dissociation of alpha and beta, gamma subunits
Dissociated subunits can activate/inactivate other cellular components
Off switch to GTP
Alpha subunit is a GTPase that hydrolyzes GTP to GDP + Pi
Becomes inactive
Adenylate Cyclase
Turns ATP into cAMP
Produces PPi
Phosphodiesterase
Turns cAMP into AMP
Requires H2O
Caffeine inhibits this enzyme increase the lifetime of cAMP
Protein Kinase A (PKA) is activated by the binding of ___
cAMP
Phosphorylation cascade
cAMP activates Protein Kinase A (PKA)
PKA phosphorylates Phosphorylase Kinase and phosphorylates Glycogen Synthase (inactive)
Phosphorylase Kinase activates Glycogen Phosphorylase
Muscle Phosphorylase Kinase is allosterically activated by ___
Calcium
Binding subunit is called calmodulin
PP1 is a ___ regulator
Covalent modification
___ allosterically activates dephosphorylated glycogen synthase
G-6P
