Glossary of Glucose Storage

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a readily mobilized storage form of glucose
what is the most common glycosidic linkage in glycogen?
alpha 1-4
what are the branching glycosidic bonds numberered?
alpha 1-6
app. how many alpha 1,6 links are there for every alpha 1,4 glycosidic bond?
most controlling enzyme of glycogen metabolism
glycogen phosphorylase
2 methods of regulating phosphorylase
-allosteric signaling of cell's energy state

-hormonal signaling by reversible phosphorylation via insulin, epinephrine, and glucagon.
2 tissues that control glycogen metabolism in different ways:
liver and muscle
two forms of phosphorylase:
phosphorylase a and b
what's special about phosphorylase a?
there's a Ser near its interface between its two subunits that is phosphorylated. this one is usually active.
which phosphorylase type is more active? A or B?
what are the two "states" or phosphorylase a and b?
R - relaxed
T - taught.

A favors R
B favors T
how do you convert phosphorylase b into a?
phosphorylating its ser residue
what enzyme converts phosphorylase b into a?
phosphorylase kinase phosphorylates the ser residue of phosphorylase b
gluconeogenic pathway does WHAT
converts pyruvate into glucose
noncarbohydrate precursors of pyruvate;
amino acids
where does gluconeogenesis occur

regulates the overall glucose blood level so brain and muscle can dip into supply whenever needed.
where is pyruvate carboxylase located
in the mitochondria
how do you get oxaloacetate out of mitochondria for gluconeogeneis in cytosol?
first reduce it to malate
then shuttle it out into cytosol
then reoxidize it to oxaloacetate.
what do PHOSPHATASES do?
HYDROLYZE phosphate groups without phosphorylating ADP; only uses water and produces orthophosphate.
what is linked to gluconeogenesis that makes it more favorable?

What is the delta G for gluconeogenesis vs. glycolysis reversal?
Additional 2 GTP hydrolysis' and 2 ATP hydrolysis wiht those last two steps of gluconeogenesis.

-9 vs. +20
what happens to UNphosphorylated glucose? (plain glucose)
it will not stay in the cell; exports. need to remain glucose-6-p in order to keep glucose in cell.
what are the three fates of glucose-6-p from gluconeogenesis?
1. Glycogen (from glucose-1-phosphate)
2. Pyruvate (from glucose-6-phosphate)
3. Ribose 5-phosphate (Nucleic acid met)
ONLY ONE reason why pyruvate is reduced to LACTATE:
to regenerate NAD+ when muscles are exerting and in erythrocytes so glycolysis can keep going (needs NAD+)
What inhibits turning on glycolysis?
high energy levels. if the cell already has enough energy, why make more?

-Citrate (biosynthetic intermediate)
-H+ (have plenty of all this don't need to make more!)
what promotes turning on glycolysis?
low energy levels - need energy! break down glucose to get some:

-Fructose 2,6-BP
what tells gluconeogenesis not to start?
-allosteric factors alter pyruvate carboxykinase, PEPCK, and fructose 1,6-bisphosphatase.

-factors like AMP, ADP signal low energy so you don't want to make glucose, but break it down.
What favors gluconeogenesis?

lots of biosynthetic precursors (acetyl CoA, pyruvate, ATP.

low energy levels - ADP.
which ends of glucose are glucose residues added to and removed from the most in glycogen?
C4 ends
what is glycogen?
storage form of glucose
how many glucose molecules per glycogen polymer?
10000 - 10^4
what does glycogen phosphorylase do
removes glycogen molecules (g-1-p) one at a time from glucose polymer.
what are the two enzymes present in DEBRANCHING ENZYME?
alpha 1,6-glucosidase
what does transferase do on debranching enzyme
moves 3 glucose residues from the branch to the core. leaves one left.
what does alpha 1,6-glucosidase do?
cleaves the branched glycogen to give GLYCOGEN (n-1) + glucose normal
what does phosphoglucomutase do?
mutates glucose-1-phosphate into glucose-6-phosphate to be used in glycolysis
what are the two posible fates of glucose-6-phosphate from glycogen cleavage? (after mutase)
send to glycolysis, bypass hexokinase.

send to glucose-6-phosphatase, to give normal glucose + Pi.
what catalyzes glucose activation for glycogen synthesis?
UDP-glucose pyrophosphorylase
what MUST occur to glucose before glycogen synthesis will go?
ACTIVATION of glucose-1-phosphate by UTP to give PPi and UDP-glucose
key enzyme in glycogen synthesis
glycogen synthase
what are the two ways of regulating phosphorylase (glycogen)?
-covalent modification

what are 2 covalent modifiers of phosphorylase?
-protein kinases (phosphorylate b - a)
-protein phosphatases (remove phosphate)
how do allosteric regulators affect glycogen phosphatase?
regulate R-T transition; examples are:

-Glycogen (binds to spot on A, destabilizes it so it switches to T.
-AMP (binds to spot on B, stabilizes it)

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