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;
- 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:
- 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?
- 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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