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44 Cards in this Set
- Front
- Back
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Glycogen
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a readily mobilized storage form of glucose
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what is the most common glycosidic linkage in glycogen?
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alpha 1-4
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what are the branching glycosidic bonds numberered?
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alpha 1-6
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app. how many alpha 1,6 links are there for every alpha 1,4 glycosidic bond?
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1/10
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most controlling enzyme of glycogen metabolism
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glycogen phosphorylase
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2 methods of regulating phosphorylase
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-allosteric signaling of cell's energy state
-hormonal signaling by reversible phosphorylation via insulin, epinephrine, and glucagon. |
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2 tissues that control glycogen metabolism in different ways:
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liver and muscle
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two forms of phosphorylase:
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phosphorylase a and b
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what's special about phosphorylase a?
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there's a Ser near its interface between its two subunits that is phosphorylated. this one is usually active.
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which phosphorylase type is more active? A or B?
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A
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what are the two "states" or phosphorylase a and b?
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R - relaxed
T - taught. A favors R B favors T |
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how do you convert phosphorylase b into a?
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phosphorylating its ser residue
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what enzyme converts phosphorylase b into a?
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phosphorylase kinase phosphorylates the ser residue of phosphorylase b
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gluconeogenic pathway does WHAT
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converts pyruvate into glucose
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noncarbohydrate precursors of pyruvate;
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lactate
amino acids glycerol |
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where does gluconeogenesis occur
why? |
liver
regulates the overall glucose blood level so brain and muscle can dip into supply whenever needed. |
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where is pyruvate carboxylase located
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in the mitochondria
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how do you get oxaloacetate out of mitochondria for gluconeogeneis in cytosol?
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first reduce it to malate
then shuttle it out into cytosol then reoxidize it to oxaloacetate. |
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what do PHOSPHATASES do?
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HYDROLYZE phosphate groups without phosphorylating ADP; only uses water and produces orthophosphate.
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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 |
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what happens to UNphosphorylated glucose? (plain glucose)
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it will not stay in the cell; exports. need to remain glucose-6-p in order to keep glucose in cell.
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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 |
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what happens to UNphosphorylated glucose? (plain glucose)
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it will not stay in the cell; exports. need to remain glucose-6-p in order to keep glucose in cell.
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what are the three fates of glucose-6-p from gluconeogenesis?
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1. Glycogen (from glucose-1-phosphate)
2. Pyruvate (from glucose-6-phosphate) 3. Ribose 5-phosphate (Nucleic acid met) |
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ONLY ONE reason why pyruvate is reduced to LACTATE:
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to regenerate NAD+ when muscles are exerting and in erythrocytes so glycolysis can keep going (needs NAD+)
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What inhibits turning on glycolysis?
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high energy levels. if the cell already has enough energy, why make more?
-ATP -Citrate (biosynthetic intermediate) -H+ (have plenty of all this don't need to make more!) |
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what promotes turning on glycolysis?
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low energy levels - need energy! break down glucose to get some:
-AMP -Fructose 2,6-BP |
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what tells gluconeogenesis not to start?
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-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. |
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What favors gluconeogenesis?
Inhibits? |
lots of biosynthetic precursors (acetyl CoA, pyruvate, ATP.
low energy levels - ADP. |
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which ends of glucose are glucose residues added to and removed from the most in glycogen?
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C4 ends
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what is glycogen?
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storage form of glucose
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how many glucose molecules per glycogen polymer?
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10000 - 10^4
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what does glycogen phosphorylase do
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removes glycogen molecules (g-1-p) one at a time from glucose polymer.
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what are the two enzymes present in DEBRANCHING ENZYME?
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Transferase
alpha 1,6-glucosidase |
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what does transferase do on debranching enzyme
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moves 3 glucose residues from the branch to the core. leaves one left.
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what does alpha 1,6-glucosidase do?
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cleaves the branched glycogen to give GLYCOGEN (n-1) + glucose normal
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what does phosphoglucomutase do?
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mutates glucose-1-phosphate into glucose-6-phosphate to be used in glycolysis
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what are the two posible fates of glucose-6-phosphate from glycogen cleavage? (after mutase)
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send to glycolysis, bypass hexokinase.
send to glucose-6-phosphatase, to give normal glucose + Pi. |
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what catalyzes glucose activation for glycogen synthesis?
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UDP-glucose pyrophosphorylase
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what MUST occur to glucose before glycogen synthesis will go?
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ACTIVATION of glucose-1-phosphate by UTP to give PPi and UDP-glucose
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key enzyme in glycogen synthesis
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glycogen synthase
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what are the two ways of regulating phosphorylase (glycogen)?
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-covalent modification
-allosteric |
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what are 2 covalent modifiers of phosphorylase?
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-protein kinases (phosphorylate b - a)
-protein phosphatases (remove phosphate) |
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how do allosteric regulators affect glycogen phosphatase?
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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) |
