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CHEM 430 > Gluconeogensis > Flashcards

Gluconeogensis Flashcards

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1
Q

What is gluconeogenesis?

A

anabolic reversal of glycolysis; synthesis of pyruvate and other glycolytic intermediates

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2
Q

What tissues synthesize glucose?

A

liver and kidneys

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3
Q

What tissues use glucose as their primary energy source?

A

Brain and nervous tissues, muscle, erythrocytes, testes

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4
Q

How are glycolysis and gluconeogenesis reciprocally regulated?

A

-glycogen degredegation is ON when cell needed NADH + H+ and ATP and OFF when the cell has ample NADH, H+, and ATP
-glycogen storage is ON when the cell has ample NADH, H+, and ATP (save glucose for another day), and OFF when the cell has ample NADH, H+, and ATP

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5
Q

Where are glucose units stored?

A

liver

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6
Q

What trigger gluconeogenesis?

A

-no influx of glucose
-glycogen stores are depleted in the muscles and liver
-glucose needed badly
BASICALLY: starvation conditions, not enough energy

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7
Q

What are the four major sources of carbon for glucose synthesis ?

A

LATO (lactate, amino acids, triglycerides (glycerol), cO2)

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8
Q

What enzymes in gluconeogenesis corespond to the glycolytic enzyme pyruvate kinase?

A

pyruvate carboxylase and phophoenolpyruvate carboxykinase

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9
Q

What enzyme in gluconeogensis correspond to the glycolytic enzyme phosphofructokinase-1?

A

fructose-1,6-bisphophotase

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10
Q

What enzyme in gluconeogenesis corresponds to the glycolytic enzyme phosphofructokinase-1?

A

fructose-1.6-bisphosphotase

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11
Q

What enzyme in gluconeogenesis corresponds to the glycolytic enzyme hexokinase?

A

glucose-6-phosphotase

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12
Q

What enzymes catalyzes the interconversion of pyruvate to phosphoenolpyruvate?

A

pyruvatecarboxylase and phosphoenolpyruvate carboxykinase

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13
Q

Reaction for pyruvate carboxylase

A

pyruvate + ATP + HCO3 –> oxaloacetate (beta-keto acid) + ADP + inorganic phosphate

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14
Q

Reaction for phosphoenolpyruvate carboxykinase

A

oxaloacetate + GTP –> phosphoenolpyruvate + GDP + CO2
-GTP dependent
-decarboxylation reaction

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15
Q

What B vitamin is required for pyruvate carboxylase?

A

biotin
transfers a CO2 group onto biotin to for a carboxybiotin intermediate, the CO2 from the intermediate is added to pyruvate to get oxaloacetate

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16
Q

What is lactate role in gluconeogenesis?

A

it provides carbons for gluconeogenesis; lactate is converted to pyruvate by lactate dehydrogenase where it goes to start gluneogensis in the mitochondria

17
Q

Reaction for fructose-1,6-bisphosphotase

A

Fructose-1,6-BP + H20 –> fructose-6-P + Pi
-accompanied by the hydrolysis of water to release inorganic phosphate
-bypass reaction

18
Q

Reaction for glucose-6-phosphotase

A

G6P + H2O –> glucose and inorganic phosphate
-accompanied by the hydrolysis of water to release inorganic phosphate
-bypass reaction

19
Q

What do RBCs do in glycolytic pathway?

A

they synthesize and degrade 2,3-BPG as a detour from glycolytic pathway

20
Q

What happens if pyruvate kinase is mutated?

A

-BPG increases
-more T state
-lower affinity for O2 and increased p50
**all intermediates in stage 2 of glycolysis would accumulate (including BPG)

21
Q

What would happen if hexokinase was mutated?

A

-BPG decreases
-more R state
-higher affinity for O2 and decreased P5-
**no glycolytic intermediates would accmulate

22
Q

Why is glycogen stored in long chains rather than as individual molecules in the cell?

A

if all glucose was stored as individual glucose, Glc would approach molar quantities (would lead to bulk H2O movement)
-it prevents cells from lysing (osmoregulator problems) because storing as a long polymer reduces EFFECTIVE concentration

23
Q

Describe the structure of glycolysis?

A

long chain of glucose linked by alpha 1,4 glycosidic linkages
**branches of glucose links by alpha 1,6 glycosidic linkages

24
Q

What are main enzymes associated with glycogen synthesis?

A

hexokinase, phosphoglucomutase, UDP-glucose phyrophorylase, glycogen synthase, branching enzyme, (nucleoside diphosphate kinase-indirect)

25
Q

Reaction for glycogen synthase

A

glucose(n) –> glucose (n-1) + G1P
-removes glucose units in a repetitive process until it reaches the 4th glucose unit from branch point

26
Q

How are glucose units removed ?

A

glycogen phosphorylase with PLP coenzyme has a phosphate that plucks off an H, from there the inorganic phosphate breaks the alpha 1,4 linkage between glucose units

27
Q

What happens to the GP1 from glycogen in glycogen breakdown?

A

phosphoglucomutase converts to GP1–>G6P through a G-1,6-BP intermediate (adds phosphate from inorganic phosphate
-**NEAR EQ

28
Q

What enzymes are associated with glycogen degradation?

A

-glycogen phosphorylase
-phosphoglucosemutase
-glucose 6 phosphotase (from gluconeogenesis)
-glycogen debranching enzyme

29
Q

How many ATP are produced if glucose from blood goes through glycolysis?

A

2

30
Q

How many ATP are produced if glucose unit comes from glycogen in G1P through glycolysis?

A

net 3

31
Q

Glycogen debranching enzyme

A

hydrolyze alpha 1,4 transfer and synthsize alpha 1,4

32
Q

What is a kind of enzyme is a the debranching enzyme?

A

transferase and hydrolase

33
Q

What are the three reactions of debranching enzyme?

A
  1. Hydrolyze alpha 1,4 glycosidic linkage delta G=+15.5 kj/mol
  2. transfer branch and make alpha 1,4 glycosidic linkage delta G=-15.5 kj/mol
  3. hydrolyze last alpha 1,6 glycosidic linkage delta G= -7.1 kj/mol
34
Q

What common enzyme do glycogen synthesis and breakdown share?

A

hexokinase

35
Q

What is the path of glycogen breakdown in the liver?

A

glycogen -> G1P -> G6P -> free Glucose -> to blood

36
Q

What is the path of glycogen breakdown in the muscle cells?

A

glycogen -> G1P -> G6P -> to glycolysis

CHEM 430 (4 decks)

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