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CHEM 430 > Lesson 12 - Glucogenesis & Glycogen Metabolism > Flashcards

Lesson 12 - Glucogenesis & Glycogen Metabolism Flashcards

1
Q

What kind of pathways are glycogen metabolism and gluconeogenesis

A
  • reciprocally regulated pathways: one is the catabolism of glucose while the other is the anabolic “reverse”
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2
Q

glycolysis

A

literally means the “loosening of sugar” - it is the catabolic oxidation of 6-Carbon glucose to two 3-carbon molecules

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3
Q

gluconeogenesis

A
  • synthesis of glucose from pyruvate (end product of glycolysis) and other glycolytic intermediates
  • occurs by a series of reactions which reverse glycolysis with 3 exceptions
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4
Q

what enzymes are shared between glycolysis and gluconeogenesis

A

“near reactios”
- phosphoglucoisomerase
- aldolase
triose phosphate isomerase
- GADPH
- phosphoglycerate kinase
- phosphoglycerate mutase
- enolase

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5
Q

which enzymes are different when comparing glycolysis and gluconeogenesis

A

hexokinase, phosphofructokinase, pyruvate kinase

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6
Q

tissues that synthesize glucose

A

primarily the liver, a little bit of the kidney medulla

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7
Q

tissues that use glucose as their primary energy source

A

brain and nervous tissue, muscle, erythrocytes, testes

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8
Q

gluconeogenisis rxn: 1

A

Pyruvate + Co2 + ATP + H2O –> Oxaloacetate + ADP + Pi + H+

Enxyme: Pyruvate carboxylase

Glycolytic enzyme: pyrivate kinase

Reaction type: bypass rxn

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9
Q

gluconeogenisis rxn: 2

A

Oxaloacetate + GTP –> phosphoenolpyruvate + CO2 + GDP

Enzyme: Phosphoenolpyruvate carboxykinase

Glycolytic enzyme: pyrivate kinase

Reaction type: bypass rxn

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10
Q

gluconeogenisis rxn: 3

A

Phosphoenolpyruvate to 2-
Phosphoglycerate by Enolase
**requires addition of H2O*

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11
Q

gluconeogenisis rxn: 4

A

2-phosphoglyerate to 3-phosphoglycerate by phosphoglycerate mutase

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12
Q

gluconeogenisis rxn: 5

A

3-phosphoglycerate + ATP –> 1,3-Bisphosphate + ADP by phosphoglycerate kinase

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13
Q

gluconeogenisis rxn: 6

A

1,3-Bisphosphate + NADH + H+ –> glyceraldehyde -3-phosphate + Pi + NAD+ by GADPH

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14
Q

gluconeogenisis rxn: 7

A

glyceraldehyde -3-phosphate to dihydroxyacetone phosphate by triose phosphate isomerase

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15
Q

gluconeogenisis rxn: 8

A

dihydroxyacetone phosphate to fructose-1,6 bisphosphate by aldolase

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16
Q

gluconeogenisis rxn: 9

A

fructose-1,6 bisphosphate + H20 to fructose-6-phosphate + Pi by fructose-1,6-bisphosphatase-1

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17
Q

gluconeogenisis rxn: 10

A

fructose-6-phosphate to glucose-6-phosphate by phosphoglucose isomerase

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18
Q

gluconeogenisis rxn: 11

A

glucose-6-phosphate + H2O to glucose + Pi by glucose 6-phosphatase

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19
Q

bipass reactions

A

1,2,9,11

20
Q

how many pyruvate do you need to synthesize 1 mol of glucose

A

2

21
Q

what are the 4 major sources of carbon for glucose synthesis for gluconeogenesis

A

glycerol, CO2 fixation in chloroplasta, amimo acids, lactate

22
Q

where does a lot of pyruvate come from

A

lactate
- lactate produced in muscle cells is transported to the liver and is converted to pyruvate by lactate dehydrogenase

23
Q

pyruvate carboxylase requires what

A

the B vitamin, biotin (adds carbonyl group to pyruvate)

24
Q

intermediate made from pyruvate carboxylase

A

carboxybiotin intermediate

25
Q

what does bpg do

A

decreases the oxygen affinity of hemoglobin by binding in the central cavity of the deoxygenated form of hemoglobin

26
Q

what happens if hexokinase mutated

A

[bpg] decreases, meaning the R state is more stabilized, higher affinity for oxygen, decreased p50 value, graph of oxygen saturation v. pO2 shifts to the left

  • no glycolytic intermediates, including 2,3 bpg would accumulate
27
Q

what happens if pyruvate kinase mutated

A

[bpg] increaes, meaning the T state is more stabilized, lower affinity for oxygen, increased p50 value, graph of O2 saturation v. pO2 shifts to the right

  • all intermediates in stage II of glycolysis, including 2,3 bpg would accumulate
28
Q

degradation of glycogen

A

the glycogen polymer can be broken down into individual glucose units which can then be targeted for glycolysis

29
Q

why is the glycogen granule so highly branched and why is it a metabolic requirement for 55,000 glycogen units to be stored as a polymer instead of 55,000 individual glucose units?

A

[Glu] in the blood is about 5mM

  • if 55,000 Glc stored as individual molecules in the cell, then intracellular [Glc] would approach molar quantities –> leading to buk H2O movement into the cell and the cell would explode
  • storage as a long polymer prevents osmoregulatory problems and reduces effective conc. of glucose in the cell
  • branching provides more surface area and “free ends” to degrade
30
Q

structure of glycogen polymer

A
  • long chains of glucose linked via alpha 1,4 glycosidic linkages
  • with fewer intermittent branches being alpha 1,6 glycosidic linkages
31
Q

key reactions in glycogen metabolism

A

1: Glycogen phosphorylase
2: Glycogen Synthase
3: glycogen branching and debranching enzymes

32
Q

glycogen phosphorylase

A

Glucose n –> Glucose n-1 + G1P

** glycogen phosphorylase with PLP coenzyme

  • most active part in glycogen metabolism
  • this process is repetitive; the enxyme removes successive glucose redidues until it reaches the 4th glucose unit from a branch point
33
Q

what does phosphoglucomutase catalyze

A

the interconversion of glucose 1-phosphate (from glycogen) and glucose 6 phosphae (near equilibrium)

34
Q

glucose 6 phosphate in either the liver or muscle cells

A

in the liver cells: dephosphorylated and exported to those that need it

in the muscle cells: metabolized into glycolysis

35
Q

how many ATP if glucose is imported from blood –> glycolysis

A

from blood glucose: net 2 ATP (-2 in phase 1 and +4 in phase II)

36
Q

how many ATP if glucose unit comes from glycogen in the form of G1P –> glycolysis

A

from glycogen: Net 3 ATP (skip hexokinase: -1 in phase I and +4 in phase II)

37
Q

Glycogen debranching enzyme

A

hydrolyze alpha 1 –> 4 transfer and synthesize alpha 1 –> 4

  • group transfer top 3 glucose residues to the bottom
  • adds H2O to alpha 1,6 branch

SUMM
- glycogen phosphorylase leaves ~ 4 glucose units (sterically inhibited from phosphorylizing “nub”)
- debranching enzyme is a transferase and a hydrolase

38
Q

debranching enzyme: 2 steps, 3 reactions

A

1.) hydrolyze alpha 1 –> 4 glycosidic linkage (-15.5 KJ/mol)

2.) transfer branch and make an alpha 1 –> 4 glycosidic linkage (+15.5 KJ/mol)

3.) Hydrolyze last alpha 1 –> 6 glycosidic linkage (-7.1 KJ/mol)

39
Q

what is the debranching delta G

A

-7.1 KJ/mol

40
Q

what is the shared common enzyme between glycogen synthesis and breakdown

A

phosphoglucomutase

41
Q

step 1 of glycogen synthesis

A

glucose-6-phosphate to glucose-1-phosphate by phosphoglucomutase

  • readily reversible reaction
  • if ATP snd NADH are high; store glucose unit
42
Q

step 2 of glycogen synthesis

A

form a nucleotidyl-glucose intermediate

  • adding a glucose requires the formation of a nucleotifyl-glucose intermediate
  • this is an anabolic process

1- “molecularly” tages a G1P molecule for use in another metabolic process (UDP-Glc NOT a substrate for phosphoglucomutase)

2 - sequesters a pool of UDP - Glc for one metabolic fate

3- PPi is a good leaving group; 1Pi is exergonic

43
Q

after the glycogen branching enzyme, how many ends are there

A

3 instead of 2

44
Q

summary breakdown of glycogen in the liver

A

Glycogen –> G1P- –> G6P –> Free Glc –> to blood –> to muscles

45
Q

summary breakdown of glycogen in the muscle

A

glycogen –> G1P –> G6P –> to glycolysis

46
Q

deficiency in glucose 6 phosphate can cause what

A

enlarged liver –> cant breakdown glycogen

CHEM 430 (23 decks)

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