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47 Cards in this Set

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1. What are the unique enzymatic reactions in the glyoxylate cycle? What are the names of the enzymes and describe the reactions they catalyze?
1. Malate Synthase: Acetyl CoA + glycoaldehyde æÆ malate + CoA
Isocitrate Lyase: Isocitrate æÆ succinate + glyoxylate

The structural formulas and reactions are seen in Figure 16-20, p. 624 in Lehninger.
2. What does the glyoxylate cycle allow the organism to do with lipids and acetyl CoA? Explain why metabolism of Acetyl CoA via the TCA cycle cannot give a net synthesis of glucose?
The glyoxylate cycle allows an organism to do net gluconeogenesis with fatty acids and acetate. The fatty acids are converted to acetyl CoA which in the above reactions in answer1 can give net synthesis of a TCA cycle intermediate, succinate . Succinate is converted to oxaloacetate which in turn is converted to PEP via the PEP carboxykinase reaction. PEP via gluconeogenic reactions is then converted to glucose. In the TCA cycle condensation of acetyl CoA with oxaloacetate via citrate synthase yields citrate. However two CO2 molecules are lost in the eventual conversion of citrate to oxaloacetate via the TCA cycle reactions. Thus there is no net addition of carbons in the TCA cycle starting with acetyl CoA.
3. What is the name of the intracellular compartment or body where the glyoxylate cycle is compartmented in plants?
In germinating seeds there is an intracellular compartment called the glyoxysome. The glyoxysome contains the unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase. The source of fatty acids which are converted to acetyl CoA in the glyoxysomes are from lipid bodies.
4. How is the regulation of citric acid and glyoxylate cycles coordinately regulated? In your answer explain at what step in the glyoxylate cycle where inhibition by TCA cycle and glycolytic intermediates or by AMP and ADP occurs and at what step in the TCA cycle does covalent modification regulate TCA cycle activity. Also explain how TCA cycle and glycolytic intermediates or ADP and AMP regulate the covalent modification.
4. In the glyoxylate cycle isocitrate lyase is inhibited by excess TCA cycle and glycolytic intermediates or by excess AMP and ADP.

These are signals that formation of energy (ATP) is required and the glycolytic and TCA metabolites are at high concentrations due to active glycolysis and TCA cycle activity.

These high concentrations of metabolites, particularly AMP and ADP will activate the TCA cycle by activating a protein phosphatase which would dephosphorylate isocitrate dehydrogenase (ICDH) and make it active.

In turn activation of the protein phosphatase activates TCA cycle activity.

At the same time the high concentration of metabolites, particularly AMP and ADP would inhibit a protein kinase that phosphorylates ICDH to make it inactive.

If ATP concentrations are high (meaning AMP and ADP concentrations are low) TCA cycle activity would be at a minimum and thus the TCA cycle and glycolytic intermediates are low.

Under these conditions the protein phosphatase would be low in activity and the protein kinase high in activity.

Thus, the protein kinase would phosphorylate the ICDH and make it inactive. Thus TCA cycle activity would be low and glyoxylate cycle activity high.
The glyoxalate cycle produces what from acetate.
4-carbon compounds
Vertebrates cannot convert fatty acids or acetate to
carbohydrates. Thus acetate cannot serve as?
a precursor for glucose.
Net Reaction of the Glyoxalate Cycle is?
2 Acetyl CoA + NAD+ ===> succinate + 2 CoA + NADH + H+
In plants and some bacteria, acetate can provide
net carbons for gluconeogenesis.

This is done by?
the glyoxalate cycle
In plants and some bacteria, acetate can provide net carbons for?
gluconeogenesis.
The 2 unique reactions of the Glyoxalate Cycle are?
isocitrate lyase and malate synthase.
In coordinated regulation of glyoxylate and citric acid cycles, when isocitrate dehydrogenase (ICDH) is inactivated by phosphorylation by a protein kinase, What happens to isocitrate?
isocitrate is shunted to the glyoxylate cycle
In coordinated regulation of glyoxylate and citric acid cycles, regulation of isocitrate dehydrogenase (ICDH) activity determines?
partitioning of isocitrate between the 2 cycles.
In coordinated regulation of glyoxylate and citric acid cycles, when the inactive ICDH is dephosphorylated and activated by the protein phosphatase, What happens to isocitrate?
isocitrate then is metabolized by the TCA cycle.
What does the glyoxylate cycle allow the organism to do with lipids and acetyl CoA? (short answer)
The glyoxylate cycle allows an organism to do net gluconeogenesis with fatty acids and acetate.
How does the glyoxylate cycle allows an organism to do net gluconeogenesis with fatty acids and acetate?
The fatty acids are converted to acetyl CoA which in the above reactions in answer1 can give net synthesis of a TCA cycle intermediate, succinate . Succinate is converted to oxaloacetate which in turn is converted to PEP via the PEP carboxykinase reaction. PEP via gluconeogenic reactions is then converted to glucose.
How does the glyoxylate cycle allows an organism to do net gluconeogenesis with fatty acids and acetate? (short answer)
fatty acids ~~> acetyl CoA ~~> Succinate ~~> Oxaloacetate ~~> PEP ~~> glucose
What are the steps in the glyoxylate cycle that allows an organism to do net gluconeogenesis with fatty acids and acetate?
fatty acids are converted to acetyl CoA

acetyl CoA can give net synthesis of a TCA cycle intermediate, succinate .

Succinate is converted to oxaloacetate

oxaloacetate is converted to PEP via the PEP carboxykinase reaction.

PEP is then converted to glucose via gluconeogenic reactions
In the glyoxylate cycle, oxaloacetate is converted to PEP via?
the PEP carboxykinase reaction.
In the glyoxylate cycle, PEP is then converted to glucose via?
gluconeogenic reactions
In the TCA cycle condensation of acetyl CoA with oxaloacetate via citrate synthase yields?
citrate.
In the TCA cycle condensation of acetyl CoA with oxaloacetate from the glyoxykinase happens via what pathway to yields citrate.
citrate synthase
What type of molecules are lost in the eventual conversion of citrate to oxaloacetate via the TCA cycle reactions.
two CO2
two CO2 molecules are lost in the eventual conversion of citrate to oxaloacetate via?
the TCA cycle reactions.
How many addition net of carbons in the TCA cycle starting with acetyl CoA.
no net addition of carbons
What is the name of where the glyoxylate cycle is compartmented in plants?
In germinating seeds there is an intracellular compartment called the glyoxysome.
The glyoxysome contains the unique glyoxylate cycle enzymes, _____ & ______
isocitrate lyase and malate synthase.
The source of fatty acids which are converted to acetyl CoA in the glyoxysomes are from?
lipid bodies.
How is the regulation of citric acid and glyoxylate cycles coordinately regulated?
Regulation of isocitrate dehydrogenase (ICDH) activity determines partitioning of isocitrate between the 2 cycles.
When the inactive ICDH is dephosphorylated and activate by the protein phosphatase, isocitrate then is metabolized by the TCA cycle. When ICDH is inactivated by phosphorylation by a protein kinase, isocitrate is?
shunted to the glyoxylate cycle.
Regulation of isocitrate dehydrogenase (ICDH) activity determines partitioning of isocitrate between the 2 cycles. When the inactive ICDH is dephosphorylated and activate by the protein phosphatase, isocitrate is?
metabolized by the TCA cycle.
Introducing extra carbons into the citric acid cycle as Acetyl-CoA is futile since the two carbons are eventually lost as CO2. How would we add extra carbons into Citric acid?
Find a way to introduce extra carbons to the citric acid cycle AFTER CO2 release
Extra Acetyl CoA turns into _______ and is added to TCA
succunate
Differences btwn Glyoxylate and TCA?
2 Acetyl-CoA loss to TCA as CO2

No net loss of Acetyl-CoA in glyoxylate
The real function for glyoxylate cycle?
To produce extra succinate
What is added to the glyoxylate cycle?
2 Acetyl-CoA
2 carbons are added to TCA in the form of ?
Acetyl-CoA
What are the 5 steps in the Glyoxylate cycle?
Acetyl-CoA ~~> citrate by Citrate synthase

Citrate ~~> Isocitrate by Aconitase

Isocitrate ~~> Glyoxylate by isocitrate lyase

- Succinate is formed and enters TCA

Glyoxylate ~~> Malate by Malate Sythase

Malate ~~> Oxaloacetate by Malate dehydrogenese
In the glyoxylate cycle, Acetyl-CoA ~~> citrate by?
Citrate synthase
In the glyoxylate cycle, Citrate ~~> Isocitrate by?
Aconitase
In the glyoxylate cycle, Isocitrate ~> Glyoxylate by?
isocitrate lyase
In the glyoxylate cycle, Glyoxylate ~~> Malate by?
Malate Sythase
In the glyoxylate cycle, Malate ~~> Oxaloacetate by?
Malate dehydrogenese
What step of the Glyoxylate Cycle is the Citrate synthase catalyst involved with?
Acetyl-CoA ~~> citrate
What step of the Glyoxylate Cycle is the Aconitase catalyst involved with?
Citrate ~~> Isocitrate
What step of the Glyoxylate Cycle is the isocitrate lyase catalyst involved with?
Isocitrate ~~> Glyoxylate
What step of the Glyoxylate Cycle is the Malate Sythase catalyst involved with?
Glyoxylate ~~> Malate
What step of the Glyoxylate Cycle is the Malate dehydrogenese catalyst involved with?
Malate ~~> Oxaloacetate