Gluconeogenesis: PEP Carboxykinase (PEPCK) Flashcards
What is the structure of PEP carboxykinase (PEPCK)?
Monomeric
What does PEPCK require for decarboxylation and phosphorylation of oxaloacetate to PEP?
GTP
What molecule is eliminated with the formation of PEP from oxaloacetate?
CO2
What compound can be considered activated pyruvate with CO2?
Oxaloacetate
What is the energy expense of activating pyruvate to oxaloacetate by pyruvate carboxylase?
1 ATP
What prosthetic group facilitates the activation of pyruvate to carboxylate?
biotin
Where does the reaction from pyruvate to oxaloacetate (via pyruvate carboxylase) occur?
Mitochondria
Where does the reaction from PEP to glucose occur?
cytosol
Where does PEP carboxykinase exist?
It is evenly distributed between the cytosol and the mitochondria.
True or false: PEP can be transported across the mitochondral membrane into the cytosol by specific membrane transport proteins.
True
True of false: Oxaloacetate can be transported across the mitochondral membrane into the cytosol by specific membrane transport proteins.
False; it has no transport system.
What are the two possible routes by which oxaloacetate that is not synthesized to PEP in the mitochondria get to the cytosol?
1) Conversion to aspartate
2) Conversion to malate
What is the difference between the malate dehydrogenase and the aspartate dehydrogenase routes of getting oxaloacetate across the mitochondral membrane?
The malate dehyrdrogenase route moves reducing equivalents from the mitochondria to the cytosol (use mitochondrial NADH and produce cytosol NADH); the aspartate route uses an amino acid.
What are the steps in the route for getting oxaloacetate across the mitochondrial membrane via aspartate dehydrogenase?
1) Convert oxaloacetate to an amino acid using aspartate dehydrogenase.
2) Transport it across the membrane.
3) Convert it back to oxaloacetic acid.
True or false: The aspartate shuttle is reversible.
True
What are the steps of the malate dehydrogenase shuttle?
1) Convert the oxaloacetate to malate (uses NADH and makes NAD+ on the mitochondrial side);
2) Transport across the membrane.
3) Convert back to oxaloacetate (uses NAD+ and makes NADH on the cytosol side).
True or false: glycolysis converts NADH to NAD+.
False; it converts NAD+ to NADH.
True or false: gluconeogenesis converts NADH into NAD+ for the cytosol.
True
What is the preferred pathway for moving oxaloacetate into the cytosol?Why?
The maleate shuttle; because it transfers NADH into the cytosol, too.
What is the preferred pathway for moving oxaloacetate into the cytosol when you have just done a lot of anaerobic activity?Why?
It doesn’t matter which pathway is used, because NADH will be regenerated by homolactic fermentation in muscle cells, which takes lactate back to glucose.
In what conditions does it not matter which pathway is used to move oxaloacetate from the mitochondria into the cytosol?
When lactate is a precursor for gluconeogenesis (because NADH will come from the conversion of lactate back to pyruvate).
Which of the two transport routes–maleate and aspartate–are reversible?
Both are reversible.
What is the phosphoryl donor in the simultaneous decarboxylation and phosphorylation of oxaloacetate by PEP carboxykinase?
GTP
What drives the conversion of pyruvate to phosphoenolpyruvate?
Decarboxylation of oxaloacetate
True or false: if NAD+ is needed in the cytosol, oxaloacetate will be carried across the inner mitochondrial membrane in the form of malate.
False; it will if NADH is needed in the cytosol, not NAD+.
True or false: Gluconeogenesis requires NAD+.
False; glycolysis requires NAD+; gluconeogenesis requires NADH.
True or false: the malate and aspartate shuttles across the inner mitochondrial membrane are irreversible.
False; they are freely reversible
