Gluconeogenesis: PEP Carboxykinase (PEPCK)

Question 1

What is the structure of PEP carboxykinase (PEPCK)?

Answer 1

Monomeric

Question 2

What does PEPCK require for decarboxylation and phosphorylation of oxaloacetate to PEP?

Answer 2

GTP

Question 3

What molecule is eliminated with the formation of PEP from oxaloacetate?

Answer 3

CO2

Question 4

What compound can be considered activated pyruvate with CO2?

Answer 4

Oxaloacetate

Question 5

What is the energy expense of activating pyruvate to oxaloacetate by pyruvate carboxylase?

Answer 5

1 ATP

Question 6

What prosthetic group facilitates the activation of pyruvate to carboxylate?

Answer 6

biotin

Question 7

Where does the reaction from pyruvate to oxaloacetate (via pyruvate carboxylase) occur?

Answer 7

Mitochondria

Question 8

Where does the reaction from PEP to glucose occur?

Answer 8

cytosol

Question 9

Where does PEP carboxykinase exist?

Answer 9

It is evenly distributed between the cytosol and the mitochondria.

Question 10

True or false: PEP can be transported across the mitochondral membrane into the cytosol by specific membrane transport proteins.

Answer 10

True

Question 11

True of false: Oxaloacetate can be transported across the mitochondral membrane into the cytosol by specific membrane transport proteins.

Answer 11

False; it has no transport system.

Question 12

What are the two possible routes by which oxaloacetate that is not synthesized to PEP in the mitochondria get to the cytosol?

Answer 12

1) Conversion to aspartate

2) Conversion to malate

Question 13

What is the difference between the malate dehydrogenase and the aspartate dehydrogenase routes of getting oxaloacetate across the mitochondral membrane?

Answer 13

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.

Question 14

What are the steps in the route for getting oxaloacetate across the mitochondrial membrane via aspartate dehydrogenase?

Answer 14

1) Convert oxaloacetate to an amino acid using aspartate dehydrogenase.
2) Transport it across the membrane.
3) Convert it back to oxaloacetic acid.

Question 15

True or false: The aspartate shuttle is reversible.

Answer 15

True

Question 16

What are the steps of the malate dehydrogenase shuttle?

Answer 16

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).

Question 17

True or false: glycolysis converts NADH to NAD+.

Answer 17

False; it converts NAD+ to NADH.

Question 18

True or false: gluconeogenesis converts NADH into NAD+ for the cytosol.

Answer 18

True

Question 19

What is the preferred pathway for moving oxaloacetate into the cytosol?Why?

Answer 19

The maleate shuttle; because it transfers NADH into the cytosol, too.

Question 20

What is the preferred pathway for moving oxaloacetate into the cytosol when you have just done a lot of anaerobic activity?Why?

Answer 20

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.

Question 21

In what conditions does it not matter which pathway is used to move oxaloacetate from the mitochondria into the cytosol?

Answer 21

When lactate is a precursor for gluconeogenesis (because NADH will come from the conversion of lactate back to pyruvate).

Question 22

Which of the two transport routes–maleate and aspartate–are reversible?

Answer 22

Both are reversible.

Question 23

What is the phosphoryl donor in the simultaneous decarboxylation and phosphorylation of oxaloacetate by PEP carboxykinase?

Answer 23

GTP

Question 24

What drives the conversion of pyruvate to phosphoenolpyruvate?

Answer 24

Decarboxylation of oxaloacetate

Question 25

True or false: if NAD+ is needed in the cytosol, oxaloacetate will be carried across the inner mitochondrial membrane in the form of malate.

Answer 25

False; it will if NADH is needed in the cytosol, not NAD+.

Question 26

True or false: Gluconeogenesis requires NAD+.

Answer 26

False; glycolysis requires NAD+; gluconeogenesis requires NADH.

Question 27

True or false: the malate and aspartate shuttles across the inner mitochondrial membrane are irreversible.

Answer 27

False; they are freely reversible