Lecture 10 - Gluconeogenesis

Question 1

What is gluconeogenesis mean (broken up)

Answer 1

glucomeans glucose,neomeans new, andgenesisindicates synthesis

Question 2

What is gluconeogenesis

Answer 2

the process (or metabolic pathway) via which glucose is synthesized from non-carbohydrate precursors
(sometimes called Endogenous glucose pathway)

Question 3

What is the equation of lactate dehydrogenase

Answer 3

Lactate + NAD+ –> Pyruvate + NADH + H+

Question 4

What is the equation of aminotransferase (transaminase)

Answer 4

Alanine + alpha-Ketoglutarate —> Pyruvate + glutamate

Question 5

What are the non-carbohydrate precursors converted to in gluconeogenesis

Answer 5

Pyruvate or other intermediates of glycolysis

Question 6

Where does gluconeogenesis take place

Answer 6

Liver and Kidney (majority in the liver)

Question 7

What is the first reaction in gluconeogenesis

Answer 7

the conversion of pyruvate to phosphoenolpyruvate and this involves two steps catalysed by two enzymes.

Question 8

What is the first step in gluconeogenesis catalysed by

Answer 8

Pyruvate Carboxylase
Phosphoenolpyruvate Carboxykinase

Question 9

What does Pyruvate Carboxylase do (GNG Step 1)

Answer 9

catalyses the carboxylation of pyruvate to oxaloacetate in a reaction involving the hydrolysis of ATP:
Pyruvate + HCO3- + ATP → Oxaloacetate + ADP + Pi

Question 10

What does Phosphoenolpyruvate carboxykinase do (GNG step 1)

Answer 10

catalyses the simultaneous decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate in a reaction that involves the hydrolysis of GTP or ITP to GDP or IDP respectively:

Oxaloacetate + GTP (or ITP) → Phosphoenolpyruvate + CO2 + GDP (or IDP)

Question 11

What is the second reaction in gluconeogenesis and what is it catalysed by

Answer 11

. Fructose 1, 6-bisphosphate is converted to fructose 6-phosphate in a hydrolytic reaction catalysed by FRUCTOSE 6-PHOSPHATASE (phosphofructokinase):
Fructose 1, 6-bisphosphate + H2O → Fructose 6-phosphate + PO32-

Question 12

What is the terminal step in gluconeogenesis and what is it catalysed by

Answer 12

the conversion of glucose 6-phosphate to glucose in a reaction catalysed by GLUCOSE 6-PHOSPHATASE:

Glucose 6-phosphate + H2O → Glucose + PO32-

Question 13

Where do each of the gluconeogenic enzymes locate

Answer 13

Pyruvate carboxylase (S1) - Mitochondria
Phosphoenolpyruvate carboxykinase (S1) - Cytoplasm
Fructose-1,6-bisphosphatase (S2) - Cytoplasm
Glucose-6-phosphate (S3) - Endoplasmic Reticulum

Question 14

After the pyruvate has been produced, it cannot be transported out of the mitochondria as neither the liver or kidney have a transporter for oxaloacetate. How is this problem circumvented

Answer 14

MALATE DEHYDROGENASE converts oxaloacetate to malate. The liver and kidney do possess a transporter for malate so it can be shuttled back into the cytosol. Once in the cytosol malate is converted back to oxaloacetate.

Question 15

What is the advantage of converting Malate back to oxaloacetate in the cytosol

Answer 15

NADH is produced and can be used in subsequent reactions (e.g. the reduction of 3-phosphoglycerate to glyceraldehyde 3-phosphate).
Oxaloacetate is then converted to phosphoenolpyruvate (PEP) by PHOSPHOENOLPYRUVATE CARBOXYKINASE which is also in the cytoplasm. PEP continues through the next steps (all reverse glycolytic reactions) until glucose 6-phosphate is obtained

Question 16

How does shuttling in and out of the mitochondrion occur

Answer 16

Pyruvate enters mitochondrion
Pyruvate carboxylase catalyses the formation of oxaloacetate
Oxaloacetate CANNOT get out of the mitochondrion as no transporter
Therefore, it is converted to malate, transported into the cytosol, then converted back into oxaloacetate!
Catalysed by malate dehydrogenase (mitochondrial & cytosolic)
Transported by malate transporter

Question 17

Describe the components involved in the transport of glucose 6-phosphate into the ER

Answer 17

1. The catalytic subunit of Glucose 6-phosphatase
2. A calcium binding stabilising protein called SP necessary for catalytic activity
   Because of the localisation of the catalytic subunit on the luminal side of the E.R. transporter proteins are needed to transport the substrate and products into and out of the E.R. respectively.
3. A transporter protein, called T1, for the substrate of the reaction glucose 6-phosphate
4. A transporter protein termed T2 to remove inorganic phosphate from the E.R.
5. A transporter protein called T3 to transport glucose into the cytosol