Gluconeogenesis (exam 3)

Define gluconeogenesis

Production of glucose from non-carbohydrates precursors

Where does gluconeogenesis primarily occur?

In the liver (60%) and kidneys (40%)

In gluconeogenesis, which non-carbohydrate precursors can be used to make glucose?

Lactate, amino acids, glycerol, TCA intermediates, and pyruvate

Which enzyme converts pyruvate into oxaloacetate (OAA)?

Pyruvate carboxylase

Where does the conversion of pyruvate into oxaloacetate (OAA) occur?

mitochondrial matrix

Why does gluconeogenesis exist?

Exists to maintain blood glucose levels when dietary glucose is unavailable or glycogen stores become depleted during fasting, starvation or intense exercises

In glycolysis, which steps are irreversible and require a bypass enzyme for gluconeogenesis?

-Hexokinase

-PFK-1

-Pyruvate kinase

Which prosthetic is needed for the enzyme pyruvate carboxylase to convert pyruvate to oxaloacetate?

Biotin

What role does biotin have in gluconeogenesis?

Biotin functions as a CO₂ carrier in the pyruvate carboxylase reaction, transferring activated carbon dioxide to pyruvate to form oxaloacetate during gluconeogenesis

Describe the mechanism of the pyruvate to oxaloacetate

1.biotin is covalently linked to a lysine residue on pyruvate carboxylase (“swinging arm”)

2.ATP provides the energy needed to attach CO2 to biotin

3.Biotin carries CO2 between the 2 active sites within pyruvate carboxylase

4.Biotin transfers the CO2 to pyruvate is turning the 3-carbon molecule into the 4-carbon molecule oxaloacetate

What is the role of PEP carboxykinase in gluconeogenesis?

It is the enzyme that helps convert OAA into phosphoenolpyruvate (PEP)

Describe the mechanism of the oxaloacetate to phosphoenolpyruvate

1.PEP carboxykinase decarboxylates OAA

2.GTP phosphorylates the molecule

3.PEP is formed

What are the reactants and products of the oxaloacetate to phosphoenolpyruvate reaction in gluconeogenesis?

2 OAA+2 GTP→2 PEP+2 GDP+2 CO2

What are the reactants and products of the pyruvate to oxaloacetate reaction?

2 Pyruvate+2 CO2​+2 ATP→2 OAA+2 ADP

Where does the conversion of OAA into PEP occuring?

mitochondria

How does pyruvate enter the mitochondria?

Proton-Pyruvate transporter where proton and pyruvate bind to transporter causing a conformational change, resulting in the transporter flipping inward so that pyruvate is released inside the mitochondrial matrix

Which part of the mitochondria membrane is permeable and impermeable?

-Outer mitochondrial membrane is permeable

-Inner mitochondrial membrane is impermeable

How does PEP leave the mitochondria?

PEP shuttle transporter (SLC25A35); proton-pep antiporter where protons are coming in and PEP is coming out

What is the role of fructose-1,6-bisphosphatase-1 in gluconeogenesis?

It is an enzyme that converts fructose-1,6-bisphosphate into fructose-6-phosphate

Describe the mechanism of Fructose-1,6-bisphosphate to Fructose-6-phosphate in gluconeogenesis

1.fructose-1,6-bisphopsphate binds to fructose-1,6-bisphosphatase

2.Water is used to hydrolyze the phosphate attached to C1

3.the phosphate on C1 is removed, but the phosphate of C6 remains

4.fructose-6-phosphate is formed + Pi released

-general base catalysis

What is needed for Fructose-1,6-bisphosphatase to convert fructose-1,6-bisphosphate to fructose-6-phosphate in gluconeogenesis?

-water for hydrolysis

-Mg2+ as a cofactor

What is the role of Mg2+

Mg²⁺ serves as a cofactor for fructose-1,6-bisphosphatase by stabilizing the negatively charged phosphate groups of fructose-1,6-bisphosphate and facilitating hydrolysis of the phosphate at carbon 1, producing fructose-6-phosphate and inorganic phosphate (Pi).

What is the role of glucose-6-phosphatase in gluconeogenesis?

It is the enzyme that converts glucose-6-phosphate into glucose

Describe the mechanism of glucose-6-phosphate into glucose

1.glucose-6-phosphate binds to glucose-6-phosphatase

2.the enzyme positions the phosphate group attached to carbon 6 for removal

3.water hydrolyzes the phosphate ester bond via general base catalysis

4.glucose is formed and a Pi is released

What is the energy cost of gluconeogenesis for 1 glucose produced from 2 pyruvate?

-4 ATP, 2 GTP, 2 NADH + H⁺

Which compound cannot sustainably become glucose?

Fatty acids so they are broken down to acetyl-CoA

Why is gluconeogenesis favored when there is a high concentration of ATP?

Gluconeogenesis is favored when ATP concentrations are high because it is an energy-requiring pathway. High ATP signals that the cell has sufficient energy, inhibits glycolysis, and promotes the synthesis of glucose from non-carbohydrate precursors. Conversely, low ATP and high AMP favor glycolysis to generate energy.

when would AMP inhbit Fructose 1,6-bisphosphatase?

AMP inhibits fructose-1,6-bisphosphatase when cellular energy levels are low. Elevated AMP signals ATP depletion, causing gluconeogenesis to be inhibited and glycolysis to be stimulated so the cell can generate more ATP.

When would phosphofructokinase-1 be activated by AMP and ADP?

PFK-1 is activated by AMP and ADP when cellular energy levels are low, stimulating glycolysis to generate ATP

When would phosphofructokinase-1 be inhibited by ATP?

PFK-1 is inhibited by ATP when energy levels are high, reducing glycolysis because the cell already has sufficient energy.