Andrea: Biochem Exam 4 Gluconeogenesis and Pentose Phosphate Pathway

These flashcards cover key concepts and regulatory mechanisms of gluconeogenesis, glycolysis, and the pentose phosphate pathway.

What is gluconeogenesis?

A metabolic pathway that generates glucose from non-carbohydrate carbon substrates.

What is the starting point for gluconeogenesis?

It starts from simple organic compounds of 2-3 carbons such as acetate, lactate, and propionate.

What is the role of lactate in gluconeogenesis for mammals?

Lactate produced by anaerobic fermentation in muscle is converted to glucose in the liver.

How many steps are in the glycolysis pathway?

There are 10 steps in the glycolysis pathway.

What is produced during the payoff phase of glycolysis?

4 ATP and NADH per glucose.

Which three steps in glycolysis are essentially irreversible?

1. Glc → G6P (hexokinase) 2. F6P → FBP (PFK-1) 3. PEP → pyruvate (pyruvate kinase).

How are the irreversible steps in glycolysis characterized?

They have large negative free-energy changes (DG).

What is the first step of the first bypass in gluconeogenesis?

Pyruvate Carboxylase.

Where does the reaction of pyruvate carboxylase occur?

In the mitochondria.

What are the requirements for pyruvate carboxylase?

Biotin, bicarbonate, and ATP.

What happens to oxaloacetate for it to be transported out of the mitochondria?

It is reduced to malate.

What is the second step of the first bypass in gluconeogenesis?

Phosphoenolpyruvate carboxykinase (PEPCK).

What signal triggers gluconeogenesis?

Low blood glucose levels.

What is the overall energy cost for gluconeogenesis?

Each glucose formed requires 6 high-energy phosphate groups (4 ATP + 2 GTP).

What are glucogenic amino acids?

Amino acids that can be converted into glucose or intermediates of gluconeogenesis.

Can mammals convert fatty acids into glucose?

No, they primarily convert fatty acids to acetyl-CoA which cannot be used to generate glucose.

What plays a role in the conversion of glycerol into gluconeogenesis intermediates?

Glycerol can be phosphorylated to dihydroxyacetone phosphate.

Which enzyme catalyzes the PFK-1 reaction in glycolysis?

Phosphofructokinase-1

What regulates hexokinase IV in the liver?

It is regulated by blood glucose concentration and a specific regulatory protein.

How does high blood glucose affect hexokinase IV activity?

It increases activity as glucose concentration rises above 10 mM.

Which regulatory protein inhibits hexokinase IV in the liver?

A regulatory protein that binds tighter in the presence of fructose 6-phosphate.

What is the role of fructose 2,6-bisphosphate (F26BP)?

It acts as an allosteric activator of PFK-1 in glycolysis.

How does insulin affect the regulation of F26BP?

Insulin stimulates increased F26BP, promoting glycolysis.

What effects does glucagon have on glucose metabolism?

Glucagon signals to produce and release glucose, inhibiting glycolysis.

What regulates the cellular concentration of fructose 2,6-bisphosphate?

The rates of formation by PFK-2 and breakdown by FBPase-2.

What do PFK-2 and FBPase-2 activities have in common?

They are part of a bifunctional protein regulated by glucagon and insulin.

What occurs during the oxidative phase of the pentose phosphate pathway?

The oxidation of glucose 6-phosphate (G6P) to produce NADPH and ribulose 5-phosphate.

What essential product is generated by the pentose phosphate pathway?

NADPH.

In what conditions does G6P go through glycolysis rather than the pentose phosphate pathway?

When there is a low concentration of [NADP+].

What is the function of transketolase in the non-oxidative phase?

It catalyzes the transfer of 2-carbon fragments between sugar phosphates.

What is the function of transaldolase in the non-oxidative phase?

It transforms products from transketolase reactions to form fructose 6-phosphate and erythrose 4-phosphate.

What is the importance of NADPH in the cell?

It is required for reductive biosynthesis and protection against oxidative damage.

Which enzyme is used in both glycolysis and gluconeogenesis?

3-phosphoglycerate kinase.

What happens to pyruvate in gluconeogenesis?

It is converted to oxaloacetate by pyruvate carboxylase.

What is the energy status of gluconeogenesis compared to glycolysis?

Gluconeogenesis is more energy expensive than glycolysis.

How many ATP equivalents does gluconeogenesis use to form one glucose?

It uses 6 high-energy phosphate equivalents.

What are some feeder pathways for glycolysis?

Endogenous glycogen and starch degradation, dietary starch, and other carbohydrates.

What role does citrate play in regulating glycolysis?

Citrate is an allosteric inhibitor of PFK-1.

How does ADP and AMP affect PFK-1 activity?

They act as allosteric activators, relieving inhibition caused by ATP.

What effect does high energy supply (ATP, acetyl-CoA) have on pyruvate kinase?

It inhibits all isozymes of pyruvate kinase.

What is one major difference between the pentose phosphate pathway and glycolysis?

The pentose phosphate pathway primarily generates NADPH, while glycolysis produces ATP.

Which step in gluconeogenesis is considered a control point for pyruvate?

The conversion of pyruvate to OAA, then to PEP via pyruvate carboxylase.