Lecture Flashcards on Carbohydrate Metabolism

These flashcards cover key concepts from the lecture on carbohydrate metabolism, focusing on the Pentose Phosphate Pathway, gluconeogenesis, glycogen storage, and regulation.

What is the Pentose Phosphate Pathway (PPP) also known as?

It is also known as the hexose monophosphate shunt or the phosphogluconate pathway.

What are the main products of the Pentose Phosphate Pathway?

The PPP produces NADPH and ribose-5-phosphate from glucose-6-phosphate.

What is the net reaction of the Pentose Phosphate Pathway?

6 Glucose-6-P + 12 NADP+ + 6 H2O → 4 Fructose-6-P + 2 Glyceraldehyde-3-P + 12 NADPH + 12 H+ + 6 CO2.

What is the main role of NADPH in the metabolic processes?

NADPH is primarily used in anabolic pathways and to reduce reactive oxygen species.

What are the two phases of the Pentose Phosphate Pathway?

The two phases are the oxidative phase and the nonoxidative phase.

What regulates the flux through the Pentose Phosphate Pathway?

It is regulated based on the need for NADPH, nucleotide replenishment, or ATP levels.

What is the role of glucose-6-phosphate dehydrogenase in the Pentose Phosphate Pathway?

It catalyzes the irreversible 'commitment step' in the oxidative phase of the PPP.

What metabolic state results in the conversion of ribulose-5-P to ribose-5-P?

This occurs when nucleotide pools need to be replenished.

What are the four major carbon sources for gluconeogenesis?

Lactate, glycerol, amino acids, and citrate cycle intermediates.

What happens during Gluconeogenesis to form glucose from pyruvate?

Pyruvate is converted to glucose through a series of 11 reactions primarily occurring in the cytoplasm.

What enzymes bypass the pyruvate kinase reaction in gluconeogenesis?

Pyruvate carboxylase and phosphoenolpyruvate carboxykinase.

What is the effect of high levels of NADPH on glucose-6-phosphate dehydrogenase activity?

High levels of NADPH inhibit glucose-6-phosphate dehydrogenase, shifting flux from the PPP to glycolysis.

What is a key regulatory point in gluconeogenesis?

Fructose-1,6-bisphosphatase acts as a regulatory enzyme in gluconeogenesis.

What is glycogen composed of?

Glycogen consists of a core complex of glycogenin protein and approximately 50,000 glucose molecules.

Which enzymes regulate glycogen degradation?

Glycogen phosphorylase, glycogen synthase, and branching/debranching enzymes.

What initiates glycogen degradation?

Glycogen phosphorylase initiates the process of glycogen degradation.

Define reducing vs nonreducing ends of polysaccharides.

Reducing ends have a free anomeric hydroxyl group, while nonreducing ends do not.

What role does the glycogen branching enzyme play in glycogen synthesis?

It transfers glucose residues to create α(1→6) branches.

What cofactor is crucial for the enzyme pyruvate carboxylase?

Biotin is a vital cofactor for pyruvate carboxylase.