Chapter 14: Carbohydrate Metabolism

Flashcards covering key concepts from the biochemistry lecture on carbohydrate metabolism, including the pentose phosphate pathway, gluconeogenesis, and glycogen metabolism.

What is the main function of the Pentose Phosphate Pathway (PPP)?

To reduce NADP+ to NADPH and produce ribose-5-phosphate from glucose-6-phosphate.

Where does the Pentose Phosphate Pathway occur?

In the cytoplasm.

What is the primary role of NADPH in metabolic pathways?

It is primarily used in anabolic pathways, as well as detoxification pathways and reducing reactive oxygen species.

What are the two phases of the Pentose Phosphate Pathway?

Oxidative and Nonoxidative.

What happens to Fructose-6-Phosphate and Glyceraldehyde-3-Phosphate (GA-3-P) if NADPH is required?

They are used to replenish Glucose-6-Phosphate for more flux through the pathway.

What is the key step of the oxidative phase of the Pentose Phosphate Pathway?

It is irreversible and referred to as the commitment step, because the product of this step is not used for anything else but the PPP

What is the main function of the nonoxidative phase of the Pentose Phosphate Pathway?

To recycle carbons so they can go through the oxidative phase again.

What is the function of transketolase and transaldolase enzymes?

Transketolases transfer two-carbon units, while transaldolases transfer three-carbon units.

What is the result of a glucose-6-phosphate dehydrogenase deficiency?

Glutathione reserves are depleted, and NADPH levels are lowered.

How does high NADPH regulate the Pentose Phosphate Pathway?

High NADPH inhibits glucose-6-phosphate dehydrogenase, causing flux to shift from the pentose phosphate pathway to glycolysis.

What is gluconeogenesis?

The production of glucose from noncarbohydrate compounds.

Where does gluconeogenesis primarily occur?

Mostly in the cytoplasm, but pyruvate carboxylase occurs in the mitochondria.

Name four major carbon sources for glucose synthesis.

Lactate, amino acids, glycerol, and oxaloacetate

What is the role of biotin in gluconeogenesis?

It carries a carboxyl group and is needed for pyruvate carboxylase.

What is the effect of fructose-2,6-bisphosphate and AMP on glycolysis?

They activate glycolysis.

What is the effect of citrate and ATP on glycolysis?

They inhibit glycolysis.

How does glucagon regulate glycolysis and gluconeogenesis?

Glucagon inhibits glycolysis and promotes gluconeogenesis.

How does insulin regulate glycolysis and gluconeogenesis?

Insulin stimulates glycolysis and inhibits gluconeogenesis.

Where does glycogen degradation and synthesis occur?

In the cytosol.

What are the three key enzymes that regulate glycogen degradation and synthesis?

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

What is the function of glycogen in muscles?

To generate glucose-6-phosphate.

What is the function of glycogen in the liver?

To export glucose to other cells and regulate glucose concentration in the bloodstream.

What are reducing sugars?

Sugars that react with an oxidizing agent, ending with a free anomeric -OH.

What enzyme initiates Glycogen Degradation?

Glycogen phosphorylase.

What is the function of glycogen debranching enzyme?

Transfers 3 glucose units to nearest nonreducing end and cleaves α(1→6) glycosidic bond to release free glucose

What is required for glycogen synthesis?

Synthesis of uridine diphosphate glucose (UDP glucose).

What is the function of Glycogenin?

Anchor protein for the glycogen core particle and Catalyzes the glycosyltransferase and synthesis reactions needed to generate glycogen

What is the function of Glycogen Branching Enzyme?

Transfers 7 glucose residues from one end of the glycogen chain to a nearby chain

Which enzyme is the most unique to the pentose phosphate pathway?

glucose-6-phosphate dehydrogenase

What are Phosphatases?

enzymes that remove phosphate groups