Chapter 24, Problem 24.87EP

(a)

Interpretation Introduction

Interpretation: To determine the number of ${\text{C}}_3$ molecules involved in the Cori cycle.

Concept introduction: Glucose is converted to pyruvate by glycolysis metabolic pathway; pyruvate is further converted to lactate in the skeletal muscle cells by anaerobic reactions. The lactate is diffused into the bloodstream, by which it is transported to the liver. Lactate is reconverted to pyruvate. Gluconeogenesis metabolic pathway uses this pyruvate to synthesize glucose in the liver cells. Glucose is diffused into the bloodstream and is transported back to the active skeletal muscle cells. This cycle is known as the Cori cycle.

The Cori cycle is named after its discoverers, Gerty Radnitz Cori, and Carl Cori.

(b)

Interpretation Introduction

Interpretation: To determine the number of ${\text{C}}_3$ molecules involved in gluconeogenesis.

Concept introduction: Gluconeogenesis is an eleven-step pathway in which glucose is produced from non-carbohydrate substances. An overview of gluconeogenesis is as follows:

The molecule that contains three carbon atoms is termed as a ${\text{C}}_3$ molecule.

(c)

Interpretation Introduction

Interpretation: To determine the number of ${\text{C}}_3$ molecules involved in glycolysis.

Concept introduction: In the glycolysis metabolic pathway, a glucose molecule breaks down into two pyruvate molecules. Two ATP molecules and NADH reduced coenzymes are produced in the glycolysis pathway.

The molecule that contains three carbon atoms is termed as a ${\text{C}}_3$ molecule.

(d)

Interpretation Introduction

Interpretation: To determine the number of ${\text{C}}_3$ molecules involved in lactate fermentation.

Concept introduction: Lactate dehydrogenase enzymes convert pyruvate to lactate under anaerobic conditions in the human body. This anaerobic reduction of pyruvate to form lactate by enzymes is called lactate fermentation. The overall reaction equation for the conversion of pyruvate to lactate is as follows:

$\text{Pyruvate}+\text{NADH}+{\text{H}}^{+}\stackrel{\text{Lactate dehydrogenase}}{\to }\text{Lactate}+{\text{NAD}}^{+}$

The molecule that contains three carbon atoms is termed as a ${\text{C}}_3$ molecule.