Chapter 15, Problem 15.66EP

(a)

Interpretation Introduction

Interpretation: To determine the step in the urea cycle where citrulline is a product.

Concept introduction: Urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. It converts toxic ammonium ion to urea which is then excreted from the body in urine.

Urea cycle constitutes 4 steps. In step 1 carbamoyl phosphate transfers its carbamoyl group to ornithine to produce citrulline. Citrulline then condenses with aspartate in the second step to form argininosuccinate which then cleaves in the third step to form arginine and fumarate. In the final step, arginine reacts with water to produce urea.

(b)

Interpretation Introduction

Interpretation: To determine the step in the urea cycle where carbamoyl phosphate enters the cycle.

Concept introduction: Urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. It converts toxic ammonium ion to urea which is then excreted from the body in urine.

Urea cycle constitutes 4 steps. In step 1 carbamoyl phosphate transfers its carbamoyl group to ornithine to produce citrulline. Citrulline then condenses with aspartate in the second step to form argininosuccinate which then cleaves in the third step to form arginine and fumarate. In the final step, arginine reacts with water to produce urea.

(c)

Interpretation Introduction

Interpretation: To determine the step in the urea cycle where hydrolysis reaction occurs.

Concept introduction: Urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. It converts toxic ammonium ion to urea which is then excreted from the body in urine.

Urea cycle constitutes 4 steps. In step 1 carbamoyl phosphate transfers its carbamoyl group to ornithine to produce citrulline. Citrulline then condenses with aspartate in the second step to form argininosuccinate which then cleaves in the third step to form arginine and fumarate. In the final step, arginine reacts with water to produce urea.

(d)

Interpretation Introduction

Interpretation: To determine the step in the urea cycle where the reaction ${\text{N}}_{\text{3}}+{\text{N}}_{\text{1}}\to {\text{N}}_{\text{4}}$ occurs.

Concept introduction: Urea cycle is a cyclic biochemical pathway that involves the production of urea using ammonium ions and aspartate molecules as nitrogen sources. It converts toxic ammonium ion to urea which is then excreted from the body in urine.

Urea cycle constitutes 4 steps. In step 1 carbamoyl phosphate transfers its carbamoyl group to ornithine to produce citrulline. Citrulline then condenses with aspartate in the second step to form argininosuccinate which then cleaves in the third step to form arginine and fumarate.

In the final step, arginine reacts with water to produce urea.