Chapter 20, Problem 28P

Interpretation Introduction

(a)

Interpretation:

6-phosphoglucono-⏹-lactone should be identified.

Concept introduction:

6-phosphoglucono-⏹-lactone is formed during the pentose phosphate pathway. In the first step of pentose phosphate pathway, dehydrogenation of glucose-6-phosphate at C-1 takes produce 6-phosphoglucono-⏹-lactone.

Answer to Problem 28P

The compound C in the reaction is 6-phosphoglucono-⏹-lactone.

Explanation of Solution

6-phosphoglucono-⏹-lactone is an intramolecular ester formed by the reaction of C-1 carboxyl group and C-5 hydroxyl group. It is formed by dehydrogenation of C-1 carbon of Glucose-6-phosphate. Hydroxyl group at C-1 of glucose-6-phosphate is converted to carbonyl group. Therefore, the structure of 6-phosphoglucono-⏹-lactone is (C).

Interpretation Introduction

(b)

Interpretation:

The reactions producing NADPH should be determined.

Concept introduction:

Two molecules of NADPH are produced duringthe oxidative phase of pentose phosphate pathway.

Answer to Problem 28P

The reactions B and F produce NADPH.

Explanation of Solution

First NADPH is produced when the C-1 in glucose-6-phosphate is dehydrogenated into 6-phosphoglucono-⏹-lactone by glucose-6-phosphate dehydrogenase. This 6-phosphoglucono-⏹-lactone is hydrolyzed by a lactonase resulting 6-phosphogluconate. This 6C sugar acid is then decarboxylated by 6-phosphogluconate dehydrogenase into ribulose-5-phosphate. In this step also NADP+ acts as the electron acceptor and produce NADPH.

Therefore,reactions B and F produces NADPH.

Interpretation Introduction

(c)

Interpretation:

Ribulose-5-phosphate should be identified.

Concept introduction:

Ribulose-5-phosphate is the productof pentose phosphate pathway.

Answer to Problem 28P

The compound G in the reaction is Ribulose-5-phosphate.

Explanation of Solution

As the first step of oxidative phase of pentose phosphate pathway, C-1 of glucose-6-phosphate is dehydrogenated into 6-phosphoglucono-⏹-lactone by glucose-6-phosphate dehydrogenase. Then this 6-phosphoglucono-⏹-lactone is hydrolyzed by a lactonase resulting 6-phosphogluconate. This 6 C sugar acid is then decarboxylated by 6-phosphogluconate dehydrogenase into ribulose-5-phosphate.

Therefore, Gis Ribulose-5-phosphate.

Interpretation Introduction

(d)

Interpretation:

The CO₂generating reaction should be determined.

Concept introduction:

The decarboxylation reactions generate CO₂ as a by-product.

Answer to Problem 28P

The reactions F produce CO₂.

Explanation of Solution

The six C sugar acid, 6-phosphogluconate formed during pentose phosphate pathway is oxidatively decarboxylated by 6-phosphogluconate dehydrogenase into ribulose-5-phosphate. The final product is a five-carbon sugar, and release CO₂.

So. the reaction F produce CO₂.

Interpretation Introduction

(e)

Interpretation:

6-phosphogluconate should be identified.

Concept introduction:

6-phosphogluconate is a 6C sugar acid which forms during pentose phosphate pathway.

Answer to Problem 28P

The compound E in the reaction is 6-phosphogluconate.

Explanation of Solution

In the first step of the oxidative phase of pentose phosphate pathway, C-1 of glucose-6-phosphate is dehydrogenated into 6-phosphoglucono-⏹-lactone by glucose-6-phosphate dehydrogenase which is hydrolyzed by a lactonase resulting 6-phosphogluconate.

The end product of above reaction is 6-phosphogluconate. Thus the compound E in the reaction is 6-phosphogluconate.

Interpretation Introduction

(f)

Interpretation:

The reaction that is catalyzed by phosphopentose isomerase should be determined.

Concept introduction:

Phosphopentose isomerase is an enzyme which involves in isomerization reaction.

Answer to Problem 28P

The reactions H uses Phosphopentose isomerase enzyme.

Explanation of Solution

Ribulose-5-phosphate is isomerized to ribose-5-phosphate by phosphopentose isomerase. The enzyme, phosphopentose isomerase catalyze the conversion of a ketose sugar (Ribulose-5-phosphate ) to an aldose sugar (ribose-5-phosphate).

Therefore, the reaction H needs the enzyme phosphopentose isomerase.

Interpretation Introduction

(g)

Interpretation:

Ribose-5-phosphate should be identified.

Concept introduction:

Ribose-5-phosphate is the end product of the oxidative phase of pentose phosphate pathway.

Answer to Problem 28P

The compound I in the reaction is Ribose-5-phosphate.

Explanation of Solution

The ribulose-5-phosphate is obtained in pentose phosphate pathway when the ribose-5-phosphate is isomerized by phosphopentose isomerase.

Therefore, the compound I in the reaction is Ribose-5-phosphate.

Interpretation Introduction

(h)

Interpretation:

Reaction catalyzed by lactonase should be determined.

Concept introduction:

Lactonases catalyzes the hydrolysis of ester bonds.

Answer to Problem 28P

The reactions D uses the enzymeLactonases.

Explanation of Solution

The degydrogenated product of glucose-6-phospahte is 6-phosphoglucono-⏹-lactone. This is a 6 membered ring structure and have an ester bond between C-1 carbonyl carbon and C-5 hydroxyl Oxygen. This bond is hydrolyzed by lactonase and to produce 6-phosphogluconate. The reaction is indicated by letter D.

Interpretation Introduction

(i)

Interpretation:

Glucose-6-phosphate should be identified.

Concept introduction:

The pentose phosphate pathway is initiated by the oxidation of glucose-6-phosphate.

Answer to Problem 28P

The compound A in the reaction is glucose-6-phosphate.

Explanation of Solution

Glucose-6-phosphate is a 6-carbon sugar and have a ring structure where the hydroxyl group at C-6 is phosphorylated.

The compound A in the reaction is glucose-6-phosphate.

Interpretation Introduction

(j)

Interpretation:

The reaction catalyzed by 6-phosphogluconate dehydrogenase should be determined.

Concept introduction:

Dehydrogenases are the enzymes which catalyzes the removal of hydrogen molecules with the help of coenzymes NAD and FAD.

Answer to Problem 28P

The reactions F uses the enzymedehydrogenases.

Explanation of Solution

6-phosphogluconate is oxidatively decarboxylated by 6-phosphogluconate dehydrogenase into ribulose-5-phosphate which is indicated by reaction F.

Interpretation Introduction

(k)

Interpretation:

Reaction that is catalyzed by glucose-6-phosphate dehydrogenase should be determined.

Concept introduction:

In the first reaction of pentose phosphate pathway glucose-6-phosphate is dehydrogenated to produce phosphoglucono-⏹-lactone.

Answer to Problem 28P

The reactions B uses the enzymeglucose-6-phosphate dehydrogenases.

Explanation of Solution

In the first step of pentose phosphate pathway, Glucose-6-phosphate is dehydrogenated at C-1 by glucose-6-phosphate dehydrogenase enzyme into 6-phosphoglucono-⏹-lactone.

So, the reactions B uses the enzymeglucose-6-phosphate dehydrogenases.