Chapter 26: The Pentose Phosphate Pathway

Question 0

Pentose Phosphate Pathway consists of two phases:

Answer 0

1. ) Oxidative generation of NADPH

2. ) Non-oxidative interconversion of sugars

Question 1

The Pentose Phosphate Pathway yields…

Answer 1

NADPH and 5-Carbon Sugars

Question 2

NADPH is the source of _____ in all organisms.

Answer 2

Biosynthetic reducing power (Delivers electrons for biosynthetic pathways)

Question 3

Pentose Phosphate Pathway takes place in the _____.

Answer 3

Cytoplasm

Question 4

Second step of Pentose Phosphate Pathway. Give:

• Enzymes
• Catalyst
• If any product is generated

Answer 4

6-Phosphoglucono-delta-lactone –> 6-Phosphogluconate

-Converted by Lactonase

Question 5

Third step of Pentose Phosphate Pathway. Give:

• Enzymes
• Catalyst
• If any product is generated

Answer 5

6-Phosphogluconate –> Ribulose 5-Phosphate

• Converted by 6-Phosphogluconate Dehydrogenase
• Generates NADPH and CO2 (6C–>5C)

Question 6

Fourth step of Pentose Phosphate Pathway. Give:

• Enzymes
• Catalyst
• If any product is generated

Answer 6

Ribulose 5-Phosphate –> Ribose 5-Phosphate

-Isomerized by Phosphopentose Isomerase

Question 7

Pentose Phosphate Pathway and Glycolysis are linked by _____ and _____.

Answer 7

Transketolase and Transaldolase

Question 9

The non-oxidative phase consists of 3 reactions: Reaction 1?

Answer 9

C5 + C5 C3 + C7

By transketolase

Question 10

The non-oxidative phase consists of 3 reactions: Reaction 2?

Answer 10

C3 + C7 C6 + C4

By transaldolase

Question 11

The non-oxidative phase consists of 3 reactions: Reaction 3?

Answer 11

C4 + C5 C6 + C3

By transketolase

Question 11

Fifth step of Pentose Phosphate Pathway. Give:

• Enzymes
• Catalyst
• If any product is generated

Answer 11

Ribulose 5-Phosphate –> Xylulose 5-Phosphate

-Converted by Phosphopentose epimerase (Rearrangement)

Question 12

The net result of the non-oxidative reactions is the conversion of _____ into _____ and _____.

Answer 12

3 Pentoses –> Two Hexoses and One Triose

3C5 2C6 + C3

Question 13

Reaction 1 of the non-oxidative phase

Answer 13

Xylulose 5-Phosphate + Ribose 5-Phosphate –> Glyceraldehyde 3-Phosphate + Sedoheptulose 7-Phosphate
-By transketolose

Question 14

Reaction 2 of non-oxidative phase

Answer 14

Glyceraldehyde 3-phosphate + Sedoheptulose 7-Phosphate –> Fructose 6-Phosphate + Erythrose 4-Phosphate
-By transaldolase

Question 15

Reaction 3 of non-oxidative phase

Answer 15

Erythrose 4-phosphate + Xylulose 5-phosphate –> Fructose 6-phosphate + Glyceraldehyde 3-phosphate
-By transketolase

Question 16

The sum of the reactions catalyzed by the epimerase…

Answer 16

3 Ribose 5-phosphate –> 2 fructose 6-phosphate + Glyceraldehyde 3-phosphate

Question 17

The rate of the pentose phosphate pathway is controlled by _____.

Answer 17

NADP+ Levels

Question 18

Which reaction is the rate-limiting step of the Pentose Phosphate Pathway?

Answer 18

The first reaction: Glucose 6-phosphate –> 6 Phosphoglucono-delta-lactone
-By glucose 6-phosphate dehydrogenase

Question 19

The most important regulatory factor is the concentration of _____.

Answer 19

NADP+

Question 20

The fate of glucose 6-phosphate depends on the need for _____, _____ and _____.

Answer 20

NADPH, Ribose 5-phosphate and ATP

Question 21

The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #1?

Answer 21

Ribose 5-phosphate needs exceed the needs for NADPH

Question 22

The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #2?

Answer 22

The NADPH and ribose 5-phosphate needs are balanced

Question 23

The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #3?

Answer 23

More NADPH is needed than ribose 5-phosphate

Question 24

The Pentose Phosphate Pathway can operate in 4 distinct modes that result from various combos of the oxidative phase, nonoxidative phase, glycolysis, and gluconeogenesis. What is #4?

Answer 24

NADPH and ATP are both required

Question 25

****Mode 1. Ribose 5-phosphate needs exceed the needs for NADPH

Answer 25

Non-oxidative phase of PPP converts 2 Fructose 6-phosphate and 1 Glyceraldehyde 3-phosphate into 3 Ribose 5-phosphate

Question 26

Mode 2. The NADPH and ribose 5-phosphate needs are balanced

Answer 26

*Oxidative Glucose 6-phosphate --> 2 NADPH and 1 Ribose 5-phosphate Intermediate: Ribulose 5-phosphate

Question 27

Mode 3. More NADPH is needed than ribose 5-phosphate. | 3 steps:

Answer 27

1. Oxidative phase forms 2 NADPH and 1 Ribose 5-phosphate 2. Non-oxidative phase converts ribose 5-phosphate to fructose 6-phosphate and glyceraldehyde 3-phosphate 3. Glycolysis converts fructose 6-phosphate and glyceraldehyde 3-phosphate to pyruvate, which can be oxidized to generate ATP

Question 29

First Step of Pentose Phosphate Pathway. Give: - Enzymes - Catalyst - Any products generated

Answer 29

Glucose 6 Phosphate --> 6-phosphoglucono-delta-lactone - Converted by Glucose 6-phosphate dehydrogenase - Reduces NADP+ to NADPH

Question 30

The pentose phosphate pathway is very important for preventing damage from reactive oxygen species (ROS) and a deficiency in glucose 6-phosphate dehydrogenase leads to: - hyperglycemia. - hemolytic anemia. - type 1 diabetes. - Beriberi. - vitamin deficiency.

Answer 30

Hemolytic anemia

Question 31

T or F: The non-oxidative phase requires the enzymes transaldolase and transketolase.

Answer 31

True

Question 32

T or F: PPP produces 5 GTP per glucose entering the pathway.

Answer 32

False

Question 33

T or F: The non-oxidative phase involves the interconversion of sugars.

Answer 33

True

Question 34

T or F: PPP contains two ATP-consuming steps.

Answer 34

False

Question 35

T or F: PPP takes place in the mitochondrial matrix.

Answer 35

False

Question 36

The pentose phosphate pathway operates in four distinct modes. Mode 2 is active when the need for NADPH and ribose 5-phosphate are balanced. Which pathway(s) operate during Mode 2? - Oxidative phase only. - Non-oxidative phase only. - Oxidative phase → non-oxidative phase → gluconeogenesis. - Oxidative phase → non-oxidative phase → glycolysis. - Non-oxidative phase → citric acid cycle.

Answer 36

Oxidative Phase only