Chapter 20: The Pentose Phosphate Pathway

Question 1

Two stages of the PPP

Answer 1

• Oxidative

- Non-oxidative

Question 2

Shunts of the PPP

Answer 2

• Pentose shunt

- Monophosphate shunt

Question 3

PPP is a mostly

Answer 3

• Anabolic cytoplasmic pathway

- Connection with glycolysis

Question 4

PPP is significant in organs/tissues

Answer 4

• Liver
• Kidney
• Adipose tissue
• Adrenal cortex
• Neurones
• RBCs (along with glycolysis)

Question 5

PPP is significant in cells

Answer 5

• Neutrophils

- Macrophages

Question 6

Neutrophils and macrophages kill

Answer 6

• Microorganisms

- Minimal importance in muscle

Question 7

PPP is responsible for synthesis and degradation of

Answer 7

• Pentoses

Question 8

PPP is central to formation of

Answer 8

• NADPH

Question 9

There is no direct consumption or production of

Answer 9

• ATP in the pentose phosphate pathway

Question 10

Non-oxidative phase of the PPP involves

Answer 10

• Isomerization/epimerization phase

- Rearrangement phase

Question 11

Overall, the PPP produces

Answer 11

• NADPH upon oxidation of glucose-6-phosphate to ribulose-5-phosphate

Question 12

Glucose-6-phosphate dehydrogenase is

Answer 12

• The rate limiting enzyme

Question 13

G-6-P DH is highly specific for

Answer 13

• NADP+

- Primary regulation point

Question 14

G-6-P DH is strongly inhibited by

Answer 14

• NADPH

Question 15

The most common of all human enzymopathies (G-6-P DH)

Answer 15

• Favism (consumption of fava beans) and hemolytic anemia

- Leads to reduced formation of NADPH

Question 16

Mutant enzyme (G-6-P DH) is rapidly degraded

Answer 16

• And RBCs (lacking a nucleus) cannot re-synthesize it

Question 17

Individuals with G-6-P DH enzymopathy react to

Answer 17

• Antimalarial drugs (primaquine)

Question 18

Mutations of G-6-P DH protect against

Answer 18

• Malaria (just like sickle cell)

Question 19

6-phosphogluconate dehydrogenase catalyzes

Answer 19

• Oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate
• Produces NADPH

Question 20

Overall reaction of the oxidative phase of PPP

Answer 20

• Glucose-6-phosphate + 2NADP+ + H2O –> Ribulose-5-phosphate + 2NADPH + 2H+ + CO2

Question 21

Interconversion of ribulose-5-phosphate with ribose-5-phosphate or xylulose-5-phosphate produces

Answer 21

• 5 C sugars

Question 22

Ribose-5-phosphate can be rearranged to regenerate

Answer 22

• Glycolytic intermediates

Question 23

The rearrangement of ribose-5-phosphate is brought about through the action of

Answer 23

• Transketolase

- Transaldolase

Question 24

Transketolase is a family of enzymes with

Answer 24

• Broad substrate specificity

Question 25

Transketolase transfers a

Answer 25

- 2 carbon unit --> ketose to aldose

Question 26

Transketolase requires

Answer 26

- TPP cofactor (thus defective in alcoholics)

Question 27

Transketolase appears in assay of

Answer 27

- RBC diagnostic of thiamine deficiency

Question 28

Transaldolase is a family of enzymes with

Answer 28

- Broad substrate specificity

Question 29

Transaldolase transfers a

Answer 29

- 3 carbon unit --> ketose to aldose

Question 30

The PPP is closely linked with

Answer 30

- The glycolytic pathway

Question 31

Degradation of pentoses occurs via

Answer 31

- Transketolase (2C) activity | - Transaldolase (3C) activity

Question 32

Functions of the PPP is to provide

Answer 32

- NADPH - Pentoses - Pathway for synthesis/degradation

Question 33

PPP provides NADPH for biosynthesis of

Answer 33

- Fatty acids - Steroids - Neurotransmitters - Reduced glutathione

Question 34

PPP provides pentoses for

Answer 34

- Nucleic acid synthesis

Question 35

PPP provides a pathway for the synthesis and degradation of

Answer 35

- Pentoses (to glycolytic intermediates)

Question 36

Cellular NADPH from PPP is utilized by

Answer 36

- Fatty acid synthesis | - Regeneration of tripeptide GSH

Question 37

Regenration of tripeptide GSH is important in

Answer 37

- Protection from cancer - Protection from hemolysis & hemolytic anemia - Detoxification - Activation of sulfhydryl enzymes

Question 38

Protection of RBCs from hemolysis and hemolytic anemia maintains

Answer 38

- RBC integrity

Question 39

Reduced glutathione is regenerated by

Answer 39

- NADPH-dependent glutathione reductase

Question 40

GSH reacts with reactive oxygen metabolites including peroxides (H2S2) in a reaction catalyzed by

Answer 40

- Glutathione peroxidase

Question 41

H2S2 can irreversibly damage

Answer 41

- Hb

Question 42

Glucose-6-phopshate is used in both

Answer 42

- Glycolysis | - Pentose phosphate pathway

Question 43

Excess ribose-5-phopshate (R5P) can be converted to

Answer 43

- Glycolytic intermediates

Question 44

Flux of G6P through the PPP is governed by

Answer 44

- The situation that prevails within the given cell | - Relative requirements for ribose-5-phosphate and NADPH

Question 45

The PPP is entirely

Answer 45

- Cytoplasmic | - Neither consumes nor produces ATP

Question 46

PPP activity is high in

Answer 46

- Adrenal glands - Site of steroid hormone biosynthesis - Liver - Site of cholesterol - Fatty acid synthesis - Testes - Adipose tissue - Mammary glands

Question 47

Glucose-6-phopshate dehydrogenase catalyzes the irreversible, rate limiting oxidation of

Answer 47

- Glucose-6-phosphate to 6-phosphogluconolactone | - Primary control point of the PPP

Question 48

Defects in the G6P enzyme represent a common enzymopathy and affected individuals suffer from

Answer 48

- Hemolytic anemia, but are resistant to malaria

Question 49

The PPP produces NADPH for

Answer 49

- Reductive biosynthesis | - Reduction of oxidized glutathione

Question 50

The PPP produces pentoses for

Answer 50

- Nucleic acid biosynthesis