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Biochemistry I > Chapter 20: The Pentose Phosphate Pathway > Flashcards

Chapter 20: The Pentose Phosphate Pathway Flashcards

1
Q

Two stages of the PPP

A
  • Oxidative

- Non-oxidative

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2
Q

Shunts of the PPP

A
  • Pentose shunt

- Monophosphate shunt

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3
Q

PPP is a mostly

A
  • Anabolic cytoplasmic pathway

- Connection with glycolysis

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4
Q

PPP is significant in organs/tissues

A
  • Liver
  • Kidney
  • Adipose tissue
  • Adrenal cortex
  • Neurones
  • RBCs (along with glycolysis)
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5
Q

PPP is significant in cells

A
  • Neutrophils

- Macrophages

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6
Q

Neutrophils and macrophages kill

A
  • Microorganisms

- Minimal importance in muscle

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7
Q

PPP is responsible for synthesis and degradation of

A
  • Pentoses
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8
Q

PPP is central to formation of

A
  • NADPH
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9
Q

There is no direct consumption or production of

A
  • ATP in the pentose phosphate pathway
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10
Q

Non-oxidative phase of the PPP involves

A
  • Isomerization/epimerization phase

- Rearrangement phase

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11
Q

Overall, the PPP produces

A
  • NADPH upon oxidation of glucose-6-phosphate to ribulose-5-phosphate
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12
Q

Glucose-6-phosphate dehydrogenase is

A
  • The rate limiting enzyme
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13
Q

G-6-P DH is highly specific for

A
  • NADP+

- Primary regulation point

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14
Q

G-6-P DH is strongly inhibited by

A
  • NADPH
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15
Q

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

A
  • Favism (consumption of fava beans) and hemolytic anemia

- Leads to reduced formation of NADPH

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16
Q

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

A
  • And RBCs (lacking a nucleus) cannot re-synthesize it
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17
Q

Individuals with G-6-P DH enzymopathy react to

A
  • Antimalarial drugs (primaquine)
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18
Q

Mutations of G-6-P DH protect against

A
  • Malaria (just like sickle cell)
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19
Q

6-phosphogluconate dehydrogenase catalyzes

A
  • Oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate
  • Produces NADPH
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20
Q

Overall reaction of the oxidative phase of PPP

A
  • Glucose-6-phosphate + 2NADP+ + H2O –> Ribulose-5-phosphate + 2NADPH + 2H+ + CO2
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21
Q

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

A
  • 5 C sugars
22
Q

Ribose-5-phosphate can be rearranged to regenerate

A
  • Glycolytic intermediates
23
Q

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

A
  • Transketolase

- Transaldolase

24
Q

Transketolase is a family of enzymes with

A
  • Broad substrate specificity
25
Q

Transketolase transfers a

A
  • 2 carbon unit –> ketose to aldose
26
Q

Transketolase requires

A
  • TPP cofactor (thus defective in alcoholics)
27
Q

Transketolase appears in assay of

A
  • RBC diagnostic of thiamine deficiency
28
Q

Transaldolase is a family of enzymes with

A
  • Broad substrate specificity
29
Q

Transaldolase transfers a

A
  • 3 carbon unit –> ketose to aldose
30
Q

The PPP is closely linked with

A
  • The glycolytic pathway
31
Q

Degradation of pentoses occurs via

A
  • Transketolase (2C) activity

- Transaldolase (3C) activity

32
Q

Functions of the PPP is to provide

A
  • NADPH
  • Pentoses
  • Pathway for synthesis/degradation
33
Q

PPP provides NADPH for biosynthesis of

A
  • Fatty acids
  • Steroids
  • Neurotransmitters
  • Reduced glutathione
34
Q

PPP provides pentoses for

A
  • Nucleic acid synthesis
35
Q

PPP provides a pathway for the synthesis and degradation of

A
  • Pentoses (to glycolytic intermediates)
36
Q

Cellular NADPH from PPP is utilized by

A
  • Fatty acid synthesis

- Regeneration of tripeptide GSH

37
Q

Regenration of tripeptide GSH is important in

A
  • Protection from cancer
  • Protection from hemolysis & hemolytic anemia
  • Detoxification
  • Activation of sulfhydryl enzymes
38
Q

Protection of RBCs from hemolysis and hemolytic anemia maintains

A
  • RBC integrity
39
Q

Reduced glutathione is regenerated by

A
  • NADPH-dependent glutathione reductase
40
Q

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

A
  • Glutathione peroxidase
41
Q

H2S2 can irreversibly damage

A
  • Hb
42
Q

Glucose-6-phopshate is used in both

A
  • Glycolysis

- Pentose phosphate pathway

43
Q

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

A
  • Glycolytic intermediates
44
Q

Flux of G6P through the PPP is governed by

A
  • The situation that prevails within the given cell

- Relative requirements for ribose-5-phosphate and NADPH

45
Q

The PPP is entirely

A
  • Cytoplasmic

- Neither consumes nor produces ATP

46
Q

PPP activity is high in

A
  • Adrenal glands
  • Site of steroid hormone biosynthesis
  • Liver
  • Site of cholesterol
  • Fatty acid synthesis
  • Testes
  • Adipose tissue
  • Mammary glands
47
Q

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

A
  • Glucose-6-phosphate to 6-phosphogluconolactone

- Primary control point of the PPP

48
Q

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

A
  • Hemolytic anemia, but are resistant to malaria
49
Q

The PPP produces NADPH for

A
  • Reductive biosynthesis

- Reduction of oxidized glutathione

50
Q

The PPP produces pentoses for

A
  • Nucleic acid biosynthesis

Biochemistry I (34 decks)

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