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FND 600 > Pentose Phosphate Pathway > Flashcards

Pentose Phosphate Pathway Flashcards

1
Q

Essential Pentosuria

A

-Rare, benign genetic condition

  • Lack of xylulose reductase (reduces xylulose to xylitol in uronic acid pathway)
  • Result = ↑ xylulose in urine
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2
Q

Alimentary Pentosuria

A

Occurs after consumption of large amounts of fruits (e.g. pears)

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3
Q

High fructose consumption

A
  • Fructose bypasses reaction catalyzed by Phosphfructokinase —> undergoes more rapid glycolysis than glucose
  • Results: ↑ FAs, VLDL (atherosclerosis)
  • Results: ↓ ATP synthesis, ↑ uric acid formation (gout)
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4
Q

Essential fructosuria

A
  • Lack of hepatic fructokinase
  • Benign, asymptomatic
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5
Q

Hereditary fructose intolerance

A
  • Lack of aldolase B
  • Severe hypoglycemia and vomiting after fructose consumption

Treatment: Diet low in fructose, sorbitol, sucrose

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6
Q

Galactosemia

A
  • Inability to metabolize galactose due to defects of galactokinase, uridyl transferase, or 4-epimerase
  • Instead: converted to galactitol
  • Galactitol accumulates in lens of the eye –> cataract
  • Liver failure and mental deterioration

Treatment: Galactose-free diet

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7
Q

Hemolytic anemia

A
  • Genetic deficiency of glucose-6-phosphate dehydrogenase (1st enzyme in PPP)

-RBCs destroyed when individual subjected to oxidative stress

  • Gluathione peroxidase reliant on NADPH
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8
Q

Oxidative (Irreversible) Beginning & End

A

Glucose-6-Phosphate → Ribulose -5-Phosphate

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9
Q

Nonoxidative (Reversible) Beginning & End

A

Ribulose-5-Phosphate → Glucose-6-Phosphate

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10
Q

Oxidative, Irreversible Pathway (NADPH formation)

A
  1. Glucose-6-Phosphate → 6-Phosphogluconolactone (NAPH FORMATION)

Enzyme: Glucose-6-Phosphate Dehydrogenase
- NADP+ → NADPH + H+

  1. 6-Phosphogluconolactone → 6-Phosphogluconate

Enzyme: Gluconolactone Hydrolase
-Requires Water

  1. 6-Phosphogluconate → 3-keto 6-phosphogluconate (NAPH FORMATION)

Enzyme: 6-phosphogluconate dehydrogenase
- NADP+ → NADPH + H+

  1. 3-keto 6-phosphogluconate → Ribulose-5-phosphate

Enzyme: 6-phosphogluconate dehydrogenase
- CO2 released.

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11
Q

Nonoxidative, Reversible Pathway (Ribose formation)

A
  1. Ribulose-5-phosphate → Xylulose-5-Phosphate

Enzyme: Ribulose-5-Phosphate 3-Epimerase

  1. Ribulose-5-phosphate → Endiol form → Ribose-5-Phosphate (RIBOSE FORMATION)

Enzyme: Ribose-5-Phosphate Ketoisomerase

  1. Ribulose-5-phosphate + Xylulose-5-Phosphate → Sedoheptulose-7-phosphate & Glyceraldehyde-3-Phosphate

Enzyme: Transketolase

  1. Sedoheptulose-7-phosphate + Glyceraldehyde-3-Phosphate → Fructose-6-Phosphate + Erythrose-4-Phosphate

Enzyme: Transaldolase

  1. Eryhrose-4-Phosphate + Xylulose-5-Phosphate → Fructose-6-Phosphate + Glyceraldehyde-3-Phosphate

Enzyme: Transketolase

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12
Q

Name five tissues in which the PPP is active

A

 Liver
 Adipose Tissue
 Adrenal Cortex
 Thyroid
 RBCs
 Testis
 Lactating Mammary Gland

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13
Q

PPP Basics

A

Location: Cytosol

Metabolic Pathway for Glucose

Glucose-6-Phosphate

Used NADP+

Produces CO2

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14
Q

Glycolysis Basics

A

Location: Cytosol

Metabolic Pathway for Glucose

Glucose-6-Phosphate

Used NAD+

Generates ATP

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15
Q

PPP & Glycolysis Linked by

A

Xylulose-5-Phosphate

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16
Q

Xyluose-5-Phosphate Functions

A

o Activates kinase, Inactivates Phosphatase
o ↑ Fructose 2,6-bisphosphate formation
o ↑ Phosphofructokinase activity
o ↑ Glycolysis

17
Q

Uronic Acid Pathway

A

 Location: Liver
 Products: Glucose → Glucuronic Acid & Pentoses

 Does not produce ATP
 Function: Glucuronate is precursor to proteoglycans and need for drug metabolism

18
Q

NADPH used for synthesis of…

A

Fatty Acids (NADPHATTY ACIDS)
Steroids
Amino Acids

19
Q

Even tissues with low PPP activity can synthesize ribose-5-phosphate via ____

A

reversal of nonoxidative phase utilizing fructose-6-phosphate.

20
Q

How does Xyulose-5-Phosphate link glycolysis and the PPP

A
  • Activates kinase needed for glycolysis
  • Inactivates phosphatase enzyme needed for gluconeogenesis
21
Q

_____ needed to convert glyceraldehyde 3-phosphate to glucose-6-phosphate

A

Fructose 1,6 bisphosphate

FND 600 (8 decks)

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