Pentose Phosphate Pathway

Question 1

Other names of Pentose Phosphate Pathway

Answer 1

Hexose Monophosphate Pathway
Phosphoglyconate Pathway
Pentose Monophosphate Shunt

Question 2

Pentose Phosphate Pathway

-Function

Answer 2

1) Provides biosynthetic reduction power by synthesizing NADPH
2) Catabolism/Synthesis of C5 (pentoses) carbohydrates
- nucleotide biosynthesis
3) Catabolism/Synthesis of C4 (tetroses) carbohydrates
4) linked to glycolysis

Question 3

Pentose Phosphate Pathway is divided into?

Answer 3

1) Oxidative Phase
- synthesis of NADPH
2) Nonoxidative Phase
- interconversion of C4-7 carbohydrates

Question 4

Location of Pentose Phosphate Pathway to provide NADPH?

Answer 4

1) Synthesis
- Adrenal Gland-Steroid Synthesis
- Testes- Steroid Synthesis
- Ovary- Steroid Synthesis
- Mammary gland-Fatty Acid Synthesis
- Liver- Fatty acid and Cholesterol Biosynthesis
- Adipose Tissue-Fatty acid synthesis
- Various tissues-neurotransmitter biosynthesis
- Almost all tissue- nucleotide biosynthesis

2) Detoxification
- Reduction of oxidized glutathione
- Cytochrome P450 monooxygenase

Question 5

Oxidative Phase overview:

-produces/reduces?

Answer 5

Produces:
1 Ribulose 5-phosphate

Reduces
2 NADP+ and Glucose 6-Phosphate

Question 6

Glucose 6-Phosphate Dehydrogenase

Answer 6

Glucose 6-Phosphate-> 6-Phosphoglucono-8-lactone

• Irreversible/regulated
• NADP+ reduced to NADPH
• Glucose 6-P oxidized
• dehydrogenation Ron

INHIBITED:
by low NADP+ concentration

Question 7

Lactonase

Answer 7

6-Phosphoglucono-8-lactone->6-Phosphogluconate

-Hydrolysis-ring opening at ketone group

Question 8

6-Phosphogluconate Dehydrogenase

Answer 8

6-Phosphogluconate-> ribulose 5-Phosphate + CO2

• NADP+ reduced to NADPH
• loses Carbon 6C to 5C

Question 9

Phosphopentose Isomerase

Answer 9

Ribulose 5-Phosphate-> Ribose 5-Phosphate

Question 10

Phosphopentose Epimerase

Answer 10

Ribulose 5-Phosphate-> Xylulose 5-Phosphate

Question 11

1st Step of Nonoxidative Phase

Answer 11

Xylulose 5-P + Ribose 5-P-> G3P + Sedheptulose 7-P

-Transketolase andTPP as coenzyme

Question 12

2nd Step of Nonoxidative Phase

Answer 12

G3P + Sedheptulose -> Fructose 6-P + Erythrose 4-P

• Transaldolase
• uses R group of Lysine to form Schiff Base (no prosthetic group)

Question 13

3rd Step of Nonoxidative Phase

Answer 13

Xylulose 5-P + Erythrose 4-P-> Fructose 6-P + G3P

-Transketolase

Question 14

Similiarities in Transketolase and Transaldolase mechanisms:

Answer 14

Both enzymes produce carbanions stabilized by resonance during catalysis

1) transketolase-> TPP
2) transaldolase-> Lysine

Question 15

Why does the Pentose Phosphate Pathway adjusts to Needs of the cell?

Answer 15

For production of NADPH or various carbohydrates

Question 16

Situation 1:

High demand for ribose 5-Phosphate (for DNA synthesis; Low demand for NADPH

Answer 16

Does not Use oxidative phase only non oxidative:
Glycolysis is linked to Transketolase and transaldolase

Run it through the first few steps of Glycolysis

1) Glucose 6-P -> Fructose 6-P-> Fructose 1,6-BP-> DHAP +G3P
- 2 molecules of Fructose 6-P and 1 molecule of G3P produces 3 Molecules of ribose 5-Phosphate

Question 17

Situation 2:

Balanced need for ribose 5-Phosphate and NADPH

Answer 17

Uses oxidative phase to produce 2 NADPH and 1 ribose 5-Phosphate

Question 18

Situation 3:

More NADPH than ribose 5-Phosphate required

Answer 18

Glucose 6-P completely oxidized to CO2
3 reactions
-oxidative phase of Pentose Phosphate Pathway to produce ribulose 5-P
-Transketolase and Transaldolase to produce F 6-P and G3P
-Gluconeogenesis to convert Fructose 6-P and G3P back to Glucose 6-P

Question 19

Situation 4:

Both NADPH and ATP required

Answer 19

1) Oxidative Phase of Pentose Phosphate Pathway
- Glucose 6-P-> Ribulose 5-Phosphate + CO2 + 2NADPH
2) Ribulose 5-P -> F6P and G3P via transketolase and transaldolase which enter glycolysis
3) Pyruvate is oxidized and used as precursors to produce ATP

Question 20

Glutathione

• structure
• Protect?
• reaction?

Answer 20

Protects against Reactive Oxygen Species (ROS) when its in reduced form

Gluathione-tripeptide of ECG with a free sulfhydryl
**peptide bone to Glutamate is attached to R group

GSH-> GSSG

• GSH=reduced
• GSSH=oxidized
• catalyzed by Glutathione reductase containing FAD
• oxidized NADPH to NADP+