Pentose Phosphate Pathway

Describe the four metabolic fates of Glucose 6-phosphate in liver cells

G6P → G1P → Glycogen

G6P → F6P → pyruvate

G6P → 6-phosphogluconate → ribose-5-phosphate

G6P → Glucose

List the two metabolic products of PPP

NADPH and Ribose-5-phosphate

What is the overall function of NADPH

anabolic reactions

What is the overall function of ribose-5-phosphate 

synthesis of nucleotides, DNA and RNA

What is the role of the oxidative portion of PPP (what two reactions occur)

Form NADPH from NADP+ and decarboxylation of G6P into ribulose-5-phosphate 

What is happening in the non-oxidative portion of PPP

Excess ribulose-5-phosphate is interconverted into GAP and F6P for glycolysis

Write the reaction occurring in the oxidative phase along with the number of carbon atoms

G6P + 2NADP+ → Ribulose-5-phosphate + 2NADPH + CO2

6 carbons to 5 carbons

Write the reactions occurring in non-oxidative portion of PPP along with the carbon number changes (there are 3 overall reactions) (ex. molecule1 + molecule 2 → molecule3 + molecule 4 (#C1 + #C2 → #C3 + #C4))

Xylulose-5-phosphate + Ribose-5-phosphate → GAP + sedoheptulose-7-phosphate (5C + 5C → 3C + 7C)

GAP + sedoheptulose-7-phosphate → F6P + Erythrose-4-phosphate (3C + 7C → 6C +4C_

Erythrose-4-phosphate + Xylulose-5-phosphate → F6P + GAP (4C + 5C → 6C + 3C)

What is the key regulatory enzyme for the PPP

Glucose-6-phosphate dehydrogenase

What is the principle way G6P DH is regulated

concentration of NADP+

What enzyme class converts Ribulose-5-phosphate into Ribose-5-phosphate

Isomerase

What enzyme converts Ribulose-5-phosphate into Xylulose-5-phosphate

Epimerase

Two key enzymes involved in non-oxidative part of PPP

Transketolase and Transaldolase

How many carbon atoms are transferred in reactions catalyzed by transketolase

2

How many carbon atoms are transferred in reactions catalyzed by transaldolase 

3

Flow of metabolites through PPP when cells need ribose-5-phosphate

G6P gets converted into F6P and GAP and reversal of sugar swapping from PPP creates R5P

Flow of metabolites through PPP when cells need Ribose-5-phosphate and NADPH

G6P gets converted to R5P and two molecules of NADPH by PPP

Flow of metabolites through PPP when cells need NADPH

G6P gets converted into R5P and two molecules of NADPH; sugar rearrangement produces F6P and GAP which will create more G6P by gluconeogenesis and then more NADPH

Flow of metabolites through PPP when cells need NADPH and ATP

NADPH is created and the sugar rearrangement process gets carried out to produce F6P and GAP; these metabolites will be used in glycolysis to produce pyruvate and ATP