Pentose Phosphate Pathway Lecture

19 vocabulary flashcards covering enzymes, intermediates, and regulatory concepts from the Pentose Phosphate Pathway lecture.

Non-oxidative Phase (of PPP)

Ribose-5-P transformed into glycolytic intermediates. Shuffles sugars. 3 R5P → 2 fructose-6P + Ga3P

NADPH

Supports reductive biosynthesis, such as FAS, cholesterol synthesis, and pyrimidine synthesis

Ribose-5-phosphate (R-5-P)

Serves as a precursor for nucleotides, coenzymes, and nucleic acids, FAD, NAD+

Glucose 6-phosphate uses

Partitioned between glycolysis and PPP, determined by concentrations of NADP+ and NADPH

Transaldolase

Enzyme that transfers a three-carbon fragment, forming fructose-6-P and erythrose-4-P in the non-oxidative PPP.

Cells that need the PPP

Rapidly dividing cells: use R5P to make RNA, DNA, coenzymes

Organs that carry out extensive FAS (liver, adipose, lactating mammary gland) require NADPH

Organs synthesizing cholesterol and steroid hormones (liver, adrenal glands, gonads) require NADPH

oxidative phase of PPP

Goals: make NADPH, end with R5P. G6P + 2 NADP+ + H2O → R5P + 2 NADPH + 2H+ + CO2

PPP oxidative phase step 1: oxidation

G6P + NADP+ → (via G6P DH) 6pP-glucono-delta-lactone + NADPH + H+

PPP oxidative step 2: hydrolysis

6-P-glycono-delta-lactone + H2O → (via lactonase + Mg2+) 6-P-gluconate; opens ring structure

PPP oxidative step 3: oxidation + decarboxylation

6-P-gluconate + NADP+ → (via 6-P-gluconate DH + Mg2+) ribulose-5-P + NADPH + H+ + CO2

PPP oxidative step 4: isomerization

ribulose 5-P → (via phosphopentose isomerase) ribose-5-P

PPP nonoxidative step 1: epimerization

ribose 5P → ribulose 5P → (via ribulose 5P epimerase) xylylose 5P

PPP nonoxidative step 2: transketolase rxn

xylulose 5P + ribose 5P (new) → (via transketolase, TPP) Ga3P + sedoheptulose 7P

Transketolase

Catalyzes the transfer of a 2-C fragment from a ketose donor to an aldose acceptor (CH2OH-C=O)

PPP nonoxidative step 3: transaldolase rxn

sedoheptulose 7P + Ga3P → (via transaldolase) erythrose 4P + F6P (leaves)

Transaldolase reaction

Catalyzes the condensation of a 3-C fragment from an aldose donor to a ketose acceptor ( O=C-CH2OH-HOCH

PPP nonoxidative step 4: second transketolase rxn

erythrose 4P + xylulose 5-P (from step 1) → fructose-6P + Ga3P (both done)

oxidation reaction intermediate uses

form NADPH for FAS, cholesterol and nucleic acid synthesis

isomerization + epimerization reactions for R5P for nucleotide synthesis, NAD+, FAD, CoA synthesis

C rearranement, transaldolase, and transketolase rxns form F6P and Ga3P for glycolysis and gluconegenesis; E4P for AA synthesis