what are the main functions of the PPP
generating:
NADPH, a key molecule that donates electrons in biosynthetic and antioxidant reactions
Ribose-5-phosphate, a sugar essential for the synthesis of nucleotides and nucleic acids
where does the glycolysis, gluconeogenesis, and PPP pathways all start
glucose-6-phosphate
what is the currency for reducing power
NADPH
how is NADPH produced
through photosynthesis in plants, and through the PPP in non-photosynthetic organisms
where are tissues of synthesis
adrenal gland: steroid synthesis
liver: fatty acid and cholesterol synthesis
Testes: steroid synthesis
adipose tissue: fatty acid synthesis
ovary: steroid synthesis
Mammary gland: fatty acid synthesis
RBCs: maintenance of reduced glutathione
what are the phases of the pentose phosphate pathway
the oxidative phase (makes NADPH and ribose-5-phosphate) and the non-oxidative phase (rearranges sugars).
If the cell makes too much ribose-5-phosphate and doesn’t need it for DNA/RNA, the pathway can convert it into glycolysis intermediates. Those can then be used to:
make ATP
or be used in other metabolic pathways
So basically:
The PPP can send extra sugars back into glycolysis so nothing is wasted.
for every glucose 6 P molecule that enters the PPP, how many NADPH are produced
2
steps of the oxidative phase
Glucose-6-phosphate → 6-phosphoglucono-δ-lactone
Enzyme: glucose-6-phosphate dehydrogenase
→ produces NADPH
6-phosphoglucono-δ-lactone → 6-phosphogluconate
Enzyme: lactonase
→ adds water (hydrolysis) and produces H+
6-phosphogluconate → ribulose-5-phosphate
Enzyme: 6-phosphogluconate dehydrogenase
→ produces NADPH + CO₂
Key outputs:
2 NADPH
ribulose-5-phosphate (→ can become ribose-5-phosphate)
non-oxidative phase
The major goal of this phase is to convert ribulose-5-P to ribose-5-P, which is catalyzed by an isomerase
how is the sugars recycled in the PPP
The Pentose Phosphate Pathway makes ribose-5-phosphate, which is used to build DNA and RNA.
But the cell usually doesn’t need that much ribose-5-phosphate.
So instead of wasting it, the cell recycles the extra.
Special enzymes rearrange the sugars and turn the extra ribose-5-phosphate into molecules that can go into glycolysis:
Transketolase and transaldolase reshuffle carbons
This produces glyceraldehyde-3-phosphate and fructose-6-phosphate
Those can go back into glycolysis to make energy or other molecules
Also:
An epimerase converts ribulose-5-phosphate → xylulose-5-phosphate so the reshuffling reactions can happen.
what are transketolase and transaldolase
Transketolase and transaldolase are enzymes in the non-oxidative phase of the Pentose Phosphate Pathway (PPP) that rearrange carbon atoms between sugars.
Transketolase
Moves a 2-carbon unit from one sugar to another
Helps convert pentose sugars into glycolysis intermediates
Requires a cofactor: thiamine (vitamin B1)
Transaldolase
Moves a 3-carbon unit between sugars
Continues the rearranging process so excess ribose-5-phosphate can be recycled
what is the ribose 5 p converted to
Fructose-6-phosphate
Glyceraldehyde-3-phosphate
where does PPP take place
in the cytosol
what plays the biggest role in regulation of PPP
cytosolic concentration of NADP+
what is the rate limiting step in the PPP
glucose 6 p dehydrogenase
