module 4- Pentose Phosphate Pathway Flashcards
what does the PPP yield?
1 NADPH & ribuose 5-P
how is the PPP primarily regulated?
by the cytosolic concentration of NADP+
what pathway is coordinately regulated with the PPP?
PPP & glycolysis
what enzyme ties the PPP & glycolysis together?
glucose 6-P
where is the PPP carried out?
cytosol of tissues
plants vs animals synthesis of NADPH
plants- via photosynthesis
animals- via PPP
T or F: PPP has an oxidative phase & non-oxidative phase
T
what phase # is the oxidative phase
phase 1
what happens in phase 1 of PPP (what is oxidized & what is reduced)
glucose 6-P is oxidized and NADP is reduced to NADPH
what phase # is the non-oxidative phase
phase 2
what happens in phase 2?
ribulose 5-P is converted to ribose 5-P
what allows excessive 5-carbon sugars to be converted into intermediates of glycolysis
interconversions
how are glycolysis & PPP connected?
shared intermediates- primarily glucose 6-P
T or F: need for NADPH is greater than need for ribose 5-P
T
how many NADPH are produced per 1 glucose 6-P molecule?
2 NADPH per 1 glucose 6-P molecule
is NADPH formed in phase 2?
no, this is where ribulose 5-P is converted to ribose 5-P
what enzyme catalyzes ribulose 5-P -> ribose 5-P
isomerase
what enzyme catalyzes conversion of ribulose 5-P to xylulose 5-P
epimerase
what kind of reactions (reversible/irreversible) do transketolase & transaldolase catalyze?
reversible reactions
what molecule does the transketolase reaction produce?
glyceraldehyde 3-P
what molecule does the transaldolase reaction produce?
fructose 6-P
what enzyme catalyzes phase 1 reaction?
glucose 6-P dehydrogenase
what step # is the rate limiting / point of regulation of PPP?
1st step - where NADPH is produced
NADPH is competitive ( ) of NADP+ for binding to glucose 6-P dehydrogenase
inhibitor
high demand for NADPH = (low/high) NADP+ levels = glucose 6-P is metabolized via (glycolysis/PPP)
low, PPP
low demand for NADPH = (low/high) NADP+ levels = glucose 6-P is metabolized via (glycolysis/PPP)
high, glycolysis
what is the determining factor if glucose 6-P is metabolized via glycolysis or PPP? (3)
NADP+ levels, need for ribose 5-P & ATP
PPP modes 1-4: need for NADPH & ribose 5-P
1) ribose 5-P > NADPH
2) ribose 5-P = NADPH
3) NADPH > ribose 5-P
4) NADPH & ATP are required
how many ribose 5-P molecules are produced per every NADPH molecule produced in the PPP?
0.5
what is the enzyme that catalyzes the 1st committed step in the PPP?
Glucose 6-P dehydrogenase
what 3 enzymes are shared between PPP & glycolysis?
glucose 6-P, glyceraldehyde 3-P, fructose 6-P
What two enzymes catalyze the reversible interconventions of the various sugars in the PPP?
transketolase & transaldolase
every glucose 6-P is oxidized into ( ) CO2 & ( ) NADPH
6, 12
what activates phosphorylase b in muscle? and what inhibits?
AMP, ATP & glucose 6-P
what inhibits glycogen phosphorylase?
glucose
what enzyme converts GPA -> GPB
phosphatase
what enzyme converts GPB -> GPA
kinase
