Pentose phosphate pathway Flashcards
where does the PPP occur? what does it produce?
cytosol
-NADPH and Ribolose-5-phosphate
what molecules in the PPP are combined and used as intermediates in glycolysis? where do they enter glycolysis?
xylulose-5-phosphate (Xu5P) and ribulose-5-phosphate (R5P)
-join to make F6P and GAP
what are the roles of NADPH?
1) synthesis of molecules (cholesterol and FA)
2) prevention of oxidative damage
which tissues would you expect the PPP to be very active in? state whether this would be due to needs for synthesis of FA/cholesterol, protection against oxidative damage or synthesis of DNA
Synthesis of cholesterol /FA: Liver, adrenal glands, testes, mammary glands (tissues that make steroid hormones)
Oxidative protection (tissues exposed to O2): RBCs
DNA synthesis: rapidly dividing tissues
is the PPP normally active in skeletal muscle?
no, only if there is a lot of damage or high energy needs
what is the difference between NAD+ and NADP+? what part of the structure accepts electrons?
attachment of phosphate
-nicotinamide ring will accept electrons
what is the general role of NADH vs NADPH?
NADH favours oxidation
NADPH favours reduction
why does it make sense that the ratio of NAD+/NADH is ~1000 while NADP+/NAPH is ~0.01?
NAD+ is favoured in order to pull electrons to it (oxidize other molecules)
NADPH is favoured in order to reduce other molecules
in what other 2 rxns (other than PPP) can NADPH be produced?
isocitrate dehydrogenase + malic enzyme
what is the impact of ROS’s?
cause free radical oxidative stress
What is the master antioxidant? where is present in high levels?
Glutathione
-present at high levels in RBCs
what functional group is contained within glutathione that makes it the master antioxidant?
SH group
What is the role of glutathione peroxidase? what other molecules does this rxn generate?
Oxidizes glutathione from the reduced form to oxidized form
-watder and a FA hydroxyl group
what form do we want glutathione in? why? what catalyzes this rxn?
The reduced form, using glutathione reductase
-the reduced form is needed to work as an antioxidant
what cofactor is needed to reduce glutathione?
NADPH
how is the reduced vs oxidized form of glutathione written?
reduced: GSH
oxidized:GSSG
how many GSH produce how many GSSG?
2 GSH produce 1 GSSG
Explain the steps of the GSH redox cycle (include products, reactants and enzymes needed): what kind of metabolic pathway is this?
1: G6P converted into 6-phospho-gluconate, reducing NADP+ to NADPH
-uses G6P-dehydrogenase
2: GSSG is reduced to 2GSH molecules, oxidizing NADPH to NAD+
-uses glutathione reductase
3: Lipid peroxide (toxic) is converted to Lipid-OH (non-toxic), oxidizing GSH to GSSG
-uses glutathione peroxidase
this is an ETC
what enzyme is the most common mutation in the world?
G6P-dehydrogenase
what are the 2 major phases in the PPP? what are there roles?
Oxidative: produces majority of NADPH and R5P
Non-oxidative: provides flexibility through isomerization reactions depending on cellular demands
in the oxidative phase of the PPP, what 3 reactoins are seen? where does this also occcur?
1) oxidation
2) hydration
3) oxidaton + decarboxylation
-the last 3 steps of the CAC
what is the first oxidative rxn in the PPP? what enzyme is used? what is released? what is formed?
Oxidation of Glucose-6-phosphate to generate 6-phosphoglucono-lactone
-used glucose-6-phosphate dehydrogenase and produced NADH
what occurs in the second step of the oxidative phase? what enzyme is used? what is generated? what type of bond is formed?
Hydration of 6-phosphoglucono-lactone to generate 6-phosphogluconate, which contains an ester bond
-6-phosphogluconolactonase is used
what occurs in step 3 of the oxidative phase of the PPP? what enzyme is used? what is generated?
Oxidation of 6-phosphogluconate generates Ribulose-5-phosphate (RU5P), NADPH and CO2
-6-phosphogluconate dehydrogenase is used
