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49 Cards in this Set

  • Front
  • Back
What is the PURPOSE of the Pentose phosphate pathway? (2)
1. Provide reducing equiv via NADPH (to drive biochemical processes)
2. Provide Ribose-5-Phosphate for nucleotide synthesis.
What are the 2 main stages of the PPP?
1. Oxidative - generates NADPH
2. Nonoxidative - generates various 3-7 carbon sugars
What are defects in the PPP most typically associated with?
Hemolytic anemias
What is the main difference between NADH and NADPH?
NADH is involved in E production

NADPH involved in biosynthesis
What biosynthesis is NADPH involved in?
-Fatty acid
What other role does NADPH have other than in biosynthesis?
Maintaining a reducing environment in cells to prevent ROS stress.
How do the cell concentrations of NAD vs NADP differ?
NAD+/NADH = 700:1

NADPH/NADP+ = 70:1
How do the 2 branches of the PPP mainly differ?
Branch1: Irreversible/Oxidative

Branch2: Reversible/Nonoxidative
What does Branch 1 produce and where can it go?
G6P -> Ribulose5P + CO2
-Produces 2 NADPH
-Can make Ribose5P for NT synth
What does Branch 2 produce adn where can it go?
Ribulose5P -> F6P, then to:
-Isomerize to Ribose5P for NT's
What enzymes are active in Branch 2?
Where does the PPP take place?
What 4 tissues mainly require NADPH, and why?
-Liver/Mammary glands/Fat tissue for fatty acid biosynthesis.

-Adrenal cortex for Microsomal P450 monooxygenase system
What is the microsomal p450 monooxygenase system for?
Steroid biosynthesis.
Through what molecule does NADPH mostly combat the bad effects of oxidants?
Reduced glutathione (GSH)
How does NADPH help GSH?
It keeps GSSH reduced to GSH after the former is produced in reducing oxidants.
So what are the 3 things the PPP accomplishes in producing NADPH?
1. Allows for FA and Steroid Biosynthesis
2. Prevents oxidative stress
3. Produces 5C sugars for NT biosynthesis de novo
What enzyme catalyzes the step of commitment of stage one of PPP?
G6P Dehydrogenase
What regulates G6P dehydrogenase?
-Substrate availability of NADP+
-Competitive inhibition by NADPH
*unusual for committed step
What is Glucose-6P oxidized to in step 1?
A lactone - requires reduction of NADP+ to NADPH!! First one..
What happens in step 2, and what enzyme catalyzes it?
Lactone opening; spontaneous but rate increased by 6-Phosphogluconolactone Hydrolase
What results from the lactonase reaction of step 2?
What is step 3 of stage one; what enzyme catalyzes it?
A B-ketoacid reaction; oxidation-decarboxlation.
Enzyme is 6-phosphogluconate dehydrogenase.
What are the products of step 3?
What is a similar b-ketoacid reaction in the TCA cycle?
Isocitrate Dehydrogenase rxn.
What is the product of stage one?
A mix of 3 isomers:
-Ribulose 5-P
What enzymes isomerise the 3 molecules?
-RibP e-Epimerase for Xylulose5P

-Phosphopentose Isomerase for Ribose5P.
How are the Ribulose and Ribose isomers different?
Ribulose = ketose

Ribose = aldose
How does Ribulose get to the ribose structure?
Via an enediol intermediate bound to the enzyme Phosphopentose isomerase
How are Ribulose and Xylulose different?
By the configuartion about a SINGLE CARBON.
How does Ribulose get to the Xylulose structure?
Via an enzyme-bound enediol intermediate - to Phosphophentose EPIMERASE.
So what does generation of ribose5P and xylulose5P yield?
The substrates needed for the nonoxidative sugar intercovnersions of stage 2.
What 2 enzymes catalyze stage 2 sugar interconversions?

What does a Transketolase do?
Transfers 2-carbon keto fragments from a ketose donor to an aldose acceptor.
What is an essential component of Transketolase?
Thiamine pyrophosphate cofactor
What is required of both Xylulose5P and Sedoheptulose7P for Transketolase to work on them?
Both MUST be in the L configuration.
Why is TPP a good cofactor?
It has a C-H in between very electroneg N and S atoms; this forms a Carbanion (strong Nu:)
What reaction does the carbanionic C- of TPP undergo?
Attack of the 2 carbon fragment to be transferred (the whole purpose of "ketolase")
What does a TransALDOLASE do?
Transfers 3-carbon keto fragments from a ketose donor to an aldose acceptor.
How is Transaldolase different from Transketolase?
Transaldolase DOES NOT require a cofactor.
What is the mechanism of Transaldolase?
-Active site Lysine forms Schiff base intermediate with keto carbonyl group to be transferred.
What portion of the PPP is for:
-Biosynthesis or GSSG reduction

-NT synthesis
Biosynth/GSSG reduction is from STAGE 1; stage 2 is just so carbons don't get wasted.

NT Synth: from STAGE 2 only - no need for stage 1 at all!
Why is it important to know about PPP and G6P dehydrogenase?
That enzyme's deficiency is the most common enzyme abnormality affecting humans!!!
What type of inheritance pattern is shown in G6P Dehydrog defic?
Principle clinical manifestation of G6P dehydrog defic:
Hemolytic anemia
Where are enzyme mutations in:
-Mild G6P dehydrog defic?

Mild: at amino term end

Severe: at carboxyl NADP+ binding domain
What morphology results from severe forms of the deficiency?
Nonspherocytic - this is G6PD deficiency - cookie bite cells.
When will symptoms show in pts
with mild form?
Mild: only under oxidative stress precipitated by drugs.
What drugs are oxidants?