Chapter 12 The Pentose Phosphate Pathway Flashcards
What are the products of the oxidative phase of the pentose phosphate pathway?
5 carbon sugar ribose 5- phosphate and 2 molecules of NADPH.
What are the products of the non-oxidative phases of the pentose phosphate pathway?
glucose-6-phosphate which allows the continued production of NADPH.
In what cells is the PPP active?
active in rapidly dividing cells and cells experiencing oxidative stress.
What enzymes are involved in the oxidative phases of the pentose phosphate pathway?
dehydrogenase, lactonase, isomerase, epimerase.
What enzymes are involved in the non-oxidative phases of the pentose phosphate pathway?
transaldolase, transketolase
How many carbon fragments are transferred in transketolation?
2 carbon fragments from the ketose donor.
How many fragments are transferred in transaldolation?
3 carbon fragments.
Which reaction is catalyzed by the dehydrogenase enzyme?
Glucose 6-phosphate to 6-phosphogluconolactone.
How is the first step of the PPP regulated?
NADP+ levels are high dehydrogenase is activated.
What reaction is catalyzed by lactonase?
6-phosphogluconolactone to 6-phosphogluconate
How is 6-phosphogluconate converted to ribulose 5-phosphate
decarboxylation, loss of CO2.
In which steps is NADPH generated?
Glucose 6-phosphate to 6-phosphogluconolactone.
6-phosphogluconate to ribulose 5-phosphate.
What reaction is catalyzed by isomerase?
D-ribulose 5-phosphate to D- ribose 5-phosphate
What reaction is catalyzed by epimerase?
D-ribulose 5-phosphate to Xylulose 5-phosphate.
What are the transketolation reactions that take place?
- Xylulose 5-phosphate and D-ribose phosphate giving sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate.
- Xylulose 5-phosphate and Erythrose 4-phosphate giving glyceraldehyde 3-phosphate and fructose 6-phosphate.
Which reaction uses a TPP cofactor?
Transketolation, because we are not breaking a favorable C-C bond, we need to use the pretend carbonyl.
What is the transadolation reaction that takes place?
glyceraldehyde 3-phosphate and sedoheptulose-7-phosphate forming erythrose 4-phosphate and fructose-6-phosphate.
What is the relationship between Glucose 6-phosphate and NADP+
Concentration of NADP+ high, glucose 6-phosphate is stimulated to move through the PPP.
When NADP+ is converted to NADPH the concentration is much lower and glucose is shuttled into glycolysis.
How is Xylulose 5-phosphate the master regulator?
Xylulose 5-phosphate activates phosphatases resulting in the dephosphorylation of the dual PFK-2/FBPase protein
This results in phosphorylation of F-6-P to F-2,6-P enhancing glycolysis.
What is the Wernicke’s Korsakoff syndrome?
deficiency in thiamine Vitamin B1, failure of the pentose phosphate pathway.
Glutathione
acts a reducing agent and is important in maintaining the redox balance of the cell.
How is glutathione generated?
NADPH generates glutathione.
How is the NADPH pool regenerated?
Through the pentose phosphate pathway.
What is function of reduced glutathione?
protects the cell by destroying hydrogen peroxide and hydroxyl free radicals.
What is G6P deficiency?
loss of one or more copies of the gene that codes for G-6-P.
Why should individuals with G6P deficiency not consume fava beans?
Individuals with G6p deficiency are susceptibile to oxidative stress. Fava beans induce cellular oxidative stress.
Why are individuals with G6P deficiency protected from malaria?
these individuals have lower levels of NADPH which creates an environment that is less favorable for the survival of the malaria parasite.
What are vicine?
chemical compound found in fava beans.
What are pamaquine?
first antimalarial drug.
Why are vicine and pamaquine deadly for individuals with G6P deficiency?
Both induce oxidative stress.
What is the function of the CytochromeP450 family enzymes?
use NADPH to add hydroxyl groups
What is the general chemical equation that describes the function of these enzymes?
RH + O2 + NADPH —-> ROH + H2O + NADP+
Why should you not drink grapefruit juice with certain drugs?
grapefruit juice contains molecules such as bergamottin which compete with some drugs for the active site.
Draw the mechanism for transketolation
refer to slides
Draw the mechanism for transaldolation
refer to slides
