Lecture 37 Flashcards
What are functions of the pentose phosphate pathway?
1) Provide reduced NADP for synthetic reactions (e.g. fatty acid synthesis & reduction of glutathione)
2) Provide pentose phosphate for nucleic acid synthesis
3) Forms an alternative mechanism for the oxidation of glucose (hexose monophosphate shunt)
What are the two oxidative reactions (irreversible) in the pentose phosphate pathway?
1) Glucose-6-phosphate + H2O –> 6-phosphoglutanate (glucose 6-phosphate dehydrogenase + 6-phosphogluconolactone hydrolase)
2) 6-phosphoglutanate –> Ribulose-5-phosphate + CO2 (6-phosphogluconate dehydrogenase)
What do each of the oxidative reactions form that assist in reductive anabolic pathways?
1) NADP+ –> NADPH + H+
2) NADPH can be oxidized in reductive anabolic pathways
What are the 5 nonoxidative reactions (reversible) in the pentose phosphate pathway?
1) Ribulose-5-phosphate –> Ribose 5-phosphate (ribose 5-phosphate isomerase)
2) Ribulose 5-phosphate –> Xylulose 5-phosphate (phosphopentose epimerase)
3) Ribose 5-phosphate + Xylulose 5-phosphate –> Sedoheptulose 7-phosphate + Glyceraldehyde 3-phosphate (transketolase; coenzyme: thiamine pyrophosphate)
4) Sedoheptulose 7-phosphate + Glyceraldehyde 3-phosphate –> Erythrose 4-phosphate + Fructose 6-phosphate (transaldolase)
5) Erythrose 4-phosphate + Xylulose 5-phosphate –> Fructose 6-phosphate + Glyceraldehyde 3-phosphate (transketolase; coenzyme: thiamine pyrophosphate)
What is Ribose 5-phosphate used for?
1) It is primarily used in Nucleic Acid biosynthesis
2) In the presence of NADPH in cells that require many reductive anabolic pathways, but may not require much nucleic acid synthesis, ribose 5-phosphate can be converted to other sugars (to be used in the glycolytic pathway)
What is the sole source of NADPH in RBCs?
The pentose phosphate pathway
What is NADPH used for?
NADPH is used to keep the peptide glutathione in a reduced state
What happens if there is not enough glutathione in a reduced state?
With a low concentration of reduced glutathione, the RBC is more sensitive to oxidative stress and there is a tendency to develop hemolytic anemia
Where is the gene for glucose-6-phosphate dehydrogenase located?
On the X chromosome
What is glucose-6-phosphate dehydrogenase deficiency?
Glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency) also known as favism (after the fava bean) is an X-linked recessive genetic condition that predisposes to hemolysis (spontaneous destruction of red blood cells) and resultant jaundice in response to a number of triggers, such as certain foods, illness, or medication
Deficiency of glucose-6-phosphate dehydrogenase may give some degree of resistance to _____
Malaria
What is the main function of hexokinase?
Unless the intracellular concentration of fructose becomes unusually high, hexokinase is saturated with and phosphorylates glucose rather than fructose
How is fructose primarily broken down?
1) Fructose –> Fructose 1-phosphate (Fructokinase)
a) requires ATP
2) Fructose 1-phosphate –> Glyceraldehyde + Dihydroxyacetone phosphate (DHAP) (Aldolase B)
What is essential fructosuria?
1) Lack of fructokinase
2) Autosomal recessive disease
3) Benign asymptomatic condition
4) Fructose accumulates in the urine
What is hereditary fructose intolerance (“fructose poisoning”)?
1) Absence of aldolase B leads to intracellular trapping of fructose 1-P
2) Causes severe hypoglycemia, vomiting, jaundice, hemorrhage, hepatmegaly, & hyperuricemia
3) Can cause hepatic failure and death
4) Therapy: Rapid detection and removal of fructose and sucrose from the diet
