Work Sheet 24
Gluconeogenesis
/ Pentose Phosphate Pathway
1. Identify the
three main functions of the pentose
phosphate pathway.
Source of NADPH
(reductive synthesis, maintainence of glutathione in the reduced state), pentoses
for nucleic acid synthesis, interconversion of pentoses with hexoses and
trioses.
2. Identify the enzymes of glutathione metabolism and the
relationship of this metabolism to the pentose pathway and protection of the
cell against oxidants.
Glutathione: Tripeptide (Glu-Cys-Gly)
Glutathione Reduced: Glu-Cys(SH)-Gly
Glutathione Oxidized:
Glu-Cys-Gly
Glu-Cys-Gly
Glutathione Reductase:
Glutathioneoxidized + NADPH + H+ ----------------> 2 Glutathionereduced + NADP+
Contains bound FAD which it uses to transfer electrons from NADPH to Glutathioneoxidized
Glutathione Peroxidase:
2 Glutathionereduced + H2O2 ---------------------> Glutathioneoxidized + 2 H2O
Glutathionereduced: removes peroxides maintaining RBC membrane integrity and preventing hemolytic anemia.
3. Identify gluconeogenic precursors, products and enzymes and their general pathways of metabolism. Pay particular
attention to those reactions that differ from glycolysis.
Lactate as a Precursor: ~40% contribution
Alanine as a Precursor: ~25% contribution
Glycerol as a Precursor: ~10% contribution
Fructose 1,6-bisphosphatase: (Fructose-1,6-bisphosphate ------>
Fructose-6-phosphate + Pi)
Can form a futile cycle with
phosphofructokinase-1 (PFK-1)
Fructose-6-phosphate + ATP ------> Fructose-1,6-bisphosphate + ADP
The two enzymes are reciprocally
regulated or ATP would be lost without energy conservation.
Glucose-6-Phosphatase: (Glucose-6-phosphate ------> Glucose)
Can form a second futile cycle with hexokinase/glucokinase
Glucose + ATP --------> Glucose-6-phosphate + ADP
The two enzymes are reciprocally
regulated or ATP would be lost without energy conservation.
4. Describe the Cori and glucose-alanine
cycles, and their relationship to
gluconeogenesis.
Lactate as a Precursor: ~40% contribution
Derived from RBC's or from muscle during exercise.
Shows an interrelationship
between liver and RBC's.
Alanine as a Precursor: ~25% contribution
Alanine is converted to pyruvate via alanine aminotransferase.
Shows an interrelationship
between liver and muscle.
Glycerol as a Precursor: ~10% contribution
Produced from the breakdown of triacylglycerols in adipose tissue.
Glycerol ------> -------> DHAP, involves only enzymatic reactions in the cytosol.