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Chapter 21 Biochem

PPP and other pathways of Hexose Metabolism

Alternative route for metabolism of glucose Pentose Phosphate Pathway
PPP does not lead to the formation of ATP
PPP leads to the formation of ---- for synthesis of fatty acids and steroids and maintaining reduced glutathione for antioxidant activity NADPH
PPP leads to the synthesis of ----- for nucleotide and nucleic acid formation Ribose
Two major functions of PPP Formation of NADPH and synthesis of ribose
Main hexoses that are absorbed from GI tract Glucose, fructose and galactose
Glucose is derived from Starch
Fructose is derived from Sucrose
Galactose is derived from Lactose
Fructose and galactose can be converted to ----- mainly in the liver Glucose
First enzyme of PPP Glucose 6 Phosphate Dehydrogenase
Deficiency to glucose 6 phosphate dehydrogenase will yield to acute hemolysis of RBC leading to Hemolytic anemia
Glucoronic acid is synthesized from glucose via what pathway Uronic acid pathway
Uronic acid pathway is important for the conjugation and excretion of metabolites and foreign chemicals as Glucuronide
A defieciency in uronic acid pathway will yield to Essential pentosuria
The lack of one enzyme of uronic acid pathway explains why vit c is a dietary requirement for humans but not most other mammals Gulonolactone oxidase
Other term for PPP Hexose monophosphate shunt
More complex pathway than glycolysis PPP
3 molecules of glucose 6 phosphate will give rise to 3 molecules of CO2 and 3 5-carbon sugars
How many molecules of glyceraldehyde 3 phosphate in order to regenerate glucose 6 phosphate 2 molecules
Reactions of PPP occur in Cytosol
Unlike glycolysis, PPP's oxidation is achieved by dehydrogenation using ----- as the hydrogen acceptor NADP
The sequence of reactions of PPP may be divided into 2 phases Irreversible oxidative phase and reversible nonoxidative phase
In the first phase of PPP glucose 6 phosphate undergoes dehydrogenation and decarboxylation to produce Pentose, ribulose 5 phosphate
In the second phase of PPP ribulose 5 phosphate is converted back to ----- by a series of reactions involving mainly by two enzymes ----- Glucose 6 phosphate.......transaldolase and transketolase
The oxidative phase of PPP generates NADPH
Dehydrogenation of glucose 6 phosphate to 6 phosphogluconate occurs via the formation of 6 phosphogluconolactone catalyzed by Glucose 6 phosphate dehydrogenase
The hydrolysis of 6 phosphogluconolactone is accomplished by the enzyme Gluconolactone hydrolase
A second oxidative step is catalyzed by ---- which also requires NADP as hydrogen acceptor 6 Phosphogluconate dehydrogenase
In the ER an isoenzyme of glucose 6 phosphate dehydrogenase which is ----- provides NADPH for hydroxylation reactions and also for 11 beta hydroxysteroid dehydrogenase 1 Hexose 6 phosphate dehydrogenase
This enzyme catalyzes the reduction of inactive cortisone to active cortisol in liver, the NS and adipose tissue Hexose 6 phosphate dehydrogenase
It is the major source of cortisol in tissues and may be important in obesity and metabolic syndrome Hexose 6 phosphate dehydrogenase
The nonoxidative phase generates Ribose precursors
Enzyme that alters the configuration about carbon 3, forming the epimer xylulose 5 phosphhate , also a ketopentose Ribulose 5 phosphate 3 epimerase
Enzyme which converts ribulose 5 phosphate to the corresponding aldopentose, ribose 5 phosphate which is used for nucleotide and nucleic acid synthesis Ribulose 5 phosphate ketoisomerase
Enzyme that transfers the two carbon unit comprising carbons 1 and 2 of a ketose onto the aldhyde carbon of an aldose sugar Transketolase
Transketolase requires what coenzyme Mg2+ and thiamin diphosphate
Vit B1 or known as Thiamin
Enzyme that catalyzes the transfer of a 3 carbon duhydroxyacetone moiety from the ketose sedoheptulose 7 phosphate onto aldose glyceraldehyde 3 phosphate Transaldolase
What enzyme in nonoxidative phase that requires no cofactor Transaldolase
It serves as a donor of glycoaldehyde Xylulose 5 phosphate
When fructose 1,6 bisphosphatase is absent in tissues this enzyme follows the normal pathway of glycolysis to pyruvate Glyceraldehyde 3 phosphate
Characteristic product of PPP CO2
Major product of glycolysis which is not produce in PPP ATP
These are generated in those tissues specializing in reductive syntheses Reducing equivalents
Activity of PPP is low in Nonlactating mammary gland and skeletal muscle
It can be synthesized in virtually all tissues Ribose
Little or no ----- circulates in the bloodstream Ribose
They protect erythrocytes against hemolysis Glutathione peroxidase and PPP
In RBC ---- is the only sole source of NADPH for the reduction of oxidized gluathione catalyzed by ----- PPP.....glutathione reductase
Reduced glutathione removes H2O2 in a reaction catalyzed by Glutathione peroxidase
Glutathione peroxidase is an enzyme that contains Selenium
It decreases the life span of RBC H2O2
In other tissues NADPH can also be generated by the reaction catalyzed by the Malic enzyme
A precursor of proteoglycan and conjugated glucuronides is a product of uronic acid pathway Glucuronate
Uronic acid pathway does not lead to the formation of ATP
Glucose 6 phosphate is isomerized to glucose 1 phosphate which then reacts with uridine triphosphate to form uridine diphosphate glucose in a reaction catalyzed by UDPGIc pyrophosphorylase
UDPGIc is oxidized at carbon 6 by NAD dependent in a two step reaction to yield UDP glucuronate UDPGIc dehydrogenase
The source of glucuronate for reactions involving its incorporations into proteoglycans UDP glucuronate
Direct precursor of ascorbate L-gulonate
Ingestion of large quantities of ----- has profound metabolic consequences Fructose
It undergoes a more rapid glycolysis in the liver because it bypasses the regulatory step catalyzed by phosphofructokinase Fructose
Enzyme that catalyzes the phosphorylation of fructose to fructose 1 phosphate Fructokinase
Fructokinase is not affected by Fasting or insulin
Fructose 1 phosphate is cleaved to D-glyceraldehyde and dihydroxyacetone phosphate by Aldolase B
An enzyme found in the liver which also functions in glycolysis in the liver by cleaving fructose 1,6 bisphosphate Aldolase B
D-glyceraldehyde enters glycolysis via phosphorylation to glyceraldehyde 3 phosphate catalyzed by Triokinase
Created by: analyncosim



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