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Chapter 21 Biochem
PPP and other pathways of Hexose Metabolism
| Question | Answer |
|---|---|
| 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 |
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