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7 Cards in this Set

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1.) A) What is the fate of carbon 1 of glucose in glycolysis and in the oxidative pentose phosphate pathway when pyruvate is the terminal product?
1.) A) Glucose -C1 ‡‡‡ dihydroxy-acetone-P-C1 + Glyceraldehyde-3-P-C3. Upon conversion to pyruvate you form pyruvate which has the glucose-C1 as pyruvate-C3.
1. B) What is the fate of carbon 2 of glucose when ribose-5-P is formed via the oxidative pentose-P pathway?
B) When Glc-carbon one goes via the oxidative portion of pentose phosphate cycle it evolves as CO2. Thus, no carbon one of Glc becomes part of pyruvate if it goes through the oxidative portion of the pentose phosphate cycle and the pentose-P is recycled back to glycolysis intermediates. Glucose-C2 becomes ribose-5-P C1 in the oxidative pathway.
2.) Indicate the cofactor for the enzyme, transketolase and what is the enzyme mechanism allowing it to catalyze a two carbon transfer?
2.) Thiamine pyrophosphate. The carbanion of the thiazole group binds to the carbonyl group of either xylulose-5-P or seduheptulose-7-P or fructose-6-P to form an activated aldehyde unit (1,2 hyroxyethyl-TPP) that is stabilized via resonance of two forms, one a carbanion. This carbanion form can add to an aldose sugar-P, either ribose-5-P, glyceraldehyde-P or erythrose-4-P. See P. 553 and 554 (Fig. 14-26a) in Lehninger.
3.) What glycolytic enzyme has a similar reaction mechanism as transaldolase and what are the differences in their reaction mechanisms?
3.) Aldolase. Both transaldolase and aldolase have a C3-schiff base intermediate. Instead of transferring the C3 to an aldose sugar-P, aldolase transfers the C-3 to water.
4.) What are the respective intermediates for the ribulose-5-P epimerase and isomerase reactions?
4.) Ribulose-5-P isomerase; a 1,2 cis-enediolate intermediate. Ribulose-5-P 3’ epimerase; a 2,3 cis-enediolate.
5.) There are some patients with glucose-6-P dehydrogenase deficiency subject to lysis of their blood cells when conditions induce stimulation of hydrogen peroxide and organic peroxide formation. Why does lysis occur and what has been attributed to glucose-6-P dehydrogenase as an important function in maintaining erythrocyte membranes?
5) Lysis occurs when peroxides (H2O2, e.g.) in the blood are in excess and they form peroxides of the red cell membrane unsaturated fatty acids. These peroxides are unstable and the fatty acid chain can be broken causing damage to the red cell membrane and thus, lysis. It is believed that glucose-6-P dehydrogenase is the biggest contributor to NADPH formation and one of its functions is to maintain GSH in its reduced form via the GSH reductase reaction, GSSG + NADPH + H+ ----> 2GSH + NADP+. The reason why GSH is important is that via the GSH peroxidase reaction GSH degrades peroxides or superoxide, ∑O2`. 2GSH + ROOH ---> GSSG + ROH + H2O.
6.) Why are some populations in the Mediterranean or in Africa with a glucose-6-P dehydrogenase deficiency have resistance to malaria?
6.) Due to a glucose-6-P deficiency in the red cells these patients are not ideal hosts for the malaria parasite which requires pentose-P intermediates, NADPH and an intact red cell. The red blood cell of those patients have a tendency to lyse prematurely before the complete maturation of the parasite.