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Flashcards in Glycolysis and PPP Deck (12)
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describe the GLUT transporters 

  • GLUT 2 = liver
  • GLUT 1 and 3 = neurons and brain
  • GLUT 1 = erythrocytes
  • GLUT 4 = adipose tissue and muscle in response to insulin
    • increases in presence of insulin 


describe the formation of glucose 6 phosphate

  • glucokinase in liver has high Km (more active when the blood glucose is elevated; functions as a glucose sensor)
    • also present in B-cells of pancreas (MODY-2 = rare inherited form of DM since the B-cells of pancreas cannot respond to high blood glucose levels)
  • other tissues contain hexokinase which has a low Km for glucose


describe the major points of PPP

  • all enzymes are in the cytosol 
    • glucose 6 phosphate dehydrogenase (key enzyme)
  • pentose phosphate pathway forms NADPH
  • PPP forms ribose phosphate which is used for purine and pyrimidine nucleotide synthesis
  • transketolase requires thiamine pyrophosphate (TPP aka vit. B1)


describe the energy investment phase of glycolysis

  • 2 phosphorylation rxns that requires 2 ATP 
  • PFK-1 is the 2nd irreversible rxn of glycolysis and also the most important regulated step (allosteric regulated enzyme)


describe the cleavage of 6C sugar into 3C intermediates (stage 2)

  • aldolase A is present in muscle and aldolase B is in liver
  • the isomerase converst the dihydroxyacetone phosphate to glyceraldehyde 3-phosphate to enable it to be further metabolized by glycolysis
  • glucose is cleaved to 2 molecules of glyceraldehyde 3-phosphate


describe the energy generation phase of glycolysis (stage 3)

  • glyceraldehyde 3-phosphate dehydrogenase results in the formation of an NADH
  • phosphoglycerate kinase results in the formation of the first ATP (substrate level phosphorylation, SLP)
  • 1,3-BPG is a high energy intermediate that results in the formation of ATP without involving the mitochondrial ETC
    • SLP important during hypoxia


describe the second part of the energy generation phase (2-phosphoglycerate to pyruvate)

  • phosphoenolpyruvate is a high energy compound that results in the formation of ATP without the involvement of the ETC in mt (substrate level phosphorylation)
    • SLP important during hypoxia and in RBC
  • pyruvate kinase is an irreversible rxn


describe the Cori cycle


describe the anaerobic fate of pyruvate

  • pyruvate formed in glycolysis is metabolized anaerobically in the absence of mt or poorly vascularized tissues
  • the NADH formed by the glyceraldehyde 3-P dehydrogenase rxn is reoxidized to form NAD+; this allows glycolysis to proceed even in the absence of mt
  • LDH is a cytosolic enzyme
  • the direction of the rxn depends on the NADH/NAD+ ratio
    • higher the NADH levels, the rxn is driven towards lactate formation


name the 3 irreversible rxns (regulatory steps) in glycolysis

  • glucokinase/hexokinase
  • phosphofructokinase-1
  • pyruvate kinase


name the 2 SLP rxns in glycolysis

  • phosphoglycerate kinase (reversible)
  • pyruvate kinase (irreversible)


name inhibitors of glycolysis

  • pentavalent arsenate poisoning results in inhibition of glyceraldehyde 3-P dehydrogenase enzyme
  • in clinical labs, blood is collected in fluoride containing tubes for the estimation of blood glucose
    • if fluoride is not added, there would be reduction in the glucose due to its utilization by RBC and WBC, which leads to erroneously low blood glucose
    • fluoride inhibits enolase