Ch 17.3 Text

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Ch 17.3 Text
2014-11-30 00:48:23
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  1. ·         The Citric acid cycle also provides __ for biosynthesis. For example, most of the carbon atoms in __ come from __. Many of the amino acids are derived from __ and __
    ·         Citric acid cycle intermediates must be __if any are __
    o   The CAC will operate to a reduced extent unless new __is formed, because acetyl CoA cannot enter the cycle unless it __; a minimal level mst be maintained to allow the cycle to function 
    • intermediates
    • porphyrins
    • succinyl CoA
    • alpha-ketoglutarate and oxaloacetate
    • replenished 
    • drawn off for biosynthesis
    • oxaloacetate 
    • condenses with oxaloacetate
  2. ·         How is oxaloacetate replenished? 
    • o   Mammals lack the enzymes for the net conversion of acetyl CoA into oxaloacetate or any other CAC intermediate. Rather, oxaloacetate is formed by the carboxylation of pyruvate, in a reaction catalyzed by the biotin-dependent enzyme pyruvate carboxylase
    • §  Pyruvate + CO2 + ATP + H20 à oxaloacetate + ADP + Pi + 2 H+
  3. ·         __ plays a crucial role in __. It is active only in the presence of __, which signifies __
    o   If the energy charge is high, oxaloacetate is __. If the energy charge is low, oxaloacetate __

    §  The synthesis of oxaloacetate by the carboxylation of pyruvate is an __, a reaction that leads to the net synthesis, or replenishment of pathway components
    • Pyruvate carboxylase
    • gluconeogenesis
    • acetyl CoA
    • the need for more oxaloacetate
    • converted into glucose
    • replenishes the CAC
    • anaplerotic reaction
  4. ·         __, a neurologic and cardiovascular disorder, is caused by a __
    o   It is partly ameliorated if the __; some of the thiamine in the husk then leaches into the rice kernel
    o   The problem is exacerbated if the rice is __, because ony the outer layer contains significant amounts of thiamine
    • Beriberi
    • dietary deficiency of thiamine
    • whole rice grain is soaked in water before milling
    • polished
  5. o   Characterized by __ and __ 
    Damage to the peripheral nervous system is expressed as __(3)__; the heart may be enlarged and the cardiac output inadequate
    • neurologic and cariac symptoms
    • pain in the limbs, weakness of the musculature, and distorted skin sensation
  6. ·         thiamine is the precursor of the __.
    o   This cofactor is the prosthetic group of three important enzymes: __(3)__
    §  __functions in the pentose phosphate pathway
    • cofactor thiamine pyrophosphate
    • pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase
    • Thransketolase
  7. o   The common feature of enzymatic reactions utilizing TPP is the __
    §  In beriberi, the levels of __ and __ in the blood are higher than normal
    ·         The increase in the level of __in the blood is especially pronounced after the ingestion of glucose
    • transfer of an activated aldehyde unit
    • pyruvate and alpha-ketoglutarate
    • pyruvate
  8. ·         The nervous system relies on __as its only fuel. The product of glycolysis, __, can enter the CAC only through the __
    o   With that enzyme deactivated, the NS has no source of fuel; other tissues can use __as a source of fuels for the CAC
    • glucose 
    • pyruvate
    • pyruvate dehydrogenase complex
    • fats
  9. ·         Symptoms similar to those of beriberi appear in organisms exposed to __ or __. Both materials have a high affinity for neighboring __, such as those in the reduced __ of the __

    • mercury or arsenite
    • sulfhydryls
    • dihydrolipoyl groups of the E3 component
    • pyruvate dehydrogenase complex
  10. o   The binding of mercury or arsenite to the dihydrolipoyl groups does what?
    inhibits the complex and leads to the CNS pathologies
  11. ·         Treatment for these poisons is the __
    o   The reagent-metal complex is excreted in the urine
    §  2,3-dimercaptopropanol was developed for it
    administration of sulfydryl reagents with adjacent sulfhydryl groups to compete with the dihydrolipoyl residues for binding with the metal ion
  12. ·         The CAC was most likely assembled from preexisting reaction pathways. Many of the intermediates formed in the citric acid cycle are used in __
    o   Thus, compounds like __ were present early in evolution for biosynthetic purposes
    metabolic pathways for amino acids and porphyrins

    pyruvate, alpha-ketoglutarate, and oxaloacetate
  13. §  The __ of these __ is favorable thermodynamically and can be used to drive the synthesis of both acyl CoA derivatives and NADH
    ·         These reactions almost certainly formed the core of processes that preceded the CAC evolutionarily
    • oxidative decarboxylation
    • alpha-ketoacids
  14. o   Interestingly, __ can be directly converted into __by __ of the respective amino acids by __, another key biosynthetic enzyme
    Thus, cycles comprising smaller numbers of intermediates used for a variety of biochemical purposes could have existed before the present form evolved. 



    aspartate aminotransferase

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