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  1. #1
    Roxanita is offline Senior Member
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    Q-1) Metabolism N*

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    In the biosynthesis of glucose from pyruvate by the liver, the first intermediate formed from pyruvate is
    A) acetyl CoA
    B) alanine
    C) lactate
    D) methylmalonyl CoA
    E) oxaloacetate

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    usmlerock is offline Newbie
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    Answer E

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    BioPatel is offline Member
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    Re: Q-1) Metabolism N*

    Quote Originally Posted by Roxanita
    In the biosynthesis of glucose from pyruvate by the liver, the first intermediate formed from pyruvate is
    A) acetyl CoA
    B) alanine
    C) lactate
    D) methylmalonyl CoA
    E) oxaloacetate
    My answer is E..

    Krebs Cycle1 Krebs CycleOutline - Chapter 11 in Text Reactions of Pyruvate Formation of Oxaloacetate
    Formation of Acetyl-CoA

    Reactions of Krebs Cycle
    Regulation of Krebs Cycle
    2 Pyruvate to Oxaloacetate
    Pyruvate Oxaloacetate First step in gluconeogenesis
    Requires CO2
    3 Pyruvate to Acetyl-CoASee text, Figure 11.4, page 295

    Reaction occurs inside mitochondria
    Partial Net Reaction:
    CH3 -C(O)-COO - CH3 -C(O)-S-CoA + CO2
    Pyruvate oxidized: Oxidative decarboxylation
    Lipoic acid undergoes reduction of disulfide group
    Dihydrolipoic acid + FAD lipoic acid + FADH2
    4 Pyruvate Dehydrogenase

    Krebs Cycle Pictures and SummaryAs the above diagram illustrates, this is truly a continuous cycle. Acetyl coenzyme A binds to the oxaloacetate in order to convert it to citrate. Water is released from the citrate and then regained in order to form isocitrate. NAD+ binds to isocitrate, leaves as NADH, and carbon dioxide is lost in order to form a-ketoglutarate. NAD+ binds to a-ketoglutarate, leaves as NADH, coenzyme A binds and carbon dioxide is lost in order to form succinyl CoA. Coenzyme A leaves in order to form succinate. FAD binds to succinate and leaves as FADH2 in order to form fumarate. Water binds to fumarate and forms malate. NAD binds to malate and leaves as NADH which creates a new oxaloacetate molecule ready to bind to another acetyl coenzyme A to start the process over again.



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