MEDIUM - S9 Bioenergetics and Biochemical Reactions
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Questions and Answers

What is the primary function of ATP in cellular metabolism?

  • To donate phosphoryl, pyrophosphoryl, and adenylyl groups
  • To couple group transfer reactions to unfavorable reactions (correct)
  • To synthesize ADP and Pi
  • To harness the energy of hydrolysis

    • Why must ATP concentration be held high?

  • To maintain the equilibrium concentration
  • To maintain its high group transfer potential (correct)
  • To prevent energy-yielding reactions
  • To inhibit catabolic reactions

    • What is the equation for ΔGp in ATP hydrolysis?

  • ΔGp = ΔG´° - RT ln ([ADP][Pi] / [ATP])
  • ΔGp = ΔG´° × RT ln ([ADP][Pi] / [ATP])
  • ΔGp = ΔG´° + RT ln ([ADP][Pi] / [ATP]) (correct)
  • ΔGp = ΔG´° / RT ln ([ADP][Pi] / [ATP])

    • What type of reaction is phosphoryl group transfer?

    <p>Two-step reaction</p> Signup and view all the answers

    What is the energy currency of the cell?

    <p>ATP</p> Signup and view all the answers

    Why is ATP hydrolysis favorable in the cell?

    <p>Because the free energy release is higher inside the cell than in standard conditions</p> Signup and view all the answers

    What is the consequence of a spontaneous reaction in cellular metabolism?

    <p>The reaction will proceed in the forward direction</p> Signup and view all the answers

    What is the purpose of energy coupling in cellular metabolism?

    <p>To drive unfavorable reactions forward</p> Signup and view all the answers

    What is the result of phosphoryl group transfer?

    <p>The transfer of energy from one reaction to another</p> Signup and view all the answers

    What is the significance of the phosphate group in cellular metabolism?

    <p>It is the energy currency of the cell</p> Signup and view all the answers

    What is the role of ATP in cellular metabolism?

    <p>To store energy in the form of phosphate bonds</p> Signup and view all the answers

    What is the definition of phosphorylation potential?

    <p>The energy stored in the bonds of ATP</p> Signup and view all the answers

    What is the purpose of ATP hydrolysis in cellular metabolism?

    <p>To release energy from ATP</p> Signup and view all the answers

    What is the result of converting the concentration from µM to M?

    <p>The concentration is divided by 10^6</p> Signup and view all the answers

    What is the role of ATP in cellular metabolism?

    <p>To serve as the major energy currency of the cell</p> Signup and view all the answers

    During ATP hydrolysis, what happens to the phosphate group?

    <p>It is released into the medium</p> Signup and view all the answers

    What is the standard free energy of hydrolysis of ATP?

    <p>-30.5 kJ/mol</p> Signup and view all the answers

    What is the result of ATP hydrolysis in terms of pH?

    <p>The pH of the medium decreases</p> Signup and view all the answers

    What is the role of Pi in ATP hydrolysis?

    <p>It is stabilized by formation of a resonance hybrid</p> Signup and view all the answers

    What is the result of ATP hydrolysis in terms of solvation?

    <p>The products are more solvated than the reactants</p> Signup and view all the answers

    Why does the actual free energy of hydrolysis of ATP under intracellular conditions differ from the standard free energy change?

    <p>Because the concentrations of ATP, ADP, and Pi are unequal</p> Signup and view all the answers

    What connects catabolism and anabolism?

    <p>ATP</p> Signup and view all the answers

    Study Notes

    ATP and Phosphoryl Group Transfers

    • ATP (Adenosine Triphosphate) is the major energy currency of the cell, produced in exergonic reactions and consumed in endergonic reactions via hydrolysis.
    • ATP connects catabolism and anabolism.
    • ATP has three components: adenine, ribose, and triphosphate groups.

    ATP Hydrolysis

    • ATP hydrolysis involves charge separation, which relieves electrostatic repulsion.
    • Pi is stabilized by formation of a resonance hybrid.
    • ADP2- immediately ionizes at pH 7, releasing a proton into the medium, lowering pH.
    • Greater solvation of products Pi and ADP relative to ATP.

    The Phosphorylation Potential, ∆GP

    • The standard free energy of hydrolysis of ATP is -30.5 kJ/mol.
    • The actual free energy of hydrolysis of ATP in the cell (ΔGp) differs from the standard free energy change in standard conditions (ΔG´o).
    • ΔGp can be calculated using the equation: ΔGp = ΔG´° + RT ln ([ADP][Pi] / [ATP]).

    ATP Donates Phosphoryl, Pyrophosphoryl, and Adenylyl Groups

    • Each of the three phosphates of ATP is susceptible to nucleophilic attack.
    • ATP drives unfavorable reactions not by harnessing the energy of hydrolysis but through the coupling of group transfer (phosphoryl, pyrophosphoryl, or adenylyl) to a substrate or enzyme.

    Phosphoryl Group Transfer

    • Phosphoryl group transfer is generally a two-step reaction.
    • Phosphoryl group transfer is catalyzed by ATP-dependent enzymes, such as ATP-dependent glutamine synthetase.

    Free Energy Changes Are Additive

    • A favorable reaction (ΔG1 < 0) can drive an unfavorable reaction (ΔG2 > 0) when ΔG1 + ΔG2 < 0.
    • This principle has important consequences in cellular metabolism, such as energy coupling.

    Energy Coupling

    • Energy coupling allows the energy from one reaction to drive another reaction.
    • Example: the synthesis of glucose 6-phosphate, where the energy from ATP hydrolysis drives the reaction.

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    Understand the role of ATP in cellular energy transactions, its components, and the process of ATP hydrolysis.

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