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?

Two-step reaction Signup and view all the answers

What is the energy currency of the cell?

ATP Signup and view all the answers

Why is ATP hydrolysis favorable in the cell?

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

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

The reaction will proceed in the forward direction Signup and view all the answers

What is the purpose of energy coupling in cellular metabolism?

To drive unfavorable reactions forward Signup and view all the answers

What is the result of phosphoryl group transfer?

The transfer of energy from one reaction to another Signup and view all the answers

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

It is the energy currency of the cell Signup and view all the answers

What is the role of ATP in cellular metabolism?

To store energy in the form of phosphate bonds Signup and view all the answers

What is the definition of phosphorylation potential?

The energy stored in the bonds of ATP Signup and view all the answers

What is the purpose of ATP hydrolysis in cellular metabolism?

To release energy from ATP Signup and view all the answers

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

The concentration is divided by 10^6 Signup and view all the answers

What is the role of ATP in cellular metabolism?

To serve as the major energy currency of the cell Signup and view all the answers

During ATP hydrolysis, what happens to the phosphate group?

It is released into the medium Signup and view all the answers

What is the standard free energy of hydrolysis of ATP?

-30.5 kJ/mol Signup and view all the answers

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

The pH of the medium decreases Signup and view all the answers

What is the role of Pi in ATP hydrolysis?

It is stabilized by formation of a resonance hybrid Signup and view all the answers

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

The products are more solvated than the reactants 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?

Because the concentrations of ATP, ADP, and Pi are unequal Signup and view all the answers

What connects catabolism and anabolism?

ATP 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.