HARD - S9 Bioenergetics and Biochemical Reactions

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Questions and Answers

What is the primary function of ATP in cellular metabolism?

To serve as energy currency (correct)

To synthesize proteins

To store genetic information

To replicate DNA

The standard free energy of hydrolysis of ATP is -15.5 kJ/mol.

False

What is the effect of ATP hydrolysis on electrostatic repulsion?

It relieves electrostatic repulsion

The concentrations of ATP, ADP, and Pi in the cell are not only unequal but much lower than the standard ___________ concentrations.

1 M Signup and view all the answers

What is the result of ATP hydrolysis on the pH of the medium?

It decreases the pH Signup and view all the answers

Match the following components of ATP with their descriptions:

Adenosine = A ribonucleotide component of ATP Triphosphate = A group of three phosphate molecules in ATP Phosphate group = A group that can be transferred during ATP hydrolysis Signup and view all the answers

What is the term for the transfer of a phosphate group from one molecule to another?

Phosphoryl group transfer Signup and view all the answers

The actual free energy of hydrolysis of ATP under intracellular conditions (ΔGp) is the same as the standard free energy change in standard conditions (ΔG’o).

False Signup and view all the answers

What is the significance of a negative ∆G value?

The reaction is favorable Signup and view all the answers

The principle of energy coupling states that a favorable reaction can drive an unfavorable reaction.

True Signup and view all the answers

What is the function of ATP hydrolysis in cellular metabolism?

To provide energy for various cellular processes Signup and view all the answers

The phosphate group is transferred from ATP to glucose, resulting in the formation of _______________________ and H2O.

glucose 6-phosphate Signup and view all the answers

Match the terms with their definitions:

Phosphorylation potential = The energy available from ATP hydrolysis Energy currency = The molecule that provides energy for cellular processes Phosphate group transfer = The transfer of a phosphate group from one molecule to another Signup and view all the answers

What is the consequence of the principle of energy coupling in cellular metabolism?

Unfavorable reactions are made favorable Signup and view all the answers

The reaction Glucose + Pi → Glucose 6-phosphate + H2O proceeds spontaneously.

False Signup and view all the answers

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

It is a key player in energy transfer and phosphorylation reactions Signup and view all the answers

What is the equation for calculating ΔGp in ATP hydrolysis?

ΔGp = ΔG´°+ RT ln ([ADP][Pi] / [ATP]) Signup and view all the answers

The free energy release of ATP hydrolysis is lower inside the cell than in standard conditions.

False Signup and view all the answers

What is the mechanism by which ATP drives unfavorable reactions?

through the coupling of group transfer (phosphoryl, pyrophosphoryl, or adenylyl) to a substrate or enzyme Signup and view all the answers

The three phosphates of ATP are susceptible to ______________________ attack.

nucleophilic Signup and view all the answers

Match the following terms with their descriptions:

Phosphoryl Group Transfer = involves the transfer of a phosphate group from ATP to a substrate or enzyme Phosphorylation Potential = the energy available to drive reactions through ATP hydrolysis Energy Currency = a molecule that can be used to drive various cellular reactions Catabolism = energy-releasing reactions that maintain high ATP concentrations Signup and view all the answers

What is the purpose of maintaining high ATP concentrations in the cell?

to drive unfavorable reactions through group transfer 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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Description

This quiz covers the structure and function of ATP, the energy currency of the cell, including its role in catabolism and anabolism, and the process of ATP hydrolysis.