10.5-6 GIBBS FREE ENERGY OF ATP
10.5 Gibbs Free Energy

Measure of the __________ available from a reaction.

Standard Gibbs free energy is related to actual Gibbs free energy through the following
equation:
G =

When G = (___), the reaction is spontaneous (can proceed without an __________
supply of energy).

When G = (___), the reaction is nonspontaneous (energy must be supplied from
__________ the system to make the free energy negative).
Cellular Conditions

In an organism, the actual free energy change under cellular conditions must be less than
__________ in order for the reaction to occur in the direction it is written.

Many metabolic reactions have __________ standard Gibbs free energy changes! The
main condition that affects G in cells is the _______________ of the substrates and
products. This is where ___ comes into play, which is called the __________
__________ __________.

Recall that Q and K are related because they are both determined through expressions of
_______________.
o If Q and K are close, then the metabolic reaction is near-_______________.
o If Q is far from K, then the metabolic reaction is _______________.

Most enzymes catalyze near-equilibrium reactions and can __________ levels of
substrates and products to near-equilibrium status.

Some enzymes catalyze metabolically irreversible reactions, and these reactions act as
__________ points. These enzymes are usually _______________ in some way.
10.6 The Free Energy of ATP

ATP is a donor of several metabolic groups when hydrolyzed:

When a single phosphoryl group Pi is donated, _____ is left.
ATP + H2O 

When inorganic pyrophosphate PPi is donated, ______ is left.
ATP + H2O 

G° = –32 kJ/mol
G° = –45 kJ/mol
Nucleotide diphosphates and triphosphates are usually present as complexes with _____
ions (sometimes _____ ions).
This one is favored in
aqueous solution.

A large amount of energy is released during the hydrolysis of the phosphoanhydride
linkages of ATP because…
1. Loss of electrostatic _______________ among the negatively charged oxygen atoms
of the phosphoanhydride groups.
2. The products of hydrolysis are more _______________ than ATP.
3. The products of hydrolysis are more _______________ than ATP. The electrons on
terminal oxygens are more _______________ than those on bridging oxygens.

ATP, UTP, GTP and CTP are considered __________-rich compounds because of the
free energy change associated with the loss of their phosphoanhydrides.

A series of __________ (or phosphotransferases) catalyze interconversions of nucleoside
mono-, di- and triphosphates.
GMP + ATP
guanylate kinase
GDP + ATP
nucleoside diphosphate kinase

Intracellular ATP concentrations is maintained by the following two reactions:
AMP + ATP
adenylate kinase
* ADP can then be converted to ATP. The overall process is shown below:
AMP + ATP + 2 Pi

The Gibbs free energy change for ATP hydrolysis in vivo is actually __________ than the
standard Gibbs free energy change of –32 kJ/mol, as exemplified below:
o Ex: In a rat hepatocyte, the concentrations of ATP, ADP, and Pi are 3.4 mM, 1.3
mM and 4.8 mM, respectively. Calculate the Gibbs free energy change for
hydrolysis of ATP in this cell.
ATP  ADP + Pi
G° = –32 kJ/mol