10.7-8 THE METABOLIC ROLES OF ATP, THIOESTERS
Introduction

The biosynthesis of X–Y is nonspontaneous under standard conditions.
X+Y

G° = (+) kJ/mol
X–Y
The biosynthesis of X–Y is coupled to the hydrolysis of ATP so that the synthesis of
X–Y becomes _______________.
ADP + Pi + H+
ATP + H2O

G° = –32 kJ/mol
The energy released from the hydrolysis of ATP is used to __________ the synthesis of
X–Y.

The coupled reaction would look like this:
X + ATP
X–P + ADP
X–P + Y + H2O
X–Y + Pi + H+
* The group being transferred could be a phosphoryl group or a nucleotidyl group.
A. Phosphoryl-Group Transfer

Glutamine synthesis from glutamate is _______________ under cellular conditions:
Glutamate + NH4+

glutamine + H2O
G = (+) kJ/mol
This reaction must be coupled with a _______________ group transfer from _____,
which helps to drive it in the right direction. It is catalyzed by _______________
_______________.
_______________
___-__________ _______________
_______________
B. Production of ATP by Phosphoryl Group Transfer

Metabolites with high phosphoryl group-transfer potentials can donate a phosphoryl
group to _____ to form _____.
o Examples:

Phosphoenolpyruvate transfers a phosphoryl group to _____ to form
_____. The reaction is catalyzed by _______________ __________.

Phosphoenolpyruvate is an enol whose structure is __________ by the
phosphoryl group. When the phosphoryl group is removed, the molecule
_______________ forms the much more stable keto tautomer (enol-keto
tautomerization!!!), releasing about –30 kJ/mol. This metabolically
_______________ reaction is an important source of ATP.

Phosphagens
o These are energy-rich phosphate _______________ molecules found in animal
muscle cells. They are phosphoamides, and have a __________ group-transfer
potential than ATP. Their concentrations are __________ in resting muscle, but
when ATP levels fall, creatine kinase catalyzes the rapid replenishment of ATP
through transfer of a phosphoryl group to ADP.
+ ADP
+ ATP
Creatine

ATP is thermodynamically suited to be a __________ of phosphoryl groups. ATP
mediates most chemical energy transfers in _____ organisms!
C. Nucleotidyl Group Transfer

ATP can transfer its nucleotide group, as in the synthesis of acetyl-CoA:

The hydrolysis of pyrophosphate contributes to the _______________ value of Gibbs
free energy, and accompanies many synthetic reactions in metabolism.
10.8 Thioesters

Thioesters are another class of __________-rich compounds.

_______________ is an example, which occupies a central position in metabolism.

The hydrolysis of acetyl CoA is _______________:
G = –31 kJ/mol

This energy is used in the fifth step of the __________ __________ __________ when
succinyl CoA reacts with GDP (or ADP) and Pi to form _____ (or _____).

This energy can also be used to drive the synthesis of __________ __________.