chapter 6 atp and energy coupling. g 0 g 0 equilibrium = death at equilibrium, forward and...

Chapter 6ATP and Energy Coupling

G 0 G 0

Equilibrium = Death

At equilibrium, forward and reverse reactions occur at the same rate; it is a state of maximum stability.

A process is spontaneous and can perform work only when it is moving toward equilibrium.

Reactants

ProductsEnergy

Progress of the reactionF

ree

en

erg

y

Exergonic reaction

G 0 G 0

G 0

Food, or some other energy source like the sun.

Exergonic Endergonic

Cells are not in equilibrium; they are open systems experiencing a constant flow of materials.

Exergonic Endergonic

Figure 6.8a

(a) The structure of ATP

Phosphate groups

Adenine

Ribose

Figure 6.8b

Adenosine triphosphate (ATP)

The hydrolysis of ATP

Energy

Adenosine diphosphate (ADP)Inorganic

phosphate

How the Hydrolysis of ATP Performs Work

• The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP.

• In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction.

• Overall, the coupled reactions are exergonic.

© 2014 Pearson Education, Inc.

Glutamic acid

GGlu 3.4 kcal/mol

GlutamineAmmonia

• Will this reaction happen spontaneously? – No

• Is this reaction catabolic or anabolic?– Anabolic

• Is this reaction exergonic or endergonic?– Endergonic

Glutamic acid Phosphorylatedintermediate

ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant.

GlutaminePhosphorylatedintermediate

Figure 6.9c

(c) Free-energy change for coupled reaction

GGlu 3.4 kcal/mol

GATP −7.3 kcal/mol GGlu 3.4 kcal/mol

GATP −7.3 kcal/mol

G −3.9 kcal/mol Net

Figure 6.10

(a) Transport work: ATP phosphorylates transport proteins.

Transport protein

Solute transported

Solute

(a) Transport work: ATP phosphorylates transport proteins.

(b) Mechanical work: ATP binds noncovalently to motor proteinsand then is hydrolyzed.

Transport protein

Solute transported

Solute

Motor protein

Vesicle Cytoskeletal track

Protein andvesicle moved

Figure 6.11

Energy fromcatabolism(exergonic, energy-releasing processes)

Energy for cellularwork (endergonic, energy-consuming processes)