An Introduction to Metabolism

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An exergonic reaction proceeds with a net release of free energy and is spontaneous

An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous

Slide 28

Fig. 8-6

Reactants

Energy

Free energy

Products

Amount of

energy

released

(∆G < 0)

Progress of the reaction

(a) Exergonic reaction: energy released

Products

Reactants

Energy

Free energy

Amount of

energy

required

(∆G > 0)

(b) Endergonic reaction: energy required

Progress of the reaction

Slide 29

Fig. 8-6a

Energy

(a) Exergonic reaction: energy released

Progress of the reaction

Free energy

Products

Amount of

energy

released

(∆G < 0)

Reactants

Slide 30

Fig. 8-6b

Energy

(b) Endergonic reaction: energy required

Progress of the reaction

Free energy

Products

Amount of

energy

required

(∆G > 0)

Reactants

Slide 31

Equilibrium and Metabolism

Reactions in a closed system eventually reach equilibrium and then do no work

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

A defining feature of life is that metabolism is never at equilibrium

A catabolic pathway in a cell releases free energy in a series of reactions

Closed and open hydroelectric systems can serve as analogies

Slide 32

Fig. 8-7

(a) An isolated hydroelectric system

∆G < 0

∆G = 0

(b) An open hydroelectric

system

∆G < 0

∆G < 0

∆G < 0

∆G < 0

(c) A multistep open hydroelectric system

Slide 33

Fig. 8-7a

(a) An isolated hydroelectric system

∆G < 0

∆G = 0

Slide 34

Fig. 8-7b

(b) An open hydroelectric system

∆G < 0

Slide 35

Fig. 8-7c

(c) A multistep open hydroelectric system

∆G < 0

∆G < 0

∆G < 0

Slide 36

Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions

A cell does three main kinds of work: