1. COUPLED REACTIONS

2. COUPLED REACTIONS
Recall:
Exergonic reactions (ΔG<0) are spontaneous
Release free energy
Endergonic reactions (ΔG>0) are nonspontaneous
Absorb free energy

3. COUPLED REACTIONS
Cells make endergonic reactions happen by supplying them
with free energy released by exergonic reactions.
Energy coupling: The transfer of energy from one reaction
to another in order to drive the second reaction

4. COUPLED REACTIONS
Ex.1:
A  B + C ΔG = -10 kJ/mol
D + E  F ΔG = +8 kJ/mol
spontaneous
nonspontaneous
A B + C
D + E F
ΔG = -10 kJ/mol
ΔG = +8 kJ/mol
ΔG = -2 kJ/mol
When combined, the coupled reactions have a net negative ΔG, so
both reactions can occur spontaneously
+

5. COUPLED REACTIONS
Catabolic pathway - complex molecules broken down
(exergonic; overall ΔG < 0)
Anabolic pathway - complex molecules built from simpler
molecules (endergonic; overall ΔG > 0)

6. COUPLED REACTIONS

7. COUPLED REACTIONS
Living things constantly
require free energy to
move, grow, repair, and
reproduce.
Thus cells need a
constant, convenient
source of free energy,
supplied by ATP.