Cellular EnergyTopic 3.4

Energy

• All living systems require constant input of energy

• Energy-related pathways in biological systems are sequential to allow for more controlled and efficient transfer of energy

Energy

• Energy input must exceed energy loss to maintain order and to power cellular processes

• Cellular processes that release energy may be coupled with cellular processes that require energy

• Loss of order or energy flow results in death

Energy Pathway

What is free energy?

• Maximum amount of available energy to do work

Video 12:59

What does a change in Gibbs free energy (∆G ) mean?

• If ∆G is less than 0, then the reaction will release energy (exergonic) – reactions occur spontaneously (not quickly though)

• If ∆G is greater than 0, then the reaction absorbs energy (endergonic) – reactions do not occur spontaneously

• If ∆G is equal to 0, then the system is at equilibrium

Energy Coupling

• The transfer of energy from one reaction to another in order to drive second reaction

• Cells make endergonic reactions happen by supplying them with free energy released by exergonic reactions

Photosynthesis

• Endergonic reaction

• ∆G = 686 kcal/mol of energy

• ∆G > 0, the reaction absorbs energy from the sun and stores energy in the chemical bonds of glucose

Cellular Respiration

• Exergonic reaction

• ∆G = - 686 kcal/mol of energy

• ∆G < 0, the reaction releases energy when glucose is metabolized

Synthesis of ATP

• ADP + Pi → ATP

• Endergonic

• ∆G = 7.3 kcal/mol of energy

• ∆G > 0, the reaction absorbs energy when ADP is bonded to inorganic phosphate to produce ATP

Hydrolysis of ATP

• ATP → ADP + Pi

• Exergonic

• ∆G = - 7.3 kcal/mol of energy

• ∆G < 0, the reaction releases energy when the terminal (last) inorganic phosphate is removed from ATP to produce ADP

ADP + Pi ATPVideo 1:55