ATP & Thermodynamics AP Biology Chapter 8

Section 8.1 An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics

Metabolism All of an organism’s chemical reactions Catabolic – breaking down molecules, releases energy Anabolic – building molecules, requires energy

Laws of Thermodynamics 1st: energy can be transferred or transformed but not created nor destroyed 2nd: energy transfer or transformation increases entropy (disorder, randomness) of the universe

(a) First law of thermodynamics (b) Second law of thermodynamics Chemical energy

Focus: 2nd Law of Thermodynamics

Section 8.2 The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously

Gibbs Free Energy Free energy is energy available to do work Gibbs free energy – the amount of energy a system has available to do useful work ΔG = ΔH – TΔS G = change in free energy ΔH = change in total energy TΔS = temperature x change in entropy Spontaneous reactions – ΔG is always negative Non-spontaneous reactions – ΔG is positive or zero

Endergonic reactions Exergonic reactions Absorbs free energy from surroundings G is positive (energy is being stored) Non-spontaneous Photosynthesis Exergonic reactions Releases free energy to surroundings G is negative (energy is being lost) Spontaneous Cellular Respiration

Section 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions

ATP Adenosine triphosphate Has unstable phosphate bonds Release of phosphate groups = release of energy for cellular work

ATP Powers Cellular Work Cells need energy to do chemical, transport and/or mechanical work ATP is usable, free energy for the cell Chemical energy from food  ATP for cells

ATP Cycle