Chapter 4: The Energy of Life 4.1 All Cells Capture and Use Energy 4.2 Chemical Reactions Sustain Life

High potential energy High kinetic energy Types of EnergyExamples Potential EnergyChemical (covalent bonds of organic molecules) Concentration gradient across a membrane Kinetic EnergyLight (photons moving in waves) Sound waves (particles moving in waves) Thermal (movement of atoms and molecules) Mechanical (muscle contraction, wheels rolling) Electrical (movement of e - in a current) Energy is the ability to do work; energy takes different forms. What does “work” mean for a cell?

Energy Is Converted from One Form to Another First law of thermodynamics: energy is never created nor destroyed. Total amount of energy in the universe is constant.

Notice that heat energy is lost at each step. Heat energy is disordered and cannot be converted back to a useful form of energy. Energy Transformations Are Inefficient

Entropy Entropy is a measure of the randomness, or disorder, of the universe. Since heat energy is constantly being lost to the universe, and heat energy is disordered, the entropy of the universe is increasing. This is called the second law of thermodynamics.

Metabolism All of the chemical reactions and changes that take place in a cell or an organism – Includes: Building up reactions (anabolism/biosynthesis) – Requires an input of energy; products are more ordered than reactants – Ex- Dehydration synthesis/condensation (amino acids  protein) – Photosynthesis Breaking down reactions (catabolism/decomposition) – Energy is released; products are less ordered than reactants – Ex- Hydrolysis (glycogen  glucoses) – Cellular Respiration

Sunlight energy Photosynthesis in chloroplasts Cellular respiration in mitochondria ATP powers most cellular work Heat energy ATP CO 2 + H 2 O C 6 H 12 O 6 + O 2

Chemical Reactions Sustain Life Chemical reactions may require energy input (endergonic) or release energy (exergonic).

Most energy transformations in organisms occur in oxidation-reduction reactions. OIL RIG Oxidation is Loss of ElectronsOxidation is Loss of Electrons Reduction is Gaining ElectronsReduction is Gaining Electrons

Photosynthesis and CR rely on ETC An electron transport chain (ETC) is a series of membrane proteins participating in sequential oxidation-reduction reactions. Energy is released at each step.

In the reaction at the end of the electron transport chain, molecule X is being ___ and molecule Y is being ____. A. oxidized … reduced B. reduced … oxidized molecule X molecule Y

In the reaction at the end of the electron transport chain, molecule X is being ___ and molecule Y is being ____. A. oxidized … reduced B. reduced … oxidized molecule X molecule Y