The totality of an organism’s chemical reactions is called metabolism. Catabolic pathways release energy by breaking down complex molecules to simpler compounds. Anabolic pathways consume energy to build complicated molecules from simpler compounds. The chemistry of life is organized into metabolic pathway Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The first law of thermodynamics states that energy can be transferred, but it cannot be created or destroyed. Plants transform light to chemical energy; they do not produce energy. Kinetic energy is the energy of motion. Objects in motion, photons, and heat are examples. Potential energy stored energy in chemical bonds. The second law of thermodynamics - every energy transformation must make the universe more disordered, Entropy Energy released as heat Organisms transform energy

Chemical reactions can be classified as either exergonic or endergonic An exergonic reaction - release of free energy lower potential energy in endproduct Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.6a

An endergonic reaction is one that absorbs free energy from its surroundings. Endergonic reactions store energy greater potential energy in endproduct Sunlight- source of free energy for the photosynthesis Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.6b

ATP couples exergonic reactions to endergonic reactions ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.8a

The bonds between phosphate groups can be broken by hydrolysis. ATP is regenerated by adding a phosphate group to ADP.

A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction. An enzyme is an organic catalyst. Enzymes speed up metabolic reactions by lowering energy barriers Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Activation energy is the amount of energy necessary to push the reactants over an energy barrier. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.12

Enzyme speed reactions by lowering E A. The transition state can then be reached even at moderate temperatures (body temperature). Enzymes hasten reactions that would occur eventually. enzymes are selective they determine which chemical processes will occur at any time. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 6.13

A substrate is a reactant which binds to an enzyme at its active site. Enzymes are substrate specific Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Cofactor Coenzyme