Energy and Chemical ReactionsEnergy and Chemical Reactions

Living things undergo thousands of chemical reactions as part of the life process

The collection of these reactions is called metabolism

Energy TransferEnergy Transfer

Much of the energy organisms need is provided by sugar (food)

Undergoes a series of chemical reactions in which energy is released (cellular respiration)

The net release of free energy is called an exergonic (exothermic) reaction ~ energy or heat given off.

Reactions that involve an input of free energy are called endergonic (endothermic) reactions

Photosynthesis is an example

Most reactions in living organisms are endergonic; therefore living organisms require a constant source of energy

Energy TransferEnergy Transfer

Most chemical reactions require energy to begin

The amount of energy needed to start the reaction is called activation energy

Energy TransferEnergy Transfer

Certain chemical substances (catalysts) reduce the amount of activation energy required

Biological catalysts are called enzymes

EnzymesEnzymes

Enzymes are an important class of catalysts in living organisms– Mostly protein– Thousands of different kinds– Each specific for a different

reaction (1 enzyme : 1 substrate)

EnzymesEnzymes

Enzyme StructureEnzyme Structure

Enzymes work on substances called substrates

Substrates must fit into a place on an enzyme called the active site

Enzymes are reusable!