Chemical Reactions and
Enzymes
Living things undergo thousands of chemical reactions as part
of the life process
Many are very complex involving multistep sequences called
biochemical pathways
Energy and Chemical Reactions
• Chemical equations represent
chemical reactions
• Reactants are shown on the
left side of the equation
• Products are shown on the
right side
• A+B
C+D
Energy Transfer
• Much of the energy organisms need
is provided by sugar (food)
• Undergoes a series of chemical
reactions in which energy is released
(cell respiration)
• The net release of free energy is
called an exothermic reaction
• Cellular Respiration is an example
Energy Transfer
• Reactions that involve a net absorption of
free energy are called endothermic reactions
• Photosynthesis is an example
Energy Transfer
• Most chemical reactions require energy to begin
• The amount of energy needed to start the reaction is
called activation energy
Catalysts
• Certain chemical substances
(catalysts) reduce the amount
of activation energy required
• Biological catalysts are called
enzymes
• The catalyst is not altered or used
up by the reactions.
Catalysts
• Enzymes are an important class of catalysts in living
organisms
• Mostly protein
• with “ase” suffix (proteins)
• Thousands of different kinds
• Each specific for a different chemical reaction
Enzyme-Substrate Complex
Enzyme Structure
• Enzymes lower the activation energy by
bringing the reactants (substrates)
together
• Enzymes work on substances called
substrates
• Substrates must fit into a place on
an enzyme called the active site
• Enzymes are reusable!
Enzyme-substrate complex
• ESC is held together by hydrogen bonds, electrical attraction, or
covalent bonds
Dehydration Synthesis
• Joining molecules with the loss of water
• Also called Condensation Reaction
Hydrolysis
• Breaking molecules apart with addition of water
PROTEINS AS ENZYMES
• Create your own enzyme that increases the speed
of a particular metabolic reaction. This can be
either dehydration synthesis or hydrolysis.
• Draw your enzyme, its substrate and active site.
• Label each part.
• Describe what your enzyme does using complete
sentences.