2.5: Enzymes
Enzymes are catalysts for chemical reactions in
living things.
Chemical Reactions
• Substances are
changed into
different
substances by
Reactants  Products
breaking and
forming chemical
bonds
– Reactants are changed to
form products
Chemical Reactions in Organisms
Cell growth, reproduction, interaction with the
environment, and response to stimuli are the
result of a chemical reaction
Catalysts
• Lowers activation energy
• Speeds up chemical reactions
Activation Energy
• Energy that needs to be absorbed for
a chemical reaction to start
–Energy reactants need in order to react
• Break bonds and form new ones
Rate of Chemical Reactions
• Biochemical reactions must occur at certain
speeds, or rates, in order to be useful.
• Rate of a reaction depends on:
– Temperature
– Concentration of the chemicals
– Surface area
Enzymes as Catalysts
• Enzymes are mostly proteins
• Make reactions that happen in cells possible
– Lower activation energy and speed up reaction
rate
• Without enzymes, many reactions would not
happen
– Others would occur too slowly for the organism to
survive
• Enzyme will not be used up or changed during
the reaction
Structure of Enzymes
• Gives reactants a site where
they can come together to
react
substrates
(reactants)
– Substrates-reactants affected
by enzyme
• Substrates bind to the active
site
• Shape of substrate and active
site are complimentary, or
opposite
– Fit together like a lock and key
enzyme
Substrates bind to an
enzyme at certain places
called active sites.
Lock and Key Model
Illustrates how enzymes function
Substrates bind to an
enzyme at certain places
called active sites.
The enzyme brings
substrates together and
weakens their bonds.
The catalyzed reaction forms
a product that is released
from the enzyme.
Structure of Enzymes
• Allows only certain reactants to bind to the
enzyme
– An organism may have thousands of different
enzymes
– Each is specific to one chemical reaction
• An enzyme’s function depends on its
structure.
Functions of Enzymes
• Energy-releasing enzymes power cell
functions
• Enzymes in nerve cells produce
neurotransmitters to carry impulses from
nerves to muscles
• Muscle cells have enzymes that are triggered
in response to the neurotransmitters
Functions of Enzymes
• Blood contains enzyme carbonic anhydrase
– Catalyzes reaction in your blood where carbon
dioxide combines with water to form carbonic acid
– Makes reaction one million times faster so that
carbon dioxide does not build up in your blood,
which could be fatal
• Enzyme lipase in the pancrease
– Speeds up digestion of lipids
Uses of Enzymes
• Biological washing
powders for clothes
• Food
–
–
–
–
Alcohol
Meat tenderizer
Cheese
Chocolate covered mints
• Industry
– Textile and paper
production
– Photography
– Pharmaceuticals
– Crime Scene Investigating
Functions of Enzymes
• Disruptions in homeostasis can
prevent enzymes from functioning.
– Enzymes function best in a small range of
conditions.
– Changes in temperature and pH can break
hydrogen bonds.
– Destroyed at temperatures above 50˚C
– Work best at pH of 7