A.P. Biology
Mr. Tesoro
 Homework Reminder:

Do now: What does S. salivaris produce that
seems to prevent S. mutans from destroying
tooth enamel?
 http://news.sciencemag.org/sciencenow/2011
/04/a-bacterium-that-acts-like-atoothbrush.html?ref=hp
 A Bacterium That Acts Like a Toothbrush
 from ScienceNOW Daily News
 Researchers have identified a new ally in the war
against tooth decay: an enzyme produced by a
mouth bacterium that prevents plaque formation.
The finding could eventually lead to the
development of toothpaste that harnesses the body's
own plaque-fighting tools.
 The human mouth is awash with bacteria. More than
700 species thrive in the hot, moist conditions,
including Streptococcus mutans, one of the main
components of plaque. Clinging to the teeth in thin
layers called biofilms, S. mutans digests sugars and
produces acids that can eat into enamel and cause
cavities. Other bacteria are more gracious guests. In
2009, for example, scientists found that S. salivarius, a
type of bacterium found on the tongue and other soft
tissues in the mouth, decreases the buildup of S. mutans
biofilms.
 Hidenobu Senpuku, a biologist at the National Institute of
Infectious Diseases in Tokyo, and colleagues wanted to
know what substance conferred S. salivarius's cavityfighting powers. Using chromatography, a method that
divides the molecules in a mixture based on charge or size,
they separated out individual proteins from samples of the
microbe. The scientists then mixed each kind of protein with
S. mutans cells and measured which cultures grew the
smallest amount of biofilm on plates in the lab. The protein
FruA, an enzyme that breaks apart complex sugars, was the
most powerful biofilm blocker.
Aim: What are enzymes and how
do they function?
What are enzymes?
 Enzymes are organic catalysts required to
maintain the proper metabolism of the cell.
 A catalyst is a chemical agent that changes
the rate of a reaction without being
consumed by the reaction.

An enzyme is a catalytic protein.
Why are enzymes required for
metabolic reactions to occur?
 1) A biochemical reaction can proceed
spontaneously if it releases free energy. –ΔG
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bond breaking and bond forming.
To hydrolyze sucrose, the bond between glucose and
fructose must be broken and then new bonds formed with
a hydrogen ion and hydroxyl group from water.
Why are enzymes required for
metabolic reactions to occur?
 2) Most biochemical reactions have
activation energies too high to occur without
a catalyst.
 Activation energy is the amount of energy
necessary to push the reactants over an
energy barrier.
Why are enzymes required for
metabolic reactions to occur?
 3) Catalysts, such as
enzymes, lower the
activation energy
enough to allow
reactions to proceed
quickly at normal body
temperatures.
 Enzymes do not
change the ΔG of the
reaction.
What are some facts about
enzymes?
 1) Enzymes are highly selective.

Maltase hydrolyzes maltose but not sucrose.
 2) The name of most enzymes ends with a
‘ase’ suffix.
What are some facts about
enzymes?
 3) Enzymes usually are globular proteins.
They work specifically with chemicals called
substrates.
Enzyme
Substrate
Product
Maltase
Maltose
Glucose
Sucrase
Sucrose
Glucose and
fructose
What are some facts about
enzymes?
 4) Most enzymes make use
of the Induced Fit Model.
 The place on the enzyme
where the catalysis occurs
is called the ‘active site’.
 It is typically a pocket or
groove on the surface of
the protein into which the
substrate fits.
Induced Fit Model
 The active site is made up of specific R groups.
 Substrates that are compatible are attracted to the
active site and bond temporarily. This is called the
enzyme-substrate complex.
 The same enzyme that is used to synthesize
macromolecules can also hydrolyze them.


H2O + maltose  2 glucose (hydrolysis using maltase)
2 glucose  H2O + maltose (synthesis using maltase)
Induced Fit Model
 As the substrate binds,
the enzyme changes
shape leading to a
tighter induced fit,
bringing chemical
groups in position to
catalyze the reaction.
Induced Fit Model
What are some facts about
enzymes?
 5) Many enzymes require the binding of a prosthetic
group in order to activate them.
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Minerals (inorganic cofactors) such as zinc and iron are
necessary.
Many vitamins are coenzymes or coenzyme precursors.
 6) Both the enzyme and coenzyme are reusable and
needed in small amounts. A single enzyme molecule can
catalyze thousands or more reactions a second.
What are some facts about
enzymes?
 8) Enzymes cease to function if they are
denatured. Denaturing alters the three
dimensional contour of globular proteins and
changes the active site.


Substrates can no longer enter these sites.
Sickness and death may result.
What are some facts about
enzymes?
 9) Enzymes are greatly
affected by temperature,
pH, substrate concentration
or enzyme concentration.

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As temperature increases,
collisions between substrates
and active sites occur more
frequently as molecules
move faster.
Each enzyme has an optimal
temperature.
Temperature increases above
the optimal temperature lead
to the denaturing of the
enzyme.
What are some facts about
enzymes?
 Because pH also influences
shape and therefore reaction
rate, each enzyme has an
optimal pH too.
 This falls between pH 6 - 8 for
most enzymes.
 However, digestive enzymes in
the stomach are designed to
work best at pH 2 while those
in the intestine are optimal at
pH 8, both matching their
working environments.
What are some methods of
controlling enzyme activity?
 1) Competitive inhibition:


A chemical similar in structure to the substrate
binds to the active site. This chemical, an
inhibitor, competes for the enzyme and makes
less enzymes available.
Most competitive inhibitions are reversible.
However, an example of a nonreversible
competitive inhibition is carbon monoxide
poisoning of hemoglobin molecules.
What are some methods of
controlling enzyme activity?
What are some methods of
controlling enzyme activity?
 2) Noncompetitive inhibition:
 Certain enzymes have more than one active
site. They are allosteric. One active site is
for the substrate while another may be
occupied by an inhibitor.
 Such enzymes exist in two forms: an active
form and an inactive form.
What are some methods of
controlling enzyme activity?
 2) Noncompetitive inhibition: (continued)



In the active form, the enzyme is freely catalyzing the
substrate.
In the inactive form, the inhibitor binds to the
inhibitor site and alters the configuration (shape) of
the substrate active site.
Such inhibitors are called ‘modulators’.
 Reversible inhibition of enzymes is a natural part of
the regulation of metabolism.
What are some methods of
controlling enzyme activity?
Negative modulators (inhibitors) –
turn off enzymes
Positive modulators (activators) –
turn enzymes on
Sometimes the substrate product
acts as its own allosteric
inhibitor and turns off the very
enzyme that created it!!!
This is called feedback inhibition.