Identifying and investigating the role of enzymes
INVESTIGATING ENZYMES
ENZYMES
Enzymes speed up metabolic reactions by
lowering energy barriers
 Enzymes are substrate specific
 The active site is an enzyme’s catalytic center
 A cell’s physical and chemical environment
affects enzyme activity

ENZYMES
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

THE ACTIVATION ENERGY BARRIER
Enzymes speed up metabolic reactions by
lowering energy barriers
 Initial investment of energy for starting a
reaction is known as activation energy
 Activation energy is energy required to break
bonds

THE ACTIVATION ENERGY BARRIER

An enzyme speeds the reaction by reducing the
uphill climb to the transition state
ENZYMES AND ACTIVATION ENERGY
Some chemical reactions that make life possible
have activation energies that are too high
 Catalysts speed up the rate of chemical
reactions
 Catalysts work by lowering a reaction’s
activation energy
 Enzymes are proteins that act as biological
catalysts

ENZYMES ARE SUBSTRATE SPECIFIC

Enzymes have an active site to match up with
their substrate
ENZYMES ARE SUBSTRATE SPECIFIC
Enzyme
Substrate(s) ---------> Product(s)
For example,
Sucrase
Sucrose + H2O ---------> Glucose + Fructose
ENZYMES ARE SUBSTRATE SPECIFIC
An enzyme can distinguish its substrate from
even closely related properties
 Each type of enzyme catalyzes a particular
reaction
 For example, sucrase will act only on sucrose
and will reject other disaccharides, such as
maltose

ENZYMES ARE SUBSTRATE SPECIFIC
Active sites are restricted regions of the enzyme
molecule that bind to the substrate
 The active site is typically a pocket or a groove on
the surface of the protein

ENZYMES ARE SUBSTRATE SPECIFIC

Specificity of an enzyme is due to a compatible
fit between the shape of its active site and the
shape of the substrate

The substrate
binds to the active
site to form an
enzyme-substrate
complex
THE CATALYTIC CYCLE OF AN ENZYME
Side chains (R groups) of amino acids make up
the active site
 Side chains catalyze the conversion of
substrate to product

THE CATALYTIC CYCLE OF AN ENZYME
After the conversion from substrate to product,
the product departs from the active site
 After the cycle, the enzyme is then free to take
another substrate molecule into its active site
 Enzymes emerge from the reaction in their
original form

THE CATALYTIC CYCLE OF AN ENZYME
The rate at which a given amount of enzyme
converts substrate to product is partly a
function of the initial concentration of the
substrate
 The more substrate molecules available, the
more frequently they access the active sites of
the enzyme molecules


http://youtu.be/qhiG6_83pbc
DENATURING
Denaturing is the process of changing an
enzyme’s shape because of high temperatures
or extreme pH values
 Denaturing makes the enzyme less effective of
even completely useless

EFFECTS OF TEMPERATURE
The velocity of enzymatic activity reaction
increases with increasing temperature
 With increasing temperatures, substrates
collide with active sites more frequently
 Beyond that temperature, bonds that stabilize
active conformation become disrupted
 When this occurs, the protein molecule
denatures

EFFECTS OF TEMPERATURE
Each enzyme has an optimal temperature at
which its reaction rate is fastest
 This temperature allows the greatest number of
molecular collisions without denaturing the
enzyme

EFFECTS OF PH

The optimal pH values of most enzymes falls in
the range of pH 6-8
ENZYME INHIBITORS
Inhibitors slow down or stop the activity of an
enzyme
 Inhibitors usually bond to the protein and
change the shape of the enzyme, causing it to
become ineffective

ENZYME INHIBITORS
Competitive inhibitors mimic the substrate and
competes for the active site
 Competitive inhibitors reduce the productivity
of enzymes by blocking substrates from
entering active sites

ENZYME INHIBITORS
Non-competitive inhibitors do not directly
compete with the substrate at the active site
 Noncompetitive inhibitors slow enzymatic
reactions by binding to another part of the
enzyme
 This alters the conformation of the enzyme so
that the active site is no longer fully functional

ENZYME INHIBITORS
SALIVARY AMYLASE
Enzyme that catalyzes the hydrolysis of starch
into simpler compounds
 Present in human saliva
 If salivary amylase were not present, we would
not be able to break down complex sugars into
simpler compound sugars in our mouths, which
would make digestion of sugars difficult

PEPSIN (PROTEASE)
Pepsin helps breakdown proteins like those in
dairy, meat, nuts, and eggs
 Without pepsin, the body would be unable to
breakdown proteins into their peptide amino
acid parts

LACTASE
Found in the small intestine, liver, and kidney
 Breaks down the milk sugar and lactose into
simpler sugars (glucose and galactose)
 Without lactase, the body is unable to
breakdown milk products
 People without lactase are said to be lactose
intolerant

CATALASE
Found throughout the body, usually in cell
organelles called peroxisomes
 Breaks down hydrogen peroxide into water and
oxygen
 Hydrogen peroxide is a waste product of cells,
but is toxic to the body
 Without catalase, hydrogen peroxide would
build up and cause cell and tissue damage


http://youtu.be/BjEGUMd-_Gs