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3.2.1 What are
Action Molecules?
Enzyme
• Enzymes are proteins that
act as catalysts and help
complex reactions occur
everywhere in life.
• Catalyst- a substance that
increases the rate of a
chemical reaction without
itself undergoing any
permanent chemical
change
• Examples: enzymes in
saliva & intestines to help
breakdown food
Substrate
• A substrate is a molecule
upon which an enzyme
acts.
• The substrate bonds with
the enzyme active site,
and an enzymesubstrate complex is
formed.
Why are Enzymes Important?
• Enzymes control the speed of
chemical reactions in your body.
• Without enzymes, reactions would
be too slow to keep you alive.
• Catabolic enzymes: enzymes break
down large molecules into smaller
ones.
– Ex: pepsin in stomach
• Anabolic enzymes: use small
molecules to build up large
complex ones.
– Ex: enzymes that make DNA
• Enzymes also help cells to
communicate with each other,
keeping cell growth, life and death
under control.
How are Enzymes Named?
• Enzymes are commonly
named by adding a suffix "ase" to the root name of
the substrate molecule it is
acting upon.
• For example, Lipase
catalyzes the hydrolysis of a
lipid triglyceride.
• Sucrase catalyzes the
hydrolysis of sucrose into
glucose and fructose.
•
lactase – breaks down lactose (milk
sugars)
•
diastase – digests vegetable starch
•
sucrase – digests complex sugars and
starches
•
maltase – digests disaccharides to
monosaccharides (malt sugars)
•
glucoamylase – breaks down starch to
glucose
•
protease – breaks down proteins found
in meats, nuts, eggs, and cheese
•
lipase – breaks down fats found in most
dairy products, nuts, oils, and meat
•
cellulase – breaks down cellulose, plant
fibre; not found in humans
Where are Enzymes Made?
• Enzymes are made from amino
acids, and they are proteins.
• When an enzyme is formed in a
ribosome, it is made by stringing
together between 100 and 1,000
amino acids in a very specific and
unique order.
• The chain of amino acids then
folds into a unique shape.
• That shape allows the enzyme to
carry out specific chemical
reactions -- an enzyme acts as a
very efficient catalyst for a specific
chemical reaction.
• The enzyme speeds that reaction
up tremendously.
Lock & Key Model of Enzyme Action
• In this analogy, the
lock is the enzyme
and the key is the
substrate.
• Only the correctly
sized key (substrate)
fits into the key hole
(active site) of the
lock (enzyme).
Induced Fit Model of Enzyme Action
• When an enzyme binds to the
appropriate substrate, subtle
changes in the active site occur.
• This alteration of the active site
is known as an induced fit.
• Induced fit enhances catalysis,
as the enzyme converts
substrate to product.
• Release of the products
restores the enzyme to its
original form.
• The enzyme can repeat this
reaction over and over, as long
as substrate molecules are
present.
Active Sites
• In biology, the active site
is a small port in an
enzyme where substrate
molecules bind and
undergo a chemical
reaction.
• This chemical reaction
occurs when a substrate
collides with and slots
into the active site of an
enzyme.
Co-Enzymes
• Coenzymes are small
molecules.
• They cannot by
themselves catalyze a
reaction but they can
help enzymes to do so.
• In technical terms,
coenzymes are organic
nonprotein molecules
that bind with the
protein molecule to form
the active enzyme.
Co-Enzyme Examples
• Thiamine Pyrophosphate
– found in Vitamin B, meat, leafy
green vegetables
– Function: used when glucose is
converted to ATP
• Flavin adenine dinucleotide
(FAD)
– found in vitamin B, milk, meat
– Function: reactions in
mitochondria (Energy)
• Nicotinamide adenine
dinucleotide (NAD)
– found in vitamin Niacin, meat,
leafy green vegetables
– Function: carries hydrogen
during energy production
Factors that Affect Enzyme ActivityTemperature
Factors that Affect Enzyme Activity- pH
Factors that Affect Enzyme ActivitySubstrate Concentration