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WHAT ARE ENZYMES?
• Enzymes are proteins (what is their monomer?)
• These proteins are used by the cell to speed up and
regulate chemical reactions
• Enzymes can also be called catalysts
• They remain unchanged by the reaction
HOW DO ENZYMES WORK?
• Enzymes lower the activation energy of a reaction
–Activation energy = the minimum amount of energy
needed for a chemical reaction to occur
• They do this by adding some of their own energy to the
reaction
• If there were no enzymes, many reactions would require
higher temperatures to occur
PLEASE NOTE
• Enzymes do NOT increase how much product is
made (just how quickly and easily it is made)
• Enzymes do NOT get used up in the reaction
(therefore, they can continue to catalyze reactions over
and over again)
ENZYME STRUCTURE
• Enzymes are proteins with a 3-dimentional shape caused by the folding of the protein
• The specific shape of the enzyme determines which substrate it works with
– Substrate = substances acted on by enzymes
• Most enzymes end with -ase
– Lipase acts of lipids
– Maltase acts on maltose
– Protease acts on proteins
– Lactase acts on lactose
All enzymes end
with –ase….so if I
say “Studentase”
what type of
enzyme is this?
ACTIVE SITE
• The substrate is temporarily bound to its enzyme at the
active site
• Only substrates that are the same size and shape as the
active site can bind to an enzyme (specificity)
• The enzyme may change shape slightly to accommodate the
substrate (induced fit)
– Induced fit helps substrates react to form product(s)
TWO JOBS
• Enzymes can break down substrates into their
component parts (what is this called? Example?)
OR
• Enzymes can put multiple substrates together into
one larger molecule (what is this called? Example?)
CHAINS
• Enzymes often work as a series of reactions that turn
substrates into products
• If one step in the chain doesn’t work, the product cannot
be made
DENATURE
• If enzyme #4 in the image above stopped functioning
correctly, what would happen?
– Would the green substrate be turned into the orange substrate?
– Would the orange substrate be turned into the yellow substrate?
– Would the yellow substrate be turned into the purple substrate?
– Would the purple substrate be turned into the blue substrate?
– Would the blue substrate be turned into the red substrate?
• Which substrate would you have the most of?
DENATURE
• Enzymes work within a narrow range of environmental
factors
– Temperature, pH, and concentration must be correct if an
enzyme is to function properly
• If the environment is not conducive to enzyme activity, the
enzyme may fall apart. This distorts the shape of the active
site, which means the substrate cannot attach to the enzyme,
and the enzyme cannot do its job
• If the enzyme comes apart and its active site no longer has the
correct shape, it is said to be “denatured”
FACTORS AFFECTING ACTIVITY
• Temperature
–The temperature where the enzyme functions most
effectively is called the optimal temperature
– If the temperature is lowered too much, enzyme activity
will slow down and eventually stop
– If the temperature is raised too far above the optimal
temperature, the enzyme will become denatured and stop
functioning
FACTORS AFFECTING ACTIVITY
• Temperature
1. What is the optimal temperature
for enzyme A? _________
2. What is the optimal temperature
for enzyme B? _________
3. Knowing that room temperature is approximately 22°
Celsius, which enzyme would work best? _________
FACTORS AFFECTING ACTIVITY
• pH
–pH tells you how acidic (or basic) a solution is
–pH is a measure of the number/concentration of hydrogen
ions in solution [H+]
• pH = 7 is neutral and occurs when [H+] = [OH-]
• pH lower than 7 is acidic and occurs when [H+] > [OH-]
• pH higher than 7 is basic and occurs when [H+] < [OH-]
– If the pH is lowered or raised outside optimal, the
enzyme will denature & stop functioning
FACTORS AFFECTING ACTIVITY
• pH
1. What is the optimal pH for
the enzyme found in your
stomach? ________
2. What is the optimal pH for
the enzyme found in your intestines? ________
3. What organic substances are both of these enzymes
digesting? ___________
Gastric Protease
Intestinal Protease
FACTORS AFFECTING ACTIVITY
• Concentration
–Concentration = amount of enzyme and/or substrate
present
–The larger the concentration of the enzyme, the faster
the rate of the reaction (up to a point)
–Saturation point is the point at which no more substance
can be absorbed/worked on
FACTORS AFFECTING ACTIVITY
• Rate of the reaction depending on the concentration of
the substrate (with or without enzymes)
INHIBITION
• Enzyme inhibitor: a molecule that binds to an enzyme and decreases its activity
(2 types)
– Competitive: the inhibitor is competing with the substrate for access to the active site
– Non-competitive: the inhibitor binds to the enzyme at the allosteric site (which is
different than the active site). This binding changes the shape of the active site,
making it impossible for the substrate to bind