Download Enzymes Notes #2- Enzyme Substrate Complexes and Factors

Enzymes
Notes #2- Enzyme Substrate
Complexes and Factors Affecting
Enzymes
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Agenda
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Video
Notes
Short Video
Group Activity
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– Planning and presentation
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Practice
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Video
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https://www.youtube.com/watch?v=XTUm-75-PL4
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Enzymes
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Catalysts are substances that speed up chemical
reactions. Organic catalysts (contain carbon) are
called enzymes.
Enzymes are specific for one particular reaction or
group of related reactions.
Many reactions cannot occur without the correct
enzyme present.
They are often named by adding “ASE" to the name
of the substrate. Example: Dehydrogenases are
enzymes that remove hydrogen.
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Enzyme-Substrate Complexes
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When a substrate binds to the active site of an
enzyme it is said form a complex.
The original theory on how this worked was called
the LOCK and KEY model
– This was because the substrate shape fits into a specific
enzyme because of it’s shape like a specific key fits only a
specific lock
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Lock and Key Model
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As the substrates bind to the enzyme active site they
are brought closer together allowing the reaction to
occur
Sometimes the active site changes shape to bring the
substrates even closer together
The reaction occurs and the product(s) are released.
The enzyme returns to it’s normal tertiary
configuration
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Induced Fit Theory – Most current
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“Induced-Fit model” is very similar but it
claims that the enzyme has the ability to
slightly alter its shape. The two models
basically work the same way.
The substrate molecule does not fit
exactly in the active site. This induces a
change in the enzymes conformation
(shape) to make a closer fit.
After the reaction, the products are
released and the enzyme returns to its
normal shape.
Only a small amount of enzyme is needed
because they can be used repeatedly.
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Video
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https://www.youtube.com/watch?v=V4OPO6JQLO
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Roles of Enzymes
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Some enzymes simply complex with substrates
bringing them close together to react
Other enzymes participate in the reaction occuring:
– Example: Trypsin
» Trypsin digests protein by breaking peptide bonds
» Active site contains 3 amino acids with R groups that interact
with the peptide bonds
» Breaks the bond and brings in water
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Rate of Reaction
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Reactions with enzymes are up to 10 billion times
faster than those without enzymes.
Enzymes typically react with between 1 and 10,000
molecules per second. Fast enzymes catalyze up to
500,000 molecules per second.
Substrate concentration, enzyme concentration,
Temperature, and pH affect the rate of enzyme
reactions.
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Group Activity
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6 groups:
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Substrate concentration
Temperature
pH
Enzyme concentration
Competitive inhibitor
-non-competitive inhibitor (and heavy metals)
– Use page 108/109 and handout to prepare presentation
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What is it?
Why/How does it impact speed of reaction
Key characteristics
Use a diagram…
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Substrate Concentration
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Rate of Reaction
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At lower concentrations, the active sites on most of the
enzyme molecules are not filled because there is not much
substrate. Higher concentrations cause more collisions
between the molecules. With more molecules and collisions,
enzymes are more likely to encounter molecules of reactant.
The maximum velocity of a reaction is reached when the
active sites are almost continuously filled. Increased substrate
concentration after this point will not increase the
rate. Reaction rate therefore increases as substrate
concentration is increased but it levels off.
Enzyme
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Active Site is
Saturated
Substrate Concentration
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Enzyme Concentration
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Rate of Reaction
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If there is insufficient enzyme present, the reaction will
not proceed as fast as it otherwise would because there is
not enough enzyme for all of the reactant molecules.
As the amount of enzyme is increased, the rate of reaction
increases. If there are more enzyme molecules than are
needed, adding additional enzyme will not increase the
rate. Reaction rate therefore increases as enzyme
concentration increases but then it levels off.
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Enzyme Concentration
Even when adding
more enzymes, there
isn’t any more
available substrate to
create product at a
faster rate
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Rate of Reaction
Effect of Temperature on Enzyme
Activity
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Temperature
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Increasing the temperature causes
more collisions between substrate
and enzyme molecules. The rate of
reaction therefore increases as
temperature increases.
Rate of Reaction
Effect of Temperature on Enzyme
Activity
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40
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Temperature
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Effect of Temperature on Enzyme
Enzymes denature when
Activity
the temperature gets too
Rate of Reaction
high. The rate of reaction
decreases as the enzyme
becomes nonfunctional.
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Temperature
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Temperature
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Rate of Reaction
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Higher temperature causes more collisions between the atoms,
ions, molecules, etc. It therefore increases the rate of a reaction
– “Turnover Rate”. More collisions increase the likelihood that
substrate will collide with the active site of the enzyme.
Above a certain temperature, activity begins to decline because
the enzyme begins to denature (unfold).
The rate of chemical reactions therefore increases with
temperature but then decreases.
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Temperature
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Denaturation
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If the hydrogen bonds within an enzyme are broken, the
enzyme may unfold or take on a different shape. The enzyme
is denatured.
A denatured enzyme will not function properly because the
shape of the active site has changed.
If the denaturation is not severe, the enzyme may regain its
original shape and become functional.
The following will cause denaturation:
– Heat
– Changes in pH
– Heavy-metal ions (lead, arsenic, mercury)
– Alcohol
– UV radiation
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Effect of pH on Enzyme Activity
Rate of Reaction
Each enzyme has its own optimum pH.
Pepsin
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Trypsin
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pH
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pH
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Rate of Reaction
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Each enzyme has an optimal pH. Pepsin, an enzyme found in the
stomach, functions best at a low pH. Trypsin, found in the intestine,
functions best at a neutral pH.
A change in pH can alter the ionization of the R groups of the amino
acids. When the charges on the amino acids change, hydrogen bonding
within the protein molecule change and the molecule changes shape.
The new shape may not be effective.
The diagram shows that pepsin functions best in an acid environment.
This makes sense because pepsin is an enzyme that is normally found in
the stomach where the pH is low due to the presence of hydrochloric
acid. Trypsin is found in the duodenum (small intestine), and therefore,
its optimum pH is in the neutral range to match the pH of the
duodenum.
Pepsin
Trypsin
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pH
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Regulation of Enzymes
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The next several slides illustrate how cells
regulate enzymes. For example, it may be
necessary to decrease the activity of certain
enzymes if the cell no longer needs the product
produced by the enzymes.
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Regulation of Enzymes
Cell can turn on
DNA genes to build
more enzymes when
needed
genetic
regulation
competitive
inhibition
regulation of enzymes
already produced
noncompetitive
Inhibition
Cells can use
certain chemicals
to slow down
existing enzymes
(next slide)
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Competitive Inhibition
In competitive inhibition,
a similar-shaped molecule
competes with the
substrate for active sites.
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Competitive Inhibition
Active site is
being occupied
by competitive
inhibitor
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This substrate
cannot get into
active site at
this time
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Noncompetitive Inhibition
Active site
Inhibitor
Altered active site
Enzyme
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Another form of inhibition involves an inhibitor that
binds to an allosteric site of an enzyme. An
allosteric site is a different location than the active
site.
The binding of an inhibitor to the allosteric site alters
the shape of the enzyme, resulting in a distorted
active site that does not function properly.
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Noncompetitive Inhibition
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The binding of an inhibitor to an allosteric
site is usually temporary. Poisons are
inhibitors that bind irreversibly. For example,
penicillin inhibits an enzyme needed by
bacteria to build the cell wall. Bacteria
growing (reproducing) without producing
cell walls eventually rupture.
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Agenda
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Homework Check
Assignment Answer Review
Quiz
Video
Notes
Demo Activity
Review Worksheet
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Video
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Feedback Inhibition
The goal of this hypothetical metabolic
pathway is to produce chemical D from A.
A
enzyme 1
B
enzyme 2
C
enzyme 3
D
B and
are intermediates.
Enzyme regulation
by C
negative
feedback inhibition is
similar to the thermostat example. As an enzyme's product
The next several slides will show how
accumulates, it turns off the enzyme just as heat causes a
feedback inhibition regulates the amount
thermostat to turn off the production of heat.
of D produced.
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Feedback Inhibition
C and D will decrease
because B is needed to
produce C and C is
needed to produce D.
The amount of B in the cell will
decrease if enzyme 1 is inhibited.
A
enzyme 1
X
B
X
enzyme 2
C
X
enzyme 3
D
X
Enzyme 1 is structured in a way that causes it
to interact with D. When the amount of D
increases, the enzyme stops functioning.
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Feedback Inhibition
B, C, and D can now be synthesized.
A
enzyme 1
B
X
enzyme 2
C
X
enzyme 3
D
X
When the amount of D
drops, enzyme 1 will no
longer be inhibited by it.
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Feedback Inhibition
A
enzyme 1
X
B
enzyme 2
C
enzyme 3
D
As D begins to increase, it inhibits enzyme
1 again and the cycle repeats itself.
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Thyroxin and It’s Role in Metabolic Rate
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Thyroxin: (AKA “Thyroid Hormone” “Thyroxine”)
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- Thyroxin is a protein hormone that is secreted into the blood
stream by cells of the thyroid gland
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- The thyroid gland, which is located in the neck, accumulates
iodine in order to produce the thyroxin hormone.
Thyroid Hormone Structure
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Thyroxin acts by attaching to receptor sites on the
surfaces of our body’s cells. When receptor sites are
triggered they stimulate other chemicals in the cell to
govern the rate at which the cells will consume
oxygen. Thyroxin ultimately controls the body’s
metabolism.
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- Thyroxin does not have a target organ; but
instead, stimulates most of the cells of the body
to metabolize at a faster rate. It does this by
increasing the production of respiratory
enzymes, as well as stimulating the increase of
oxygen uptake.
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- Thyroxin not only governs metabolic rate but it also
helps regulate the growth and development of an
individual.
- Thyroglobulin is the storage (precursor) form of
Thyroxin. Iodine is required for thyroglobulin to be
made. Without the presence of iodine the thyroid gland
will increase in size in an effort to produce more
Thyroxin.
- Unfortunately, a lack of Iodine in the diet, results in a
lack of thyroxin in the body (HYPOTHYROIDISM).
This often leads to a condition known as simple goiter.
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Simple Gloiter
-A
simple goiter occurs when the thyroid gland is unable
to produce a sufficient amount of Thyroxin, the thyroid
cannot meet the metabolic demands of the body.
-The thyroid gland compensates by enlarging, this
mechanism will often overcome a mild deficiency of the
thyroid hormone.
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Exophthalmic Goiter (Graves’ disease)
This type of Goiter is not caused by a lack of thyroxin but
rather by the excessive production of the thyroid hormone
(HYPERTHYROIDISM). –
- This condition is characterized by an enlarged thyroid
gland, protrusion of the eyeballs, tachycardia (super fast
heart rate) and nervous excitability.
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Hypothyroidism vs. Hyperthyroidism
Symptoms of Hypothyroidism: Low thyroxin in the
blood
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