Bio A - Biochemistry
Bio A Study Guide 2 – Biochemistry Test - Enzymes
Enzymes:
1. Define an enzyme – a molecule (usually a protein), that speeds up a reaction, but doesn’t
actually get change by the reaction. Once it releases the product, an enzyme can be used
again and again.
2. How does an enzyme work? (you need to know how to read an energy chart)
An enzyme works by lowering the activation energy (we can think of energy as the “cost” required
for a reaction to start. An enzyme is like having a coupon, it lowers the cost (or amount of energy)
required to start a reaction.
In reality, it does this by increasing the likelihood that a reaction will occur (orients the
molecules). Also should know that this is an exothermic reaction (overall energy of product is less
than reactant (energy is released). Need to know that activation energy is required regardless of
exo or endothermic.
3. Label the following on a diagram:
-
the enzyme, substrate, active site, enzyme-substrate complex, products and competitive inhibitor
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Bio A - Biochemistry
4. What does it mean to say that enzymes have specificity?
Why can they only affect one
specific kind of reaction?
One enzyme can only work on one substrate (and cannot reverse the reaction) Sucrase works on
sucrose and breaks it down to glucose and fructose. It cannot put glucose and fructose back
together again.
5. Discuss the following
a. What is a substrate? How does the amount (concentration) of substrate affect the speed
of a reaction? The molecule that is the reactant in the equation and
that is being changed. For a given enzyme concentration, as the
concentration of substrate (reactant) increases, enzyme activity
(the rate of change of substrate to product) will increase, until all
the enzyme molecules are “busy”. Then the activity (rate of
reaction) will continue at a constant rate even if the amount of
substrate increases
b.
How does the amount of enzyme affect the speed of a reaction?
Now we assume we have a “constant” supply of substrate
(reactant). That means as fast as we turn it into prouct, more
of it shows up. This time the amount of enzyme is increasing,
so our graph will look like
c.
What does the word “optimal” mean? If you are not at an optimal pH (either too high or
too low), what can happen to the enzyme?
Optimal means “best”. If you are at an optimal pH, the reaction
will go at it’s fastest rate.. Many enzymes works within a small pH
range. There is a pH at which its activity is greatest (the optimal
pH). This is because changes in pH can make and break intra- and
intermolecular bonds, changing the shape of the enzyme and,
therefore, its effectiveness.
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Bio A - Biochemistry
d. can an enzyme have an optimal pH that is NOT at pH 7? What do you think the optimal
pH of an enzyme in the stomach (like pepsin).
Different enzymes have different “optimal pH”.
Optimal is the “best”, it can be low (like in the stomach)
or it can be higher (like in the small intestine)
e. Low temperatures will slow the reaction rate of an enzyme, but will not harm the
enzyme. How is this different that heating an enzyme above its’ optimal temperature?
. There is a certain temperature at which an enzyme's activity is at its
greatest (see graph). This optimal temperature is usually around
human body temperature (37.5 oC) for the enzymes in human cells.
Above this temperature the enzyme structure begins to break down
(denature) since at higher temperatures intra- and intermolecular
bonds are broken as the enzyme molecules gain even more kinetic
energy.
Inhibition
An inhibitor is a molecule that can bind to the active site and
prevents a substrate from binding to the active site.
Competitive inhibitors compete with the substrate to “sit” in
the site. This decreases enzyme availability, and decreases or
stops the reaction
Non-competitive inhibition is when a molecule binds to a site
on the molecule other than the active site. This molecule
changes the shape of the active site when it binds and
substrate can no longer “fit” in the active site.
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Bio A - Biochemistry
Example Enzyme Questions:
You have an enzyme that is supposed to have a particular shape, but instead is deformed.
6. What is the vocabulary word for the “deformed” enzyme?
7. Identify two things that could have caused your enzyme to change shape.
8. Will the enzyme still work in the deformed shape? Why or why not?
1. Identify one way to shut off an enzyme without changing the shape?
2. Let’s say that lactose requires 500 units of energy to break into glucose and galactose without an
enzyme. If we added an enzyme to this reaction, would it still take 500 units of energy to change
lactose into its products? Why or why not? USE YOUR VOCAB!
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