Download Enzymes are Most Effective at Optimal Conditions

Enzymes are Most Effective at
Optimal Conditions
enzyme may even stop functioning completely.
Enzymes typically work best under certain
narrowly defined conditions, such as
temperature, pH, and ion concentration.
Changing these alter the rate of reaction caused
by the enzyme. In nature, organisms adjust the
conditions of their enzymes to produce an
optimum rate of reaction, where necessary, or
they may have enzymes which are adapted to
function well in extreme conditions where they
live.
All enzymes have an optimal temperature in
which they work the best. The rate of the reaction
increases with rise in temperature (fig. 1a). This
is because the heat enhances the kinetic energy
of the enzyme and substrate molecules which
results in more number of collisions between the
substrate and active site. On the other hand, in
low temperature conditions, the reaction
becomes slow as there is less contact between
the substrate and the enzyme. However, extreme
temperatures are not good for the enzymes.
Under the influence of very high temperature, the
weak H-bonds of the enzyme tend to break, due
to which the rate of reaction decreases or stops
all together. In other words, a denatured enzyme
fails to carry out its normal functions. In the
human body, the optimum temperature at which
most enzymes become highly active lies in the
range of 95°F to 104°F (35°C to 40°C). There are
some enzymes that prefer a lower temperature
than this.
The efficiency of an enzyme is largely influenced
by the pH value of its surroundings. This is
because the charge of its component amino
acids changes with the change in the pH value.
Each enzyme becomes active at a certain pH
level. In general, most enzymes remain stable
and work well in the pH range of 6 and 8 (fig. 1b).
However, there are some specific enzymes
which work well only in acidic or basic
surroundings. The favorable pH value for a
specific enzyme actually depends on the
biological system in which it is working. When the
pH value becomes very high the OH- groups
removes H+ ions and causes H-bonds in the
protein to break and the enzyme denatures. Or,
when the pH is too low, the H+ ions can also
cause the H-bonds to break and the enzyme to
denature. As a result, the active site of the
enzyme fails to bind well with the substrate
properly and the rate of reaction decreases. The
Substrate concentration plays a major
role in various enzyme activities. This is because
a higher concentration of substrate means it
takes less time for substrate molecules to collide
with the active site of the enzyme and the
reaction rate increases (fig. 2b). Whereas, a low
concentration of substrate means it takes longer
for substrate molecules to collide with the active
site of the enzyme and the reaction rate
decreases. When the rate of an enzymatic
reaction is at its maximum, an increase in the
concentration of substrate will not make any
difference in the enzyme activity. In this
condition, the substrate is continuously replaced
by new ones at the active site of the enzyme–the
enzyme is working as fast as it can.
In any enzymatic reaction, the amount of
substrate molecules involved is usually more
than the number of enzyme molecules. An
increase in enzyme concentration will increase
the enzyme reaction rate for the simple reason
that more enzymes are participating in the
reaction (fig. 2a). The rate of the reaction is
directly proportional to the quantity of enzymes
available for it. However, that does not mean that
a constant rise in concentration of enzymes will
lead to a steady rise in the rate of reaction.
Rather, a very high concentration of enzymes
where all the substrate molecules are already
used up does not have any impact on the
reaction rate. To be precise, once the rate of
reaction has reached its maximum, an increase
in the quantity of enzymes does not affect the
rate of reaction anymore.
Inhibitors are substances that have a tendency to
prevent activities of the enzymes. Enzyme
inhibitors interfere with the enzyme functions in
two different ways (fig. 3). Based on this, they
are divided into two categories: competitive
inhibitors and noncompetitive inhibitors. A
competitive inhibitor has a structure which is the
same as that of a substrate molecule, and so it
fits into the active site of the enzyme easily and
restricts the substrate from attaching. This
decreases the rate of the reaction. A
noncompetitive inhibitor binds with the enzyme at
a site other than the active site, the allosteric site.
This causes the enzyme to change its shape,
altering the shape of the active site. In this
condition, the substrate molecule cannot bind
itself to the active site and thus, the subsequent
enzyme activities are blocked and no reactions
can occur.
Adapted from Mukherjee, Bidisha. (Nov. 16, 2011). “Important
Factors That Influence Enzyme Activity”. (Retrieved October 9,
2013). http://www.buzzle.com/articles/important-factors-thatinfluence-enzyme-activity.html.
Adapted from Solomon, Berg, and Martin. (1999). “Enzymes are
th
chemical regulators”. In: Biology, 5 ed., pp. 144-150. Harcourt, Inc.
Fig. 1 retrieved October 9, 2013 enzyme_activity.html
08_18EnzymeEnvironFactors.jpg.
Fig. 2 retrieved October 9, 2013 www.skinnersbiology.co.uk.
Fig. 3 retrieved October 9, 2013 chemistry.tutorvista.com.
Instructions for Reading Article
Focus Question: How do different environmental conditions affect the rate of an enzymatic reaction?
As you read…
 Number the paragraphs
 Circle the environmental conditions that affect enzymes
 Underline what the condition does to the enzyme—structure and function
 Box what the condition does to the rate of reaction
After reading and discussing article, complete graphic organizer in Ch. 5 Enzyme packet.
WU: Enzymes are Most Effective at Optimal Conditions
Name _______________________
Date ______________ Per _____
Use the article from yesterday to answer the following questions. Answer using complete sentences where
appropriate.
1. What is the optimal temperature range for most enzymes? _____________ Explain why most enzymes
function best at these temperatures.
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2. What is the optimal temperature for the enzymes found in thermophilic bacteria? __________________
3. Where in the article was this information found? ____________________________________________
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4. What does it mean to be thermophilic? ___________________________________________________
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5. Where in the article was this information found? ____________________________________________
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6. Why would the enzyme pepsin no longer function in digestion when it enters the small intestine?
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7. Why will adding excess amounts of enzyme not continue to speed up the rate of reaction?
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8. Both a competitive inhibitor and a non-competitive inhibitor will decrease the rate of an enzymatic
reaction. Explain the difference in how each inhibitor affects the enzyme’s ability to function.
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