Lab#:
Name: Elizabeth Bonner
Date:January 23,2023
Title: Enzymes
Aim: To determine the effect of substrate concentration on an enzyme-catalyzed reaction
Materials and Apparatus: 2% yeast suspension, 50 cm3beaker, hydrogen peroxide,forceps,
discs filter paper, stop watch, measuring cylinders
Method
1. A 50cm 3 beaker was filled to the 40cm3 mark with 3% hydrogen peroxide solution.
2. With the use of a pair of forceps, a disc of filter paper was dipped into the yeast
suspension
3. The disc was gently shaken once to remove excess liquid
4. Filter paper was held 1 cm above the surface of the hydrogen peroxide solution. The
filter paper was then dropped into the solution
5. The filter paper was observed over the next minute
6. The observations were recorded and the filter paper was removed after
7. The behaviour of the filter paper soaked with yeast suspension in different hydrogen
peroxide solutions were investigated. A disc of filter paper that was dipped into yeast
solutions was dropped into the sample of 3 % hydrogen peroxide that was used
previously. A stop watch was used as the filter paper touched the bottom of the
container. The time was stopped as the disc rose from the bottom of the container to
the surface of the solution. The disc of filter paper was removed
8. This procedure was repeated twice using the 3% of hydrogen peroxide solution and
three times for each of the other three other hydrogen peroxide solutions
Table showing the time and average time taken of the reaction with different
concentrations of hydrogen peroxide
Concentration
of H2O2 (%)
Time taken
For discs
To float (s)
`1
2
3
Average time
taken for disc
to float (s)
3.0
1.73
1.82
1.00
1.52
2.0
2.13
2.06
2.91
2.37
1.5
3.95
3.575
2.935
3.48
1.0
2.30
1.94
3.12
2.45
Discussion
Enzymes are globular protein molecules with a tertiary structure that are capable of
catalyzing chemical reactions of biological origin. In order for enzymes to maintain their
tertiary structure, they contain : disulphide, hydrogen, ionic and hydrophobic bonds.
Also, enzymes react with substrates by the means of an active site. The substrate is a
molecule that an enzyme reacts with,whereas, the active site is a part of an enzyme that
directly bonds with a substrate to carry out a reaction.Enzymes are specific in action because
they bind to a specific substrate that fit into their active site which has a precise shape, size
and functional group.The lock and theory is an analogy that supports that enzymes are
specific in action where the substrate acts as they key that fits into the active site and the
enzyme is the lock that has a specific shape( active site). In some instances, enzymes may
require a non-protein component to function called a co-factor.
The enzyme Catalase is found in aerobic organisms. It is an antioxidant enzyme that
speeds up the breakdown of hydrogen peroxide so cells do not die. It catalyses H2O2
(hydrogen peroxide) into water and oxygen in an energy efficient manner. 2 H2O2 → 2H2O +
O2. This is a catabolic reaction where the larger molecule is broken down into smaller
molecules. The filter paper rises because the enzyme breaks down the hydrogen peroxide into
water and oxygen gas, the bubbles of oxygen collect underneath the filter paper disc and
allows it to rise to the surface of the hydrogen peroxide. Therefore, the time it takes for the
filter paper to rise is an indication of the rate of enzyme activity.
When an enzymatic reaction occurs there are factors that can affect the speed of the
reaction. An example of this is enzyme-substrate concentration which is when there is a
change in substrate concentration, it can affect the rate of reaction.When the hydrogen
peroxide concentration was 1%, there was a recorded average time of 2.45s, the recorded
time should be slower but due to human error this was the recorded time. This is because
there is a low concentration of molecules,therefore, decreasing the rate of reaction. With a
concentration of 1.5%, the average time was 3.48s which was the slowest time recorded
because it still was a low concentration. This was because of the low frequency with which
the enzyme and substrate collided. When there was a concentration of 2% the rate of reaction
increased indicating a higher frequency of collisions.Lastly, when hydrogen peroxide was at
its highest concentration,3%, it recorded its fastest average time at 1.52s. This is an
indication that the collision rate between the enzyme and substrate was at its fastest.
Limitations
When hydrogen peroxide is exposed to light it causes it to breakdown,therefore, affecting the
concentration. To reduce the probability of hydrogen peroxide breaking down, place in a dark
cupboard until it needs to be used. Also, the discs in each beaker can absorb a different
amount of yeast.
Conclusion
In conclusion, an increase in hydrogen peroxide concentration is directly proportional to the
rate of reaction of the enzyme Catalase.The highest concentration of hydrogen peroxide had
the fastest average time. This is because when the substrate concentration increases so does
the rate of reaction.