Download Honors Biology - LangdonBiology.org

Honors Biology
Enzymology Homework
This graph show the activity of two enzymes involved in
digestion relative to pH. Use the graph to answer the
following questions:
1. The enzyme that works best at neutral pH is:
Salivary amylase (best at pH 7)
2. The enzyme that works best at high
concentrations of H+ ions is: these are acidic
conditions, so pepsin
3. If you needed both enzymes to work at the same
time in the same test tube, what pH should you
use? pH of 5
What would be the efficiency (% activity) of each enzyme? 20%
This diagram represents a reaction curve for a simple chemical
reaction (it appears much more complicated because it is from a
chemistry text).
4. Which letter (a-e) represents the activation energy of the
reaction? B
5. On this graph, redraw the curve showing the effect of an
enzyme on this reaction.
6. If you did not have an enzyme, how else could you speed up this reaction?
Reactions can be sped up by increasing the temperature, pressure (if gasses are involved),
surface area, or by adding more reactants.
7. Describe how an enzyme would convert a dipeptide (two amino acids bound together) into two
amino acids. Your paragraph should correctly incorporate the following terms: substrate,
active site, product, enzyme-substrate complex, and induced fit model.
The dipeptide is the substrate for the enzyme. It binds in the active site, a depression or cleft in
the enzyme with a shape complementary to the dipeptide. As the substrate fits into the site, it
induces (causes) a change in the shape of the enzyme, which is the induced fit model of enzyme
function. While the substrate and the enzyme are bound together, they are referred to as the
enzyme-substrate complex. This E-S complex will quickly catalyze the hydrolysis of the dipeptide
into two amino acids. These products of the reaction are released, and the enzyme is available
to catalyze more reactions.
8. Why are enzymes so sensitive to changes in pH or temperature? Anything that denatures
(changes the shape of) a protein also changes the shape of active site. If the active site is
destroyed, the enzyme cannot bind the substrates correctly and thus cannot catalyze any
reactions.
9. Why are enzymes so specific for a single substrate? The shape of the active site matches the
shape of the substrate. Usually, only one substrate fits into the active site of an enzyme.
10. This table shows the results of an experiment testing the activity of an enzyme at various
temperatures. Graph the enzyme activity (y-axis) vs. temperature (x-axis).
Temperature
(°C)
30
35
37.5
40
42.5
45
50
Activity
(%)
25
65
85
100
75
50
0
Where would you expect to find a creature that contains an enzyme like this (arctic, tropical
rainforest, temperate forest)? The temperature optimum is 40°C (104° F), so most likely in a
tropical rainforest or other area with a high ambient temperature.
11. What are coenzymes? Coenzymes are chemicals that work along with an enzyme and its
substrate to perform certain chemical reactions. Examples of coenzymes are vitamins like
vitamin C, riboflavin, and niacin.
12. Describe how competitive inhibition works. Competitive inhibition involves a regulatory
molecule that mimics the shape of the substrate. However, when the competitive inhibitor
enters the active site, it blocks it, preventing the substrate from reacting. Because both the
inhibitor molecule and the substrate are racing for occupancy of the active site, it is competitive
inhibition.
Describe how noncompetitive inhibition works. A noncompetitive inhibitor binds to its own site
on the enzyme, away from the active site. When the inhibitor is bound, it causes a shape
change in the enzyme that involves the active site. As long as the inhibitor is bound, the active
site cannot bind its substrate.