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AP Biology
Problem Set 5
Metabolism and Enzyme Activity (Chapter 8)
due Monday, October 4, 2010
Instructions: Read Chapter 8 in the Campbell text (chapter 6 if you still have the green
book). Some questions may require you to look elsewhere in the textbook, or to make
your own predictions or educated guesses. Please answer the questions thoroughly and in
complete sentences. I encourage you to talk with others as you work to think about the
questions. However, you should write the answers on your own.
Grading: As usual, each question is worth 5 points. Your answers will be graded on the
basis of completeness, accuracy, effort, and mechanics (spelling, punctuation, and
grammar do count!) Be sure to read each question carefully and answer it fully. Your
answers should be written neatly or typed. No credit will be awarded for answers that
quote from the textbook or other sources, or answers copied from other students.
Part A – Basic Knowledge (Choose 3 of the 4 questions.)
1. Endergonic and exergonic reactions…
a) What is the difference?
b) Give an everyday example (not from the book) of each.
c) Which type of reaction requires ATP to happen in living systems? Why? Why
do BOTH of these reaction types generally require enzymes?
2. ATP is one of the most important molecules in many cellular reactions.
a) In one sentence, what is ATP’s job in cells?
b) What does ATP stand for?
c) Diagram the molecular structure of an ATP molecule. Label the “high-energy”
phosphate bonds. Why is the term “high energy” actually somewhat misleading?
d) Come up with an analogy to describe ATP’s role in cells. How does this illustrate
the importance of coupled reactions?
3. Take a look at the “Metabolic Pathways” poster in the science lab. It shows most of
the typical metabolic reactions that happen in cells.
a) There will be a quiz on this poster tomorrow. You should memorize the reactants
and products of each reaction, as well as the enzyme that catalyzes it. The
enzymes are listed in black on both sides of the column.
b) Just kidding.
c) For real – estimate the total number of different enzymes needed for all of the
reactions on this poster.
d) Enzymes, as you know, are proteins – made up of amino acids. How can cells
possibly make hundreds of different enzymes using only the same 20 amino
acids?
e) The SHAPE of an enzyme is extremely important in allowing it to catalyze
specific reactions. What determines the shape of an enzyme? Be specific,
relating your answer to the 4 levels of protein structure.
4. Describe and explain what would happen to the structure and function of an
enzyme if…
 the enzyme were heated to high temperatures
 the enzyme were placed in an highly acidic or basic solution
 a mutation in the gene coding for the enzyme caused a change in one or more
amino acids located in the enzyme’s active site
Note: Describe means tell what happens; explain means tell why it happens. This is
language that is very common on open response questions in AP Bio. To get full credit
on this question, you must do both for each bullet.
Part B – Application (Choose 2 questions)
5. The enzyme phenol oxidase, present in the cells of fruits and vegetables such as
apples, pears, and potatoes, catalyzes the oxidation of catechol molecules into
benzoquinone, a brown-colored product. This is why these fruits and vegetables turn
brown when they are exposed to air for a while. Because brown apple slices are
unappealing to eat, caterers preparing apple slices to be served at a party often
squeeze some lemon juice on the freshly cut apples, which prevents them from
turning brown. Why does lemon juice have this effect?
6. What are the optimal pHs of the enzymes trypsin and pepsin? What are the functions
of these enzymes? Where in the body are they found? Why do you think their
structures have evolved to function optimally in such different pHs?
7. How are enzymes regulated by other biological molecules? Explain the difference
between competitive inhibition, noncompetitive inhibition, and allosteric regulation
of enzymes.
Enzyme activity
8. The graph below shows the activity (in terms of millimoles of reactant used up per
mL per minute) of a typical enzyme in a human cell.
a) Summarize the relationship between
35
temperature and enzyme activity,
30
according to this graph.
25
20
15
10
5
0
0
10
20
30
40
Temperature (degrees Celcius)
50
b) Explain the shape of the curve. Include
a separate explanation for why the curve
has a positive slope initially and a
negative slope at high temps.