Download Biology - PHA Science

AP Biology
Problem Set 4
Carbon Compounds & Biochemistry (Campbell Chapter 5)
due Monday, September 27, 2010
Instructions: For this problem set, you must answer #1 and three of the four other
questions, for a total of 4 questions. As usual, start with the textbook, your notes, and
other resources if necessary. Answers should be typed and in your own words;
diagrams should be drawn on your own (not a pasted-in image) except for in #4, where
you may copy and paste a diagram of a triglyceride as long as you label and explain it
yourself.
Grading: As usual, each question is worth 5 points! If you answer all 5 questions, you’ll
get grades for the best 4 (but you must do #1).
1. Proteins are essential for all life on earth.
a) Diagram an amino acid and label its functional groups. What is the importance of
the R group?
b) Describe the four different levels of protein structure. What kind of chemical
interactions (e.g. hydrogen bonds, peptide bonds, covalent bonds, hydrophobic
interactions) does each level depend on?
c) Explain what would happen (and why) to the overall shape of the protein if…
 one amino acid is substituted for another in the peptide chain
 the protein is heated to high temperatures
 the protein is placed in a strong acid, base, or hydrophobic solution
2. Compare and contrast the roles that starch and cellulose play both in the plants where
they are produced, and in the animals who eat them. What is the chemical structure
of each polymer, and how does this structure relate to its functions? Why can cows,
termites, and fungi use cellulose for energy while humans cannot?
3. Why don’t lipids and water interact? Draw the structure of a typical triglyceride, and
use the diagram to explain why it repels water. Be sure to use specific chemical
vocabulary in your diagram and explanation.
4. Carbohydrates and lipids are both used to store energy. What are the advantages and
disadvantages to using carbohydrates versus using lipids? Why do plants tend to
store energy as starch while animals tend to store energy as fat? (Bonus: Why do you
think plants and fish tend to use oils (unsaturated fats) as lipid storage, while
mammals use saturated fats?)
5. Imagine that you are studying an enzyme that breaks down fatty acids for energy in
cells. Look at the diagrams of amino acids in Figure 5.17. Which amino acids would
you predict to be in the part of the enzyme that binds to the fatty acid? Why? Why
might this part of the enzyme be buried in a “pocket” of the enzyme molecule, instead
of on the surface of the enzyme?