1. Chapter 3
The Molecules of Cells

2. Concept Check
This lysozyme protein molecule is found in tears and protects the eye from bacterial infections. Which of the following best describes the outside of the molecule?
The R-groups on the surface of the molecule are mostly hydrophobic.
The R-groups on the surface of the molecule are mostly hydrophilic.
The R-groups on the surface of the molecule are mostly non-polar.
The R-groups on the surface of the molecule are constantly changing between non-polar and polar as the protein chain bends and folds.
Answer: 2

3. Answer
This lysozyme protein molecule is found in tears and protects the eye from bacterial infections. Which of the following best describes the outside of the molecule?
2) The R-groups on the surface of the molecule are mostly hydrophilic.

4. Concept Check
When proteins are heated, they usually denature. If moderate heat was applied to this molecule of DNA what part of the molecule would break down or break apart first? (Use your knowledge of chemical bonds.)
The nucleotides along each side would break apart.
The sugar-phosphate backbone would separate from the nitrogen bases.
The nitrogen base pairs would separate in the interior of the molecule.
Answer: 3

5. Answer
When proteins are heated, they usually denature. If moderate heat was applied to this molecule of DNA what part of the molecule would break down or break apart first? (Use your knowledge of chemical bonds.)
The nitrogen base pairs would separate in the interior of the molecule.

6. Interpreting Data
The amino acid “R” groups interact to create the three-dimensional structures of proteins. Some amino acids have hydrophilic side groups; others have hydrophobic side groups. In the hydrophilic group, some “R” groups are acids and others are bases:
Acid “R” groups end with a carboxyl group.
Basic “R” groups end with an amino group.

7. Interpreting Data -COOH -COO- -NH2 - NH3+
Interpreting Data
The key to a protein’s function is its shape. The shape can be altered (or denatured) under unfavorable conditions. The pH of the solution is an important factor in determining protein shape. Depending on the pH of the solution, carboxyl groups and amine groups may or may not be charged.
-COOH COO-
-NH NH3+

8. Interpreting Data
This graph indicates how the charge on an amino acid “R” group can be determined by the pH of the solution. The green line across the middle of the graph represents the neutral pH of most cells.
At neutral pH (7), which of the following amino acids carry charge?
Aspartic acid
Glutamic acid
Lysine
All of the above
Answer: 4

9. Answer
This graph indicates how the charge on an amino acid “R” group can be determined by the pH of the solution. The green line across the middle of the graph represents the neutral pH of most cells.
At neutral pH (7), which of the following amino acids carry a charge?
All of the above

10. Interpreting Data
At an acidic pH of 3, which of the following amino acids carry a charge?
Aspartic acid
Glutamic acid
Lysine
All of the above
Answer: 3

11. Answer
At an acidic pH of 3, which of the following amino acids carry a charge?
Lysine

12. Interpreting Data
At a basic pH of 12, which of the following amino acids carry a charge?
Aspartic acid
Glutamic acid
Lysine
Both 1 and 2
Answer: 4

13. Answer
At a basic pH of 12, which of the following amino acids carry a charge?
Both 1 and 2

14. Strongly A B C D E Strongly
Science and Society
Seeking to gain an edge over the competition, some athletes have turned to anabolic steroids to enhance their performance. Due in part to the negative health effects of steroid use, most sports organizations ban the use of steroids.
Do you believe that sports organizations should ban the use of performance-enhancing drugs?
Disagree Agree
Strongly A B C D E Strongly

15. Strongly A B C D E Strongly
Science and Society
Olympic track and field records appear to have leveled off and perhaps even declined from a high point in the early to mid-1990s. Some have suggested that many of the records set during this time period were due to drug-based enhancement.
Should these records be thrown out?
Disagree Agree
Strongly A B C D E Strongly