TLW 7e Chapter 11 Answers
DNA: The Genetic Material
Test Your Understanding
1. Figure 11.4c
What are some of the possible problems that could occur if the C nucleotide indicated
with the red arrow is accidentally replaced with an A nucleotide?
First, the DNA molecule would no longer bind the two sides together properly. If it did
manage to hold together until cell division and mitosis occurred, the two daughter cells
would have two different copies of the DNA; one would have the old version, with the C
nucleotide, and the second would have the new version with an A nucleotide.
Second, if it were to be read by an mRNA molecule, one of the codons might code for the
wrong amino acid (depending on where in the codon the switch occurred). That would
change the configuration of the future protein, which might not then fold into the correct
shape and would not work properly.
2. Table 11.1 What types of mutations in the table result in a shift in the reading frame of
the DNA? Explain.
All of the mutations below the normal sequence because any mutation alters the
expression of the protein that the gene is coding for.
Apply Your Understanding
1. The discovery that DNA is the genetic material was an experimental journey rather
than a flash of insight. Highlighting individual experiments, use this journey to defend
the statement, attributed to Sir Isaac Newton in 1676 (though some say that Bernard of
Chartes said it first, way back in about 1130!) that scientists build new ideas in science by
“standing on the shoulders of giants.”
Each experiment or discovery uses the prior knowledge as a foundation to move further.
Mendel already knew of the work of previous researchers who had studied inheritance in
peas. Avery knew the work of Griffith with his “transforming principle” in bacteria,
showing that proteins were not the information carriers, and Hershey and Chase took the
next step with viruses, showing the same thing. Rosalind Franklin’s work with X-ray
crystallography of DNA molecules, along with Chargaff’s rule, gave the clues needed for
Watson and Crick to figure out the double helix structure of DNA.
2. Certain strains of bacteria are resistant to the antibiotic tetracycline, while other strains
are sensitive to it. Design an experiment you would carry out to determine whether or not
tetracycline resistance is an inherited trait specified by the DNA of the resistant strain.
Obtain a sample of the resistant bacteria’s DNA and compare it to the sensitive strain’s
DNA.