In the discussion, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?

What is the experimental basis for concluding that DNA replicates semiconservatively in both bacteria and eukaryotes?

In the discussion, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?

How do we know that in vivo DNA synthesis occurs in the 5' to 3' direction?

In the discussion, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?

How do we know that DNA synthesis is discontinuous on one of the two template strands?

In the discussion, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?

What observations reveal that a 'telomere problem' exists during eukaryotic DNA replication, and how did we learn of the solution to this problem?

Write a short essay that distinguishes between the terms replication and synthesis, as applied to DNA. Which of the two is most closely allied with the field of biochemistry?

Compare conservative, semiconservative, and dispersive modes of DNA replication.

Describe the role of ¹⁵N in the Meselson–Stahl experiment.

Predict the results of the experiment by Taylor, Woods, and Hughes if replication were

(a) conservative and

(b) dispersive.

What are the requirements for in vitro synthesis of DNA under the direction of DNA polymerase I?

How did Kornberg assess the fidelity of DNA polymerase I in copying a DNA template?

Which characteristics of DNA polymerase I raised doubts that its in vivo function is the synthesis of DNA leading to complete replication?

Kornberg showed that nucleotides are added to the 3' end of each growing DNA strand. In what way does an exposed 3'-OH group participate in strand elongation?

What was the significance of the polA1 mutation?

Summarize and compare the properties of DNA polymerase I, II, and III.

List and describe the function of the ten subunits constituting DNA polymerase III. Distinguish between the holoenzyme and the core enzyme.

Distinguish between

(a) unidirectional and bidirectional synthesis, and

(b) continuous and discontinuous synthesis of DNA.

List the proteins that unwind DNA during in vivo DNA synthesis. How do they function?

Define and indicate the significance of

(a) Okazaki fragments,

(b) DNA ligase, and

(c) primer RNA during DNA replication.

Outline the current model for DNA synthesis.

Why is DNA synthesis expected to be more complex in eukaryotes than in bacteria? How is DNA synthesis similar in the two types of organisms?

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Newly synthesized DNA contains many mismatched base pairs.

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Okazaki fragments accumulate, and DNA synthesis is never completed.

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

No initiation occurs.

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Synthesis is very slow.

Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.

Supercoiled strands remain after replication, which is never completed.

Many of the gene products involved in DNA synthesis were initially defined by studying mutant E. coli strains that could not synthesize DNA.

The dnaE gene encodes the α subunit of DNA polymerase III. What effect is expected from a mutation in this gene? How could the mutant strain be maintained?

Many of the gene products involved in DNA synthesis were initially defined by studying mutant E. coli strains that could not synthesize DNA.

The dnaQ gene encodes the ε subunit of DNA polymerase. What effect is expected from a mutation in this gene?

Assume a hypothetical organism in which DNA replication is conservative. Design an experiment similar to that of Taylor, Woods, and Hughes that will unequivocally establish this fact. Using the format established in Figure 11.5, draw sister chromatids and illustrate the expected results establishing this mode of replication.

In 1994, telomerase activity was discovered in human cancer cell lines. Although telomerase is not active in most human adult cells, all cells do contain the genes for telomerase proteins and telomerase RNA. Since inappropriate activation of telomerase may contribute to cancer, why do you think the genes coding for this enzyme have been maintained in the human genome throughout evolution? Are there any types of human body cells where telomerase activation would be advantageous or even necessary? Explain.