Chapter 13 DNA History

Frederic Griffith used the word transformation to describe the changes in bacteria that he observed.

Which is the most useful definition of transformation?

• a permanent change in gene expression

• a permanent change in the function or activity of a cell

• a temporary change in the genetic composition of an organism

• a permanent change in the genetic composition of an organism

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In the Hershey-Chase experiment, the components of bacteriophages were labeled with radioactive isotopes of sulfur and phosphorus.

What was the Hershey-Chase experiment designed to determine?

• whether or not bacteriophages can infect bacteria

• whether DNA or RNA is the genetic material of the virus

• whether cells use DNA or proteins to store genetic information

• whether or not viruses satisfy the criteria for life

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The result of the Hershey-Chase experiment was that radioactivity could be detected inside the bacterial cells when they were infected by bacteriophages marked with phosphorus-32.

What did the investigators conclude from this result?

• Bacteriophages inject their DNA into the bacterial cells.

• Bacteriophages inject their protein into the bacterial cells.

• Bacteriophages inject carbohydrates into the bacterial cells.

• Bacteriophages absorb DNA from bacterial cells.

If 35% of an organism’s DNA is thymine, what is the percentage of guanine?

• 15%

• 35%

• 70%

• 50%

Chargaff's rules of base pairing are explained by which structural feature of DNA?

• Each strand of DNA contains a phosphate and sugar backbone.

• The nucleotides of DNA may be arranged in a wide variety of sequences.

• DNA is double stranded, and covalent bonds between identical nucleotides hold the two strands together.

• DNA is double stranded, and hydrogen bonds between base pairs hold the two strands together.

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The model of the double-helix model of the DNA molecule resembles a twisted ladder.

What makes up the rungs of the twisted ladder?

• paired phosphate groups

• paired nitrogenous bases

• paired sugars

• hydrogen and oxygen atoms

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This figure shows a section of a double-stranded DNA molecule.

What aspects of the structure of DNA are explained by this model?

(Select all that apply.)

• Paired nucleotides are held together by covalent bonds.

• Adenine is paired with thymine and guanine is paired with cytosine.

• Paired nucleotides are held together by hydrogen bonds.

• The two strands of DNA each have phosphate-sugar backbones.

• The numbers of each nucleotide determine genetic information.

How does the double-helical structure of DNA explain how the molecules can be copied or replicated?

• Because of base pairing, each strand has all the information to serve as a template for the synthesis of the other strand.

• Each strand receives the information from the DNA polymerase attached to the replication fork.

• The nitrogenous bases on one strand are copied to the other strand.

• The nitrogenous bases line up on each strand and are attached to each other.

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As cells pass through the cell cycle, their volume of DNA alternately halves and doubles.

Which statement about DNA correctly explains this pattern?

• DNA replication occurs during all phases of the cell cycle.

• DNA replication occurs only during the G₁ phase of the cell cycle.

• DNA replication occurs only during the S phase of the cell cycle.

• DNA replication occurs randomly, and is unrelated to the cell cycle.

A scientist uses radioactive isotopes to label a double-stranded molecule of DNA. Then the DNA undergoes replication in a non-radioactive medium.

Where are the two original radioactive strands of DNA?

• Both strands are intact, and both are part of the same molecule of DNA.

• Both strands are intact, and each are part of a different molecule of DNA.

• One strand is intact, and the other strand is broken apart and distributed among the new DNA molecules.

• Both strands are broken apart, and their pieces are distributed among the new DNA molecules.