AP Biology CHAPTER 16 - PART3

In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?

A + G = C + T

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in ¹⁵N medium for several generations and then transfer them to ¹⁴N medium. Which pattern in the figure above would you expect if the DNA was replicated in a conservative manner?

B

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (¹⁵N) and then transferred them to a medium containing ¹⁴N. Which of the results in the figure above would be expected after one round of DNA replication in the presence of ¹⁴N?

D

Which of the following statements describes chromatin?

Heterochromatin is highly condensed, whereas euchromatin is less compact.

The elongation of the leading strand during DNA synthesis

depends on the action of DNA polymerase.

A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?

DNA ligase

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

DNA polymerase can join new nucleotides only to the 3' end of a growing strand.

Why do histones bind tightly to DNA?

Histones are positively charged, and DNA is negatively charged.

Once the pattern found after one round of replication was observed, Meselson and Stahl could be confident of which of the following conclusions?

Replication is not conservative.

Grains represent radioactive material within the replicating eye. 47) In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (³H thymidine) for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure above represents the results. Which of the following is the most likely interpretation?

There are two replication forks going in opposite directions

In a nucleosome, the DNA is wrapped around

histones

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent

leading strands and Okazaki fragments.

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?

nuclease, DNA polymerase, DNA ligase

Which of the following represents the order of increasingly higher levels of organization of chromatin?

nucleosome, 30-nm chromatin fiber, looped domain

E. coli cells grown on ¹⁵N medium are transferred to ¹⁴N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?

one low-density and one intermediate-density band

In his work with pneumonia-causing bacteria and mice, Griffith found that

some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic.