Chapter 16

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

nar002-1.jpg 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

What is meant by the description "antiparallel" regarding the strands that make up DNA?

The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

Which of the following statements is true of histones?

Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

It joins Okazaki fragments together.

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

8%

Use the following list of choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes synthesizes short segments of RNA

V

Which of the following would you expect of a eukaryote lacking telomerase?

a reduction in chromosome length in gametes

How do we describe transformation in bacteria?

assimilation of external DNA into a cell

To repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

endonuclease, DNA polymerase I, DNA ligase

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

nucleosome, 30-nm chromatin fiber, looped domain

What is the function of topoisomerase?

relieving strain in the DNA ahead of the replication fork

nar002-1.jpg 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 trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

DNA contains phosphorus, whereas protein does not.

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

DNA in both daughter cells would be radioactive.

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

Which enzyme catalyzes the elongation of a DNA strand in the 5' mc007-1.jpg 3' direction?

DNA polymerase III

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.

Which of the following statements describes chromatin?

Heterochromatin is highly condensed, whereas euchromatin is less compact.

Use the following list of choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes separates the DNA strands during replication?

I

Use the following list of choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes covalently connects segments of DNA? a. I

III

Use the following list of choices for the following questions: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments?

IV

Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?

gaps left at the 5' end of the lagging strand

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in which of the following?

sequence of bases

In a linear eukaryotic chromatin sample, which of the following strands is looped into domains by scaffolding?

the 30-nm chromatin fiber

The leading and the lagging strands differ in that

the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

What is the function of DNA polymerase III?

to add nucleotides to the 3' end of a growing DNA strand