Researchers found a strain of E. coli bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results?

The proofreading mechanism of DNA polymerase was not working properly.

Which of the following effects might be caused by reduced or very little active telomerase activity?

Cells age and begin to lose function.

Which of the following types of cells are affected most by telomere shortening?

only eukaryotic cells

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?

Telomerase eliminates telomere shortening and retards aging.

What are telomeres?

the ends of linear chromosomes

Which of the following statements correctly describes the difference between the leading strand and the lagging strand in DNA replication?

The leading strand is synthesized continuously in the 5' → 3' direction, while the lagging strand is synthesized discontinuously in the 5' → 3' direction.

Use the figure to answer the following question.

Referring to the figure, what bases will be added to the primer as DNA replication proceeds?

5′ A, G, A, C, G, A, C 3′

DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed during DNA replication?

DNA polymerase

Who performed classic experiments that supported the semiconservative model of DNA replication?

Meselson and Stahl

In DNA replication, the resulting daughter molecules contain one strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?

DNA replication is semiconservative.

Semiconservative replication involves a template. What is the template?

one strand of the DNA molecule

Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine, and cytosine forms hydrogen bonds with guanine. What is the significance of the structural arrangement?

It permits complementary base pairing.

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). Which two classes of DNA do these different samples represent?

leading strands and Okazaki fragments

After the first replication was observed in their experiments testing the nature of DNA replication, Meselson and Stahl could be confident of which of the following conclusions?

Replication is not conservative.

Use the figure to answer the following question.

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 would you expect if the DNA was replicated in a conservative manner?

B

Use the figure to answer the following question.

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" (radioactive) nitrogen (13N) and then transferred them to a medium containing 14N (non-radioactive). Which of the results in the figure would be expected after one round of DNA replication in the presence of 14N?

D

Which of the following characteristics would you expect of a eukaryotic organism that lacks the enzyme telomerase?

a reduction in chromosome length in gametes

Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight, and mutations to the DNA in their skin cells are left uncorrected. Why are the mutations not corrected in individuals with this disorder?

The disorder causes cells to be unable to repair thymine dimers.

Which of the following types of molecules help to hold the DNA strands apart while they are being replicated?

single-strand DNA binding proteins

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

It joins Okazaki fragments together.

What is the function of the enzyme topoisomerase in DNA replication?

relieving strain in the DNA ahead of the replication fork caused by the untwisting of the double helix

Why does a new DNA strand elongate only in the 5' to 3' direction during DNA replication?

DNA polymerase can add nucleotides only to the free 3' end.

Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA during DNA replication?

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.

Which of the following statements correctly describes the difference between ATP and the nucleotides used during DNA synthesis?

The nucleotides have the sugar deoxyribose; ATP has the sugar ribose.

In E. coli, what is the function of DNA polymerase III?

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

In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

nuclease, DNA polymerase, DNA ligase

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork:

3' C C T A G G C T G C A A T C C 5'

An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

5' A C G U U A G G 3'

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?

It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.

Which of the following characteristics of eukaryotic telomeres cause them to replicate differently than the rest of the chromosome?

gaps left at the 5' end of the lagging strand template

In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?

DNA polymerase III

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?

No replication fork will be formed.

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.

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

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 accurately describes the differences between DNA replication in prokaryotes and DNA replication in eukaryotes?

Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?

the 3' OH

Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?

DNA

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms 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.

In an analysis of the nucleotide composition of a molecule of DNA, which of the following combinations of base pairs will be found?

A + C = G + T

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?

sequence of bases

Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?

22%

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%

Which of the following investigators was (were) responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?

Erwin Chargaff

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?

DNA contains phosphorus, whereas protein does not.

A heat-killed, phosphorescent (light-emitting) strain of bacteria is mixed with a living, non-phosphorescent strain. Further observations of the mixture show that some of the living cells are now phosphorescent. Which of the following observations would provide the best evidence that the ability to phosphoresce is a heritable trait?

phosphorescence in descendants of the living cells

Which of the following statements describes the process of transformation in bacteria?

External DNA is taken into a cell, becoming part of the cell's genome.

In his transformation experiments, what phenomenon did Griffith observe?

Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.