Intro to Cell Biology Exam 5

The radioactive isotope 32P labels the T2 phage's _____.

DNA

telomerase is needed to ___

prevent the loss of DNA bases at the ends of linear chromosomes

Who demonstrated that DNA is the genetic material of the T2 phage?

Hershey and Chase

As DNA replication continues and the replication bubble expands, the parental double helix is unwound and separated into its two component strands. This unwinding and separating of the DNA requires three different types of proteins: helicase, topoisomerase, and single-strand binding proteins. Sort the phrases into the appropriate bins depending on which protein they describe.

helicase binds at the replication forkbreaks H-bonds between bases topoisomerase binds ahead of the replication forkbreaks covalent bonds in DNA backbone single-strand binding protein binds after the replication forkprevents H-bonds between bases

After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.

labeled DNA...DNA

As the two parental (template) DNA strands separate at a replication fork, each of the strands is separately copied by a DNA polymerase III (orange), producing two new daughter strands (light blue), each complementary to its respective parental strand. Because the two parental strands are antiparallel, the two new strands (the leading and lagging strands) cannot be synthesized in the same way. Drag each phrase to the appropriate bin depending on whether it describes the synthesis of the leading strand, the synthesis of the lagging strand, or the synthesis of both strands.

leading strand made continuouslydaughter strand elongates toward replication forkonly one primer needed lagging strand made in segmentsmultiple primers neededdaughter strand elongates away from replication fork both strands synthesized 5' to 3'

1. Each Okazaki fragment has its own primer ___ 2. The DNA strand that is synthesized continuously is called the lagging strand ___ 3. The DNA strand that is synthesized discontinuously is called the leading strand ___ 4. DNA ligase joins adjacent Okazaki fragments together into a complete strand ___ 5. DNA polymerases cannot initiate synthesis of a new DNA strand, they can only add bases to an existing strand ___

T,F,F,T,T

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.

why does telomerase have a built-in template for DNA synthesis?

telomerase is involved in adding DNA to the end of the lagging strand

Griffith, a British microbiologist, used a bacteria and mice to demonstrate transformation. His results clearly offered evidence for that process. Transformation is

the ability to transfer genetic materials from one cell to another

What is a telomere?

the ends of linear chromosomes

What aspect of DNA structure makes it possible for the enzymes of nucleotide excision repair to recognize many different types of DNA damage?

the regularity of DNA's overall structure

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

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

In a nucleotide triphosphate, to which carbon on the deoxyribose will the base be found?

1'

Hershey and Chase used _____ to radioactively label the T2 phage's proteins.

35S

QUANTITATIVE Assuming that each replication fork moves at a rate of 500 base pairs per second, how long would it take to replicate the E. coli chromosome (with 4.6 million base pairs) from a single origin of replication?

4600 sec

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'

An Okazaki fragment has which of the following arrangements?

5' RNA nucleotides, DNA nucleotides 3'

Which of the following investigators was/were responsible for the following discovery? Confirmation of the one gene, one enzyme hypothesis from studies with nutritional mutants in breads mold.

Beedle and Tatum

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?

DNA polymerase

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

DNA polymerase III

A new DNA strand elongates only in the 5' to 3' direction because

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

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.

What appears to be a dark side to telomerase activity with regard to human health?

Telomerase is active in most cancer cells

Which of the following statements about the Hershey-Chase experiment is false?

The virus-infected bacteria contained radioactive sulfur.

The Meselson-Stahl experiment was designed to answer which question?

What part of newly replicated DNA comes from the parental molecule and what part is newly synthesized?

Of the following, which is the most current description of a gene?

a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

Can you identify the banding patterns predicted by each model after the second round of replication? (Note: The dispersive model's prediction is already shown; see Hint 1 if you need help understanding it.) Drag the test tubes to the appropriate locations in the table to show the banding patterns that each model predicts. Test tubes may be used once or not at all.

a. 14N/14N (top), 14N/15N (intermediate) b. 14N/14N (top), 15N/15N (bottom)

Rank the primers in the order they were produced. If two primers were produced at the same time, overlap them.

earliest ha bg cf de latest

In Griffith's transformation experiments,

mice infected with heat-killed S form and live R form caused pneumonia and death in the mice.

the primers used for DNA synthesis are ___.

short RNA sequences

Griffith worked with

Streptococcus

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have _____.

T4 protein and T4 DNA.

Alkapton urea is a familial disease that is autosomal recessive. The defective enzyme in affected individual prevents the metabolism of _____________

homogentisic acid

Complete the following vocabulary exercise related to DNA replication. Match the words in the left-hand column with the appropriate blank in the sentences in the right-hand column.

1. The enzyme that can replicate DNA is called DNA polymerase. 2. Okazaki fragments are the short sections of DNA that are synthesized on the lagging strand of the replicating DNA. 3. The new DNA strand that grows continuously in the 5' to 3' direction is called the leading strand. 4. After replication is complete, the new DNAs, called daughter DNA, are identical to each other. 5. During DNA replication, an open section of DNA, in which a DNA polymerase can replicate DNA, is called a replication fork.

Given the experimental procedure explained in the question above, which centrifuge tube (obtained after two DNA Replications) would represent the band distribution indicating that DNA replication is

C (light and intermediate band towards the top)

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.

The Hershey-Chase experiment answered the question of whether protein or DNA was the genetic material by learning whether ______.

DNA or protein from a virus entered bacterial cells during infection

For the experiment shown in Figure 15.2, which additional piece of evidence would prove that the viral capsids were shaken off the bacterial cells by the agitation step?

Examination of the pellet by electron microscopy to show that no capsids are present

1. Because the 2 strands of a DNA molecule run in opposite directions, they are said to be bidirectional ____ 2. DNA polymerases can add new DNA nucleotides only to the 5 prime end of an existing strand ____ 3. Because the 2 strands of a DNA molecule run in opposite directions and because DNA polymerases can synthesize new strands only in the 5 prime to 3 prime direction, polymerases on opposite strands must synthesize DNA in opposite directions. ____ 4. The DNA strand that grows away from the replication fork is synthesized continuously from one initial primer____ 5. The DNA strand that grows toward the replication fork is synthesized discontinuously in short pieces called Okazaki fragments____1/

F,F,T,F,F

Drag the correct labels to the appropriate locations in the diagram to show the composition of the daughter DNA molecules after one and two cycles of DNA replication. In the labels, the original parental DNA is blue and the DNA synthesized during replication is red.

First cycle: two strands of blue and red spiraled second cycle: four strands two with blue and red spiral and two plain red

In DNA replication in bacteria, the enzyme DNA polymerase III (abbreviated DNA pol III) adds nucleotides to a template strand of DNA. But DNA pol III cannot start a new strand from scratch. Instead, a primer must pair with the template strand, and DNA pol III then adds nucleotides to the primer, complementary to the template strand. Each of the four images below shows a strand of template DNA (dark blue) with an RNA primer (red) to which DNA pol III will add nucleotides. In which image will adenine (A) be the next nucleotide to be added to the primer?

In the example above, DNA pol III would add an adenine nucleotide to the 3' end of the primer, where the template strand has thymine as the next available base. You can tell which end is the 3' end by the presence of a hydroxyl (-OH) group. The structure of DNA polymerase III is such that it can only add new nucleotides to the 3' end of a primer or growing DNA strand (as shown here). This is because the phosphate group at the 5' end of the new strand and the 3' -OH group on the nucleoside triphosphate will not both fit in the active site of the polymerase.

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

Meselson and Stahl

What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?

Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins of replication.

Meselson and Stahl designed an experiment that would allow them to discern whether DNA replication occurs in a dispersive, semiconservative, or conservative manner. They started with E. coli that had been growing for many generations in medium containing 15N. They then transferred the bacteria into medium containing only 14N, and allowed the bacteria to undergo two rounds of DNA replication. After each round of replication, the scientists performed density-gradient centrifugation of the DNA. The scientists reasoned that each of the three models would predict different DNA banding patterns after the two rounds of replication. Can you identify the banding patterns predicted by each model after the first round of replication? (Then, in Part C, you will identify the banding patterns predicted after the second round of replication.) Drag the test tubes to the appropriate locations in the table to show the banding patterns that each model predicts. Test tubes may be used once, more than once, or not at all.

a. 14N/15N b. 14N/15N c. 14N/14N (top), 15N/15N (bottom)

The experimental technique: Density-gradient centrifugation When a solution of cesium chloride (CsCl) is subjected to high-speed centrifugation, a stable density gradient is formed. Meselson and Stahl found that when cell contents were subjected to centrifugation with a CsCl solution, a band of DNA formed at the CsCl density that matched the density of the DNA. This technique is called density-gradient centrifugation. The test tubes below show the results of density-gradient centrifugation of five different DNA samples. Drag the description of each DNA sample to the appropriate location to identify the expected appearance of the DNA band(s) after density-gradient centrifugation.

a. DNA from E.coli cells grown in 14N b. DNA containing one strand of 15N-DNA and one strand of 14N-DNA c. DNA from E.coli cells grown in 15N d. a 1:1 mixture of DNA from cells grown in 14N and cells grown in 15N e. A 1:1 mixture of DNA from cells grown in 14N and 15N, heated (to disrupt hydrogen bonds) and cooled (to allow reannealing)

The diagram below shows a bacterial replication fork and its principal proteins. Drag the labels to their appropriate locations in the diagram to describe the name or function of each structure. Use pink labels for the pink targets and blue labels for the blue targets.

a. breaks hydrogen bonds, unwinding DNA double helix b. synthesizes RNA primers on leading and lagging strands c. replaces RNA primers with DNA nucleotides d. catalyzes phophodiester bond formation, joining DNA fragments e. lagging strand f. leading strand g. relaxes supercoiled DNA h. coats single-stranded DNA i. synthesizes DNA 5' to 3' on leading and lagging strands

___ are viruses that attack bacteria

bacteriophage

what would be the consequence(S) for DNA synthesis if primase were defective?

both leading and lagging strand synthesis would be incomplete

which human cells have active telomerase?

cancer cells, cells that produce gametes, and some somatic cells

what is the relationship between defective DNA repair and cancer?

defective DNA repair→ the increased number of mutations→ the increased probability that cancer-causing mutations will occur

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

Which of the following characteristics, structures, or processes is common to bacteria and viruses?

genetic material composed of nucleic acid

Information obtained by Franklin from X-ray crystallography on DNA suggested that it is a _______.

helix

Avery, MacLeod, and McCarty's experiments revealed that the transforming principle had all of the following properties except

its activity was destroyed by treatment with proteases.

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

Okazaki fragments are found ___.

only on the lagging strand

This is an image of a _____.

phage

nucleotide excision repair

recognizes and repairs thymine dimers and other damaged bases in DNA

What is the function of topoisomerase?

relieving strain in the DNA ahead of the replication fork

Which of the following help(s) to hold the DNA strands apart while they are being replicated?

single-strand DNA binding proteins

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

When nonvirulent bacteria were mixed with dead virulent bacteria, Griffith unexpectedly found that the injected mice died. He explained this behavior by suggesting the nonvirulent strain of bacteria as being

transformed

Drag the labels to their appropriate locations in the flowchart below, indicating the sequence of events in the production of fragment B. (Note that pol I stands for DNA polymerase I, and pol III stands for DNA polymerase III.)

1. poll III binds to 3' end of primer B 2. poll III moves 5' to 3', adding DNA nucleotides to primer B 3. pol I binds to 5' end of primer A 4. pol I replaces primer A with DNA 5. DNA ligase links fragments A and B

Put the following steps of DNA replication in chronological order. 1. Single-stranded binding proteins attach to DNA strands. 2. Hydrogen bonds between base pairs of antiparallel strands are broken. 3. Primase binds to the site of origin. 4. DNA polymerase binds to the template strand. 5. An RNA primer is created.

2,1,3,5,4

To confirm the semiconservative model of replication, it was important for Meselson and Stahl to quantify the amount of DNA in each band produced by density-gradient centrifugation. To accomplish this, they took advantage of the fact that DNA absorbs ultraviolet light, and used UV light to photograph each tube. By scanning the UV photographs with a microdensitometer, graphs like the ones below were produced. The height of each peak in the graph is directly proportional to the concentration of DNA in the corresponding band. Also, the position of each peak reflects the 14N and 15N content of the band.

2nd: small peaks 3rd: big, small 4th: bigger, smaller

If a deoxynucleotide is part of a polydeoxynucleotide chain, to which carbon on the deoxyribose will the next nucleotide to join the chain be attached?

3'

For the Meselson-Stahl experiment shown in Figure 15.5, what would be the composition of the DNA after three generations?

3/4 low-density and 1/4 intermediate-density

The DNA double helix is composed of two strands of DNA; each strand is a polymer of DNA nucleotides. Each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases. The structure and orientation of the two strands are important to understanding DNA replication. Drag the labels to their appropriate locations on the diagram below. Use only the pink labels for the pink targets, and the blue labels for the blue targets. Labels can be used once, more than once, or not at all.

5' end; hydrogen bond; 3' end; deoxyribose sugar; nitrogenous base; phosphate group; 3' end; 5' end

Given the experimental procedure explained in the question above, which centrifuge tube (obtained after one DNA Replication) would represent the band distribution indicating that DNA replication is

A (single band)

In an analysis of the nucleotide composition of DNA, which of the following will be found?

A+C = G+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.

You are trying to test your hypothesis that DNA replication is conservative - that is, the parental strands separate, newly made complementary strands join together to make a new DNA molecule, and the parental strands then rejoin. You take a sample of E. Coli grown in a medium containing only heavy nitrogen (15N) medium and transfer it to a medium containing light nitrogen (14N). After allowing time for only one DNA replication you centrifuge a sample and compare the density band(s) formed to the bands formed from bacterial grown on either normal 14N or 15N medium. Which band location would support your hypothesis of conservative DNA Replication?

B (heavy and light band at equal distance from the ends of the tube)

The herpes viruses are important enveloped DNA viruses that cause disease in vertebrates and in some invertebrates such as oysters. Some of the human forms are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can later reactivate, replicate again, and infect others. In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty." Which of the following best fits these observations?

The viral envelope mediates entry into the cell, the capsid mediates entry into the nuclear membrane, and the genome is all that enters the nucleus.

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

Which type of DNA repair is most likely to be compromised if there is a failure in the system that allows repair enzymes to distinguish old and newly synthesized DNA?

mismatch repair

Within a double-stranded DNA molecule, adenine forms hydrogen bonds with thymine and cytosine forms hydrogen bonds with guanine. This arrangement _____.

permits complementary base pairing