General Biology Chapter 15
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
At a specific area of a chromosome, the following sequence of nucleotides 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' (Be aware that this is for RNA, RNA uses U. DNA uses A.
In an analysis of the nucleotide composition of DNA, which of the following will be found?
A + C = G + T
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.
If the lower DNA molecule shown in step 4 of Figure 15.12 undergoes another round of DNA replication, how will the two daughter DNAs differ from the parent DNA?
Another round of replication will lead to two DNA helices where the lagging ends will show the parental DNA strands to be longer than the new daughter DNA strands.
What would be the consequence(s) for DNA synthesis if primase were defective?
Both leading and lagging strand synthesis would be incomplete. Primase is required to synthesize the RNA primers on both the leading and lagging strands (all DNA polymerases require a primer).
RNA primers must be present on which strand during DNA synthesis?
Both leading and lagging strands. But the spacing between primers is different on the two strands.
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.
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
What catalyzes DNA synthesis?
DNA polymerase This enzyme catalyzes DNA synthesis.
Which statement best describes the activity of DNA polymerase I?
DNA polymerase I is used predominately on the lagging strand because this strand is synthesized in numerous small fragments.
What happens to with the daughter cells generation by generation in DNA Replication?
During DNA replication, each strand in the parental DNA serves as the template for the production of a daughter strand by complementary base pairing. Therefore, one cycle of replication will produce two daughter DNA molecules, each with one parental strand and one newly synthesized strand. During a second cycle of replication, all four strands in the two DNA molecules will serve as templates, resulting in four molecules (eight strands of DNA).
What happens during DNA replication?
During replication, DNA synthesis occurs in the 5′ to 3′ direction along both template strands. On one template strand, synthesis proceeds continuously toward the replication fork, generating the leading strand. On the other template strand, DNA is synthesized away from the replication fork in segments called Okazaki fragments, generating the lagging strand. Several proteins are involved in DNA replication, including the following: Topoisomerase cuts swivels and rejoins DNA strands ahead of the replication fork. Helicase breaks the hydrogen bonds between the parental DNA strands and unwinds the double helix. Single-strand binding proteins bind to the single strands of DNA, preventing them from re-forming hydrogen bonds with each other and allowing synthesis to occur on both strands. DNA polymerase III synthesizes the new strands, but it requires an existing 3′ hydroxyl (—OH) group to add nucleotides. Primase creates short RNA primers, initiating DNA synthesis on both template strands. DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides. On the lagging strand, DNA ligase joins Okazaki fragments by forming phosphodiester bonds between them, thus completing DNA replication.
What kinds of organisms require telomerase?
Eukaryotes, they contain linear chromosomes and therefore require telomerase to prevent loss of the ends of the chromosomes.
Who demonstrated that DNA is the genetic material of the T2 phage?
Hershey and Chase did a series of classic experiments demonstrating that DNA is the genetic material of the T2 phage.
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 is not a property of DNA polymerase?
It is associated with a sliding clamp only on the leading strand.
What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
It joins Okazaki fragments together.
In the Hershey-Chase experiment, what was this single difference?
Labeling viral DNA or labeling viral proteins.
Which strand of DNA is synthesized toward the middle of the replication bubble?
Lagging strand. DNA polymerase can only work in the 5' to 3' direction.
Who performed classic experiments that supported the semiconservative model of DNA replication?
Meselson and Stahl
What is the virus image called?
Phage.
Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?
Phosphate groups
Which of the following enzymes creates a primer for DNA polymerase?
Primase. This RNA polymerase synthesizes an RNA primer antiparallel to the template DNA strand.
Which of the following statements about DNA synthesis is true?
Primers are short sequences that allow the initiation of DNA synthesis. When a primer is added to a single strand of DNA, DNA polymerase can start adding nucleotides to synthesize a complementary strand.
What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have multiple origins of replication.
The coat of the T2 virus consists of what kind of macromolecules?
Protein, this helped show that DNA was the hereditary material in cells
Hershey and Chase used _____ to radioactively label the T2 phage's proteins.
Radioactive sulfur, ^35S
In the experiment shown in Figure 15.18b, why do increasing doses of UV light cause increasing amounts of radioactive nucleotides to be incorporated into DNA?
Repair of DNA damage caused by UV light involves the replacement of damaged nucleotides. Nucleotide excision repair removes thymine dimers and many other types of damage that distort the DNA helix and replaces the damaged DNA with correct newly synthesized DNA.
The Meselson-Stahl experiment supported which mechanism for DNA replication?
Semiconservative replication. Each new daughter DNA molecule consisted of one old strand and one new strand.
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.
How does telomerase prevent linear chromosomes from shortening during replication?
Telomerase binds to the overhang at the end of a chromosome. Once bound, and using its --RNA-- template as a guide, it begins catalyzing the --addition-- of deoxyribonucleotides to the overhang in the --5'->3'--direction, lengthening the overhang. This creates a single strand of DNA that is then used as a template on which primase, --DNA-- polymerase, and ligase add deoxyribonucleotides to the lagging strand in the --5'->3'-- direction, restoring the lagging strand.
Why does telomerase have to have a built-in template for DNA synthesis?
Telomerase is involved in adding DNA to the end of the lagging strand. At the ends of linear chromosomes (telomeres), telomerase uses its built-in RNA template to extend the parent DNA template near the end of the lagging strand, providing room for an RNA primer so that lagging strand synthesis can be completed to the end of the chromosome.
According to Figure 15.14, is donor age or telomere length more important in determining how many cell divisions a cell will undergo?
Telomere length is more important in determining the number of cell divisions because all cells with longer telomeres divided more times than cells with shorter telomeres, regardless of donor age.
The radioactive isotope 32P labels the T2 phage's _____.
The T2 phage consists of a protein coat and DNA. It is the DNA that contains P.
In a healthy cell, the rate of DNA repair is equal to the rate of DNA mutation. When the rate of repair lags behind the rate of mutation, what is a possible fate of the cell?
The cell can be transformed into a cancerous cell
Which statement is correct concerning DNA synthesis catalyzed by DNA polymerases?
The new DNA strand is synthesized in the 5'—>3' direction; the template strand is read in the 3'—>5' direction. DNA synthesis by DNA polymerases always proceeds in the 5'—>3' direction, using a complementary, antiparallel strand as template.
Recent studies have shown that xeroderma pigmentosum (an error in the nucleotide excision repair process) can result from mutations in one of seven genes. What can you infer from this finding?
There are several proteins involved in the nucleotide excision repair process.
For the experiment shown in Figure 15.2, predict what the investigator would have concluded if they had found both radioactive DNA and protein in the pellet.
They would have concluded viral genes consist of both DNA and protein.
Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?
Topoisomerase. This enzyme untwists the coils that occur in the DNA as it is being unwound into a single-stranded template.
True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions.
True. When the 3' end of one DNA strand points in the same direction as the 5' end of the other DNA strand, the strands are said to be antiparallel.
Which of the following statements about Okazaki fragments in E. coli is true?
While DNA is synthesized continuously on the leading strand, Okazaki fragments are formed on the lagging strand because DNA synthesis always proceeds in the 5' to 3' direction.
What would be the consequence(s) for DNA synthesis if DNA ligase were defective?
Without DNA ligase activity, Okazaki fragments on the lagging strand would not be joined together; leading strand synthesis would be largely unaffected.
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
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.
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. Since the phage DNA entered the infected cell, it makes sense that DNA is the genetic material.
Ciprofloxacin inhibits DNA gyrase, a bacterial topoisomerase that cuts DNA ahead of the replication fork, winds the DNA in a direction that relieves the twists added during DNA synthesis, and then reseals the DNA. In ciprofloxacin-treated bacteria, newly synthesized DNA is found in fragments. Based on this evidence, what activity of DNA gyrase is likely to be inhibited by ciprofloxacin?
ligase activity
Which one of the following is least likely to cause mutations in DNA?
light from an incandescent bulb
Semiconservative replication involves a template. What is the template?
one strand of the DNA molecule
A DNA replication bubble forms at a specific sequence of bases called the ___________.
origin of replication. Bacterial chromosomes form a single replication bubble, but eukaroytes can form several along each chromosome.
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
The enzyme that synthesizes RNA primers for use in DNA replication is _______________.
primase
DNA is synthesized through a process known as _____.
semiconservative replication
Which of the following help(s) to hold the DNA strands apart while they are being replicated?
single-strand DNA binding proteins
In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and _____ of the last nucleotide in the polymer.
the 3' OH
If you could engineer an activity into DNA polymerase to allow both strands to follow the replication fork, what would this additional activity be?
the ability to synthesize DNA in the 3' → 5' direction
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
In humans, xeroderma pigmentosum (XP) is a disorder of the nucleotide excision repair mechanism. These individuals are unable to repair DNA damage caused by ultraviolet light. Which of the following are the most prominent types of DNA lesions in individuals suffering from xeroderma pigmentosum?
thymine dimers
How are Okazaki fragments synthesized?
using the lagging strand template, and synthesizing 5' → 3'
For the Meselson-Stahl experiment shown in Figure 15.5, what would the composition of the DNA be after three generations? (Semiconservative replication.
¾ low-density and ¼ intermediate-density. Semiconservative replication of the second-generation DNA would produce a ratio of two hybrids to six 14N double helices (1:3).