Chapter 13
The segment of DNA shown in the figure has restriction sites I and II, which create restriction fragments A, B, and C. Which of the gels produced by electrophoresis shown below best represents the separation and identity of these fragments?
CAB (E)
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 would be expected after one round of DNA replication in the presence of 14N?
D
In an analysis of the nucleotide composition of DNA, which of the following will be found?
A+C = G+T
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'
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%
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
Why is it so important to be able to amplify DNA fragments when studying genes?
A gene may represent only a millionth of the cell's DNA
What are chromosomes made of?
DNA and proteins
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.
During DNA replication, which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments?
DNA polymerase I
Which enzyme catalyzes the elongation of a DNA strand in the 5' → 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 preexisting strand.
A new DNA strand elongates only in the 5' to 3' direction because
DNA polymerase can only add nucleotides to the free 3' end.
The lagging strand is characterized by a series of short segments of DNA (Okazaki fragments) that will be joined together to form a finished lagging strand. The experiments that led to the discovery of Okazaki fragments gave evidence for which of the following ideas?
DNA polymerase is a directional enzyme that synthesizes leading and lagging strands during replication.
During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so?
DNA synthesis can take place only in the 5' to 3' direction.
After mixing a heat-killed, phosphorescent (light-emitting) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observation(s) would provide the best evidence that the ability to phosphoresce is a heritable trait?
Descendants of the living cells are also phosphorescent.
DNA replication is said to be semiconservative. What does this mean?
Each new double helix consists of one old and one new strand.
What is the most logical sequence of steps for splicing foreign DNA into a plasmid and inserting the plasmid into a bacterium?
Extract plasmid DNA from bacterial cells. Cut the plasmid DNA using restriction enzymes. Hydrogen-bond the plasmid DNA to nonplasmid DNA fragments. Use ligase to seal plasmid DNA to nonplasmid DNA. Transform bacteria with a recombinant DNA molecule.
Who conducted the X-ray diffraction studies that were key to the discovery of the structure of DNA?
Franklin
Which of the following statements correctly describes chromatin?
Heterochromatin is highly condensed, whereas euchromatin is less compact.
Why do histones bind tightly to DNA?
Histones are positively charged, and DNA is negatively charged.
Which of the following is true of DNA during interphase?
It exists as chromatin and is less condensed than mitotic chromosomes.
Which of the following statements accurately describes why Taq polymerase is used in PCR?
It is heat stable and can withstand the heating step of PCR.
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 helicase in DNA replication?
It untwists the double helix and separates the two DNA strands.
Which of the following statements describes one difference between DNA replication in prokaryotes and DNA replication in eukaryotes?
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many
What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA?
The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?
The DNA strands at the origin of replication will separate, but replication will not progress.
If a cell were unable to produce histone proteins, which of the following would be a likely effect?
The cell's DNA couldn't be packed into its nucleus.
Archaeologists unearthed a human skull with a small dried fragment of the scalp still attached. They extracted a tiny amount of DNA from the scalp tissue. How could they obtain sufficient DNA for an analysis of the ancient human's genes?
Use the polymerase chain reaction.
How is transformation in bacteria most accurately described?
assimilation of external DNA into a cell
Assume that you are trying to insert a gene into a plasmid. Someone gives you a preparation of genomic DNA that has been cut with restriction enzyme X. The gene you wish to insert has sites on both ends for cutting by restriction enzyme Y. You have a plasmid with a single site for Y, but not for X. Your strategy should be to
cut the DNA again with restriction enzyme Y and insert these fragments into the plasmid cut with the same enzyme.
The elongation of the leading strand during DNA synthesis __________.
depends on the action of DNA polymerase
Which "ingredients" for PCR and for the dideoxy chain-termination method of DNA sequencing are the same?
free nucleotides, DNA polymerase, DNA primers
During DNA replication, which of the following enzymes separates the DNA strands during replication?
helicase
In a nucleosome, the DNA is wrapped around __________.
histones
Bacteria that contain the plasmid, but not the eukaryotic gene, would grow
in all four types of broth
Bacteria containing a plasmid into which the eukaryotic gene has integrated would grow
in the ampicillin broth and the nutrient broth.
Which of the following is an example of "recombinant DNA technology"?
introducing a human gene into a bacterial plasmid
Gel electrophoresis separates DNA fragments on the basis of what characteristic?
length
During DNA replication, which of the following enzymes covalently connects segments of DNA?
ligase
In nucleotide excision repair, damaged DNA is excised by what enzyme(s)?
nuclease
What process repairs damage to a preexisting double helix?
nucleotide excision repair
Which of the following enzymes synthesizes short segments of RNA?
primase
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 binding proteins
What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?
telomeres
The leading and the lagging strands of DNA formed during DNA replication 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.
Bacteria that do not take up any plasmids would grow on which media?
the nutrient broth only
What is the function of DNA polymerase III?
to add nucleotides to the 3' end of a growing DNA strand
Why might they be conducting such an experiment?
to find which of the students has which alleles