Chapter 14 HW
Which of the following is a characteristic of double-stranded DNA?
2 nanometers in width, 10 base pairs per turn, and .34 nanometers per base pair
Arrange the following proteins in the proper order in which they participate in DNA replication 1 = Primase 2 = Helicase 3 = Single-strand binding proteins 4 = DNA polymerase I
2, 3, 1, 4
If 28% of the nucleotides in a DNA molecule contain the base T, what percent will contain the base G?
22
DNA polymerases use their ________ activity to remove a mismatched basepair.
3' -> 5' exonuclease
DNA Polymerase uses what kind of enzymatic activity in the process of proofreading?
3' to 5' exonuclease activity to remove the mismatched bases 5' to 3' polymerase activity to replace the excised bases
Which of the following DNA sequences is complementary to 5' TAGAC 3'?
5' GTCTA 3'
According to Chargaff's rule, which of the following statements about double-stranded DNA is TRUE?
A = T and C = G and A+G = C+T
______ acts on the lagging strand to remove RNA primers and replace them with DNA.
DNA Pol I
_____ does not appear to play a role in replication but is involved in DNA repair
DNA Pol II
______ is the main replication enzyme; it is responsible for the bulk of DNA synthesis
DNA Pol III
How do DNA polymerase I and DNA Polymerase III differ?
DNA Polymerase III synthesizes the majority of the DNA, while DNA Polymerase I synthesizes DNA in the regions where the RNA primers were laid down on the lagging strand
RNA primers are removed by the action of the enzyme
DNA pol I
Which of the following synthesizes the daughter strands during DNA replication?
DNA polymerase
Which of the following synthesizes the new DNA strand?
DNA polymerase
The enzyme that travels along the leading strand assembling new nucleotides on a growing new strand of DNA is
DNA polymerase III
Enzymes required to replicate DNA
DNA primase DNA gyrase DNA polymerases DNA ligase DNA helicase
If DNA ligase was nonfunctional, what would be a likely consequence?
DNA replication would occur, but the lagging strand would have numerous single-strand breaks
Evaluate the statements below and determine which is the best explanation for why bacteria don't use telomerase.
Bacteria have circular chromosomes that do not shorten.
How is bacterial DNA replication different from eukaryotic DNA replication?
Bacterial DNA replication moves out from the origin of replication in two directions, while eukaryotic DNA replication moves out from the origin of replication in only one direction
How is bacterial DNA replication similar to eukaryotic DNA replication?
Both bacterial and eukaryotic DNA replication is semi-conservative
Which of the following statements about the DNA double helix is TRUE?
Complementary base pairing across the double helix allows information to be transferred via RNA transcription and DNA replication
Why do complementary nucleotides across the double stranded DNA bond together using hydrogen bonds rather than covalent bonds?
Covalent bonds would be too strong to allow the double helix to easily separate and make templates available for replication and transcription
Before the lagging strand can begin assembling new DNA nucleotides, which of the following must occur?
Primase constructs a short RNA primer
Which of the following statements is TRUE?
Primase, an RNA polymerase, is capable of synthesizing RNA without attaching the incoming nucleotide to a pre-existing, free, 3' hydroxyl group
Cells can repair damage that produces breaks in DNA using enzymes related to those involved in ________during meiosis.
Recombination
If an organism had a DNA polymerase III that lost its ability to proofread, which of the following statements would be TRUE?
The mutation rate would increase, and more substitutions would be seen in its DNA
Evaluate the statements below and select the one that best explains why is the replication machinery found at the replication fork?
The replication machinery must have access to the leading and lagging strands for replication, and it must be able to open and stabilize the template DNA
Which of the following is NOT a mechanism that cells use to ensure their DNA is accurately replicated?
When mismatched nucleotides are detected, DNA polymerase will begin to synthesize DNA in the 3' to 5' direction to correct the mistake
Telomerase is unique because it contains
an RNA molecule
Proofreading by DNA polymerase involves the removal of
several bases on the newly-synthesized strand of DNA
DNA polymerases cannot replicate
the 3' end of linear chromosomes
Which of the following DNA molecules is the most stable?
GCGTGCAC CGCACGTG
The enzyme that unwinds a segment of the DNA molecule is
Helicase
The proofreading function of DNA polymerase reduces the error rate from about one in a million basepairs to about one in a ________ basepairs.
Hundred million
With each cell division, chromosomes gradually shorten in the absence of telomerase activity.
True
When telomerase is added to cells grown in culture, their lifespan decreases relative to controls that have no telomerase added.
False
DNA replication in bacteria begins at
A single origin and proceeds in both directions
The genetic material in bacteria is
Double-stranded DNA
Without the replication of telomeres by the enzyme telomerase, linear chromosomes would gradually get longer with each round of replication
False
Telomeres are replicated by an enzyme called telomerase, which utilizes an internal RNA strand as a template rather than a strand of parental DNA
True
In _______, the damaged section of one DNA strand is removed and replaced with new DNA that is synthesized using the undamaged strand as a template
Excision repair
"Proofreading" effectively eliminates all errors during DNA replication
False
Any agent that decreases the number of mutations below background levels is called a mutagen
False
Because the 2 strands of a DNA molecule run in opposite directions, they are said to be bidirectional
False
Cells cannot escape exposure to mutagens, but they have evolved systems that enable them to repair all of the damage
False
Cells that divide frequently tend to have relatively low levels of telomerase.
False
DNA pol III can initiate DNA synthesis
False
DNA polymerases can add new DNA nucleotides only to the 5' end of an existing strand
False
During embryonic and childhood development in humans, telomerase activity is relatively low compared to the level of activity in most somatic cells of an adult.
False
During replication of a linear DNA molecule, the lagging strand can be completely replicated, but when the last RNA primer is removed from the leading strand, DNA polymerases cannot replace it with DNA
False
Error correcting mechanisms during DNA replication cause cells to accumulate errors at a higher rate, which leads to higher levels of deleterious or lethal mutations
False
Telomeres are composed of a long DNA sequence that is repeated twice
False
Telomeres are specialized structures that are found at the ends of prokaryotic chromosomes.
False
The DNA strand that grows away from the replication fork is synthesized continuously from one initial primer
False
The DNA strand that grows toward the replication fork is synthesized discontinuously in short pieces called Okazaki fragments
False
The DNA strand that is synthesized continuously is called the lagging strand
False
The DNA strand that is synthesized discontinuously is called the leading strand
False
The activity of telomerase in most mature somatic cells is kept high by increasing the expression of the gene encoding this enzyme.
False
Which of the following best describes the function of telomerase at the telomere?
It adds new DNA to the longer strand of the telomere overhang
What might result for a eukaryotic organism that lacked functional telomerase?
It would have shorter chromosomes with every round of mitosis, leading to abnormal cells
Serves as a template for a new DNA molecule
Parental DNA strands
The correct structure of DNA monomers can be presented as
Phosphate-sugar-base
A system that only repairs thymine dimers is ______
Photorepair
Repair systems that use a single repair mechanism to repair multiple types of damage in DNA are called _______ systems.
Nonspecific repair
Not directly required for DNA replication
Nucleoside monophosphates Ribose
Building blocks needed to assemble a new DNA molecule
Nucleoside triphosphates
Which of the following is required to replicate the lagging strand of DNA?
Okazaki fragments, primase, and DNA ligase
DNA replication is said to be
Semi-conservative
Telomeres protect the ends of chromosomes from nucleases and help maintain the integrity of linear chromosomes
True
Repair systems that target a single type of damage in DNA and repair only that type of damage are called _______ systems.
Specific repair
A mutation has occurred that has made UvrC non-functional. What result will this have on damaged DNA?
The damaged DNA will be recognized, but no cut will be made to the damaged segment
Which statement about the major and minor grooves is TRUE
The major and minor grooves are important for DNA binding proteins to attach to the DNA
Which of the following prevents supercoiling of the DNA strands ahead of the replication bubble?
Topoisomerase
Agents that damage DNA can lead to mutations
True
All cells that have been examined show multiple pathways for repairing damaged DNA and for reversing errors that occur during replication
True
Although most mutations are harmful, some may be beneficial.
True
Because the 2 strands of a DNA molecule run in opposite directions, and because DNA polymerases can synthesize new strands only in the 5' to 3' direction, polymerases on opposite strands must synthesize DNA in opposite directions
True
Cancer cells generally have high levels of telomerase activity, which allows them to divide indefinitely without the chromosomes getting shorter and shorter
True
DNA ligase joins adjacent Okazaki fragments together into a complete strand
True
DNA polymerases cannot initiate synthesis of a new DNA strand; they can only add bases to an existing strand
True
Each Okazaki fragment has its own primer
True
If DNA polymerase III (DNA poly III) could add nucleotides in either direction, Okazaki fragments would no longer form
True
In addition to errors that occur during DNA replication, cells are constantly exposed to agents that can damage DNA, such as UV light, X-rays, and chemicals in the environment
True
Many DNA polymerases have 3'-to-5'exonuclease activity that allows "proofreading" and replacement of incorrect bases
True
Mice with low telomerase activity appear to be normal for up to six generations, but they show steadily decreasing telomere length that eventually leads to nonviable offspring.
True
Telomerase uses an internal RNA template to lengthen the telomeres, which are composed of repeated nucleotide sequences that are complementary to the RNA template
True
What protein cuts the damaged DNA strand?
UvrC
Which protein has a helicase function?
UvrD
UV light damages DNA by causing
covalent bonds to form between thymine nucleotides next to each other on the same DNA strand
