The enzyme that synthesizes the new DNA strand during replication is
A. DNA polymerase I B. DNA polymerase III C. RNA primase D. DNA ligase E. Cholinesterase
B. DNA polymerase III
What is the function of the enzyme gyrase?
A. Starts DNA replication B. Stabilizes the single strands C. Adds the primer D. Relieves the torque from rapid untwisting E. None of the above
E. None of the above
Where are the Okazaki fragments found?
A. On the lagging strand B. On the leading strand C. At the replication origin D. In the cytoplasm E. On both strands
A. On the lagging strand
Name the enzyme that links Okazaki fragments
A. DNA polymerase I B. RNA primase C. DNA ligase D. Helicase E. ATP synthase
C. DNA ligase
The Meselson-Stahl experiment demonstrated that DNA replication is
A. Conservative
B. Semi-conservative
C. Disruptive
D. Differentiated
B. Semi-conservative
During DNA replication, what enzyme is responsible for untwisting the DNA helix?
DNA polymerase I RNA primase DNA ligase DNA polymerase III Helicase
E. Helicase
Chargaff’s rule states that
A. DNA strands are in antiparallel alignment
G matches with C, and T matches with A
B. The DNA molecule is a double helix
C. DNA transformation occurs when an organism
incorporates DNA from the environment
D. The nuclei of cells are totipotent
B. The DNA molecule is a double helix
Phosphodiester bonds link the 5´ of one nucleotide to the 3´ of the next nucleotide via the phosphate group. This bond is a strong covalent bond.
A. This is True
B. This is False
A. True
Why does replication proceed in opposite directions on the leading and lagging strands?
A. The polymerase enzyme needs a primer
B. DNA polymerase III can only add to the 3´ end of a strand
C. The Okazaki fragments are only on the leading strands
D.The parent strands are oriented in the same direction
E. Helicase only allows for replication of one strand at a time
B. DNA polymerase III can only add to the 3’ end of a strand
Mutations can be caused by copying mistakes, and by exposure to chemicals or electromagnetic radiation.
A. This is True
B. This is False
A. True
If a strand of DNA had the sequence AGTCCA, which of the following would be the complementary DNA strand?
A. CATGGT B. TCAGGT C. TCAAAU D. AGTCCA E. GGTTCA
B. TCAGGT
If a DNA molecule contains 40% thymine, how much guanine will it contain?
A. 10%
B. 20%
C. 30%
4. 40%
A. 10%
The enzyme telomerase attaches the last few bases on the lagging strand. As cells age, telomerase activity drops. What would happen to the chromosomes in the absence of telomerase activity?
A. Chromosome replication would be terminated
B. Okazaki fragments would not be linked together
C. Chromosomes would shorten during each division
D. The leading strand would become the lagging strand
E. The cells would become cancerous
C. Chromosomes would shorten during each divison
Which of the following is a potential mutagen?
A. UV light B. Chemicals C. Nicotine D. X-rays E. All of the above
E. All of the above
What would be the immediate consequence of a non-functional primase enzyme?
A. The strands would break due to the torsional strain from rapid untwisting
B. The helix could be opened
C. The DNA polymerase III enzyme would have nothing to bind to
D. The Okazaki fragments would not be linked together
E. The single DNA strands could not be held open
C. The DNA polymerase III enzyme would have nothing to bind to
Mixing a killed virulent strain of bacteria and a living strain of benign bacteria together produces virulent bacteria. What does this demonstrate?
A. Genes are inactivated when a cell dies
B. DNA can only be passed on during reproduction
C. Cells can pick up genes from the environment
D. All bacteria are virulent
E. None of the above
C. Cells can pick up genes from the environment
What was the key finding from Griffith’s experiments using live and heat-killed pathogenic bacteria?
Genetic material can be transferred from dead to live bacteria.
Which of the following is NOT a component of DNA?
A. The pyrimidine uracil
B. Five-carbon sugars
C. The purine adenine
D. Phosphate groups
A. The pyrimidine uracil
Chargaff studied the composition of DNA from different sources and found that
the proportions of A equal that of T and G equals C.
The bonds that hold two complementary strands of DNA together are
hydrogen bonds
The basic mechanism of DNA replication is semiconservative with two new molecules,
each with one new and one old strand
One common feature of all DNA polymerases is that they
synthesize DNA in the 5’-to-3’ direction
Which of the following is NOT part of the Watson-Crick model of the structure of DNA?
A. DNA is composed of two strands
B. The two DNA strands are oriented in parallel (5’-to-3’)
C. Purines bind to pyrimidines
D. DNA forms a double helix
B. The two DNA strands are oriented in parallel (5’-to-3’)
If one strand of a DNA is 5’ ATCGTTAAGCGAGTCA 3’; then the complementary strand would be:
5’TGACTCGCTTAACGAT3’
Hershey and Chase used radioactive phosphorus and sulfur to
differentially label DNA and protein
The Meselson and Stahl experiment used a density label to be able to
distinguish between newly replicated and old strands
The difference in leading-versus lagging-strand synthesis is a consequence of
both the physical structure of DNA and the action of polymerase enzyme
If the activity of DNA ligase was removed from replication, this would have a greater affect on
synthesis on the lagging strand versus the leading strand
Successful DNA synthesis requires all of the following EXCEPT
A. helicase
B. endonuclease
C. DNA primase
D. DNA ligase
B. endonuclease
The synthesis of telomeres
requires telomerase, which uses an internal RNA as template
When mutations that affected DNA replication were isolated two kinds were found. In cultures that were not synchronized (that is, not all dividing at the same time), one class put an immediate halt to replication, whereas the other put a much slower stop to the process. The first class affects functions at the replication fork like polymerase and primase. The second class affects functions necessary for
initiation: cells complete replication but cannot start a new round
Transformation, a transfer of virulence from one cell to another, was described in the experiments by the British chemist Roslind Franklin
False
The fact that some viruses use DNA to direct their heredity was demonstrated by finding:
radioactive phosphorus from a bacteriophage in a bacterium.
Genes are functional units of DNA that contain the information to specify traits and are located on chromosomes.
True
In the Avery experiments, removing nearly all of the protein from the dead S Streptococcus did not reduce the transforming activity. What properties of the transforming substance suggested that it was DNA?
when spun at high speeds in an ultracentrifuge, it migrated to the same level as DNA
Griffith infected mice with different strains of bacteria to demonstrate the presence of genetic material in bacteria. Which best describes Griffith’s explanation for one of his observations?
Genetic material in type S bacteria allowed them to evade the immune system.
The fact that some viruses use DNA to direct their heredity was demonstrated by finding:
radioactive phosphorus from a bacteriophage in a bacterium.
Genes are functional units of DNA that contain the information to specify traits and are located on chromosomes.
True
Chargaff found that the amount of adenine present in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. The Watson-Crick model, explains this because adenine will only properly hydrogen bond with thymine and guanine with cytosine.
True
When deoxyribose molecules bind in DNA, a phosphodiester bond is formed.
True
The 2-nanometer diameter is maintained because a small pyrimidine always pairs with a larger pyrimidine.
False
Chargaff found that the amount of adenine present in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. The Watson-Crick model, explains this because adenine will only properly hydrogen bond with thymine and guanine with cytosine.
True
When deoxyribose molecules bind in DNA, a phosphodiester bond is formed.
True
The 2-nanometer diameter is maintained because a small pyrimidine always pairs with a larger pyrimidine.
False
The two strands of DNA found in a double helix are:
Antiparrallel
What functional group is found at the 5′ end of a DNA strand?
a hydroxyl group
The nitrogenous bases are always attached to what carbon of the sugar in a nucleic acid?
5′
1′
The free hydroxyl group is attached to what carbon of the sugar in nucleic acids?
3′
According to Chargaff’s rules, if the DNA of a species contains 20% thymine, what percent of guanine will it contain?
30%
Which is true of standard Watson-Crick base-pairing in a molecule of DNA?
Purines base pair with pyrimidines.
Which feature of the DNA helix contributes to its stability?
hydrogen bonding between bases
A two-ringed nitrogenous base, such as adenine or guanine.
purine
The proportion of adenine always equals thymine; the proportion of guanine always equals cytosine.
Chargaff’s rules
A white, slightly acidic material extracted from nuclei, discovered by Miescher, known as DNA or RNA today.
nucleic acid
Each strand of a DNA molecule can be used to specify the other by base-pairing
complimentary
Linkage of a phosphate group to two sugars by means of a pair of ester bonds allowing DNA to form long chains.
phosphodiester bond
A single-ringed nitrogenous base, such as thymine or cytosine in DNA, or uracil or cytosine in RNA.
pyrimidine
A nucleotide is a subunit of DNA consisting of a five-carbon sugar, a PO4 group, a nitrogenous base.
True
What is the evidence for the conclusion that DNA replication is semiconservative?
DNA was first cultured in a medium containing 15N, and then transferred to a medium containing 14N.
The next generation of DNA was intermediate in weight between that grown on 14N medium and that grown on 15N medium.
DNA replication is called semiconservative. How much of the original duplex appears in the new duplex?
none
Half
A model for DNA replication in which one strand of a parental duplex remains intact in the daughter strands is called semiconservative.
True
All DNA polymerases add new bases to the 5’ end of existing strands. They synthesize in a 3’-to-5’ direction by extending a strand base-paired to the template.
False, All new bases are added to 3’ ends
The building blocks used in replication are deoxynucleotide triphosphates with high energy bonds; they do not require any additional energy.
True
In DNA replication, DNA polymerase III cannot attach nucleotides directly to a chain that is already paired with the parent strand. It attaches them to an RNA primer, and they are later attached to the parent chain
True
Replication on the leading strand occurs away from the replication fork instead of toward it.
False
The single-strand binding protein is needed in DNA replication because without the single-strand binder, the single strand might be cleaved or re-annealed.
True
DNA gyrase can relieve the torsional strain caused by unwinding and prevent transformation.
False
DNA polymerase I, unlike the other DNA polymerases, has 5′ to 3′ exonuclease activity that is essential during lagging strand replication to:
remove the RNA primers.
What statement best describes why DNA replication requires a helicase enzyme?
Complementary strands of the parental DNA need to be separated to create new daughter strands.
The DNA strand where replication occurs discontinuously and requires multiple priming events.
Lagging strand
Short sections of DNA synthesized discontinuously and then ligated together.
Okazaki fragments
The ability of a polymerase to remain attached to a template, primarily due to the action of the β subunit.
processivity
The partial unwinding of a DNA double helix to form two single stands where the replisome is formed.
replication fork
The DNA strand on which replication occurs continuously from one initial primer.
Leading strand
Enzymes that can chew away at an end of a DNA molecule.
exonuclease
A single functional unit consisting of the complete chromosome plus the origin in prokaryotes.
replicon
The topological state of the DNA that determines how the double helix coils in space.
supercoiling
Enzymes that can break phosphodiester bonds between nucleotides internally.
endonuclease
A multiprotein complex containing a primosome and two DNA pol III enzymes capable of DNA replication.
replisome
Bacterial replication
It initiates at an oriC sequence.
Two separate replisomes are loaded at the origin.
Replication proceeds bidirectionally.
There is one unique termination site.
What statement best describes why synthesis of the lagging strand is discontinuous?
DNA polymerase can synthesize DNA only in the 5′-3′ direction.
The main eukaryotic replication polymerase is a complex of two enzymes that work together are:
DNA polymerase delta and DNA polymerase epsilon
Since the first nucleotide cannot be linked in a newly synthesized strand in DNA replication, what is required?
an RNA primer
Telomerase is not activated in cancer cells.
False
An enzyme that synthesizes the ends of chromosomes using an internal RNA template is called a anamerase.
False, an enzyme that synthesizes the ends of chromosomes using an internal RNA template is called a telomerase.
Anameres are specialized structures that protect the ends of eukaryotic chromosomes from nucleases.
False, telomeres are specialized structures that protect the ends of eukaryotic chromosomes from nucleases.
Excision repair is considered to be a nonspecific repair pathway because:
bases surrounding the damaged base are also removed from the DNA.
A thymine dimer is the covalent linkage between two adjacent thymine bases in the DNA caused by UV radiation.
True
Endocision repair is a nonspecific form of repair in which a damaged region in the DNA is removed and replaced by DNA synthesis.
False, Exocision repair is a nonspecific form of repair in which a damaged region in the DNA is removed and replaced by DNA synthesis.
Errors from replication, which seldom occur, and damage induced by chemical agents or UV light, do not lead to mutations.
False, Errors from replication and damage induced by chemical agents or UV light can lead to mutations.
Without repair mechanisms, cells would accumulate mutations until inviability occurred.
True
Some repair systems are nonspecific, such as excision repair that removes and replaces damaged regions.
True
The enzyme photolyase uses energy from ATP to cleave thymine dimers caused by UV light.
False, The enzyme photolyase uses energy from visible light to cleave thymine dimers caused by UV light.
A mutagen is any agent that increases the number of mutations above background levels.
True
What was the key finding from Griffith’s experiments using live and heat-killed pathogenic bacteria?
Genetic material can be transferred from dead to live bacteria.
Which of the following is NOT a component of DNA?
a. The pyrimidine uracil
b. Five-carbon sugars
c. The purine adenine
d. Phosphate groups
a. The pyrimidine uracil
Chargaff studied the composition of DNA from different sources and found that
the proportions of A equal that of T and G equals C.
The bonds that hold two complementary strands of DNA together are
hydrogen bonds
The basic mechanism of DNA replication is semiconservative with two new molecules,
each with one new and one old strand.
One common feature of all DNA polymerases is that they
synthesize DNA in the 5′-to-3′ direction.
Which of the following is not part of the Watson–Crick model of the structure of DNA?
The two DNA strands are oriented in parallel (5′-to-3′)
If one strand of a DNA is 5′ ATCGTTAAGCGAGTCA 3′, then the complementary strand would be:
a. 5′ TAGCAATTCGCTCAGT 3′.
b. 5′ ACTGAGCGAATTGCTA 3′.
c. 5′ TGACTCGCTTAACGAT 3′.
d. 5′ ATCGTTAAGCGAGTCA 3′.
c. 5′ TGACTCGCTTAACGAT 3′
Hershey and Chase used radioactive phosphorus and sulfur to
differentially label DNA and protein.
The Meselson and Stahl experiment used a density label to be able to
distinguish between newly replicated and old strands.
The difference in leading- versus lagging-strand synthesis is a consequence of
both the physical structure of DNA and the action of polymerase enzyme.
If the activity of DNA ligase was removed from replication, this would have a greater affect on
synthesis on the lagging strand versus the leading strand.
Successful DNA synthesis requires all of the following except
a. helicase.
b. endonuclease.
c. DNA primase.
d. DNA ligase.
b. endonuclease
The synthesis of telomeres
requires telomerase, which uses an internal RNA as a template.
When mutations that affected DNA replication were isolated, two kinds were found. In cultures that were not synchronized (that is, not all dividing at the same time), one class put an immediate halt to replication, whereas the other put a much slower stop to the process. The first class affects functions at the replication fork like polymerase and primase. The second class affects functions necessary for
initiation: cells complete replication but cannot start a new round.
Serves as a template for a new DNA molecule
Parental DNA strands
Building blocks needed to assemble a new DNA molecule
NUCLEOSIDE TRIPHOSPHATES
Enzymes required to replicate DNA
DNA primase DNA gyrase DNA polymerases DNA ligase DNA helicase
Not directly required for DNA replication
Nucleoside Monophosphates
Ribose
Telomeres are specialized structures that are found at the ends of prokaryotic chromosomes
False
The prokaryotic genome is composed of a circular DNA molecule which has no ends. Telomeres are specialized structures found at the ends of eukaryotic chromosomes.
Telomeres protect the end of chromosomes from nucleases and help maintain the integrity of linear chromosomes
True
Telomeres are composed of specific DNA sequences, but they are not made by the replication complex
Telomeres are composed of a long DNA sequence that is repeated twice
False
Telomeres are composed of short DNA sequences that are repeated many times
Telomeres are replication of telomeres by the enzyme telomerase, which utilizes an internal RNA strand as a template rather than a strand of parental DNA
True
Telomerase is used to lengthen the end of the lagging stand in a linear DNA molecule
Without the replication of telomeres by the enzyme telomerase, linear chromosomes would gradually get longer with each round of replication
False
Without the replication of telomeres by the enzyme telomerase, linear chromosomes would gradually get shorter with each round of replication
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
During replication of a linear DNA molecule, the leading strand can be completely replicated, but when the last RNA primer is removed from the lagging strand, DNA polymerases cannot replace it with DNA
Telomerase uses a internal RNA template to lengthen the telomeres, which are composed of repeated nucleotide sequences that are complementary to the RNA template
True
Multiple rounds of synthesis by telomerase produce the repeated nucleotide sequences
Which characteristic of DNA allows each strand of the molecule to act as a template that specifies the exact sequence of nucleotides in the other strand?
Complementarity of the bases
In DNA, adenine always pairs with thymine and guanine always pairs with cyrosine, we refer to this pattern of base-pairing as complementary, which means that although the strands are not identical, they each can be used to specify the other by base-pairing if the sequence of one strand is ATGC, then the complementary strand sequence must be TACG. This characteristic is critical for DNA replication and gene expression