Question 1

When comparing the three key models of DNA replication,the model that included the separation of the two strands of the original DNA (template)and using those strands as templates to synthesize two new DNA strands is called:

Accepted Answer

Semiconservative replication is the model that includes the separation of the two strands of the original DNA and using them as templates to synthesize two new DNA strands. In this model, each of the new DNA molecules is composed of one strand from the original molecule and one newly synthesized strand. This model has been supported by numerous experiments, including the famous Meselson-Stahl experiment. Conservative replication suggests that the original DNA molecule remains intact and completely acts as a template for the synthesis of a new DNA molecule. Dispersive replication suggests that the original DNA molecule is cut into small fragments, and each fragment is replicated independently. Both of these models have been refuted by experimental evidence. Liberal replication is not a commonly used term in the field of molecular biology.

Question 2

If Escherichia coli,grown for a period of time in ¹⁵N,is transferred to ¹⁴N for one generation of DNA replication,the resulting DNA should have ¹⁴N added to all "new" DNA.If conservative replication is occurring,the ¹⁴N-containing "new" DNA will compose:

Accepted Answer

Conservative replication means that the original DNA molecule is conserved, and a completely new molecule is synthesized. Therefore, if Escherichia coli is transferred to a medium with ¹⁴N for one generation, the new DNA (containing ¹⁴N) will be found in both strands of DNA in half of all bacterial chromosomes, as the other half will retain the original DNA strands.

Question 3

Initiation of replication occurs at an "origin of replication" site that typically includes an AT-rich region.Initiation benefits from these AT-rich regions because:

Accepted Answer

Adenine and thymine only form two hydrogen bonds, while guanine and cytosine form three hydrogen bonds. This means that the AT-rich region will be more easily separated during the unwinding process needed to initiate replication.

Question 4

The following data were obtained from three organisms : an RNA virus,a DNA virus,and a wombat (an Australian mammal).Which is likely the sample from the RNA virus?

Accepted Answer

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Question 5

In eukaryotic DNA replication,re-association of histones with newly formed DNA is accomplished by:

Accepted Answer

The re-association of histones with newly formed DNA is accomplished by chromatin assembly factor 1 (CAF-1) and histones binding to the sliding clamp structure. This allows for efficient and accurate assembly of chromatin on the newly synthesized DNA strands. Choice A is incorrect because histones do not spontaneously associate with DNA, but are actively guided by protein factors. Choice B is incorrect because CAF-1 does not attach to the primase enzyme, but rather interacts with the sliding clamp. Choice C is incorrect because histones can associate with new DNA as it is being synthesized, not just after the entire chromosome has finished replicating. Choice D is incorrect because histones must release DNA during replication in order for the DNA polymerase to access the DNA template.

Question 6

Cell-cycle progress enables the initiation of genome replication by:

Accepted Answer

Cell-cycle progress enables the initiation of genome replication by providing Cdc6 and Cdt1, which aid assembly of initiation components at the origin of replication. These proteins help to load the MCM helicase onto DNA at the origin, which is the initial step in replication initiation. Other factors, such as the ORC protein and helicase proteins, may also be involved in this process but are not directly activated by cell-cycle progress. Histone degradation also plays a role in replication initiation, but it occurs after MCM loading and is not directly activated by cell-cycle progress. Therefore, the best choice is B.

Question 7

Topoisomerase and helicase have distinct functions that include which of the following?

Accepted Answer

Helicase is responsible for unwinding the double helix (separating strands) during DNA replication, allowing the two strands to be copied.

Question 8

Experiments on chromosome structure and function have shown that in eukaryotic chromatids:

Accepted Answer

Eukaryotic chromatids have multiple DNA replication origins, resulting in more than one DNA replicating point per chromatid. This allows for efficient and timely DNA replication during S phase of the cell cycle.

Question 9

In 1959,Arthur Kornberg isolated DNA polymerase activity from Escherichia coli cells,revealing its ability to copy DNA by mixing ___________________ in a tube and measuring synthesis of a DNA strand.

Accepted Answer

Arthur Kornberg isolated DNA polymerase activity from Escherichia coli cells by mixing dATP, dGTP, dTTP, dCTP, template DNA, and pure DNA polymerase enzyme in a tube and measuring the synthesis of a DNA strand. This experiment demonstrated that DNA polymerase could copy DNA in vitro, leading to significant advancements in the understanding of DNA replication. Choice D includes all the necessary components for this experiment.

Question 10

Linus Pauling proposed at one time that the DNA molecule was,in fact,a triple helix.If so,how would this situation affect cellular division?

Accepted Answer

The fact that the DNA had three nucleotide strands would make it difficult to replicate the DNA and reassemble the copies. The machinery for DNA replication and cellular division is designed to handle a double-stranded DNA molecule, and a triple-stranded DNA molecule would be difficult to replicate without errors. This would likely result in cell death or mutations, and the organism would not be able to divide properly. Therefore, choice D is the correct answer.

Question 11

The complexity of lagging strand replication is necessary because:

Accepted Answer

The lagging strand must be synthesized in consecutive small fragments because polymerization occurs only in the 5′ to 3′ direction. This is necessary to ensure that the DNA synthesis occurs smoothly without introducing any errors or mismatches. The complexity of lagging strand replication is mainly due to this reason. The other options are not correct as they do not accurately describe the challenges associated with lagging strand replication.

Question 12

The spontaneous (though infrequent)change of a nitrogenous base to a slightly distinct form is called:

Accepted Answer

The spontaneous change of a nitrogenous base to a slightly distinct form is called tautomerization. This can occur due to the shifting of hydrogen atoms in the base, leading to a temporary alteration in its structure. Tautomerization can lead to mutations in DNA, as the altered base may pair with an incorrect partner base during replication.

Question 13

When replicating the end of a chromosome,the lagging strand cannot copy the last ~10 nucleotides at the end of the chromosome.As a result,chromosomes contain telomere sequences at their ends,which are defined as:

Accepted Answer

Telomere sequences are noncoding, repetitive sequences that can be copied independently of the replisome. They serve as a buffer against the loss of genetic information during DNA replication, as the lagging strand cannot copy the last ~10 nucleotides at the end of the chromosome. These repeated sequences protect the genetic information at the end of the chromosome from being degraded or lost during subsequent cell divisions.

Question 14

Telomerase activity relies upon ________________ for appropriate priming.

Accepted Answer

Telomerase contains a short, telomeric RNA sequence within its structure which serves as a template for the synthesis of telomeres. The RNA template provides the appropriate priming for telomerase activity.

Question 15

The replisome contains a protein subunit responsible for unwinding the double helix to enable DNA replication.This subunit/enzyme is named:

Accepted Answer

Helicase is the enzyme responsible for unwinding the double helix during DNA replication. It is a subunit of the replisome, which coordinates the synthesis of new DNA strands. The other proteins listed (pol III holoenzyme, beta clamp, primase, and ligase) are also involved in DNA replication, but do not directly participate in the unwinding process like helicase does.

Question 16

The replisome contains a protein subunit responsible for attaching free ends of DNA on the newly formed strand.This subunit/enzyme is named:

Accepted Answer

The enzyme responsible for attaching free ends of DNA on the newly formed strand is ligase. Ligase seals any nicks or gaps in the phosphodiester backbone of DNA by catalyzing the formation of phosphodiester bonds between adjacent nucleotides. The other options are not involved in this specific function.

Question 17

If Escherichia coli,grown for a period of time in ¹⁵N,is transferred to ¹⁴N for one generation of DNA replication,the resulting DNA should have ¹⁴N added to all "new" DNA.If semiconservative replication is occurring,the ¹⁴N-containing "new" DNA will compose:

Accepted Answer

Semiconservative replication means that each new DNA molecule consists of one old strand and one new strand. Therefore, if E. coli is transferred to a medium with ¹⁴N for one generation, the new DNA synthesized in this medium will be found in one strand of all bacterial chromosomes, consistent with the semiconservative model of DNA replication.

Question 18

When comparing the three key models of DNA replication,the model that included the synthesis of a brand new double-stranded DNA molecule from an original molecule was named:

Accepted Answer

Conservative replication suggests that the entire double-stranded DNA molecule serves as a template for a new molecule of DNA, which would be entirely synthesized from new nucleotides, leaving the original DNA molecule intact. This contrasts with semiconservative replication, where each strand of the original DNA serves as a template for a new strand, and dispersive replication, where segments of the original DNA and newly synthesized DNA are interspersed in both strands of each daughter molecule.

Question 19

The Meselson-Stahl experiment made clear predictions regarding experimental outcomes if dispersive,conservative,or semiconservative DNA replication was occurring in their Escherichia coli cells.To begin the experiment,cells were grown for a period of time in media containing __________ to label the chromosome.

Accepted Answer

The Meselson-Stahl experiment used heavy nitrogen (15N) to label the chromosome of Escherichia coli cells. This allowed for the detection and separation of different DNA molecules based on their density using centrifugation.

Question 20

The Meselson-Stahl experiment made clear predictions regarding experimental outcomes if dispersive,conservative,or semiconservative DNA replication was occurring in their Escherichia coli cells.This experiment enables the detection of "new" and "old" DNA by assessing the _______________ of DNA molecules in the cells.

Accepted Answer

The Meselson-Stahl experiment involved labeling the DNA of E. coli cells with a heavy isotope of nitrogen, allowing the researchers to track the distribution of isotope-labeled DNA in subsequent generations. By performing centrifugation gradient assays, the researchers were able to separate DNA molecules based on their density. Conservative replication would result in two distinct bands of DNA, one consisting entirely of heavy-labeled DNA and the other entirely of light-labeled DNA. Dispersive replication would result in a smear of intermediate-density DNA molecules. Semiconservative replication, the actual mechanism of DNA replication, would result in two bands, one consisting entirely of light-labeled DNA and one consisting of molecules with intermediate densities. Thus, the density of the DNA molecules allowed the researchers to distinguish between the different modes of replication.

Quiz 7: Dna: Structure and Replication

When comparing the three key models of DNA replication,the model that included the separation of the two strands of the original DNA (template) and using those strands as templates to synthesize two new DNA strands is called:

If Escherichia coli,grown for a period of time in ¹⁵N,is transferred to ¹⁴N for one generation of DNA replication,the resulting DNA should have ¹⁴N added to all "new" DNA.If conservative replication is occurring,the ¹⁴N-containing "new" DNA will compose:

Initiation of replication occurs at an "origin of replication" site that typically includes an AT-rich region.Initiation benefits from these AT-rich regions because:

The following data were obtained from three organisms : an RNA virus,a DNA virus,and a wombat (an Australian mammal) .Which is likely the sample from the RNA virus?

In eukaryotic DNA replication,re-association of histones with newly formed DNA is accomplished by:

Cell-cycle progress enables the initiation of genome replication by:

Topoisomerase and helicase have distinct functions that include which of the following?

Experiments on chromosome structure and function have shown that in eukaryotic chromatids:

In 1959,Arthur Kornberg isolated DNA polymerase activity from Escherichia coli cells,revealing its ability to copy DNA by mixing ___________________ in a tube and measuring synthesis of a DNA strand.

Linus Pauling proposed at one time that the DNA molecule was,in fact,a triple helix.If so,how would this situation affect cellular division?

The complexity of lagging strand replication is necessary because:

The spontaneous (though infrequent) change of a nitrogenous base to a slightly distinct form is called:

When replicating the end of a chromosome,the lagging strand cannot copy the last ~10 nucleotides at the end of the chromosome.As a result,chromosomes contain telomere sequences at their ends,which are defined as:

Telomerase activity relies upon ________________ for appropriate priming.

The replisome contains a protein subunit responsible for unwinding the double helix to enable DNA replication.This subunit/enzyme is named:

The replisome contains a protein subunit responsible for attaching free ends of DNA on the newly formed strand.This subunit/enzyme is named:

If Escherichia coli,grown for a period of time in ¹⁵N,is transferred to ¹⁴N for one generation of DNA replication,the resulting DNA should have ¹⁴N added to all "new" DNA.If semiconservative replication is occurring,the ¹⁴N-containing "new" DNA will compose:

When comparing the three key models of DNA replication,the model that included the synthesis of a brand new double-stranded DNA molecule from an original molecule was named:

Quiz 7: Dna: Structure and Replication

When comparing the three key models of DNA replication,the model that included the separation of the two strands of the original DNA (template) and using those strands as templates to synthesize two new DNA strands is called:

If Escherichia coli,grown for a period of time in 15N,is transferred to 14N for one generation of DNA replication,the resulting DNA should have 14N added to all "new" DNA.If conservative replication is occurring,the 14N-containing "new" DNA will compose:

Initiation of replication occurs at an "origin of replication" site that typically includes an AT-rich region.Initiation benefits from these AT-rich regions because:

The following data were obtained from three organisms : an RNA virus,a DNA virus,and a wombat (an Australian mammal) .Which is likely the sample from the RNA virus?

In eukaryotic DNA replication,re-association of histones with newly formed DNA is accomplished by:

Cell-cycle progress enables the initiation of genome replication by:

Topoisomerase and helicase have distinct functions that include which of the following?

Experiments on chromosome structure and function have shown that in eukaryotic chromatids:

In 1959,Arthur Kornberg isolated DNA polymerase activity from Escherichia coli cells,revealing its ability to copy DNA by mixing ___________________ in a tube and measuring synthesis of a DNA strand.

Linus Pauling proposed at one time that the DNA molecule was,in fact,a triple helix.If so,how would this situation affect cellular division?

The complexity of lagging strand replication is necessary because:

The spontaneous (though infrequent) change of a nitrogenous base to a slightly distinct form is called:

When replicating the end of a chromosome,the lagging strand cannot copy the last ~10 nucleotides at the end of the chromosome.As a result,chromosomes contain telomere sequences at their ends,which are defined as:

Telomerase activity relies upon ________________ for appropriate priming.

The replisome contains a protein subunit responsible for unwinding the double helix to enable DNA replication.This subunit/enzyme is named:

The replisome contains a protein subunit responsible for attaching free ends of DNA on the newly formed strand.This subunit/enzyme is named:

If Escherichia coli,grown for a period of time in 15N,is transferred to 14N for one generation of DNA replication,the resulting DNA should have 14N added to all "new" DNA.If semiconservative replication is occurring,the 14N-containing "new" DNA will compose:

When comparing the three key models of DNA replication,the model that included the synthesis of a brand new double-stranded DNA molecule from an original molecule was named:

If Escherichia coli,grown for a period of time in ¹⁵N,is transferred to ¹⁴N for one generation of DNA replication,the resulting DNA should have ¹⁴N added to all "new" DNA.If conservative replication is occurring,the ¹⁴N-containing "new" DNA will compose:

If Escherichia coli,grown for a period of time in ¹⁵N,is transferred to ¹⁴N for one generation of DNA replication,the resulting DNA should have ¹⁴N added to all "new" DNA.If semiconservative replication is occurring,the ¹⁴N-containing "new" DNA will compose: