Chapter 16-17 Test - AP Biology
- 1.
For a couple of decades, biologists knew the nucleus contained DNA and proteins. The prevailing opinion was that the genetic material was proteins, and not DNA. The reason for this belief was that proteins are more complex than DNA. This is because
- A.
Proteins have a greater variety of three-dimensional forms than does DNA.
- B.
Proteins have two different levels of structural organization; DNA has four.
- C.
Proteins are made of 20 amino acids and DNA is made of four nucleotides.
- D.
Only A and C are correct.
- E.
A, B, and C are correct.
Correct Answer
D. Only A and C are correct.Explanation
The prevailing opinion that proteins were the genetic material instead of DNA was based on the belief that proteins are more complex than DNA. This is because proteins have a greater variety of three-dimensional forms and are made up of 20 different amino acids, while DNA is made up of only four nucleotides. Therefore, options A and C are correct in explaining why proteins were initially thought to be the genetic material.Rate this question:
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- 2.
In his transformation experiments, Griffith observed that
- A.
Mutant mice were resistant to bacterial infections.
- B.
Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
- C.
Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
- D.
Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.
- E.
Mice infected with a pathogenic strain of bacteria can spread the infection to other mice.
Correct Answer
B. Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.Explanation
Griffith's transformation experiments showed that mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form. This implies that there is a transfer of genetic material from the dead pathogenic cells to the living nonpathogenic cells, causing them to become pathogenic. This observation provided evidence for the concept of bacterial transformation, which is the transfer of genetic material between bacteria.Rate this question:
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- 3.
What does transformation involve in bacteria?
- A.
The creation of a strand of DNA from an RNA molecule
- B.
The creation of a strand of RNA from a DNA molecule
- C.
The infection of cells by a phage DNA molecule
- D.
The type of semiconservative replication shown by DNA
- E.
Assimilation of external DNA into a cell
Correct Answer
E. Assimilation of external DNA into a cellExplanation
Transformation in bacteria involves the assimilation of external DNA into a cell. This process allows bacteria to take up and incorporate foreign DNA into their own genome. It is a natural mechanism that allows bacteria to acquire new genetic material, such as antibiotic resistance genes, from their environment. This ability to incorporate foreign DNA is a key feature of bacterial adaptability and evolution.Rate this question:
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- 4.
Avery and his colleagues purified various chemicals from pathogenic bacteria and showed that ________ was (were) the transforming agent.
- A.
DNA
- B.
Protein
- C.
Lipids
- D.
Carbohydrates
- E.
Phage
Correct Answer
A. DNAExplanation
Avery and his colleagues purified various chemicals from pathogenic bacteria and demonstrated that DNA was the transforming agent. This suggests that DNA is responsible for transferring genetic information and causing hereditary changes in bacteria. This finding was significant in understanding the role of DNA in genetics and further supported the idea that DNA is the genetic material.Rate this question:
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- 5.
Tobacco mosaic virus has RNA rather than DNA as its genetic material. In a hypothetical situation where RNA from a tobacco mosaic virus is mixed with proteins from a related DNA virus, the result could be a hybrid virus. If that virus were to infect a cell and reproduce, what would the resulting "offspring" viruses be like?
- A.
Tobacco mosaic virus
- B.
The related DNA virus
- C.
A hybrid: tobacco mosaic virus RNA and protein from the DNA virus
- D.
A hybrid: tobacco mosaic virus protein and nucleic acid from the DNA virus
- E.
A virus with a double helix made up of one strand of DNA complementary to a strand of RNA surrounded by viral protein
Correct Answer
A. Tobacco mosaic virusExplanation
If RNA from a tobacco mosaic virus is mixed with proteins from a related DNA virus, the resulting "offspring" viruses would be a hybrid: tobacco mosaic virus protein and nucleic acid from the DNA virus. This is because the RNA from the tobacco mosaic virus would provide the genetic material, while the proteins from the DNA virus would contribute to the structure of the virus.Rate this question:
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- 6.
The following scientists made significant contributions to our understanding of the structure and function of DNA. Place the scientists' names in the correct chronological order, starting with the first scientist(s) to make a contribution. I. Avery, McCarty, and MacLeod II. Griffith III. Hershey and Chase IV. Meselson and Stahl V. Watson and Crick
- A.
V, IV, II, I, III
- B.
II, I, III, V, IV
- C.
I, II, III, V, IV
- D.
I, II, V, IV, III
- E.
II, III, IV, V, I
Correct Answer
B. II, I, III, V, IVExplanation
The correct answer is II, I, III, V, IV. This represents the chronological order of the scientists' contributions to our understanding of the structure and function of DNA. Griffith was the first to make a contribution, followed by Avery, McCarty, and MacLeod. Hershey and Chase made their contribution next, followed by Watson and Crick. Meselson and Stahl made their contribution last.Rate this question:
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- 7.
After mixing a heat-killed, phosphorescent strain of bacteria with a living non-phosphorescent strain, you discover that some of the living cells are now phosphorescent. The best evidence that the ability to fluoresce is a heritable trait would be an observation that
- A.
DNA passed from the heat-killed strain to the living strain.
- B.
Protein passed from the heat-killed strain to the living strain.
- C.
The phosphorescence in the living strain is especially bright.
- D.
Descendants of the living cells are also phosphorescent.
- E.
Both DNA and protein passed from the heat-killed strain to the living strain.
Correct Answer
D. Descendants of the living cells are also phosphorescent.Explanation
The best evidence that the ability to fluoresce is a heritable trait would be if the descendants of the living cells are also phosphorescent. This suggests that the trait is being passed down from one generation to the next, indicating that it is a heritable trait. The other options do not provide direct evidence of heritability.Rate this question:
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- 8.
In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?
- A.
DNA does not contain sulfur, whereas protein does.
- B.
DNA contains phosphorus, but protein does not.
- C.
DNA contains nitrogen, whereas protein does not.
- D.
A and B only
- E.
A, B, and C
Correct Answer
D. A and B onlyExplanation
Hershey and Chase used the fact that DNA contains phosphorus, while protein does not, to determine whether DNA or protein is the genetic material. They also used the fact that DNA does not contain sulfur, whereas protein does. These observations allowed them to conclude that DNA, not protein, is the genetic material.Rate this question:
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- 9.
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?
- A.
There is no radioactive isotope of nitrogen.
- B.
Radioactive nitrogen has a half-life of 100,000 years, and the material would be too dangerous for too long.
- C.
Meselson and Stahl already did this experiment.
- D.
Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
- E.
Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.
Correct Answer
E. Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.Explanation
Labeling the nitrogens of the DNA instead of the phosphates would not work because amino acids and proteins also have nitrogen atoms. Therefore, the radioactivity from the labeled nitrogens would not be able to distinguish between DNA and proteins.Rate this question:
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- 10.
When T2 phages infect bacteria and make more viruses in the presence of radioactive sulfur, what is the result?
- A.
The viral DNA will be radioactive.
- B.
The viral proteins will be radioactive.
- C.
The bacterial DNA will be radioactive.
- D.
Both A and B
- E.
Both A and C
Correct Answer
B. The viral proteins will be radioactive.Explanation
When T2 phages infect bacteria and make more viruses in the presence of radioactive sulfur, the result is that the viral proteins will be radioactive. This is because T2 phages use the host cell's machinery to produce new viral proteins, and if radioactive sulfur is present, it will be incorporated into these proteins during synthesis. The viral DNA, on the other hand, does not directly interact with sulfur during replication, so it will not be radioactive. The bacterial DNA will also not be radioactive as it is separate from the viral replication process. Therefore, the correct answer is that the viral proteins will be radioactive.Rate this question:
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- 11.
Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately, what percentage of the nucleotides in this sample will be thymine?
- A.
12
- B.
24
- C.
31
- D.
38
- E.
It cannot be determined from the information provided.
Correct Answer
B. 24Explanation
In DNA, cytosine (C) always pairs with guanine (G), and thymine (T) always pairs with adenine (A). The percentage of cytosine (C) in DNA will be the same as the percentage of guanine (G). Therefore, the percentage of thymine (T) will be the same as the percentage of adenine (A).
If cytosine makes up 38% of the nucleotides, then guanine also makes up 38% of the nucleotides.
The total percentage of cytosine (C) and guanine (G) combined is 38% + 38% = 76%.
Since the total percentage of nucleotides is 100%, and cytosine (C) and guanine (G) together make up 76%, the remaining percentage for thymine (T) and adenine (A) combined will be 100% - 76% = 24%.
Because adenine (A) pairs with thymine (T), the percentage of thymine (T) will be the same as the percentage of adenine (A), which is 24%.
Therefore, approximately 24% of the nucleotides in this sample will be thymine (T).Rate this question:
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- 12.
Chargaff's analysis of the relative base composition of DNA was significant because he was able to show that
- A.
The relative proportion of each of the four bases differs from species to species.
- B.
The human genome is more complex than that of other species.
- C.
The amount of A is always equivalent to T, and C to G.
- D.
Both A and C
- E.
Both B and C
Correct Answer
D. Both A and CExplanation
Chargaff's analysis of the relative base composition of DNA was significant because he was able to show that the relative proportion of each of the four bases differs from species to species. This finding demonstrated that DNA is not a uniform molecule, but rather has a specific composition that varies between different organisms. Additionally, Chargaff's analysis revealed that the amount of adenine (A) is always equivalent to thymine (T), and the amount of cytosine (C) is always equivalent to guanine (G). This discovery provided crucial insights into the structure and function of DNA.Rate this question:
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- 13.
All of the following can be determined directly from X-ray diffraction photographs of crystallized DNA except the
- A.
Diameter of the helix.
- B.
Helical shape of DNA.
- C.
Sequence of nucleotides.
- D.
Spacing of the nitrogenous bases along the helix.
- E.
Number of strands in a helix.
Correct Answer
C. Sequence of nucleotides.Explanation
X-ray diffraction photographs of crystallized DNA provide information about the helical shape of DNA, the spacing of the nitrogenous bases along the helix, and the number of strands in a helix. However, determining the sequence of nucleotides requires other techniques such as DNA sequencing methods. Therefore, the sequence of nucleotides cannot be directly determined from X-ray diffraction photographs of crystallized DNA.Rate this question:
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- 14.
The DNA double helix has a uniform diameter because ________, which have two rings, always pair with ________, which have one ring.
- A.
Purines; pyrimidines
- B.
Pyrimidines; purines
- C.
Deoxyribose sugars; ribose sugars
- D.
Ribose sugars; deoxyribose sugars
- E.
Nucleotides; nucleoside triphosphates
Correct Answer
A. Purines; pyrimidinesExplanation
The DNA double helix has a uniform diameter because purines, which have two rings, always pair with pyrimidines, which have one ring. This pairing allows the two strands of DNA to fit together perfectly, maintaining a consistent diameter throughout the molecule.Rate this question:
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- 15.
What kind of chemical bond is found between paired bases of the DNA double helix?
- A.
Hydrogen
- B.
Ionic
- C.
Covalent
- D.
Sulfhydryl
- E.
Phosphate
Correct Answer
A. HydrogenExplanation
The correct answer is hydrogen. Hydrogen bonds are formed between the paired bases of the DNA double helix. These bonds are relatively weak compared to covalent bonds, but they play a crucial role in stabilizing the structure of DNA. The hydrogen bonds occur between specific base pairs, with adenine (A) forming two hydrogen bonds with thymine (T) and guanine (G) forming three hydrogen bonds with cytosine (C). These hydrogen bonds help to hold the two strands of DNA together and allow for the complementary base pairing that is essential for DNA replication and protein synthesis.Rate this question:
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- 16.
Which of the following statements does not apply to the Watson and Crick model of DNA?
- A.
The two strands of the DNA form a double helix.
- B.
The distance between the strands of the helix is uniform.
- C.
The framework of the helix consists of sugar-phosphate units of the nucleotides.
- D.
The two strands of the helix are held together by covalent bonds.
- E.
The purines form hydrogen bonds with pyrimidines.
Correct Answer
D. The two strands of the helix are held together by covalent bonds.Explanation
The Watson and Crick model of DNA states that the two strands of the DNA form a double helix, the distance between the strands of the helix is uniform, the framework of the helix consists of sugar-phosphate units of the nucleotides, and the purines form hydrogen bonds with pyrimidines. However, the model does not propose that the two strands of the helix are held together by covalent bonds. Instead, they are held together by hydrogen bonds between the nitrogenous bases.Rate this question:
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- 17.
It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in its
- A.
Sequence of bases.
- B.
Phosphate-sugar backbones.
- C.
Complementary pairing of bases.
- D.
Side groups of nitrogenous bases.
- E.
Different five-carbon sugars.
Correct Answer
A. Sequence of bases.Explanation
After completing their model of the DNA molecule, Watson and Crick realized that the sequence of bases in the DNA molecule could carry a vast amount of hereditary information. The sequence of bases, which includes adenine (A), thymine (T), cytosine (C), and guanine (G), determines the genetic code and is responsible for encoding the instructions for building and maintaining an organism. This discovery was crucial in understanding how DNA carries and transmits genetic information.Rate this question:
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- 18.
In an analysis of the nucleotide composition of DNA, which of the following is true?
- A.
A = C
- B.
A = G and C = T
- C.
A + C = G + T
- D.
G + A = T + C
- E.
Both C and D
Correct Answer
E. Both C and DExplanation
In an analysis of the nucleotide composition of DNA, it is true that A + C = G + T (option C) and G + A = T + C (option D). This means that the amount of adenine (A) combined with the amount of cytosine (C) in DNA is equal to the amount of guanine (G) combined with the amount of thymine (T). Additionally, the amount of guanine (G) combined with the amount of adenine (A) is equal to the amount of thymine (T) combined with the amount of cytosine (C). Therefore, both options C and D are correct.Rate this question:
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- 19.
Which of the following statements is false when comparing prokaryotes with eukaryotes?
- A.
The prokaryotic chromosome is circular, whereas eukaryotic chromosomes are linear.
- B.
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
- C.
The rate of elongation during DNA replication is higher in prokaryotes than in eukaryotes
- D.
Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not.
- E.
Eukaryotes have telomeres, and prokaryotes do not.
Correct Answer
D. Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not.Explanation
The production of Okazaki fragments during DNA replication is a characteristic feature of prokaryotes, not eukaryotes. Okazaki fragments are short, discontinuous segments of DNA that are synthesized on the lagging strand during DNA replication. In prokaryotes, the circular nature of the chromosome and the bidirectional replication process require the synthesis of Okazaki fragments to ensure the complete replication of both strands. In contrast, eukaryotes have linear chromosomes and utilize a different mechanism called continuous replication, where the lagging strand is synthesized in a continuous manner without the need for Okazaki fragments.Rate this question:
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- 20.
The strands that make up DNA are antiparallel. This means that
- A.
The twisting nature of DNA creates nonparallel strands.
- B.
The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.
- C.
Base pairings create unequal spacing between the two DNA strands.
- D.
One strand is positively charged and the other is negatively charged.
- E.
One strand contains only purines and the other contains only pyrimidines.
Correct Answer
B. The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.Explanation
The correct answer is that the 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. This is because DNA strands are antiparallel, meaning they run in opposite directions. One strand has a 5' end and a 3' end, while the other strand has a 3' end and a 5' end. This antiparallel arrangement allows for the complementary base pairing between the strands, where adenine pairs with thymine and guanine pairs with cytosine.Rate this question:
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- 21.
Suppose one were provided with an actively dividing culture of E. coli bacteria to which radioactive thymine had been added. What would happen if a cell replicated once in the presence of this radioactive base?
- A.
One of the daughter cells, but not the other, would have radioactive DNA.
- B.
Neither of the two daughter cells would be radioactive.
- C.
All four bases of the DNA would be radioactive.
- D.
Radioactive thymine would pair with nonradioactive guanine.
- E.
DNA in both daughter cells would be radioactive.
Correct Answer
E. DNA in both daughter cells would be radioactive.Explanation
If a cell replicated once in the presence of radioactive thymine, the DNA in both daughter cells would be radioactive. This is because during replication, the DNA strands separate and each strand serves as a template for the synthesis of a new complementary strand. Since the radioactive thymine is incorporated into the DNA strands, both daughter cells would inherit the radioactive DNA.Rate this question:
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- 22.
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 above results would be expected after one DNA replication in the presence of 14N?
Correct Answer
D
dExplanation
After one DNA replication in the presence of 14N, it is expected that the DNA strands will consist of one heavy (15N) strand and one light (14N) strand. This is because during DNA replication, the original DNA molecule serves as a template for the synthesis of a new complementary strand. Therefore, each original heavy strand will be replicated to produce one heavy strand and one newly synthesized light strand. Hence, the expected result after one DNA replication in the presence of 14N is a mixture of DNA molecules with one heavy strand and one light strand.Rate this question:
- 23.
Which enzyme catalyzes the elongation of a DNA strand in the 5' ïƒ 3' direction?
- A.
Primase
- B.
DNA ligase
- C.
DNA polymerase
- D.
Topoisomerase
- E.
Helicase
Correct Answer
C. DNA polymeraseExplanation
DNA polymerase is the enzyme responsible for catalyzing the elongation of a DNA strand in the 5' to 3' direction. This enzyme adds nucleotides to the growing DNA strand, using the template strand as a guide. It also proofreads the newly synthesized DNA strand to ensure accuracy. Primase is involved in synthesizing RNA primers, DNA ligase joins Okazaki fragments during DNA replication, topoisomerase relieves tension in the DNA molecule, and helicase unwinds the DNA double helix.Rate this question:
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- 24.
A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in Figure 16.1 would you expect if the DNA was replicated in a conservative manner?
Correct Answer
b
BExplanation
If the DNA was replicated in a conservative manner, it means that after each replication, one of the daughter DNA molecules would consist entirely of newly synthesized strands, while the other would consist entirely of the original parental strands. This would result in a pattern where one DNA molecule would have all 15N nucleotides (b) and the other DNA molecule would have all 14N nucleotides (B).Rate this question:
- 25.
What determines the nucleotide sequence of the newly synthesized strand during DNA replication?
- A.
The particular DNA polymerase catalyzing the reaction
- B.
The relative amounts of the four nucleoside triphosphates in the cell
- C.
The nucleotide sequence of the template strand
- D.
The primase used in the reaction
- E.
Both A and D
Correct Answer
C. The nucleotide sequence of the template strandExplanation
The nucleotide sequence of the template strand determines the nucleotide sequence of the newly synthesized strand during DNA replication. The template strand serves as a guide for the DNA polymerase to match complementary nucleotides and create a complementary strand. The DNA polymerase adds nucleotides in a sequence that corresponds to the template strand, resulting in a newly synthesized strand with the same nucleotide sequence as the template strand. The other options, such as the particular DNA polymerase, the relative amounts of nucleoside triphosphates, and the primase used, may have roles in DNA replication but do not directly determine the nucleotide sequence of the newly synthesized strand.Rate this question:
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- 26.
What is the function of DNA polymerase?
- A.
To unwind the DNA helix during replication
- B.
To seal together the broken ends of DNA strands
- C.
To add nucleotides to the end of a growing DNA strand
- D.
To degrade damaged DNA molecules
- E.
To rejoin the two DNA strands (one new and one old) after replication
Correct Answer
C. To add nucleotides to the end of a growing DNA strandExplanation
DNA polymerase is an enzyme responsible for adding nucleotides to the end of a growing DNA strand. During DNA replication, DNA polymerase attaches to the template strand and adds complementary nucleotides to the growing daughter strand, following the base pairing rules (A with T, G with C). This process ensures that the new DNA strand is an exact copy of the original template strand. DNA polymerase plays a crucial role in DNA replication, as it helps to maintain the integrity and accuracy of the genetic information.Rate this question:
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- 27.
Which of the following is least related to the others on the list?
- A.
Okazaki fragments
- B.
Replication fork
- C.
Telomerase
- D.
DNA polymerase
- E.
Semiconservative model
Correct Answer
C. TelomeraseExplanation
Telomerase is the least related to the others on the list because it is involved in the maintenance of telomeres, which are the protective caps at the ends of chromosomes. Telomerase plays a role in preventing the shortening of telomeres during DNA replication, which is not directly related to the other concepts listed. In contrast, Okazaki fragments, replication fork, DNA polymerase, and the semiconservative model are all directly involved in DNA replication.Rate this question:
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- 28.
You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent
- A.
Leading strands and Okazaki fragments.
- B.
Lagging strands and Okazaki fragments
- C.
Okazaki fragments and RNA primers.
- D.
Leading strands and RNA primers.
- E.
RNA primers and mitochondrial DNA.
Correct Answer
A. Leading strands and Okazaki fragments.Explanation
The presence of very large molecules in one class of labeled DNA suggests that these molecules are the leading strands, which are synthesized continuously during DNA replication. The presence of short stretches of DNA in the other class indicates that these are Okazaki fragments, which are synthesized discontinuously on the lagging strand. This is because the lagging strand is synthesized in short fragments that are later joined together. Therefore, the two classes of DNA likely represent leading strands and Okazaki fragments.Rate this question:
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- 29.
Refer to the following list of enzymes to answer the following questions. The answers may be used once, more than once, or not at all. A. helicase B. nuclease C. ligase D. DNA polymerase I E. primase removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments
Correct Answer
d
DExplanation
DNA polymerase I is the enzyme that removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments. This enzyme is responsible for the process of DNA replication, specifically in the synthesis of the lagging strand. It has both exonuclease and polymerase activities, allowing it to remove the RNA primer and replace it with DNA. The correct answer, d,D, refers to DNA polymerase I.Rate this question:
- 30.
Refer to the following list of enzymes to answer the following questions. The answers may be used once, more than once, or not at all. A. helicase B. nuclease C. ligase D. DNA polymerase I E. primase separates the DNA strands during replication
Correct Answer
a
AExplanation
The correct answer is "helicase". Helicase is an enzyme that separates the DNA strands during replication. This process is necessary for the DNA strands to be copied and for new DNA strands to be synthesized. Helicase unwinds the double helix structure of DNA by breaking the hydrogen bonds between the base pairs, allowing the DNA strands to separate and serve as templates for the synthesis of new DNA strands.Rate this question:
- 31.
Refer to the following list of enzymes to answer the following questions. The answers may be used once, more than once, or not at all. A. helicase B. nuclease C. ligase D. DNA polymerase I E. primase covalently connects segments of DNA
Correct Answer
c
CExplanation
DNA ligase is the enzyme responsible for covalently connecting segments of DNA. It plays a crucial role in DNA replication and repair, as well as in recombinant DNA technology, where it is used to join DNA fragments together. The enzyme catalyzes the formation of a phosphodiester bond between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of another nucleotide, thereby linking the DNA segments together.Rate this question:
- 32.
Refer to the following list of enzymes to answer the following questions. The answers may be used once, more than once, or not at all. A. helicase B. nuclease C. ligase D. DNA polymerase I E. primase synthesizes short segments of RNA
Correct Answer
e
EExplanation
Enzyme E, also known as primase, synthesizes short segments of RNA. This is an important step in DNA replication, as these RNA segments serve as primers for DNA polymerase to begin synthesizing new DNA strands. Primase adds a short RNA sequence to the DNA template, providing a starting point for DNA polymerase to attach and begin adding nucleotides to form a new DNA strand. Therefore, enzyme E is responsible for the initiation of DNA replication by synthesizing RNA primers.Rate this question:
- 33.
Refer to the following list of enzymes to answer the following questions. The answers may be used once, more than once, or not at all. A. helicase B. nuclease C. ligase D. DNA polymerase I E. primase DNA-cutting enzymes used in the repair of DNA damage
Correct Answer
b
BExplanation
The correct answer is "b, B". The question asks for DNA-cutting enzymes used in the repair of DNA damage. The enzyme "nuclease" is responsible for cutting DNA strands, and it is commonly used in DNA repair processes. Therefore, option b, which includes the enzyme "nuclease", is the correct answer. Option B, which is the same as option b, is also correct as it represents the same enzyme.Rate this question:
- 34.
The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that
- A.
The nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.
- B.
The nucleoside triphosphates have two phosphate groups; ATP has three phosphate groups.
- C.
ATP contains three high-energy bonds; the nucleoside triphosphates have two.
- D.
ATP is found only in human cells; the nucleoside triphosphates are found in all animal and plant cells.
- E.
Triphosphate monomers are active in the nucleoside triphosphates, but not in ATP.
Correct Answer
A. The nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.Explanation
The correct answer is that the nucleoside triphosphates used during DNA synthesis have the sugar deoxyribose, while ATP has the sugar ribose. This means that the nucleoside triphosphates are specific to DNA synthesis, while ATP is a more general energy molecule used in various cellular processes.Rate this question:
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- 35.
The Y-shaped structure where the DNA double helix is actively unwound during DNA replication is called the
- A.
Replication fork.
- B.
Replication Y.
- C.
Elongation junction.
- D.
Unwinding point.
- E.
Y junction.
Correct Answer
A. Replication fork.Explanation
The Y-shaped structure where the DNA double helix is actively unwound during DNA replication is called the replication fork. This is the site where the DNA strands separate and new complementary strands are synthesized. The replication fork is formed by the action of enzymes called helicases, which unwind the DNA molecule, and DNA polymerases, which synthesize the new strands. The replication fork moves along the DNA molecule as replication progresses, unwinding and synthesizing new DNA strands in a continuous or discontinuous manner. This process ensures accurate replication of the genetic material.Rate this question:
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- 36.
The leading and the lagging strands differ in that
- A.
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
- B.
The leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the lagging strand is synthesized by adding nucleotides to the 5' end.
- C.
The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short fragments that are ultimately stitched together.
- D.
Both A and B
- E.
Both A and C
Correct Answer
E. Both A and CExplanation
The leading and lagging strands differ in multiple ways. The leading strand is synthesized in the same direction as the movement of the replication fork, while the lagging strand is synthesized in the opposite direction. Additionally, the leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments that are ultimately stitched together. Therefore, both options A and C are correct.Rate this question:
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- 37.
Which of the following best describes the addition of nucleotides to a growing DNA chain?
- A.
A nucleoside triphosphate is added to the 5' end of the DNA, releasing a molecule of pyrophosphate.
- B.
A nucleoside triphosphate is added to the 3' end of the DNA, releasing a molecule of pyrophosphate.
- C.
A nucleoside diphosphate is added to the 5' end of the DNA, releasing a molecule of phosphate.
- D.
A nucleoside diphosphate is added to the 3' end of the DNA, releasing a molecule of phosphate.
- E.
A nucleoside monophosphate is added to the 3' end of the DNA.
Correct Answer
B. A nucleoside triphosphate is added to the 3' end of the DNA, releasing a molecule of pyrophosphate.Explanation
When nucleotides are added to a growing DNA chain, a nucleoside triphosphate is added to the 3' end of the DNA. This addition results in the release of a molecule of pyrophosphate. This process is known as DNA synthesis or DNA replication. The 3' end of the DNA chain is where the new nucleotide is added because the 3' end has a free hydroxyl group (-OH) that can form a phosphodiester bond with the incoming nucleoside triphosphate. The release of pyrophosphate provides the energy needed for the formation of this bond.Rate this question:
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- 38.
A new DNA strand elongates only in the 5' to 3' direction because
- A.
DNA polymerase begins adding nucleotides at the 5' end of the template.
- B.
Okazaki fragments prevent elongation in the 3' to 5' direction.
- C.
The polarity of the DNA molecule prevents addition of nucleotides at the 3' end.
- D.
Replication must progress toward the replication fork.
- E.
DNA polymerase can only add nucleotides to the free 3' end.
Correct Answer
E. DNA polymerase can only add nucleotides to the free 3' end.Explanation
The correct answer is that DNA polymerase can only add nucleotides to the free 3' end. DNA polymerase is the enzyme responsible for synthesizing a new DNA strand during replication. It can only add nucleotides to the 3' end of the growing strand because it catalyzes the formation of a phosphodiester bond between the 3' hydroxyl group of the existing nucleotide and the 5' phosphate group of the incoming nucleotide. This results in the elongation of the DNA strand in the 5' to 3' direction.Rate this question:
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- 39.
Replicating the lagging strand of DNA-that is, adding bases in the 3' ïƒ 5' direction-utilizes which of the following?
- A.
DNA ligase
- B.
RNA primers
- C.
Okazaki fragments
- D.
A and B only
- E.
A, B, and C
Correct Answer
E. A, B, and CExplanation
The replication of the lagging strand of DNA, which involves adding bases in the 3' -> 5' direction, utilizes DNA ligase, RNA primers, and Okazaki fragments. DNA ligase is responsible for joining the Okazaki fragments together, while RNA primers are necessary for initiating DNA synthesis. Okazaki fragments are short DNA fragments that are synthesized on the lagging strand during DNA replication. Therefore, all three options (A, B, and C) are required for the replication of the lagging strand of DNA.Rate this question:
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- 40.
What kind of molecule or substance is the primer that is used to initiate the synthesis of a new DNA strand?
- A.
RNA
- B.
DNA
- C.
Protein
- D.
Phosphate
- E.
Sulfur
Correct Answer
A. RNAExplanation
The primer used to initiate the synthesis of a new DNA strand is RNA. RNA primers are short sequences of RNA that are synthesized by an enzyme called primase. These primers provide a starting point for DNA polymerase to begin synthesizing the complementary DNA strand during DNA replication. RNA primers are later removed and replaced with DNA by another enzyme called DNA polymerase, resulting in a complete double-stranded DNA molecule. Therefore, RNA is the correct answer as it serves as the initial template for DNA synthesis.Rate this question:
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- 41.
What is the function of topoisomerase?
- A.
Relieving strain in the DNA ahead of the replication fork
- B.
Elongation of new DNA at a replication fork by addition of nucleotides to the existing chain
- C.
The addition of methyl groups to bases of DNA
- D.
Unwinding of the double helix
- E.
Stabilizing single-stranded DNA at the replication fork
Correct Answer
A. Relieving strain in the DNA ahead of the replication forkExplanation
Topoisomerase is responsible for relieving strain in the DNA ahead of the replication fork. During DNA replication, the double helix structure of DNA becomes tightly wound and twisted, causing strain and tension. Topoisomerase enzymes work by breaking and rejoining the DNA strands, allowing the DNA to unwind and relieve the strain. This process is crucial for the smooth progression of DNA replication and prevents DNA damage or breakage.Rate this question:
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- 42.
What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
- A.
Synthesize RNA nucleotides to make a primer
- B.
Catalyze the lengthening of telomeres
- C.
Join Okazaki fragments together
- D.
Unwind the parental double helix
- E.
Stabilize the unwound parental DNA
Correct Answer
C. Join Okazaki fragments togetherExplanation
During DNA replication, the lagging strand is synthesized in short fragments called Okazaki fragments. DNA ligase plays a crucial role in the elongation of the lagging strand by joining these Okazaki fragments together. It catalyzes the formation of phosphodiester bonds between the adjacent nucleotides, effectively sealing the gaps between the fragments and creating a continuous strand. This process ensures that both the leading and lagging strands are fully synthesized and complete.Rate this question:
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- 43.
All of the following are functions of DNA polymerase in DNA replication except
- A.
Covalently adding nucleotides to the new strands.
- B.
Proofreading each added nucleotide for correct base pairing.
- C.
Replacing RNA primers with DNA.
- D.
Initiating a polynucleotide strand.
- E.
None of the above
Correct Answer
D. Initiating a polynucleotide strand.Explanation
DNA polymerase is an enzyme responsible for catalyzing the addition of nucleotides to the growing DNA strands during replication. It is involved in several functions, including covalently adding nucleotides to the new strands, proofreading each added nucleotide for correct base pairing, and replacing RNA primers with DNA. However, it does not have the role of initiating a polynucleotide strand, as this is typically carried out by other proteins such as DNA primase. Therefore, the correct answer is "initiating a polynucleotide strand."Rate this question:
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- 44.
Which of the following help to hold the DNA strands apart while they are being replicated?
- A.
Primase
- B.
Ligase
- C.
DNA polymerase
- D.
Single-strand binding proteins
- E.
Exonuclease
Correct Answer
D. Single-strand binding proteinsExplanation
Single-strand binding proteins help to hold the DNA strands apart while they are being replicated. These proteins bind to the single-stranded DNA and prevent the strands from reannealing or forming secondary structures, allowing the replication machinery to access the DNA template and synthesize a new complementary strand. Primase is responsible for synthesizing RNA primers, ligase joins the Okazaki fragments, DNA polymerase synthesizes the new DNA strands, and exonuclease removes nucleotides from the ends of DNA strands. However, none of these directly hold the DNA strands apart during replication.Rate this question:
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- 45.
Which of these mechanisms ensures that the DNA sequence in the genome remains accurate?
- A.
Proofreading during DNA replication
- B.
Mismatch repair
- C.
Excision repair
- D.
Complementary base pairing during DNA replication
- E.
All of the above
Correct Answer
E. All of the aboveExplanation
All of the mechanisms mentioned in the options ensure that the DNA sequence in the genome remains accurate. Proofreading during DNA replication involves the correction of errors made during the copying of DNA. Mismatch repair is a process that corrects errors that occur after DNA replication. Excision repair is a mechanism that repairs DNA damage caused by environmental factors. Complementary base pairing during DNA replication ensures that the new DNA strand is accurately synthesized based on the template strand. Therefore, all of these mechanisms work together to maintain the accuracy of the DNA sequence in the genome.Rate this question:
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- 46.
Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight because their cells have an impaired ability to
- A.
Replicate DNA.
- B.
Undergo mitosis.
- C.
Exchange DNA with other cells.
- D.
Repair thymine dimers.
- E.
Recombine homologous chromosomes during meiosis.
Correct Answer
D. Repair thymine dimers.Explanation
Individuals with xeroderma pigmentosum have a genetic disorder that impairs their ability to repair thymine dimers. Thymine dimers are a type of DNA damage that is caused by exposure to ultraviolet (UV) radiation from sunlight. When these dimers are not repaired, they can lead to mutations in the DNA, which can increase the risk of skin cancer. Therefore, individuals with xeroderma pigmentosum are hypersensitive to sunlight because their cells cannot effectively repair thymine dimers, making them more susceptible to DNA damage and the harmful effects of UV radiation.Rate this question:
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- 47.
Which of the following is analogous to telomeres?
- A.
The pull tab on a soft drink can
- B.
The two ends of a shoelace
- C.
The central spindle that a CD fits around while in the case
- D.
The mechanism of a zipper that allows the separated parts to be joined
- E.
The correct letters used to replace errors in a document after they have been deleted in a word processor
Correct Answer
B. The two ends of a shoelaceExplanation
Telomeres are protective caps at the ends of chromosomes that prevent them from deteriorating or fusing with neighboring chromosomes. Similarly, the two ends of a shoelace have protective caps called aglets that prevent the lace from fraying and make it easier to thread through the eyelets of a shoe. Both telomeres and shoelace ends serve a similar function of protecting and maintaining the integrity of their respective structures.Rate this question:
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- 48.
A eukaryotic cell lacking telomerase would
- A.
Have a high probability of becoming cancerous.
- B.
Produce Okazaki fragments.
- C.
Be unable to repair thymine dimers.
- D.
Undergo a reduction in chromosome length.
- E.
Be highly sensitive to sunlight.
Correct Answer
D. Undergo a reduction in chromosome length.Explanation
A eukaryotic cell lacking telomerase would undergo a reduction in chromosome length. Telomerase is an enzyme that adds repetitive DNA sequences called telomeres to the ends of chromosomes. These telomeres protect the chromosomes from degradation and prevent them from fusing with each other. Without telomerase, the telomeres gradually shorten with each cell division, leading to a reduction in chromosome length. This can eventually result in genomic instability and increased risk of cancer.Rate this question:
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- 49.
Which of the following statements about telomeres is correct?
- A.
They contain multiple copies of a short RNA sequence.
- B.
They are present at the ends of eukaryotic chromosomes.
- C.
They can be extended by an enzyme called telomerase.
- D.
Both A and B
- E.
Both B and C
Correct Answer
E. Both B and CExplanation
Telomeres are repetitive DNA sequences found at the ends of eukaryotic chromosomes. They protect the chromosomes from degradation and fusion with other chromosomes. Telomeres can be extended by an enzyme called telomerase, which adds additional repetitive sequences to the ends of chromosomes. Therefore, the correct statement is that telomeres are present at the ends of eukaryotic chromosomes and can be extended by telomerase.Rate this question:
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- 50.
Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because
- A.
Genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes.
- B.
Enzymes are made of DNA, and affected individuals lack DNA polymerase.
- C.
Many metabolic enzymes use DNA as a cofactor, and affected individuals have mutations that prevent their enzymes from interacting efficiently with DNA.
- D.
Certain metabolic reactions are carried out by ribozymes, and affected individuals lack key splicing factors.
- E.
Metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies.
Correct Answer
A. Genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes.Explanation
Garrod hypothesized that "inborn errors of metabolism" occur because genes dictate the production of specific enzymes. This means that affected individuals have genetic defects that cause them to lack certain enzymes. This explanation aligns with the concept that genetic mutations can lead to enzyme deficiencies, resulting in metabolic disorders such as alkaptonuria.Rate this question:
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.JPG "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 above results would be expected after one DNA replication in the presence of 14N?")
.JPG "A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in Figure 16.1 would you expect if the DNA was replicated in a conservative manner?")
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Apr 03, 2024Quiz Edited by
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Feb 26, 2013Quiz Created by
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