Question 1

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?
A) No proofreading will occur.
B) The DNA strands at the origin of replication will separate, but replication will not progress.
C) The DNA will supercoil.
D) Replication will require a DNA template from another source.

Accepted Answer

Helicase is responsible for separating the DNA strands at the origin of replication. If the helicase activity is altered due to a mutation in the dnaB gene, then the DNA strands at the origin of replication will separate, but replication will not progress further, leading to replication failure. Options A, C, and D are not related to the function of helicase at the origin of replication.

Question 2

An Okazaki fragment has which of the following arrangements?
A) primase, polymerase, ligase
B) 3' RNA nucleotides, DNA nucleotides 5'
C) 5' RNA nucleotides, DNA nucleotides 3'
D) DNA polymerase I, DNA polymerase III
E) 5' DNA to 3'

Accepted Answer

An Okazaki fragment is a short segment of DNA that is synthesized in the lagging strand during DNA replication. It is composed of RNA nucleotides and DNA nucleotides arranged in a 5' to 3' direction. Primase synthesizes a short RNA primer, followed by DNA polymerase III that adds DNA nucleotides in the 5' to 3' direction. DNA polymerase I removes the RNA primer and replaces it with DNA nucleotides, and ligase seals the gaps between the adjacent Okazaki fragments. Therefore, choice C is the correct arrangement for an Okazaki fragment.

Question 3

Suppose you are provided with an actively dividing culture of Escherichia coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates 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.

Accepted Answer

During DNA replication, the parental strands are separated, and each strand acts as a template for the synthesis of a new complementary strand. In the presence of radioactive thymine, its incorporation into one of the parental strands will lead to the incorporation of a radioactive base in the newly synthesized strand. Thus, both daughter cells would contain radioactive DNA because each contains a copy of the radioactive parental DNA strand.

Question 4

What is the function of DNA polymerase III?
A) to unwind the DNA helix during replication
B) to seal together the broken ends of DNA strands
C) to add nucleotides to the 3' 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

Accepted Answer

DNA polymerase III adds nucleotides to the 3' end of a growing DNA strand during DNA replication.

Question 5

In his transformation experiments, what did Griffith observe?
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.

Accepted Answer

Griffith observed 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, which is known as transformation.

Question 6

In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine. Which of the following investigators was (were) responsible for this discovery?
A) Frederick Griffith
B) Alfred Hershey and Martha Chase
C) Oswald Avery
D) Erwin Chargaff
E) Matthew Meselson and Franklin Stahl

Accepted Answer

Erwin Chargaff discovered that the amount of adenine always equals the amount of thymine and the amount of guanine always equals the amount of cytosine in the DNA of any species.

Question 7

After mixing a heat-killed, phosphorescent (light-emitting) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observation(s) would provide the best evidence that the ability to phosphoresce is a heritable trait?
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.

Accepted Answer

The best evidence that the ability to phosphoresce is a heritable trait is to observe that the descendants of the living cells that acquired the trait are also phosphorescent. This suggests that the genetic information responsible for the trait was passed down from the initial mixing of the two strains, which could only occur through the transfer of DNA. Options A and E suggest the possibility of DNA transfer, but do not provide evidence that the trait is heritable. Option B suggests the transfer of a protein, which alone is not sufficient to suggest that the trait is heritable. Option C is not relevant to heritability, as brightness of the phosphorescence could be affected by many factors besides genetics.

Question 8

How is transformation in bacteria most accurately described?
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

Accepted Answer

Transformation in bacteria refers to the process by which external DNA (usually in the form of plasmids) is taken up by a bacterial cell and integrated into its own genome. This allows for the acquisition of new genetic traits, such as antibiotic resistance.

Question 9

What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA?
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 contains only purines and the other contains only pyrimidines.

Accepted Answer

The term "antiparallel" refers to the directionality of the two strands of DNA, with one strand running in the 5' to 3' direction and the other running in the opposite direction (3' to 5'). This allows for complementary base pairings between the strands.

Question 10

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 contains sulfur, whereas protein does not.
B) DNA contains phosphorus, whereas protein does not.
C) DNA contains nitrogen, whereas protein does not.
D) DNA contains purines, whereas protein includes pyrimidines.
E) RNA includes ribose, whereas DNA includes deoxyribose sugars.

Accepted Answer

Hershey and Chase used the fact that DNA contains phosphorus, whereas protein does not. They labeled the DNA in a bacteriophage with radioactive phosphorus and the protein with radioactive sulfur, and showed that only the bacteriophage DNA was transferred into bacterial cells during infection, demonstrating that DNA is the genetic material.

Question 11

Which of the following statements describes one difference between DNA replication in prokaryotes and DNA replication in eukaryotes?
A) Prokaryotic chromosomes have histones, whereas eukaryotic chromosomes do not.
B) Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
C) The rate of elongation during DNA replication is slower in prokaryotes than in eukaryotes.
D) Prokaryotes produce Okazaki fragments during DNA replication, but eukaryotes do not.
E) Prokaryotes have telomeres, and eukaryotes do not.

Accepted Answer

The presence of multiple origins of replication is a key difference between DNA replication in prokaryotes and eukaryotes. Prokaryotes have a single origin of replication, while eukaryotes have many because their chromosomes are much larger. This allows eukaryotic DNA replication to occur more quickly and efficiently.

Question 12

Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA strands that are aligned in parallel structures. How could these arise?
A) replication followed by mitosis
B) replication without separation
C) meiosis followed by mitosis
D) fertilization by multiple sperm
E) special association with histone proteins

Accepted Answer

Polytene chromosomes are formed through a process called endoreplication, in which DNA replication occurs without cell division. This leads to multiple identical copies of DNA strands that are aligned in parallel structures.

Question 13

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.

Accepted Answer

The main difference between ATP and the nucleoside triphosphates used during DNA synthesis is the type of sugar present. ATP contains the sugar ribose, while nucleoside triphosphates have the sugar deoxyribose. This difference in sugar structure is critical for the proper functioning of these molecules in their respective processes.

Question 14

In an analysis of the nucleotide composition of DNA, which of the following will be found?
A) A = C
B) A = G and C = T
C) A + C = G + T
D) G + C = T + A

Accepted Answer

The nucleotide composition of DNA follows Chargaff's rule, where A is always equal to T and C is always equal to G. Therefore, A + C = G + T.

Question 15

At a specific area of a chromosome, the following sequence of nucleotides is present where the chain opens to form a replication fork:
3'-C C T A G G C T G C A A T C C-5'
An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?
A) 5'-G C C T A G G-3'
B) 3'-G C C T A G G-5'
C) 5'-A C G T T A G G-3'
D) 5'-A C G U U A G G-3'
E) 5'-G C C U A G G-3'

Accepted Answer

RNA primers are synthesized using the DNA template strand, and they are complementary and antiparallel to the template. The sequence starting from the underlined T in the template is 5' AGGCT... 3'. The complementary RNA sequence would be 5' UCCGA... 3', but since the primer starts at the T, the sequence is 5' UUAGG 3', which matches option D.

Question 16

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information based on which of the following characteristics?
A) the sequence of bases
B) phosphate-sugar backbones
C) complementary pairing of bases
D) different five-carbon sugars

Accepted Answer

The sequence of bases in DNA determines the information that is carried and can be passed on through generations.

Question 17

In which order do the necessary enzymes act to repair a thymine dimer by nucleotide excision repair?
A) nuclease, DNA polymerase, RNA primase
B) helicase, DNA polymerase, DNA ligase
C) DNA ligase, nuclease, helicase
D) DNA polymerase, RNA polymerase, DNA ligase
E) nuclease, DNA polymerase, DNA ligase

Accepted Answer

Nucleotide excision repair involves the removal of a section of DNA containing the damaged region, followed by resynthesis of the missing nucleotides. This process involves several enzymes including a nuclease to cut the damaged DNA, DNA polymerase to fill in the missing nucleotides, and DNA ligase to seal the remaining gaps. Therefore, the correct order of enzyme action is nuclease, DNA polymerase, and DNA ligase, which corresponds to choice E.

Question 18

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?
A) 8%
B) 16%
C) 31%
D) 42%

Accepted Answer

The answer of Cytosine makes up 42% of the nucleotides...

Question 19

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?
A) primase
B) DNA ligase
C) DNA polymerase III
D) topoisomerase
E) helicase

Accepted Answer

DNA polymerase III is the enzyme responsible for elongating a DNA strand in the 5' → 3' direction during DNA replication.

Question 20

Which of the following characteristics can be determined directly from X-ray diffraction photographs of crystallized DNA?
A) the diameter of the helix
B) the rate of replication
C) the sequence of nucleotides
D) the frequency of A versus T nucleotides

Accepted Answer

The diameter of the helix can be determined directly from X-ray diffraction photographs of crystallized DNA by measuring the distance between the cross-hatched spots on the photograph. This distance corresponds to the distance between the helix's phosphate-sugar backbone.

Note: X-ray diffraction photographs cannot provide information on replication rates, nucleotide sequences, or relative frequencies of specific nucleotides.

Quiz 13: The Molecular Basis of Inheritance

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?

An Okazaki fragment has which of the following arrangements?

Suppose you are provided with an actively dividing culture of Escherichia coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

What is the function of DNA polymerase III?

In his transformation experiments, what did Griffith observe?

In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine. Which of the following investigators was (were) responsible for this discovery?

After mixing a heat-killed, phosphorescent (light-emitting) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observation(s) would provide the best evidence that the ability to phosphoresce is a heritable trait?

How is transformation in bacteria most accurately described?

What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA?

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

Which of the following statements describes one difference between DNA replication in prokaryotes and DNA replication in eukaryotes?

Polytene chromosomes of Drosophila salivary glands each consist of multiple identical DNA strands that are aligned in parallel structures. How could these arise?

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that

In an analysis of the nucleotide composition of DNA, which of the following will be found?

At a specific area of a chromosome, the following sequence of nucleotides is present where the chain opens to form a replication fork: 3'-C C T A G G C T G C A A T C C-5' An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information based on which of the following characteristics?

In which order do the necessary enzymes act to repair a thymine dimer by nucleotide excision repair?

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

Which of the following characteristics can be determined directly from X-ray diffraction photographs of crystallized DNA?