Question 1

In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?
A) primase
B) DNA ligase
C) DNA polymerase III
D) helicase

Accepted Answer

DNA polymerase III is the primary enzyme responsible for the elongation of a new DNA strand in the 5' -> 3' direction in E. coli. Primase is responsible for synthesizing RNA primers, DNA ligase joins the Okazaki fragments, and helicase is responsible for unwinding the double helix.

Question 2

Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?
A) 8%
B) 16%
C) 22%
D) 72%

Accepted Answer

C

Question 3

Which of the following characteristics of eukaryotic telomeres cause them to replicate differently than the rest of the chromosome?
A) the activity of telomerase enzyme
B) DNA polymerase that cannot replicate the leading strand template to its 5' end
C) gaps left at the 5' end of the lagging strand template
D) gaps left at the 3' end of the lagging strand because of the need for a primer

Accepted Answer

C

Question 4

Which of the following investigators was (were)responsible for the discovery that in DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine?
A) Alfred Hershey and Martha Chase
B) Oswald Avery, Maclyn McCarty, and Colin MacLeod
C) Erwin Chargaff
D) Matthew Meselson and Franklin Stahl

Accepted Answer

This phenomenon is known as Chargaff's rule and was discovered by Erwin Chargaff.

Question 5

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?
A) the 5' phosphate
B) C₆
C) the 3' OH
D) a nitrogen from the nitrogen-containing base

Accepted Answer

A phosphodiester bond is formed between the 3' OH group of the last nucleotide in the polymer and the phosphate group of the nucleotide being added. This creates a chain of nucleotides with a 5' phosphate end and a 3' OH end.

Question 6

In an analysis of the nucleotide composition of a molecule of DNA, which of the following combinations of base pairs 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 answer of In an analysis of the nucleotide composition...

Question 7

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?
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.

Accepted Answer

Hershey and Chase used the fact that DNA contains phosphorus, whereas protein does not, to demonstrate that DNA, not protein, is the genetic material. They conducted an experiment where they labeled virus particles with radioactive isotopes of either phosphorus (which labels DNA) or sulfur (which labels protein). They then infected bacteria with these labeled virus particles and found that only the bacteria infected with the virus labeled with radioactive phosphorus showed radioactivity, confirming that DNA was passed on to the next generation of bacteria.

Question 8

What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?
A) The double helix structure 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

When describing the two strands of DNA, "antiparallel" means that while both strands run in the 5' to 3' direction, one strand runs in the opposite direction to the other. This creates an antiparallel orientation of the two strands that make up the DNA double helix.

Question 9

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?
A) Additional proofreading will occur.
B) No replication fork will be formed.
C) Replication will occur via RNA polymerase alone.
D) Replication will require a DNA template from another source.

Accepted Answer

The protein helicase is responsible for unwinding the DNA double helix at the origin of replication to create a replication fork, which is necessary for DNA replication to occur. Therefore, a mutation in the dnaB gene that alters the helicase would prevent replication fork formation and thus halt DNA replication.

Question 10

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?
A) sequence of bases
B) phosphate-sugar backbones
C) complementary pairing of bases
D) side groups of nitrogenous bases

Accepted Answer

The sequence of bases (adenine, thymine, guanine, and cytosine) in DNA determines the genetic information carried by the molecule. The specific order of these bases in a gene determines the sequence of amino acids in a protein, which ultimately determines the physical and functional traits of an organism.

Question 11

Which of the following statements describes the process of transformation in bacteria?
A) A strand of DNA is created from an RNA molecule.
B) A strand of RNA is created from a DNA molecule.
C) Bacterial cells are infected by a phage DNA molecule.
D) External DNA is taken into a cell, becoming part of the cell's genome.

Accepted Answer

The process of transformation in bacteria involves the uptake of external DNA by a bacterial cell, which becomes part of the cell's genome. This allows for the acquisition of new traits and genetic diversity within the bacterial population. Options A and B describe transcription, which is not related to transformation. Option C describes the process of transduction, not transformation.

Question 12

Which of the following statements accurately describes the differences 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.

Accepted Answer

Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many. This is because prokaryotic chromosomes are small and circular, while eukaryotic chromosomes are much larger and linear. Having multiple origins of replication allows for more efficient and faster replication in eukaryotes. The other statements are not accurate descriptions of the differences between DNA replication in prokaryotes and eukaryotes.

Question 13

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) 42%
D) 58%

Accepted Answer

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

Question 14

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms 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) Although there are more nitrogens in a nucleotide, labeled phosphates actually have 16 extra neutrons; therefore, they are more radioactive.
D) Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.

Accepted Answer

Because amino acids/proteins also contain nitrogen atoms, labeling the nitrogen of DNA would not distinguish between DNA and proteins, making the experiment impossible to interpret accurately.

Question 15

At a specific area of a chromosome, the sequence of nucleotides below 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) 5' A C G T T A G G 3'
C) 5' A C G U U A G G 3'
D) 5' G C C U A G G 3'

Accepted Answer

The answer of At a specific area of a chromosome,...

Question 16

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
A) It adds a single 5' cap structure that resists degradation by nucleases.
B) It causes specific double-strand DNA breaks that result in blunt ends on both strands.
C) It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.
D) It adds numerous GC pairs, which resist hydrolysis and maintain chromosome integrity.

Accepted Answer

Telomerase catalyzes the lengthening of telomeres, which are the repetitive DNA sequences that cap the ends of linear chromosomes. During DNA replication, the enzymes responsible for replicating DNA cannot fully replicate the ends of chromosomes, resulting in a gradual loss of telomeres with each cell division. Telomerase compensates for this loss by adding additional repeats to the end of the telomere, thus ensuring the integrity and stability of the chromosome. The other options listed do not accurately describe the function of telomerase in replicating the ends of linear chromosomes.

Question 17

Suppose you are provided with an actively dividing culture of E. 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) DNA in both daughter cells would be radioactive.

Accepted Answer

When a cell replicates in the presence of radioactive thymine, both strands of DNA will incorporate the radioactive base during replication. Therefore, when the DNA is separated during cell division, both daughter cells will have DNA that is radioactive.

Question 18

Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?
A) protein
B) RNA
C) ribosome
D) DNA

Accepted Answer

Hershey and Chase's experiments showed that the DNA of the T2 virus entered the E. coli cell and became the genetic material that was passed on. The protein capsid of the virus remained outside the cell.

Question 19

In his transformation experiments, what phenomenon did Griffith observe?
A) Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
B) Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
C) Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.
D) Mice infected with a pathogenic strain of bacteria can spread the infection to other mice.

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. This is known as transformation, where the genetic information from the dead pathogenic cells is taken up by the living nonpathogenic cells, allowing them to become pathogenic. This was a groundbreaking discovery that laid the foundation for understanding the role of DNA in heredity.

Question 20

A heat-killed, phosphorescent (light-emitting)strain of bacteria is mixed with a living, non-phosphorescent strain. Further observations of the mixture show that some of the living cells are now phosphorescent. Which of the following observations would provide the best evidence that the ability to phosphoresce is a heritable trait?
A) evidence that DNA was passed from the heat-killed strain to the living strain
B) evidence that protein passed from the heat-killed strain to the living strain
C) especially bright phosphorescence in the living strain
D) phosphorescence in descendants of the living cells

Accepted Answer

The best evidence that the ability to phosphoresce is a heritable trait would be observing phosphorescence in descendants of the living cells. This indicates that the genetic information responsible for the phosphorescence was passed down from generation to generation. Evidence of DNA or protein transfer would not necessarily indicate that the ability to phosphoresce is a heritable trait, as these molecules can be transferred without affecting inheritance. Bright phosphorescence in the living strain could be due to other factors such as increased metabolic activity, but does not necessarily indicate heritability.

Quiz 16: The Molecular Basis of Inheritance

In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?

Thymine makes up 28% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be guanine?

Which of the following characteristics of eukaryotic telomeres cause them to replicate differently than the rest of the chromosome?

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

In the polymerization of DNA, a phosphodiester bond is formed between a phosphate group of the nucleotide being added and which of the following atoms or molecules of the last nucleotide in the polymer?

In an analysis of the nucleotide composition of a molecule of DNA, which of the following combinations of base pairs will be found?

Which of the following facts did Hershey and Chase make use of in trying to determine whether DNA or protein is the genetic material?

What is meant by the description "antiparallel" regarding the two strands that make up the DNA double helix?

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

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?

Which of the following statements describes the process of transformation in bacteria?

Which of the following statements accurately describes the differences between DNA replication in prokaryotes and DNA replication in eukaryotes?

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?

At a specific area of a chromosome, the sequence of nucleotides below 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?

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?

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

Hershey and Chase set out to determine what molecule served as the unit of inheritance. They completed a series of experiments in which E. coli was infected by a T2 virus. Which molecular component of the T2 virus actually ended up inside the cell?

In his transformation experiments, what phenomenon did Griffith observe?