Question 1

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?

Accepted Answer

Hershey and Chase's experiments showed that the DNA component of the T2 virus was the only one that ended up inside the E. coli cell, indicating that DNA was the molecule responsible for carrying genetic information.

Question 2

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

Accepted Answer

Transformation is the process by which bacteria take in external DNA from their environment and incorporate it into their genome. Option A is describing transcription, where RNA is made from DNA. Option B is describing reverse transcription, which is the process of making a DNA strand from an RNA template, typically seen in retroviruses. Option C is describing bacterial cells being infected by a virus, which is the process of transduction, not transformation.

Question 3

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

Accepted Answer

DNA polymerase III catalyzes the elongation of new DNA strands in the 5' → 3' direction in E. coli.

Question 4

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?

Accepted Answer

According to Chargaff's rules, the amount of guanine in a DNA sample is equal to the amount of cytosine. Since thymine makes up 28% of the nucleotides, adenine will also make up 28%. Therefore, the remaining 44% of the nucleotides must be guanine and cytosine, which means that guanine will make up approximately 22% of the nucleotides in the sample.

Question 5

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?

Accepted Answer

The sequence of bases in a DNA molecule is responsible for carrying hereditary information. The order of the four nitrogenous bases (adenine, thymine, guanine, and cytosine) determines the genetic instructions for an organism, similar to how the order of letters in a word determines its meaning.

Question 6

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?

Accepted Answer

The RNA primer is synthesized in the 5' to 3' direction, complementary to the template strand in the 3' to 5' direction. The correct answer is C: 5' A C G U U A G G 3'.

Question 7

In his transformation experiments, what phenomenon did Griffith observe?

Accepted Answer

Griffith observed that mixing a heat-killed pathogenic strain of bacteria (which should not be capable of causing disease) with a living nonpathogenic strain resulted in some of the living cells being transformed into the pathogenic form. This suggested that some genetic material from the dead pathogenic bacteria had been taken up and incorporated into the genetic material of the living nonpathogenic bacteria, allowing them to become pathogenic. This was the first evidence of genetic transformation.

Question 8

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

Accepted Answer

According to Chargaff's rules, in DNA, the amount of adenine (A) equals thymine (T), and the amount of cytosine (C) equals guanine (G). Therefore, the sum of purines (A + G) equals the sum of pyrimidines (C + T), which can be rearranged to A + C = G + T.

Question 9

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

Accepted Answer

Antiparallel refers to the fact that the 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. This means that one strand has a 5' end and a 3' end, while the other strand has a 3' end and a 5' end. This is important for DNA replication and transcription, as the enzymes involved can only add nucleotides in a specific direction.

Question 10

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?

Accepted Answer

In the polymerization of DNA, a phosphodiester bond is formed between the phosphate group of the nucleotide being added and the 3' OH (hydroxyl) group of the last nucleotide in the polymer. This results in the growth of the DNA chain in a 5' to 3' direction.

Question 11

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?

Accepted Answer

Erwin Chargaff discovered 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.

Question 12

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?

Accepted Answer

Labeling nitrogen would not distinguish between DNA and proteins because both contain nitrogen, making it impossible to specifically track DNA.

Question 13

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

Accepted Answer

Hershey and Chase used the fact that DNA contains phosphorus, whereas protein does not. They labeled the DNA with radioactive phosphorus and protein with radioactive sulfur, and found that only the DNA was transferred from the virus to the host, indicating that DNA is the genetic material.

Question 14

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?

Accepted Answer

In DNA, the amount of cytosine (C) is equal to the amount of guanine (G), and the amount of adenine (A) is equal to the amount of thymine (T). If cytosine is 42%, then guanine is also 42%, making up 84% of the DNA. The remaining 16% must be adenine and thymine, with each being 8%.

Question 15

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

Accepted Answer

The answer of Which of the following characteristics of eukaryotic...

Question 16

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?

Accepted Answer

If the ability to phosphoresce is a heritable trait, then it should be passed on to descendants of the living cells. Therefore, phosphorescence in descendants of the living cells is the best evidence that the ability to phosphoresce is a heritable trait. Choice A is incorrect because the passage of DNA alone does not necessarily determine if a trait is heritable. Choice B is incorrect because protein passing from the heat-killed strain is unlikely to confer a heritable trait. Choice C is incorrect because bright phosphorescence does not necessarily indicate heritability.

Question 17

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

Accepted Answer

Telomerase catalyzes the lengthening of telomeres, which are specialized structures at the ends of linear chromosomes, compensating for the shortening that could occur during replication without telomerase activity. This allows for the complete replication of the chromosome without losing important genetic information at the end of the chromosome.

Question 18

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?

Accepted Answer

When radioactive thymine is added to the radioactive culture of E. coli, it will be incorporated into the replicating DNA during the S phase of the cell cycle. Thus, both daughter cells will have a copy of the radioactive DNA, making option D the correct answer.

Question 19

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

Accepted Answer

Prokaryotic chromosomes typically have a single origin of replication, which initiates the replication process, while eukaryotic chromosomes have multiple origins of replication that allow for faster and more efficient replication. The other statements are either incorrect (A and D) or too general and may not be true in all cases (C).

Question 20

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?

Accepted Answer

Helicase unwinds DNA and creates the replication fork, so if the helicase is altered, no replication fork will be formed. Choices A, C, and D are not directly related to the function of helicase in DNA replication.

Quiz 16: The Molecular Basis of Inheritance