Question 1

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

Accepted Answer

Transformation in bacteria refers to the process where external DNA is taken up by a bacterial cell and incorporated into its own genome. This can lead to genetic changes in the bacteria.

Question 2

In DNA polymerization, 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

The phosphodiester bond in DNA polymerization is formed between the phosphate group of the incoming nucleotide and the 3' hydroxyl (OH) group of the last nucleotide in the growing polymer chain.

Question 3

Frederick Griffith heat-killed a culture of pathogenic bacteria. He split the sample and injected half of it into mice. The mice lived. He then mixed the other half of the sample with a living, nonpathogenic bacteria strain and injected the mixture into mice. The mice died. Which of the following describes a treatment that would help clarify interpretation of these data?

Accepted Answer

C) Examining tissue from the dead mice for the presence of pathogenic bacteria would help clarify whether the nonpathogenic bacteria transformed into pathogenic bacteria by acquiring genetic material from the heat-killed pathogenic bacteria, which is the essence of Griffith's experiment demonstrating the principle of transformation.

Question 4

In bacteria, which of the following proteins is responsible for removing nucleotides from the RNA primer that is used for initiation DNA synthesis?

Accepted Answer

DNA pol I is responsible for removing the RNA primers used during DNA replication and replacing them with DNA nucleotides.

Question 5

Frederick Griffith heat-killed a culture of pathogenic bacteria. He split the sample and injected half of it into mice. The mice lived. He then mixed the other half with a living, nonpathogenic bacteria strain and injected the mixture into mice. The mice died. These results best support which of the following conclusions.

Accepted Answer

Frederick Griffith's experiment demonstrated that a substance (which later was identified as DNA) could be transferred from the dead pathogenic bacteria to the living nonpathogenic bacteria, transforming them into a pathogenic form. This process is known as transformation.

Question 6

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

Accepted Answer

Prokaryotic chromosomes typically have a single origin of replication from which replication proceeds bidirectionally, whereas eukaryotic chromosomes have multiple origins of replication to accommodate their larger size and complexity.

Question 7

A phosphorescent red strain of bacteria is heat-killed and mixed with a living, colorless strain. Further observations of the mixture show that some of the living cells are now red. Which of the following observations would provide the best evidence that red color is a heritable trait?

Accepted Answer

The increase in the number of red cells as the living cells divide suggests that the red color trait is being passed on to the offspring, indicating it is heritable.

Question 8

Hershey and Chase set out to determine which type of molecule is used for genetic inheritance. They completed a series of experiments where E. coli was infected by a T2 virus. Which molecular component of the T2 virus ended up inside the cell?

Accepted Answer

Hershey and Chase's experiments showed that DNA, not protein, is the molecule of inheritance, as it was the DNA of the T2 virus that entered the E. coli cells, not the protein.

Question 9

A sample of double-stranded DNA contains 42% cytosine. Approximately what percent of the nucleotides in this sample will be thymine?

Accepted Answer

In double-stranded DNA, the amount of cytosine (C) is equal to the amount of guanine (G). If cytosine is 42%, guanine is also 42%, making up 84% of the DNA. The remaining 16% must be adenine (A) and thymine (T) combined. Since A pairs with T, thymine will be 8%.

Question 10

In E. coli, a mutation in a gene called dnaB prevents the helicase from binding at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?

Accepted Answer

Helicase is essential for unwinding the DNA double helix at the origin of replication, allowing the replication machinery to access the single-stranded DNA. Without the action of helicase, the replication fork, where the DNA is unwound and replication occurs, cannot be formed.

Question 11

Radioactive thymine is added to media containing one actively dividing E. coli bacterium. Which of the following outcomes would be seen after a single cell division?

Accepted Answer

During DNA replication, new nucleotides are added to both strands of the original DNA molecule. If radioactive thymine is present in the media, it will be incorporated into the new DNA strands of both daughter cells as they replicate their DNA, making the DNA in both daughter cells radioactive.

Question 12

Which of the following characteristics of DNA allows it to carry a vast amount of hereditary information?

Accepted Answer

The sequence of bases in DNA encodes genetic information, allowing it to carry a vast amount of hereditary information.

Question 13

Which of the following investigators was (were) responsible for determining that DNA contains equal amounts of adenine and thymine, and equal amounts of guanine and cytosine?

Accepted Answer

Erwin Chargaff discovered the base pairing rules, which state that in DNA, the amount of adenine (A) equals the amount of thymine (T), and the amount of guanine (G) equals the amount of cytosine (C). This finding was crucial for the later development of the double helix model of DNA by Watson and Crick.

Question 14

Which of the following characteristics allowed Hershey and Chase to determine whether the genetic material was made of DNA or protein?

Accepted Answer

DNA contains phosphorus, which is a component of its phosphate backbone, while proteins do not contain phosphorus in their basic structure. Hershey and Chase used radioactive phosphorus to label DNA and radioactive sulfur to label proteins in their experiments, allowing them to track which of these molecules entered bacterial cells and carried genetic information.

Question 15

Rosalind Franklin's X-ray crystallography data suggested DNA is double stranded and has a uniform diameter. These observations can be used to rule out base pairing between two of the same nucleotide because ________.

Accepted Answer

The uniform diameter of the DNA helix suggests that base pairs must consist of one purine and one pyrimidine, as purine-purine pairs (like A-A) would be too wide and pyrimidine-pyrimidine pairs (like C-C) would be too narrow.

Question 16

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

Accepted Answer

DNA polymerase III is the enzyme responsible for the elongation of a new DNA strand in the 5' → 3' direction during DNA replication in E. coli.

Question 17

Two students decided to repeat the Hershey and Chase experiment, with modifications. Like Hershey and Chase they used radioactive sulfur but they substituted radioactive nitrogen for radioactive 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. Which of the following is the biggest shortcoming in their experimental design?

Accepted Answer

The biggest shortcoming in their experimental design is that the radioactivity would not distinguish between DNA and proteins because both contain nitrogen, making it impossible to determine if the genetic material is DNA or protein based on the radioactive signal.

Question 18

Which of the following combinations of base pairs will be found in a molecule of DNA?

Accepted Answer

In a molecule of DNA, the amount of adenine (A) is equal to thymine (T), and the amount of cytosine (C) is equal to guanine (G), which means A + T = G + C, or equivalently, A + C = G + T.

Question 19

A sample of double-stranded DNA contains 28% thymine. Approximately what percent of the nucleotides in this sample will be guanine?

Accepted Answer

In double-stranded DNA, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). If thymine is 28%, then adenine is also 28%. This leaves 44% for guanine and cytosine combined, so guanine is approximately 22%.

Question 20

DNA strands are antiparallel. Which of the following statements defines "antiparallel"?

Accepted Answer

Antiparallel arrangement in DNA refers to the orientation of the two strands, where one strand runs in the 5' to 3' direction and the other runs in the 3' to 5' direction, allowing them to pair and form the double helix structure.

Quiz 16: Nucleic Acids and Inheritance