Question 1

Griffith's experiment with Streptococcus pneumoniae demonstrated that hereditary information could be transferred horizontally. Which of the following best explains the outcome when heat-killed virulent (S) bacteria were mixed with live non-virulent (R) bacteria and injected into mice?

Accepted Answer

The mice died because the R bacteria acquired hereditary material from the heat-killed S bacteria, transforming into virulent S type.

Question 2

Avery, MacLeod, and McCarty built on Griffith's findings to identify the macromolecule responsible for heredity. Which experimental result would most strongly support DNA as the hereditary material?

Accepted Answer

Destruction of DNA prevented transformation.

Question 3

In the Hershey and Chase experiment, bacteriophages labeled with $$^{32}P$$ and $$^{35}S$$ were used to infect bacteria. What was the significance of finding $$^{32}P$$ inside the bacterial cells after infection?

Accepted Answer

$$^{32}P$$ labels DNA, showing that DNA entered the bacteria and is the genetic material.

Question 4

Chargaff's rules state that in DNA, the amount of adenine equals the amount of thymine, and the amount of cytosine equals the amount of guanine. Which equation correctly represents this relationship?

Accepted Answer

$$A = T$$ \ $$C = G$$

Question 5

Which of the following best describes the structure of DNA as determined by Watson and Crick?

Accepted Answer

A double helix with antiparallel strands and complementary base pairing.

Question 6

During DNA replication, why can DNA polymerase only synthesize new DNA in the 5' to 3' direction?

Accepted Answer

Because the enzyme requires a free 3' hydroxyl group to add nucleotides.

Question 7

The Meselson-Stahl experiment used $$^{15}N$$ and $$^{14}N$$ isotopes to demonstrate the semiconservative nature of DNA replication. What would be the expected result after one round of replication in $$^{14}N$$ medium if DNA replication were conservative instead?

Accepted Answer

Half the DNA would be heavy ($$^{15}N$$), and half would be light ($$^{14}N).$$

Question 8

Which of the following is a function of methylation in prokaryotic DNA?

Accepted Answer

Serves as a signal for DNA repair and protection from restriction enzymes.

Question 9

In prokaryotic transcription, what is the role of the sigma factor?

Accepted Answer

It recognizes promoter sequences and initiates transcription.

Question 10

Which of the following best explains why transcription and translation can occur simultaneously in prokaryotes but not in eukaryotes?

Accepted Answer

Eukaryotic transcription occurs in the nucleus, while translation occurs in the cytoplasm.

Question 11

The lac operon in E. coli is an example of gene regulation that responds to environmental conditions. Under which conditions will the lac operon be highly transcribed?

Accepted Answer

When lactose is present and glucose is absent.

Question 12

Which of the following is a consequence of a frameshift mutation caused by an insertion or deletion?

Accepted Answer

The reading frame of the gene is disrupted, potentially altering all downstream amino acids.

Question 13

Which process involves the uptake of naked DNA from the environment by a bacterial cell?

Accepted Answer

Transformation

Question 14

During translation, which site on the ribosome does the incoming aminoacyl-tRNA bind to first?

Accepted Answer

A site

Question 15

Which of the following best describes a plasmid?

Accepted Answer

A small, circular DNA molecule found in prokaryotes that can carry genes such as antibiotic resistance.

Question 16

Which of the following is a function of the polycistronic operon in prokaryotes?

Accepted Answer

It allows multiple genes to be transcribed as a single mRNA molecule.

Question 17

Which of the following best explains the function of the Shine-Dalgarno sequence in prokaryotic translation?

Accepted Answer

It binds the small ribosomal subunit to the mRNA to initiate translation.

Question 18

A point mutation changes a codon from UAU (tyrosine) to UAA. What type of mutation is this, and what is its likely effect?

Accepted Answer

Nonsense mutation; introduces a premature stop codon.

Question 19

Which of the following is true regarding the directionality of DNA synthesis?

Accepted Answer

DNA is synthesized in the 5' to 3' direction because nucleotides are added to the 3' hydroxyl group.

Question 20

Which of the following best describes the function of the trp operon in E. coli?

Accepted Answer

It is a repressible operon that is inhibited when tryptophan is abundant.

Microbial Genetics: Structure, Function, and Regulation of Genetic Material

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