Deck 7: Bacterial and Viral Genetic Systems

Question 1

Bacteria can be studied in the laboratory by growing them on defined liquid or solid medium. A typical bacterial genome consists of a single circular chromosome that contains several million base pairs. Some bacterial genes may be present on plasmids, which are small, circular DNA molecules that replicate independently of the bacterial chromosome

-Which is true of plasmids?

A) They are composed of RNA.
B) They normally exist outside of bacterial cells.
C) They possess only a single strand of DNA.
D) They contain an origin of replication

Answer 1

They contain an origin of replication

Question 2

DNA may be transferred between bacterial cells through conjugation, transformation, or transduction. Each type of genetic transfer consists of a one-way movement of genetic information to the recipient cell, sometimes followed by recombination. These processes are not connected to cellular reproduction in bacteria.

-Which process of DNA transfer in bacteria requires a virus?

A) Conjugation
B) Transduction
C) Transformation
D) All of the above

Answer 2

Transduction

Question 3

Conjugation in E. coli is controlled by an episome called the F factor. Cells containing F (F⁺ cells) are donors during gene transfer; cells lacking F (F^- cells) are recipients. Hfr cells possess F integrated into the bacterial chromosome; they donate DNA to F^- cells at a high frequency. F' cells contain a copy of F with some bacterial genes

-Conjugation between an F⁺ and an F^- cell usually results in

A) two F⁺ cells.
B) an F⁺ and an F^- cell.
C) an Hfr cell and an F⁺ cell

Answer 3

two F⁺ cells.

Question 4

Conjugation can be used to map bacterial genes by mixing Hfr and F^- cells of different genotypes and interrupting conjugation at regular intervals. The amount of time required for individual genes to be transferred from the Hfr to the F^- cells indicates the relative positions of the genes on the bacterial chromosome.

-Interrupted conjugation was used to map three genes in E. coli. The donor genes first appeared in the recipient cells at the following times: gal, 10 minutes; his, 8 minutes; pro, 15 minutes. Which gene is in the middle?

Question 5

Genes can be mapped in bacteria by taking advantage of transformation-the ability of cells to take up DNA from the environment and incorporate it into their chromosomes through crossing over. The relative rate at which pairs of genes are cotransformed indicates the distance between them: the higher the rate of cotransformation, the closer the genes are on the bacterial chromosome.

-DNA from a bacterial strain with genotype his^- leu^- thr^- is transformed with DNA from a strain that is his⁺ leu⁺ thr⁺. A few leu⁺ thr⁺ cells and a few his⁺ thr⁺ cells are found, but no his⁺ leu⁺ cells are observed. Which genes are farthest apart?

Question 6

Viral genomes may be DNA or RNA, circular or linear, and double or single stranded. Bacteriophages are used in many types of genetic research.

-In which bacteriophage life cycle does the phage DNA become incorporated into the bacterial chromosome?

A) Lytic
B) Lysogenic
C) Both lytic and lysogenic
D) Neither lytic or lysogenic

Question 7

In transduction, bacterial genes become packaged into a viral coat, are transferred to another bacterium by the virus, and become incorporated into the bacterial chromosome by crossing over. Bacterial genes can be mapped with the use of generalized transduction.

-In gene mapping experiments using generalized transduction, bacterial genes that are cotransduced are

A) far apart on the bacterial chromosome.
B) on different bacterial chromosomes.
C) close together on the bacterial chromosome.
D) on a plasmid

Question 8

In a series of experiments with the bacteriophage T4, Seymour Benzer showed that recombination could take place within a single gene and created the first molecular map of a gene. Benzer used the complementation test to distinguish between functional genes (loci).

-In complementation tests, Benzer simultaneously infected E. coli cells with two phages, each of which carried a different mutation. What conclusion did he make when the progeny phages produced normal plaques?

A) The mutations were at the same locus.
B) The mutations were at different loci.
C) The mutations were close together on the chromosome.
D) The genes were in the cis configuration.

Question 9

A retrovirus is an RNA virus that integrates into its host's chromosome by making a DNA copy of its RNA genome through the process of reverse transcription. Human immunodeficiency virus, the causative agent of AIDS, is a retrovirus. It evolved from related retroviruses found in other primates.
-What enzyme is used by a retrovirus to make a DNA copy of its genome?