Chapter 14 Problems

Question 1

transfer of naked DNA

Answer 1

transformation

Question 2

transfer of DNA requiring direct physical contact

Answer 2

conjugation

Question 3

transfer of DNA between bacteria via virus particles

Answer 3

transduction

Question 4

infection by phages in which lysis of cells releases new virus particles

Answer 4

lytic cycle

Question 5

integration of phage DNA in to the chromosome

Answer 5

lysogeny

Question 6

small circular DNA molecule that can integrate into the chromosome

Answer 6

episome

Question 7

the core genes that define a bacterial species plus all of the genes unique to individual strains

Answer 7

pangenome

Question 8

requires supplements in medium for growth

Answer 8

auxotroph

Question 9

a method for mutagenizing gens in bacterial genomes

Answer 9

gene targeting

Question 10

now that the sequence of the entire E coli K12 strain genome is known, you can determine exactly where a cloned fragment of DNA came from in the genome by sequencing a few bases and matching that data with genomic information.

a. about how many nucleotides of sequence information would you need to determine exactly where a fragment is from?
b. if you had purified a protein from E coli cells, roughly how many amino acids of that protein would you need to know to establish which gene encoded the protein?
c. you determine 100 nucleotides of sequence of genomic DNA from a different E coli strain, but you cannot find a match in the E. coli K 12 genome sequence. How is this possible?

Answer 10

a. you need a sequence of about 12 nucleotides in order to define a unique position in the E. coli genome
b. If you had a sequence of 6 amino acids, you would probably know at least 12 unique nucleotides.
c. The gene you found might be strain-specific; that is, the gene is a part of the E. coli pangenome, but it is not part of the core genome

Question 11

list at least three features of eukaryotic genomes that are not found in bacterial genomes.

Answer 11

(i) multiple chromosomes, (ii) linear chromosomes, (iii) centromeres and (iv) telomeres, (v) introns and exons, (vi) large intergenic regions, (vii) enhancers, (viii) methylation of Cs; (ix) chromatin packaging into nucleosomes.

Question 12

a. Strain A had mutations in two genes, while strain B had three mutations.The reaason is that Lederberg and Tatu wanted to ensure that the phenomenon they were examining did not involve reversion of mutants. Explain the logic behind this aspect of their experimental design, assuming that the rate of reversion of a single gene is one in 10 million cells. How did these investigators know that the cells they found after icing the two cultures were indeed not due to reversion?
b. The experiment did not inform the investigators which strain was the donor and which was the recipient . Describe a way in which they could modify this experiment to answer this question.

Answer 12

a. the chance that two independent reversions would occur in the same bacterial chromosome in strain A is (1 × 10-7)2 = 1 × 10-14. In strain B, the chance of three independent reversions is (1 × 10-7)3 = 1 × 10-21. In the experiment, the cultures were grown only long enough to generate 108 cells
b. including antibiotic sensitivity/resistance markers in strain A and strain B.

Question 13

a. You want to perform an interrupted mating mapping with an E coli Hfr rain that is Pyr+, Met+, Xyl+, Tyr+, Arg+, His+, Mal+, and Str^s. Describe an appropriate bacterial strain to be used asa the partner in this mating.
b. in an Hfr x F- cross, the pyrE gene enters the recipient in 5 minutes, but at this time point there are no exconjugants the are Met+, Xyl+, Tyr+, Arg+, His+, or Mal+. The mating is now allowed to proceed for 30 minutes and Pyr+ exconjugants are selected. Of the Pyr+ cells, 32% are Met+, 94% are Xyl+, 7% are Tyr+, 59% are Arg+, 0% are His+, and 71% are Mal+. what can you conclude about the order of genes?

Answer 13

a. The partner strain should be F−, Strr, and mutant for all the markers to be transferred from the Hfr strain (Pyr−, Met−, Xyl−, Tyr−, Arg−, His−, Mal−).
b. The order of genes is: pyrE xyl mal arg met tyr his.

Question 14

You can carry out matings between an Hfr and F- strain by mixing two cell types in a small patch on a plate and the replica plating to selective medium. This methodology was used to screen hundreds of different cells for a recombination deficient recA- mutant. Why is this an assay for RecA function? would you be screening for a recA- mutation in the F- or Hfr strain using tis protocol? explain

Answer 14

this assay would detect recA− mutants in the F− cell based on the inability to form stable exconjugants