Hi can someone please help me with these 3 questions? 8.3 In what ways do the li

Question

Hi can someone please help me with these 3 questions?

8.3 In what ways do the life cycles of bacteriophages T4 and lambda differ? In what aspects are they the same?

8.10 (a) What are the genotypic differences between F? cells, F+ cells, and Hfr cells? (b) What are the phenotypic dif- ferences? (c) By what mechanism are F? cells converted to F+ cells? F+ cells to Hfr cells? Hfr cells to F+ cells?

8.17 An F+ strain, marked at 10 loci, gives rise spontaneously to Hfr progeny whenever the F factor becomes incorporated into the chromosome of the F+ strain. The F factor can integrate into the circular chromosome at many points, so that the resulting Hfr strains transfer the genetic mark- ers in different orders. For any Hfr strain, the order of markers entering a recipient cell can be determined by interrupted mating experiments. From the following data for several Hfr strains derived from the same F+ strain, determine the order of markers in the F+ strain.

Explanation / Answer

8.3 Bacteriophages are viruses of bacteria. They replicate within the bacteria following the injection of their genome into the cytoplasm. They may have lytic or lysogenic cycles, and a few viruses are capable of carrying out both.

During lytic cycle, bacterial cells are broken open (lysed) and destroyed after the immediate replication of virion. But during lysogenic cycle, viral genome integrate into the host DNA and replicate along with it fairly harmlessly. It may also remain dormant when conditions are unfavorable. Hence, it does not result in immediate lysing of the host cell.

Similarity of life cycles of bacteriophages T4 and lambda

Both T4 and lambda phages infect the host cell, reproduces and kill the host cell in the process. Both he phages thus causes lytic response in the host.

Difference in the life cycles of bacteriophages T4 and lambda

Unlike T4 bacteriophage, lambda phages are capable of lysogenic response as well. During this, it inserts its genome into the host DNA and may remain in a dormant state until favorable conditions arise.

Hence, lambda phage may exhibit both lytic and lysogenic response during their life cycle whereas T4 phages display only lytic cycle.

8.10 F factor or fertility factor refers to a plasmid in certain bacteria that enables the transfer of genetic material from a donor cell a recipient by conjugation, resulting in recombination.

(a) The genotypic difference between F- cells, F+ cells, and Hfr cells is that

F- cells lack the F factor

F+ cells have autonomous F factor (a piece of DNA that can replicate autonomously in the cell.

(a) High frequency recombination (Hfr) cells have F-factor integrated into its chromosomal DNA. Hence, they carry an integrated F factor.

(b) F+ and Hfr cells have F pili or sex pili (structures that allow the exchange of genes via the formation of mating pairs), but F- cells lack them.

(c) F- cells are converted into F+ cells by conjugative transfer of F factors from F+ cells. Hfr cells are formed when F factors in F+ cells become integrated into the chromosomes of these cells. Hfr cells become F+ cells when the integrated F factors exit the chromosome and become autonomous genetic elements.

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