Explain why transduction cannot result from virulent phages. Two bacterial strai

Question

Explain why transduction cannot result from virulent phages. Two bacterial strains are auxotrophic for two different pairs of genes. Strain A is phe^+, trp^+, met^-, his and Strain B is phe, trp, met^-1 his^+. The two strains are cultured in a U-tube where the two sides are separated by a filter. The medium and anything dissolved in it can pass between through the filter, but intact cells are too large to pass. The culture medium on both sides also contains on enzyme that destroys any external DNA. After 24 hours, all of the cells on the side with Strain A are still auxotrophic, but some of the cells on the side with Strain B are now prototrophs (phe^+, trp^+, met^+, his^+). (a) What form of recombination is ruled out by the fact that intact cells cannot pass through the filter? (b) What form of recombination is ruled out by the presence of the enzyme that would destroy external DNA? (c) What form of recombination must be responsible for the conversion of some Strain B cells to prototrophs?

Explanation / Answer

Q) Explain why transduction cannot result from virulent phages?

A) Transduction is a process by which viral vector (bacteriophage) introduces the DNA of one bacterium into the other.

When a bacteriophage infects a bacterial cell it can undergo two types of replication cycles 1. lysogenic cycle and 2. lytic cycle

1. lysogenic cycle: During the lysogenic cycle, the phage DNA replicates by integrating into the host chromosome and remains in a dormant state and can trigger lytic cycle in future. Hence the phages that undergo lysogenic cycle based replication are called temperate phages. As the phage DNA integrates into bacterial chromosome and replicates, bacterial genes are packed into phages and transfered to another bacterial cell due to recombination.

2. lytic cycle: During the lytic cycle, the phage DNA exists and replicates as an independent molecule (without integrating into host DNA) using host machinery. when the replication is completed followed by assembly of new phages the phage produce lysin resulting in breakdown of the cell wall. Hence the phages that cause lytic cycle are called as virulent phages. As the virulent DNA do not integrate into host DNA and replicate during lytic cycle the host genes are not transferred to the other bacterial cell.

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.