Researchers have isolated a mutant strain of E. coli that carries a temperature-

Question

Researchers have isolated a mutant strain of E. coli that carries a temperature-sensitive variant of the enzyme DNA ligase. At the permissive temperature, the mutant cells grow just as well as the wild-type cells. At the nonpermissive temperature, all of the cells in the culture tube die within 2 hours. DNA from mutant cells grown at the nonpermissive temperature for 30 minutes is compared with the DNA isolated from cells grown at the permissive temperature. The results are shown in Figure Q11, where DNA molecules have been separated by size by means of electrophoresis (P, permissive; NP, nonpermissive). Explain the appearance of a distinct band with a size of 200 base pairs (bp) in the sample collected at the nonpermissive temperature.

Explanation / Answer

It may seem unimportant at first, but the question says that the mutant E. coli has a special DNA ligase. DNA ligase is required to ligate, or link, two strands of DNA together. Since the enzyme functions at the permissive temperature, the DNA is ligated and only one band appears. At the nonpermissive temperature, the DNA ligase fails to function, resulting in no ligated DNA and two separate bands.

Related Questions

Navigate

• Browse (All)
• Browse R
• Subjects

---

---

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