Suppose a scientist grows cells in a medium that contains amino acids labeled wi

Question

Suppose a scientist grows cells in a medium that contains amino acids labeled with a heavy isotope. She isolates histone octamers from some of these cells and subjects the isolated proteins to density-gradient centrifugation. The centrifugation yields a single band of heavy isotope-labeled histones near the bottom of the tube. The scientist then transfers the remaining cells to a medium that contains amino acids labeled with a lighter isotope. She isolates new histone octamers from the culture after cells replicate in this medium and subjects these proteins to another round of density-gradient centrifugation. How many bands does the scientist expect to see in the second round of density-gradient centrifugation if all original histone proteins remain on one strand of DNA and new histones attach to the other strand during replication? OOne lower band containing the new histone octamers and one higher band containing the original histone octamers. One lower band containing the original histone octamers, a middle band containing octamers composed of both histone types, and a top band containing the new histone octamers. One band containing octamers composed of both original and new histones. One lower band containing the original histone octamers and one higher band containing the O new histone octamers.

Explanation / Answer

Option 3 will be the correct answer.

One band containing octamers composed of both original and new histones. The stones required for new nucleosomes are derived from two sources: parental histones (dispersively segregated to both arms of the fork) and new histones, especially new H3/H4, that are deposited during de novo nucleosome assembly, hence in the second round of density-gradient centrifugation, only one band will be present since all the nucleosomes present are now hybrids of the original and new histones.

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

---

---

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