Old H3 and H4 histones (tetramers, containing two H3+ two H4) are always found t

Question

Old H3 and H4 histones (tetramers, containing two H3+ two H4) are always found together in the newly formed nucleosomes after DNA replication. In contrast, old H2A and H2B histones (dimers) are almost always found with newly synthesized H2A and H2B partners (dimers) in the newly formed nucleosomes. If these observations are correct, which of the following cannot be correct?

A. (H3-H4) tetramers remain attached to the DNA but (H2A-H2B) tetramers breaks down to dimers

B. The local DNA retains its nucleosomal histone modifications state even after DNA replication and cell division.

C. Suppressed genes remain suppressed and activated genes remain activated after DNA replication and cell division

D. DNA replication wipes out the state of histone modification and thus the genes may go back to ground state to move to a new direction of regulation.

Explanation / Answer

Option D is the correct answer.

The statement, "DNA replication wipes out the state of histone modification and thus the genes may go back to ground state to move to a new direction of regulation." is not correct because the process of chromatin disassembly and reassembly during DNA replication is regulated to ensure that the genetic material is compactly packaged to fit into the nucleus while also maintaining the epigenetic information that is carried by the histone proteins bound to the DNA, through cell divisions. Half of the histones that are deposited during replication are from the parental chromatin and carry the parental epigenetic information, while the other half of the histones are newly-synthesized. Disassembled chromatin quickly returns to its original epigenetic state after replication

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