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nmdcat.online July 4, 2026

22. The mechanism by which histone acetyltransferase (HAT) enzymes promote structural gene activation involves the

A. Covalent addition of acetyl groups to neutralize positive histone charges
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B. Cleavage of the phosphodiester bonds at secondary constrictions
C. Methylation of cytosine bases inside centromeric DNA regions
D. De-phosphorylation of the linker histone H1 molecules

📝 Explanation

HAT enzymes add acetyl groups to basic lysine residues on histone tails, neutralizing their positive charges. This reduces their grip on DNA, transforming condensed heterochromatin into accessible euchromatin.

📖 Additional Information

  • Covalent addition of acetyl groups to neutralize positive histone charges
  • Cleavage of the phosphodiester bonds at secondary constrictions
  • Methylation of cytosine bases inside centromeric DNA regions
  • De-phosphorylation of the linker histone H1 molecules

HAT enzymes add acetyl groups to basic lysine residues on histone tails, neutralizing their positive charges. This reduces their grip on DNA, transforming condensed heterochromatin into accessible euchromatin.

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