Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologymediummcq1 pt

Histone acetyltransferases increase expression of a particular eukaryotic gene. What is the direct molecular effect of this acetylation?

A.Acetyl groups neutralize positive charges on histone tails, loosening their grip on DNA and exposing promoters to transcription factors
B.Acetyl groups add methyl marks that recruit proteins condensing nucleosomes into silent heterochromatin
C.Acetyl groups attach to the DNA backbone itself so polymerase can read the template directly
D.Acetyl groups block repressor proteins from binding the operator sequence near the promoter

Explanation

Core Concept

Histone tails carry positively charged lysine residues that hold the negatively charged DNA backbone close to the nucleosome. Histone acetyltransferases transfer acetyl groups onto these lysines and neutralize their charge. The weakened electrostatic attraction opens the chromatin so promoter sequences become accessible to general transcription factors and RNA polymerase II. This opening explains why acetylated regions are actively transcribed.

Correct Answer

AAcetyl groups neutralize positive charges on histone tails, loosening their grip on DNA and exposing promoters to transcription factors

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