DNA methylation is commonly associated with a reduction of transcription. The following data come from a study of the impact of the location and extent of DNA methylation on gene activity in eukaryotic cells. A bacterial gene, luciferase, was inserted into plasmids next to eukaryotic promoter fragments. CpG sequences, either within the promoter and coding sequence (transcription unit) or outside of the transcription unit, were methylated to various degrees, in vitro. The chimeric plasmids were then introduced into cultured cells, and luciferase activity was assayed. These data compare the degree of expression of luciferase with differences in the location of DNA methylation [Irvine et al. (2002). Mol. and Cell. Biol. 22:6689–6696]. What general conclusions can be drawn from these data?
13. Gene Regulation in Eukaryotes
Epigenetics, Chromatin Modifications, and Regulation
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Which statement about epigenetics is false?
A
Epigenetic modifications can alter gene expression without changing the DNA sequence.
B
Histone acetylation is associated with increased transcriptional activity.
C
Epigenetic changes are always permanent and cannot be reversed.
D
DNA methylation is an example of an epigenetic modification.
Verified step by step guidance1
Step 1: Understand the definition of epigenetics. Epigenetics refers to heritable changes in gene expression that do not involve changes to the underlying DNA sequence. These changes can affect how genes are turned on or off.
Step 2: Review common epigenetic modifications. Two well-known examples are DNA methylation, which typically represses gene expression, and histone acetylation, which usually increases transcriptional activity by loosening chromatin structure.
Step 3: Analyze the statement 'Epigenetic modifications can alter gene expression without changing the DNA sequence.' This is true because epigenetics involves changes in gene activity without altering the nucleotide sequence.
Step 4: Consider the statement 'Histone acetylation is associated with increased transcriptional activity.' This is true because acetylation of histones reduces their positive charge, decreasing their interaction with DNA and allowing transcription factors better access.
Step 5: Evaluate the statement 'Epigenetic changes are always permanent and cannot be reversed.' This is false because many epigenetic modifications are dynamic and reversible, allowing cells to respond to environmental changes and developmental cues.
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